


                        little cms Engine
                    http://www.littlecms.com

           How to use the engine in your applications

                          by Marti Maria

                            Ver 1.18

        ---------------------------------------------------

                         Introduction

                         BASIC USAGE
                         ===========

                         1. Basic Concepts
                         2. Step-by-step example
                         3. Embedded profiles
                         4. Device-link profiles 
                         
                         5. Built-in profiles
                         6. On-the-fly profiles
                         7. Gamma tables
                         8. Proofing
                         9.1 Black point compensation
						 9.2 Black preservation
                        
                        10. Error handling
                        11. Getting information from profiles.

                        ADVANCED TOPICS
                        ===============

                        12. Creating and writting new profiles
                        13. LUT handling
                        14. Helper functions
                        15. Color difference functions
                        16. PostScript operators
                        17. CIECAM02
                        18. Named color profiles
                         
                        19. Conclusion

                    Sample 1: How to convert RGB to CMYK and back
                    Sample 2: How to deal with Lab/XYZ spaces

                    Annex A. About intents
                    Annex B. Apparent bug in XYZ -> sRGB transforms

                    ----------------------------

Introduction:

  This file has been written to present the lcms core library to
  would-be writers of applications. It first describes the
  concepts on which the engine is based, and then how to use it
  to obtain transformations, colorspace conversions and 
  separations. Then, a guided step-by-step example, shows how to
  use the engine in a simple or more sophisticated way.

  This document doesn't even try to explain the basic concepts of
  color management. For a comprehensive explanation, I will
  recommend the excellent color & gamma FAQs by Charles A.
  Poynton,

                http://www.poynton.com

  For more details about profile architecture, you can reach the
  latest ICC specs on:

                http://www.color.org


    **PLEASE NOTE THAN lcms IS NOT AN ICC SUPPORTED LIBRARY**

  
  I will assume the reader does have a working knowledge of the C
  programming language. This don't mean lcms can only be used by
  C applications, but it seems the easiest way to present the API
  functionality. I currently have successfully used the lcms DLL
  from Delphi, C++ Builder, Visual C++, Tcl/Tk, and even Visual 
  Basic.

  DELPHI USERS:

  If you plan to use lcms from Delphi, there is a folder in the
  package containing units and samples for Delphi interface. Rest
  of document does refer to C API, but you can use same functions
  on Delphi.


1. Basic Concepts:
============================================================================

  lcms defines two kinds of structures, that are used to manage
  the various abstractions required to access ICC profiles. These
  are profiles and transforms.

  In a care of good encapsulation, these objects are not directly
  accessible from a client application. Rather, the user receives
  a 'handle' for each object it queries and wants to use. This
  handle is a stand-alone reference; it cannot be used like a
  pointer to access directly the object's data.

  There are typedef's for such handles:

        cmsHPROFILE   identifies a handle to an open profile.
        cmsHTRANSFORM identifies a handle to a transform.

  Conventions of use:

    o   All API functions and types have their label prefixed
        by 'cms' (lower-case).

    o   #defined constants are always in upper case

    o   Some functions does accepts flags. In such cases,
        you can build the flags specifier joining the values with the
        bitwise-or operator '|'

    o   An important  note is that  the engine should not  leak
        memory when  returning an error,  e.g., querying  the
        creation of an object  will allocate  several  internal
        tables  that will be freed if a disk error occurs during
        a load.

  Since these are a very generic conventions widely used, I will
  no further discuss this stuff.



2. Step-by-step Example:
============================================================================

  Here is an example to show, step by step, how a client application 
  can transform a bitmap between two ICC profiles using the lcms API

  This is an example of how to do the whole thing:



#include "lcms.h"


int main(void)
{

     cmsHPROFILE hInProfile, hOutProfile;
     cmsHTRANSFORM hTransform;
     int i;


     hInProfile  = cmsOpenProfileFromFile("HPSJTW.ICM", "r");
     hOutProfile = cmsOpenProfileFromFile("sRGBColorSpace.ICM", "r");



     hTransform = cmsCreateTransform(hInProfile,
                                           TYPE_BGR_8,
                                           hOutProfile,
                                           TYPE_BGR_8,
                                           INTENT_PERCEPTUAL, 0);


     for (i=0; i < AllScanlinesTilesOrWatseverBlocksYouUse; i++)
     {
           cmsDoTransform(hTransform, YourInputBuffer,
                                      YourOutputBuffer,
                                      YourBuffersSizeInPixels);
     }



     cmsDeleteTransform(hTransform);
     cmsCloseProfile(hInProfile);
     cmsCloseProfile(hOutProfile);

     return 0;
}


 Let's discuss how it works.

 a) Open the profiles

   You will need the profile handles for create the transform. In
   this example, I will create a transform using a HP Scan Jet
   profile present in Win95 as input, and sRGB profile as output.

   This task can be done by following lines:

     cmsHPROFILE hInProfile, hOutProfile;

     hInProfile  = cmsOpenProfileFromFile("HPSJTW.ICM", "r")
     hOutProfile = cmsOpenProfileFromFile("sRGBColorSpace.ICM", "r")


   You surely have noticed a second parameter with a small "r".
   This parameter is used to set the access mode. It describes 
   the "opening mode" like the C  function fopen(). 

   Currently lcms does support both read and write profiles.
   
   WARNING!: opening with 'w' WILL OVERWRITE YOUR PROFILE! 
   Don't do this except if you want to create a NEW profile. 
   

   NOTES:

   This only will take a small fraction of memory. The BToA or AToB tables,
   which usually are big, are only loaded at transform-time, and on demand.
   You can safely open a lot of profiles if you wish so.

   If cmsOpenProfileFromFile() fails, it raises an error signal that can
   or cannot be catched by the application depending of the state of the
   error handler. In this example, I'm using the "if-error-abort-whole-
   application" behaviour, corresponding with the LCMS_ERROR_ABORT setting 
   of cmsErrorAction(). See the error handling paragraph below for more
   information.

   lcms is a standalone color engine, it knows nothing  about where
   the profiles are placed. lcms does assume nothing about
   a specific directory (as Windows does, currently expects profiles
   to be located on SYSTEM32/SPOOL/DRIVERS/COLOR folder in main windows 
   directory), so for get this example working, you need to copy the 
   profiles in the local directory.


 b) Identify the desired format of pixels.

   lcms can handle a lot of formats. In fact, it can handle:

                - 8 and 16 bits per channel 
                - up to 16 channels
                - extra channels like alpha
                - swapped-channels like BGR
                - endian-swapped 16 bps formats like PNG
                - chunky and planar organization
                - Reversed (negative) channels
                - Floating-point numbers


   For describing such formats, lcms does use a 32-bit value, referred
   below as "format specifiers".

   There are several (most usual) encodings predefined as constants, but there
   are a lot more. See lcms.h to review the current list.

         TYPE_RGB_DBL
         TYPE_CMYK_DBL
         TYPE_Lab_DBL
         TYPE_XYZ_DBL
         TYPE_YCbCr_DBL         Takes directly the floating-point structs

         TYPE_GRAY_8            Grayscale 8 bits
         TYPE_GRAY_16           Grayscale 16 bits
         TYPE_GRAY_16_SE        Grayscale 16 bits, swap endian
         TYPE_GRAYA_8           Grayscale + alpha, 8 bits
         TYPE_GRAYA_16          Grayscale + alpha, 16 bits
         TYPE_GRAYA_16_SE       Grayscale + alpha, 16 bits
         TYPE_GRAYA_8_PLANAR    Grayscale + alpha, 8 bits, separate planes
         TYPE_GRAYA_16_PLANAR   Grayscale + alpha, 16 bits, separate planes

         TYPE_RGB_8             RGB, 8 bits
         TYPE_RGB_8_PLANAR      RGB, 8 bits, separate planes
         TYPE_BGR_8             BGR, 8 bits (windows uses this format for BMP)
         TYPE_BGR_8_PLANAR      BGR, 8 bits, separate planes
         TYPE_RGB_16            RGB, 16 bits
         TYPE_RGB_16_PLANAR     ...
         TYPE_RGB_16_SE
         TYPE_BGR_16
         TYPE_BGR_16_PLANAR
         TYPE_BGR_16_SE

         TYPE_RGBA_8            These ones with alpha channel
         TYPE_RGBA_8_PLANAR
         TYPE_RGBA_16
         TYPE_RGBA_16_PLANAR
         TYPE_RGBA_16_SE
         TYPE_ABGR_8
         TYPE_ABGR_16
         TYPE_ABGR_16_PLANAR
         TYPE_ABGR_16_SE

         TYPE_CMY_8             These ones for CMY separations
         TYPE_CMY_8_PLANAR
         TYPE_CMY_16
         TYPE_CMY_16_PLANAR
         TYPE_CMY_16_SE

         TYPE_CMYK_8            These ones for CMYK separations
         TYPE_CMYK_8_PLANAR
         TYPE_CMYK_16
         TYPE_CMYK_16_PLANAR
         TYPE_CMYK_16_SE

         TYPE_KYMC_8            Reversed CMYK
         TYPE_KYMC_16
         TYPE_KYMC_16_SE

         TYPE_XYZ_16            XYZ, xyY and CIELab
         TYPE_Yxy_16
         TYPE_Lab_8
         TYPE_Lab_16

         TYPE_CMYKcm_8          HiFi separations
         TYPE_CMYKcm_8_PLANAR
         TYPE_CMYKcm_16
         TYPE_CMYKcm_16_PLANAR
         TYPE_CMYKcm_16_SE

         TYPE_CMYK7_8
         TYPE_CMYK7_16
         TYPE_CMYK7_16_SE
         TYPE_KYMC7_8
         TYPE_KYMC7_16
         TYPE_KYMC7_16_SE
         TYPE_CMYK8_8
         TYPE_CMYK8_16
         TYPE_CMYK8_16_SE
   
         .. etc...

   For example, if you are transforming a windows .bmp to a bitmap for
   display, you will use TYPE_BGR_8 for both, input and output
   buffers, windows does store images as B,G,R and not as R,G,B.

   Other example, you need to convert from a CMYK separation to
   RGB in order to display; then you would use TYPE_CMYK_8 on
   input and TYPE_BGR_8 on output. If you need to do the
   separation from a TIFF, TYPE_RGB_8 on input and TYPE_CMYK_8 on
   output. Please note TYPE_RGB_8 and TYPE_BGR_8 are *not* same.


   The format specifiers are useful above color management. This will
   provide a way to handle a lot of formats, converting them in a single,
   well-known one. For example, if you need to deal with several pixel
   layouts coming from a file (TIFF for example), you can use a fixed
   output format, say TYPE_BGR_8 and then, vary the input format
   on depending on the file parameters. lcms also provides a flag for
   inhibit color management if you want speed and don't care about
   profiles. see cmsFLAGS_NULLTRANSFORM for more info.



 c) Create the transform

   When creating transform, you are giving to lcms all information it
   needs about how to translate your pixels. The syntax for simpler
   transforms is:


                cmsHTRANSFORM hTransform;

                hTransform = cmsCreateTransform(hInputProfile,
                                           TYPE_BGR_8,
                                           hOutputProfile,
                                           TYPE_BGR_8,
                                           INTENT_PERCEPTUAL, 0);

   You give the profile handles, the format of your buffers, the rendering
   intent and a combination of flags controlling the transform behaviour.

   It's out of scope of this document to define the exact meaning
   of rendering intents. I will try to make a quick explanation
   here, but often the meaning of intents depends on the profile
   manufacturer. See appendix A for more information.


   INTENT_PERCEPTUAL:

                Hue hopefully maintained (but not required),
                lightness and saturation sacrificed to maintain
                the perceived color. White point changed to
                result in neutral grays. Intended for images.

                In lcms: Default intent of profiles is used

   INTENT_RELATIVE_COLORIMETRIC:

                Within and outside gamut; same as Absolute
                Colorimetric. White point changed to result in
                neutral grays.

                In lcms: If adequate table is present in profile,
                then, it is used. Else reverts to perceptual
                intent.

   INTENT_SATURATION:

                Hue and saturation maintained with lightness
                sacrificed to maintain saturation. White point
                changed to result in neutral grays. Intended for
                business graphics (make it colorful charts,
                graphs, overheads, ...)

                In lcms: If adequate table is present in profile,
                then, it is used. Else reverts to perceptual
                intent.

   INTENT_ABSOLUTE_COLORIMETRIC:

                Within the destination device gamut; hue,
                lightness and saturation are maintained. Outside
                the gamut; hue and lightness are maintained,
                saturation is sacrificed. White point for source
                and destination; unchanged. Intended for spot
                colors (Pantone, TruMatch, logo colors, ...)

                In lcms: relative colorimetric intent is used
                with undoing of chromatic adaptation.


  Not all profiles does support all intents, there is a function
  for inquiring which intents are really supported, but if you
  specify a intent that the profile doesn't handle, lcms will
  select default intent instead. Usually perceptual one. This
  will force to "look nice", no matter the intent is not the one
  really desired.


  lcms tries to "smelt" input and output profiles in a single
  matrix-shaper or in a big 3D CLUT of 33 points. This will
  improve greatly the performance of the transform, but may
  induce a small delay of 1-2 seconds on some really old 
  machines.

  If you are willing to transform just a palette or a few
  colors, you don't need this precalculations. Then, the flag
  cmsFLAGS_NOTPRECALC in cmsCreateTransform() can be used to
  inhibit the 3D CLUT creation.

  See the API reference for a more detailed discussion of the flags.

  NOTES:

   Some old display profiles, only archives absolute colorimetric
   intents. For these profiles, default intents are absolute
   colorimetric ones. This is really a rare case.


 d) Next, you can translate your bitmap, calling repeatedly the processing
    function:


           cmsDoTransform(hTransform, YourInputBuffer,
                                      YourOutputBuffer,
                                      YourBuffersSize);



   This function is intended to be quite fast. You can use this
   function for translating a scan line, a tile, a strip, or whole
   image at time.


   NOTES:

   Windows, stores the bitmaps in a particular way... for speed
   purposes, does align the scan lines to double word boundaries,
   a bitmap has in windows always a size multiple of 4. This is
   OK, since no matter if you waste a couple of bytes, but if you
   call cmsDoTransform() and passes it WHOLE image, lcms doesn't
   know nothing about this extra padding bytes. It assumes that
   you are passing a block of BGR triplets with no alignment at
   all. This result in a strange looking "lines" in obtained
   bitmap.

   The solution most evident is to convert scan line by scan line
   instead of whole image. This is as easy as to add a for()
   loop, and the time penalty is so low that is impossible to
   detect.

   It is safe to use same block for input and output, but only if
   the input and output are coded in same format. For example,
   you can safely use only one buffer for RGB to RGB but you
   cannot use same buffer for RGB as input and CMYK as output.



 e) Last, free all stuff.

   This can be done by calling

                cmsDeleteTransform(hTransform);
                cmsCloseProfile(hInputProfile);
                cmsCloseProfile(hOutputProfile);

   And you are done!

   Note that cmsDeleteTransform() does NOT automatically free
   associated profiles. This works in such way to let
   programmers to use a open profile in more than one transform.



3. Embedded profiles
============================================================================

  Some image file formats, like TIFF, JPEG or PNG, does include
  the ability of embed profiles. This means that the input
  profile for the bitmap is stored inside the image file. lcms
  provides a specialised profile-opening function for deal with
  such profiles.


  cmsHPROFILE cmsOpenProfileFromMem(LPVOID MemPtr, DWORD dwSize);


  This function works like cmsOpenProfileFromFile(), but assuming
  that you are given full profile in a memory block rather than a
  filename. Here is not any "r", since these profiles are always
  read-only. A successful call will return a handle to an opened
  profile that behaves just like any other file-based.

  Memory based profiles does not waste more resources than memory,
  so you can have tons of profiles opened sumultaneously using this
  function.

NOTES:

  Once opened, you can safely FREE the memory block. lcms keeps a
  temporary copy.

  You can retrieve information of this profile, but generally
  these are minimal shaper-matrix profiles with little if none
  handy info present.

  Be also warned that some software does embed WRONG profiles,
  i.e., profiles marked as using different colorspace that
  one the profile really manages. lcms is NOT likely to understand
  these profiles since they are wrong after all.


4. Device-link profiles
============================================================================

  Device-link profiles are "smelted" profiles that represents
  a whole transform rather than single-device profiles. In theory,
  device-link profiles may have greater precision that single ones
  and are faster to load. If you plan to use device-link profiles,
  be warned there are drawbacks about its inter-operability and the
  gain of speed is almost  null.
  Perhaps their only advantage is when restoration from CMYK
  with great precision is required, since CMYK to pcs CLUTs can
  become very, very big.
 

  For creating a device-link transform, you must open the device link
  profile as usual, using cmsOpenProfileFromFile(). Then, create
  the transform with the device link profile as input and the output
  profile parameter equal to NULL:


        hDeviceLink = cmsOpenProfileFromFile("MYDEVLINK.ICC", "r");

        hTransform  = cmsCreateTransform(hDeviceLink, TYPE_RGB_8,
                                         NULL, TYPE_BGR_8,
                                         INTENT_PERCEPTUAL,
                                         0);


  That's all. lcms will understand and transparently handle the
  device-link profile.

  There is also a function for dumping a transform into a devicelink 
  profile

    cmsHPROFILE cmsTransform2DeviceLink(cmsHTRANSFORM hTransform, 
                                        DWORD dwFlags);

  This profile can be used in any other transform or saved to disk/memory.


 

5. - Built-in profiles
============================================================================

 In order to make things ease, there are several built-in profiles that 
 programmer can use without the need of any disk file. These does include:

    - sRGB profile
    - L*a*b profiles
    - XYZ profile
    - Gray profiles
    - RGB matrix-shaper.
    - Linearization device link
    - Ink-Limiting
    - Bright/Contrast/Hue/Saturation/White point adjust devicelink.

 sRGB, Lab and XYZ are very usefull for tricking & trapping. For example,
 creating a transform from sRGB to Lab could be done without any disk file.
 Something like:

        hsRGB = cmsCreate_sRGBProfile();
        hLab  = cmsCreateLabProfile()

        xform = cmsCreateTransform(hSRGB, TYPE_RGB_DBL, hLab, TYPE_Lab_DBL, 
                                        INTENT_PERCEPTUAL, cmsFLAGS_NOTPRECALC);


 Then you can convert directly form double sRGB values (in 0..1.0 range) to 
 Lab by using:

        double RGB[3];
        cmsCIELab Lab;

        RGB[0] = 0.1; RGB[1] = 0.2 RGB[2] = 0.3;
        cmsDoTransform(xform, RGB, &Lab, 1);

        .. get result on "Lab" variable ..


  Even more, you can create your own RGB or Gray profiles "on the fly" by
  using cmsCreateRGBProfile() and cmsCreateGrayProfile(). See next section
  for a explanation on how to do.
 



6. - On-the-fly profiles.
============================================================================

  There are several situations where it will be useful to build
  a minimal profile using adjusts only available at run time.
 
  Surely you have seen the classical pattern-gray trick for adjusting
  gamma: the end user moves a scroll bar and when pattern seems to
  match background gray, then gamma is adjusted.
  Another trick is to use a black background with some gray rectangles.
  The user chooses the most neutral grey, giving the white point or the
  temperature in °K.

  All these visual gadgets are not part of lcms, you must implement
  them by yourself if you like. But lcms will help you with a function for
  generating a virtual profile based on the results of these tests.

  Another usage would be to build colorimetric descriptors for
  file images that does not include any embedded profile, but
  does include fields for identifying original colorspace.

  One example is TIFF files. The TIFF 6.0 spec talks about
  "RGB Image Colorimetry" (See section 20) a "colorimetric" TIFF
  image has all needed parameters (WhitePointTag=318,
  PrimaryChromacitiesTag=318, TransferFunction=301,TransferRange=342)

  Obtain a emulated profile from such files is easy since the contents
  of these tags does match the cmsCreateRGBProfile() parameters.

  Also PNG can come with information for build a virtual profile,
  See the gAMA and cHRM chunks.


  This is the main function for creating virtual RGB profiles:


         cmsHPROFILE cmsCreateRGBProfile(LPcmsCIExyY WhitePoint,
                                        LPcmsCIExyYTRIPLE Primaries,
                                        LPGAMMATABLE TransferFunction[3]);


  It takes as arguments the white point, the primaries and 3
  gamma curves. The profile emulated is always operating in RGB
  space. Once created, a handle to a profile is returned. This
  opened profile behaves like any other file or memory based
  profile.

  Virtual RGB profiles are implemented as matrix-shaper, so they
  cannot compete against CLUT based ones, but generally are good enough
  to provide a reasonable alternative to generic profiles.


  For simplify the parameters construction, there are additional
  functions:

        LCMSBOOL  cmsWhitePointFromTemp(int TempK, LPcmsCIExyY WhitePoint);

  This function computes the xyY chromacity of white point using
  the temperature. Screen manufacturers often includes a white
  point hard switch in monitors, but they refer as "Temperature"
  instead of chromacity. Most extended temperatures are 5000K,
  6500K and 9300K

  It returns TRUE if a valid white point can be computed, or FALSE
  if the temperature were non valid. You must give a pointer to a
  cmsCIExyY struct for holding resulting white point.

  For primaries, currently I don't know any trick or proof for
  identifying primaries, so here are a few chromacities of most
  extended. Y is always 1.0


                       RED          GREEN          BLUE
                      x      y      x      y      x      y
                    ----   ----   ----   ----   ----   ----
    NTSC            0.67,  0.33,  0.21,  0.71,  0.14,  0.08
    EBU(PAL/SECAM)  0.64,  0.33,  0.29,  0.60,  0.15,  0.06
    SMPTE           0.630, 0.340, 0.310, 0.595, 0.155, 0.070
    HDTV            0.670, 0.330, 0.210, 0.710, 0.150, 0.060
    CIE             0.7355,0.2645,0.2658,0.7243,0.1669,0.0085


  These are TRUE primaries, not colorants. lcms does include a
  white-point balancing and a chromatic adaptation using a method
  called Bradford Transform for D50 adaptation.

  NOTE: Additional information about Bradford transform math can be found
  on the sRGB site:

                http://www.srgb.com

  Another kind of profiles that can be built on runtime are GrayScale 
  profiles. This can be accomplished by the function:

        cmsHPROFILE cmsCreateGrayProfile(LPcmsCIExyY WhitePoint,
                                          LPGAMMATABLE TransferFunction);

  This one is somehow easier, since it only takes the gray curve (transfer
  function) and the media white point. Of course gray scale does not need
  primaries!


 7. - Gamma tables
 ============================================================================

  The gamma tables or transfer functions are stored in a simple way,
  let's examine the GAMMATABLE typedef:

  typedef struct {
              int  nEntries;
              WORD GammaTable[1];

              } GAMMATABLE, FAR* LPGAMMATABLE;

  That is, first it comes a 32 integer for entry count, followed of
  a variable number of words describing the table. The easiest way to
  generate a gamma table is to use the function

        LPGAMMATABLE cmsBuildGamma(int nEntries, double Gamma);

  You must specify the number of entries your table will consist of,
  and the float value for gamma. The generated table has linear and non-linear
  steps, the linear ramp near 0 is for minimising noise.

  If you want to fill yourself the values, you can allocate space for your
  table by using

        LPGAMMATABLE  cmsAllocGamma(int nEntries);

  This function only creates memory for the table. The entries does
  not contain any useful value (garbage) since it is expected you will fill
  this table after created.


  You can find the inverse of a tabulated curve by using:


        LPGAMMATABLE cmsReverseGamma(int nResultSamples, LPGAMMATABLE InGamma);

  This function reverses the gamma table if it can be done. lcms does not
  detect whatever a non-monotonic function is given, so wrong input can
  result in ugly results: not to be a problem since "normal" gamma curves
  are not collapsing inputs at same output value. The new curve will be
  re-sampled to nResultSamples entries.

  You can also smooth the curve by using:

        LCMSBOOL cmsSmoothGamma(LPGAMMATABLE Tab, double lambda);

  "Smooth" curves does work better and are more pleasant to eyes.


  You can join two gamma curves with:

        LPGAMMATABLE  cmsJoinGamma(LPGAMMATABLE InGamma,
                                   LPGAMMATABLE OutGamma);


  This will let you to "refine" the generic gamma for monitors (2.1 or 2.2
  are usual values) to match viewing conditions of more or less background
  light. Note that this function uses TABULATED functions, so very exotic
  curves can be obtained by combining transfer functions with reversed
  gamma curves. Normally there is no need of worry about such gamma
  manipulations, but the functionality is here if you wish to use.

  There is a Extended join function that let specify the point it will have:

  LPGAMMATABLE cmsJoinGammaEx(LPGAMMATABLE InGamma,  
                              LPGAMMATABLE OutGamma, 
                              int nPoints);


  You must free all gamma tables you allocate (or create via
  cmsReverseGamma() or cmsJoinGamma()) by using:

        void cmsFreeGamma(LPGAMMATABLE Gamma);


  Another functions for dealing with gamma curves are:

  LPGAMMATABLE cmsDupGamma(LPGAMMATABLE Src); 
  
  Duplicates a gamma table, allocatine a new memory block

  double cmsEstimateGamma(LPGAMMATABLE t); 
  
  This one does a coarse estimation of the apparent gamma of a given curve. 
  It is intended mainly for informational purposes.

  double cmsEstimateGammaEx(LPGAMMATABLE t, double Thereshold); 

  This is similar to anterior, but it let specify the Standard deviation
  below that the curve is considered pure exponential. cmsEstimateGamma()
  does use a default value of 0.7


  LPGAMMATABLE cmsBuildParametricGamma(int nEntries, 
                                        int Type, 
                                        double Params[]);

  This one is intended to build parametric curves, as stated in ICC 
  4.0 spec. "Type" refers to ICC type plus one. If type is negative, then
  the curve is analitically reversed. This function is still experimental.

    



8. Proofing.
============================================================================

  An additional ability of lcms is to create "proofing" transforms.
  A proofing transform does emulate the colors that will appear if
  a image is rendered on a specific device. That is, for example,
  with a proofing transform I can see how will look a photo of my
  little daughter if rendered on my HP. Since most printer profiles 
  does include some sort of gamut-remapping, it is likely colors 
  will not look *exactly* as the original. Using a proofing
  transform, it can be done by using the appropriate function.

  Note that this is an important feature for final users, it is worth
  of all color-management stuff if the final media is not cheap.

  The creation of a proofing transform involves three profiles, the input
  and output ones as cmsCreateTransform() plus another, representing the
  emulated profile.


 cmsHTRANSFORM cmsCreateProofingTransform(cmsHPROFILE Input,
                                          DWORD InputFormat,
                                          cmsHPROFILE Output,
                                          DWORD OutputFormat,
                                          cmsHPROFILE Proofing,
                                          int Intent,
                                          int ProofingIntent,
                                          DWORD dwFlags);

 Also, there is another parameter for specifying the intent for
 the proof. The Intent here, represents the intent the user will select
 when printing, and the proofing intent represent the intent system is
 using for showing the proofed color. Since some printers can archive
 colors that displays cannot render (darker ones) some gamut-remapping must
 be done to accommodate such colors. Normally INTENT_ABSOLUTE_COLORIMETRIC
 is to be used: is is likely the user wants to see the exact colors on screen,
 cutting off these unrepresentable colors. INTENT_RELATIVE_COLORIMETRIC could
 serve as well. 


 Proofing transforms can also be used to show the colors that are out of the
 printer gamut. You can activate this feature by using the
 cmsFLAGS_GAMUTCHECK flag in dwFlags field.

 Then, the function:

                void cmsSetAlarmCodes(int r, int g, int b);

 Can be used to define the marker. rgb are expected to be integers
 in range 0..255


 NOTES: For activating the preview or gamut check features, you MUST
 include the corresponding flags

        cmsFLAGS_SOFTPROOFING 
        cmsFLAGS_GAMUTCHECK

 This is done in such way because the user usually wants to compare 
 with/without softproofing. Then, you can share same code. If any of the flags 
 is present, the transform does the proofing stuff. If not, the transform
 ignores the proofing profile/intent and behaves like a normal input-output
 transform. In practical usage, you need only to associate the check boxes of
 "softproofing" and "gamut check" with these flags.


9.1 Black point compensation
============================================================================

  The black point compensation feature does work in conjunction 
  with relative colorimetric intent. Perceptual intent should make no 
  difference, although it affects some profiles.

  The mechanics are simple. BPC does scale full image across gray 
  axis in order to accommodate the darkest tone origin media can 
  render to darkest tone destination media can render. As a such, 
  BPC is primarily targeting CMYK.

  Let's take an example. You have a separation (CMYK image) for,
  say, SWOP. Then you want to translate this separation to another 
  media on another printer. The destination media/printer can deliver 
  a black darker that original SWOP. Now you have several options. 

  a) use perceptual intent, and let profile do the gamut remapping for 
  you. Some users complains about the profiles moving too much the 
  colors. This is the "normal" ICC way.

  b) use relative colorimetric.This will not move any color, but 
  depending on different media you would end with "flat" images, 
  taking only a fraction of available grays or a "collapsed" images, 
  with loss of detail in dark shadows.

  c) Use relative colorimetric + black point compensation. This is 
  the discussion theme. Colors are unmoved *except* gray balance 
  that is scaled in order to accommodate to  the dynamic range of new 
  media. Is not a smart CMM, but a fist step letting the CMM to do 
  some remapping.

 The algorithm used for black point compensation is a XYZ linear scaling 
 in order to match endpoints. 

 You can enable the BPC feature by using this in the dwFlags field, it works
 on softproofs too.

                cmsFLAGS_BLACKPOINTCOMPENSATION


9.2 - Black preserving transforms
===========================================================================

Black preservation deals with CMYK -> CMYK transforms, and is intended 
to preserve, as much as possible, the black (K) channel
whilst matching color by using CMY inks. There is a tradeoff between 
accuracy and black preservation, so you lost some accuracy 
in order to preserve the original separation.  Not to be a big problem 
in most  cases, benefits of keeping K channel are huge!


For sure you have seen prints of gray images with a huge 
color cast towards magenta or green. That's very unpleasant. 

Mainly, this happens because metamerism is not taken into 
account when doing the profile. Black ink chromaticity  changes on 
different illuminants. For example, a profile is done measuring black 
ink under D50, then, under D50 this black ink have tendency to 
magenta. Ok, the profile captures such chroma and, when
reproducing colorimetrically, replaces the destination black with
CMY reproducing this magenta. Now, If you take the original K ink
and examine it under sunlight, it is not magenta anymore! But the 
reproduction using CMY keeps going magenta. Result: a nasty color 
cast . 

And this is just one of the reasons why keeping black ink is so important. 
Maybe there is a slight discontinuity, as big as the chromaticity of
blacks differ, but it is so small that the smoothing induced by the 
CLUT is enough to compensate. And this is almost nothing when 
compared with the huge cast on grays a CMYK->Lab->CMYK 
may create.


 You can enable the black preservation feature by using this flag:

			cmsFLAGS_PRESERVEBLACK



10. Error handling
============================================================================

  lcms primary goal is to be quite simple, so error handling is managed
  in a simple way. If you are using lcms as a DLL, you can tell lcms what is
  supposed to happen when an error is detected. For doing that, you can use
  this function.

        void cmsErrorAction(int nAction);


  'nAction' can be one of the following values:

        LCMS_ERROR_ABORT    0
        LCMS_ERROR_SHOW     1
        LCMS_ERROR_IGNORE   2


 Default is LCMS_ERROR_ABORT. That is, if an error is detected, lcms
 will show a MessageBox with a small explanation about the error and
 then WILL ABORT WHOLE APPLICATION. This behaviour is desirable when
 debugging, but not in final releases. For inhibit such aborting,
 you can use LCMS_ERROR_SHOW. This setting will show the error text, but
 doesn't finish the application. Some functions like cmsOpenProfileFromFile()
 or cmsCreateTransform() will return NULL instead of a valid handle as
 error-marker. Others will return FALSE.
 The last setting is LCMS_ERROR_IGNORE, that is, no message is displayed
 and only a NULL or FALSE is returned if operation fails.

 Note that if you use LCMS_ERROR_SHOW or LCMS_ERROR_IGNORE, your code
 must check the return code. This is not necessary if you are using
 LCMS_ERROR_ABORT, since the application will be terminated as soon as
 the error is detected.


 If you doesn't like this scheme, you can provide your own error handling,
 function by using:

    void cmsSetErrorHandler(cmsErrorHandlerFunction Fn);

 You need to write your own error handling function, in the form:

  int MyErrorHandlerFunction(int ErrorCode, const char *ErrorText)
  {
    ... do whatsever you want with error codes ..

  }

  And then register the error handler by using:

    cmsSetErrorHandler(MyErrorHandlerFunction);



  ErrorCode can be one of the following values:

        LCMS_ERRC_WARNING        0x1000
        LCMS_ERRC_RECOVERABLE    0x2000
        LCMS_ERRC_ABORTED        0x3000

  ErrorText is a text holding an english description of error.

  You should return 1 if you are handling the error. Returning 0, 
  throws the error back to the default error handler.

  WARNING: lcms is *not* supposed to recover from all errors. If you are 
  using your own error handling, please note that you have to abort 
  all process if you recive LCMS_ERRC_ABORTED in ErrorCode parameter.
  Incoming versions will handle this issue more properly.

11. Getting information from profiles.
============================================================================

  There are some functions for retrieve information on opened profiles. 
  These are:

        LCMSBOOL  cmsIsTag(cmsHPROFILE hProfile, icTagSignature sig);

  This one does check if a particular tag is present. Remaining does take
  useful information about general parameters.

        LCMSBOOL  cmsTakeMediaWhitePoint(LPcmsCIEXYZ Dest, cmsHPROFILE hProfile);
        LCMSBOOL  cmsTakeMediaBlackPoint(LPcmsCIEXYZ Dest, cmsHPROFILE hProfile);
        LCMSBOOL  cmsTakeIluminant(LPcmsCIEXYZ Dest, cmsHPROFILE hProfile);
        LCMSBOOL  cmsTakeColorants(LPcmsCIEXYZTRIPLE Dest, cmsHPROFILE hProfile);

        const char* cmsTakeProductName(cmsHPROFILE hProfile);
        const char* cmsTakeProductDesc(cmsHPROFILE hProfile);

        int   cmsTakeRenderingIntent(cmsHPROFILE hProfile);

        icColorSpaceSignature   cmsGetPCS(cmsHPROFILE hProfile);
        icColorSpaceSignature   cmsGetColorSpace(cmsHPROFILE hProfile);
        icProfileClassSignature cmsGetDeviceClass(cmsHPROFILE hProfile);


  These functions are given mainly for building user interfaces,
  you don't need to use them if you just want a plain translation.
  Other usage would be to identify "families" of profiles.
  The functions returning strings are using an static buffer that is
  overwritten in each call, others does accept a pointer to an specific
  struct that is filled if function is successful.


        #define LCMS_USED_AS_INPUT      0
        #define LCMS_USED_AS_OUTPUT     1
        #define LCMS_USED_AS_PROOF      2

        LCMSBOOL cmsIsIntentSupported(cmsHPROFILE hProfile, int Intent, int UsedDirection);

  This one helps on inquiring if a determinate intent is
  supported by an opened profile. You must give a handle to
  profile, the intent and a third parameter specifying how the
  profile would be used. The function does return TRUE if intent
  is supported or FALSE if not. If the intent is not supported,
  lcms will use default intent (usually perceptual).


 ADVANCED TOPICS
 ===============

  The following section does describe additional functions for advanced
  use of lcms. Several of these are expanding the capabilities of lcms
  above a 'pure' CMM. In this way, they do not belong to the CMM layer, 
  but as a low level primitives for the CMS formed by the CMM and the 
  profilers. There is no need of these function on "normal" usage.


12. Creating and writting new profiles.
============================================================================
 
  Since version 1.09, lcms has the capability of writting profiles. The
  interface is very simple, despite its use does imply certain knowleage 
  of profile internals.

  These are the functions needed to create a new profile:

    void cmsSetDeviceClass(cmsHPROFILE hProfile, icProfileClassSignature sig);
    void cmsSetColorSpace(cmsHPROFILE hProfile, icColorSpaceSignature sig);
    void cmsSetPCS(cmsHPROFILE hProfile, icColorSpaceSignature pcs);
    void cmsSetRenderingIntent(cmsHPROFILE hProfile, int RenderingIntent);

    LCMSBOOL cmsAddTag(cmsHPROFILE hProfile, icTagSignature sig, void* data);

   And the generic file management ones:

   cmsOpenProfileFromFile() and cmsCloseProfile()

   Device class, colorspace and PCS type does affect to header and overall 
   profile. cmsSetRenderingIntent() sets the (informative) intent field on
   header. Rest of information is included using cmsAddTag().

   Of course you must know which tags to include and the meaning of each tag.
   LittleCms does nothing to check the validity of newly created profiles. 
   These functions are only intended to be a low level interface to profile
   creation. 

   Creating a new profile
   -----------------------

   When you open a profile with 'w' as access mode, you got a simpler 
   Lab identity. That is, a profile marked as Lab colorspace that passes
   input untouched to output. You need to fully qualify your profile by
   setting its colorspace, device class, PCS and then add the required 
   tags. cmsAddTag() does understand following tags:

      

       Signature                   Expected data type
       ==========================  ==================

       icSigCharTargetTag               const char*
       icSigCopyrightTag                const char*
       icSigProfileDescriptionTag       const char*
       icSigDeviceMfgDescTag            const char*
       icSigDeviceModelDescTag          const char*
       icSigRedColorantTag              LPcmsCIEXYZ
       icSigGreenColorantTag            LPcmsCIEXYZ
       icSigBlueColorantTag             LPcmsCIEXYZ
       icSigMediaWhitePointTag          LPcmsCIEXYZ
       icSigMediaBlackPointTag          LPcmsCIEXYZ
       icSigRedTRCTag                   LPGAMMATABLE
       icSigGreenTRCTag                 LPGAMMATABLE
       icSigBlueTRCTag                  LPGAMMATABLE
       icSigGrayTRCTag                  LPGAMMATABLE
       icSigAToB0Tag                    LPLUT
       icSigAToB1Tag                    LPLUT
       icSigAToB2Tag                    LPLUT
       icSigBToA0Tag                    LPLUT
       icSigBToA1Tag                    LPLUT
       icSigBToA2Tag                    LPLUT
       icSigGamutTag                    LPLUT
       icSigPreview0Tag                 LPLUT
       icSigPreview1Tag                 LPLUT
       icSigPreview2Tag                 LPLUT
       icSigChromaticityTag             LPcmsCIExyYTRIPLE
       icSigNamedColor2Tag              LPcmsNAMEDCOLORLIST
	   icSigColorantTableTag		    LPcmsNAMEDCOLORLIST
       icSigColorantTableOutTag         LPcmsNAMEDCOLORLIST
	   icSigCalibrationDateTimeTag	    const struct tm*
    
    More tags are expected to be added in future revisions.
              

  Another way to create profiles is by using _cmsSaveProfile() or
  _cmsSaveProfileToMem(). See the API reference for details.



13. LUT handling
============================================================================

 LUT stands for L)ook U)p T)ables. This is a generalizad way to handle
 workflows consisting of a quite complex stages. Here is the pipeline 
 scheme, Don't panic!

   
    [Mat] -> [L1] -> [Mat3] -> [Ofs3] -> [L3] -> 
                [CLUT] -> [L4] -> [Mat4] -> [Ofs4] -> [L2]


    Mat{n} are matrices of 3x3
    Ofs{n} are offsets
    CLUT is a multidimensional LUT table


 Some or all of these stages may be missing. LUTS can handle up to 
 8 channels on input and 16 channels of output.

 The programmer can allocate a LUT by calling: 
 
        NewLUT = cmsAllocLUT();

 This allocates an empty LUT. Input is passed transparently to output 
 by default. The programmer can optionally add pre/post linearization 
 tables by using:

    cmsAllocLinearTable(LPLUT NewLUT, LPGAMMATABLE Tables[], int nTable);

 Being Table:

                1 - Prelinearization 1D table L1
                2 - Postlinearization 1D table L2
                3 - linearization 1D table L3
                4 - linearization 1D table L4
  

  The 3x3 matrices can be set by:

  
   LPLUT cmsSetMatrixLUT4(LPLUT Lut, LPMAT3 M, LPVEC3 off, DWORD dwFlags);

   Flags define the matrix to set:

        LUT_HASMATRIX:   Mat
        LUT_HASMATRIX3:  Mat3 
        LUT_HASMATRIX4:  Mat4 
   
  The CLUT is a multidimensional table where most of the magic of 
  colormanagement is done. It holds as many (hyper)cubes as ouput 
  channels and the dimension of these hypercubes is the number of
  input channels.

  To fill the CLUT with sampled values, the programmer can call:
  
    LCMSBOOL cmsSample3DGrid(LPLUT Lut, 
                        _cmsSAMPLER Sampler, 
                        LPVOID Cargo, 
                        DWORD dwFlags)  


  This function builds the CLUT table by calling repeatly a 
  callback function:


    typedef int (* _cmsSAMPLER)(register WORD In[],
                                register WORD Out[],
                                register LPVOID Cargo);


   The programmer has to write his callback function. This function
   should calculate Out[] values given a In[] set. For example, if we 
   want a LUT to invert (negate) channels, a sampler could be:

   int InvertSampler(register WORD In[],
                            register WORD Out[],
                            register LPVOID Cargo)
    {
        for (i=0; i < 3; i++)
                Out[i] = ~ In[i];

    return TRUE;
    }


    cmsSample3DGrid does call this function to build the CLUT. 
    Pre/post linearization tables may be taken into account across
    flags parameter

        Flags                   Meaning
    ================        =======================================
    LUT_HASTL1              Do reverse linear interpolation on 
                            prelinearization table before calling 
                            the callback.

    LUT_HASTL2              Do reverse linear interpolation on
                            postlinearization table after calling 
                            the callback.

    LUT_INSPECT             Does NOT write any data to the 3D CLUT, 
                            instead, retrieve the coordinates for inspection 
                            only. If using such flag, Out[] will hold
                            the CLUT contents.
                                    In[]  -> The CLUT indexes
                                    Out[] ->  The CLUT contents

        
    HASTL1 and HASTL2 Flags are intended to be used as an aid for 
    building non-uniformly spaced CLUTs. Using these flags results in 
    "undoing" any linearization that tables could apply. In such way, 
    the callback is expected to be called with In[] always the original 
    colorspace, and must return  Out[] values always in original 
    (non-postlinearized) space as well. The linearization cooking is done
    automatically.
     
    The callback must return TRUE if all is ok, or zero
    to indicate error. If error condition is raised, whole CLUT
    construction is aborted.

    Once builded, programmer can evaluate the LUT by using:

    void   cmsEvalLUT(LPLUT Lut, WORD In[], WORD Out[]);

    That does interpolate values according on pipeline tables.

    Finally, a LUT can be freed by 
    
    void   cmsFreeLUT(LPLUT Lut);

    Or retrieved from a profile using:

    LPLUT  cmsReadICCLut(cmsHPROFILE hProfile, icTagSignature sig);

    To include a LUT in a profile, use cmsAddTag() with tag signature and 
    a pointer to LUT structure as parameters. See cmsAddTag() in the API
    reference for more info.

  

 14. Helper functions
============================================================================


  Here are some functions that could be useful. They are not needed
  in "normal" usage.

  Colorimetric space conversions:

    void cmsXYZ2xyY(LPcmsCIExyY Dest, const LPcmsCIEXYZ Source);
    void cmsxyY2XYZ(LPcmsCIEXYZ Dest, const LPcmsCIExyY Source);
    void cmsXYZ2Lab(LPcmsCIEXYZ WhitePoint, LPcmsCIELab Lab, const LPcmsCIEXYZ xyz);
    void cmsLab2XYZ(LPcmsCIEXYZ WhitePoint, LPcmsCIEXYZ xyz, const LPcmsCIELab Lab);
    void cmsLab2LCh(LPcmsCIELCh LCh, const LPcmsCIELab Lab);
    void cmsLCh2Lab(LPcmsCIELab Lab, const LPcmsCIELCh LCh);

    Notation conversion: (converts from PT_* colorspaces to ICC notation)

    icColorSpaceSignature _cmsICCcolorSpace(int OurNotation);
    
    Channels of a given colorspace:

    int _cmsChannelsOf(icColorSpaceSignature ColorSpace);

    
   Chromatic Adaptation:

       LCMSBOOL cmsAdaptToIlluminant(LPcmsCIEXYZ Result, LPcmsCIEXYZ SourceWhitePt,
                                     LPcmsCIEXYZ Illuminant, LPcmsCIEXYZ Value);

   Build a balanced transfer matrix with chromatic adaptation, this
   is equivalent to "cooking" required to conform a colorant matrix.

      LCMSBOOL cmsBuildRGB2XYZtransferMatrix(LPMAT3 r,
                                          LPcmsCIExyY WhitePoint,
                                          LPcmsCIExyYTRIPLE Primaries);



 15. Color difference functions
============================================================================

 These functions does compute the difference between two Lab colors, 
 using several difference spaces


double  cmsDeltaE(LPcmsCIELab Lab1, LPcmsCIELab Lab2);
double  cmsCIE94DeltaE(LPcmsCIELab Lab1, LPcmsCIELab Lab2);
double  cmsBFDdeltaE(LPcmsCIELab Lab1, LPcmsCIELab Lab2);
double  cmsCMCdeltaE(LPcmsCIELab Lab1, LPcmsCIELab Lab2);
double  cmsCIE2000DeltaE(LPcmsCIELab Lab1, LPcmsCIELab Lab2, double Kl, double Kc, double Kh);



 16. PostScript generation
 ============================================================================
 3 functions carry the task of obtaining CRD and CSA. 


    DWORD cmsGetPostScriptCSA(cmsHPROFILE hProfile, int Intent, LPVOID Buffer, DWORD dwBufferLen);
    DWORD cmsGetPostScriptCRD(cmsHPROFILE hProfile, int Intent, LPVOID Buffer, DWORD dwBufferLen);
    DWORD cmsGetPostScriptCRDEx(cmsHPROFILE hProfile, int Intent, DWORD dwFlags, LPVOID Buffer, DWORD dwBufferLen);


 cmsGetPostScriptCRDEx allows black point compensation using 
 cmsFLAGS_WHITEBLACKCOMPENSATION in flags field.

 PostScrip colorflow is often done in a different way. Insted of creating a 
 transform, it is sometimes desirable to delegate the color management to 
 PostScript interpreter. These functions does translate input and output 
 profiles into Color Space Arrays (CSA) and Color Rendering Dictionaries (CRD)

    · CRD are equivalent to output (printer) profiles. Can be 
      loaded into printer at startup and can be stored as resources.

    · CSA are equivalent to input and workspace profiles, and are 
      intended to  be included in the document definition.

 These functions does generate the PostScript equivalents. Since the lenght of 
 the resultant PostScript code is unknown in advance, you can call the 
 functions with len=0 and Buffer=NULL to get the lenght. After that, you need 
 to allocate enough memory to contain the whole block

 Example:

      Size = cmsGetPostScriptCSA(hProfile, INTENT_PERCEPTUAL, NULL, 0);
      If (Size == 0) error()

       Block = malloc(Size); 
       cmsGetPostScriptCSA(hProfile, INTENT_PERCEPTUAL, Block, Size);
   

  Devicelink profiles are supported, as long as input colorspace matches
  Lab/XYZ for CSA or output colorspace matches Lab/XYZ for CRD. This can
  be used in conjuntion with cmsCreateMultiprofileTransform(), 
  and cmsTransform2DeviceLink() to embed complex color flow into PostScript.


  
  WARNING: Preccision of PostScript is limited to 8 bits per sample. If you 
  can choose between normal transforms and CSA/CRD, normal transforms will 
  give more accurancy. However, there are situations where there is no 
  chance.



 17. CIECAM02
 ============================================================================

  The model input data are the adapting field luminance in cd/m2
  (normally taken to be 20% of the luminance of white in the adapting field),
  La , the relative tristimulus values of the stimulus, XYZ, the relative
  tristimulus values of white in the same viewing conditions, "whitePoint",
  and the relative luminance of the background, Yb . Relative tristimulus
  values should be expressed on a scale from Y = 0 for a perfect black
  to Y = 100 for a perfect reflecting diffuser. 

  All CIE tristimulus values are obtained using the CIE 1931 Standard 
  Colorimetric Observer (2°).


    typedef struct {

              cmsCIEXYZ whitePoint; // The media white in XYZ

              double    Yb;         
              double    La;
              int       surround;
              double    D_value;

              } cmsViewingConditions, FAR* LPcmsViewingConditions;

    
    Surround can be one of these

        
        #define AVG_SURROUND       1
        #define DIM_SURROUND       2
        #define DARK_SURROUND      3



    D_value (adaptation degree) is any value between 0 and 1

    
    The functions for dealing with CAM02 appearance model are:
    
    
    LCMSHANDLE cmsCIECAM02Init(LPcmsViewingConditions pVC);
    void       cmsCIECAM02Done(LCMSHANDLE hModel);
    void       cmsCIECAM02Forward(LCMSHANDLE hModel, LPcmsCIEXYZ pIn, LPcmsJCh pOut);
    void       cmsCIECAM02Reverse(LCMSHANDLE hModel, LPcmsJCh pIn,    LPcmsCIEXYZ pOut);
        

    For example, to convert XYZ values from a given viewing condition to another:

    a) Create descriptions of both viewing conditions by using cmsCIECAM02Init
    b) Convert XYZ to JCh using cmsCIECAM02Forward for viewing condition 1
    c) Convert JCh back to XYZ using cmsCIECAM02Reverse for viewing condition 2
    d) when done, free both descriptions


        cmsViewingConditions vc1, vc2;
        cmsJCh Out;
        cmsCIEXYZ In;
        HANDLE h1, h2;

   
        vc.whitePoint.X = 98.88;
        vc.whitePoint.Y = 90.00;
        vc.whitePoint.Z = 32.03;
        vc.Yb = 18;
        vc.La = 200;
        vc.surround = AVG_SURROUND;
        vc.D_value  = 1.0;

        h1 = cmsCIECAM02Init(&vc);


        vc2.whitePoint.X = 98.88;
        vc2.whitePoint.Y = 100.00;
        vc2.whitePoint.Z = 32.03;
        vc2.Yb = 20;
        vc2.La = 20;
        vc2.surround = AVG_SURROUND;
        vc2.D_value  = 1.0;

        h2 = cmsCIECAM02Init(&vc);
      
        In.X= 19.31; 
        In.Y= 23.93; 
        In.Z =10.14;

        cmsCIECAM02Forward(h1, &In, &Out);       
        cmsCIECAM02Reverse(h2, &Out, &In);
        
        cmsCIECAM02Done(h1);        
        cmsCIECAM02Done(h2);        

 See the CIECAM02 paper on CIE site for further details.


 18. Named color profiles
 ============================================================================

 Named color profiles are a special kind of profiles handling lists of spot 
 colors. The typical example is PANTONE. CMM deals with named color profiles like 
 all other types, except they must be in input stage and the encoding supported 
 is limited to  a one single channel of 16-bit indexes.

 Let's assume we have a Named color profile holding only 4 colors:

    · CYAN     
    · MAGENTA  
    · YELLOW   
    · BLACK

 We create a transform using:


 hTransform = cmsCreateTransform(hNamedColorProfile,
                                           TYPE_NAMED_COLOR_INDEX,
                                           hOutputProfile,
                                           TYPE_BGR_8,
                                           INTENT_PERCEPTUAL, 0);

 "TYPE_NAMED_COLOR_INDEX" is a special encoding for these profiles, it 
 represents a single channel holding the spot color index. In our case 
 value 0 will be "CYAN", value 1 "MAGENTA" and so one.

 For converting between string and index there is an auxiliary function:

    int cmsNamedColorIndex(cmsHTRANSFORM hTransform, const char* ColorName);

 That will perform a look up on the spot colors database and return the color 
 number or -1 if the color was not found.  Other additional functions for named 
 color transforms are:


    int cmsNamedColorCount(cmsHTRANSFORM hTransform);

  That returns the number of colors present on transform database.


    LCMSBOOL cmsNamedColorInfo(cmsHTRANSFORM xform, int nColor, 
                                char* Name, char* Prefix, char* Suffix);

  That returns extended information about a given color. Named color profiles 
  can also be grouped by using multiprofile transforms. In such case, the database 
  will be formed by the union  of all colors in all named color profiles present in 
  transform.


  Named color profiles does hold two coordinates for each color, let's
  take our PANTONE example. This profile would contain for each color 
  the CMYK colorants plus its PCS coordinates, usually in Lab space.
 
  lcms can work with named color using both coordinates. Creating a
  transform with two profiles, if the input one is a named color, then you 
  obtain the translated color using PCS. 
  
  Example, named color -> sRGB will give the color patches in sRGB
 
  In the other hand, setting second profile to NULL, returns the device 
  coordinates, that is, CMYK colorants in our PANTONE sample. 
  
  Example: Named color -> NULL will give the CMYK amount for each spot color.
 

  The transform must use TYPE_NAMED_COLOR_INDEX on input. That is, a single
  channel containing the 0-based color index. 
  
  Then you have: 
 
        cmsNamedColorIndex(cmsHTRANSFORM xform, const char* Name)
 
  for obtaining index from color name, and 
    
        cmsNamedColorInfo(), cmsNamedColorCount() to retrieve the list.
 
  The profile is supposed to be for a unique device. Then the CMYK 
  values does represent the amount of inks THIS PRINTER needs to render 
  the spot color. The profile also has the Lab values  corresponding to 
  the color. This really would have no sense if gamut of printer were 
  infinite, but since printers does have a limited gamut a PANTONE-certified 
  printer renders colors near gamut boundaries with some limitations. 
  The named color profile is somehow explaining which are these limitation 
  for that printer.
 
  So, you can use a named color profile in two different ways, as output, 
  giving the index and getting the CMYK values or as input and getting the 
  Lab for that color. 
 
  A transform named color -> NULL will give the CMYK values for the spot 
  color on the printer the profile is describing. This would be the normal usage.
 
  A transform Named color -> another printer will give on the output printer 
  the spot colors as if they were printed in the printer named color profile 
  is describing. This is useful for soft proofing.
 
  As an additional feature, lcms can "group" several named color profiles
  into a single database by means of cmsCreateMultiprofileTransform().
  Such case works as described above, but joining all named colors as they 
  were in a single profile.



 19. Conclusion.
 ============================================================================

  That's almost all you must know to begin experimenting with profiles,
  just a couple of words about the possibilities ICC profiles can
  give to programmers:

        o ColorSpace profiles are valuable tools for converting
          from/to exotic file formats. I'm using lcms to read
          Lab TIFF using the popular Sam Leffler's TIFFLib. Also,
          the ability to restore separations are much better that
          the infamous 1-CMY method.

        o Abstract profiles can be used to manipulate color of
          images, contrast, brightness and true-gray reductions can
          be done fast and accurately. Grayscale conversions can be
          done exceptionally well, and even in tweaked colorspaces
          that does emulate more gray levels that the output device
          can effectively render.

        o lcms does all calculation on 16 bit per component basis,
          the display and output profiles can take advantage of these
          precision and efficiently emulate more than 8 bits per sample.
          You probably will not notice this effect on screen, but it can
          be seen on printed or film media.


        o There is a huge quantity of profiles moving around the net,
          and there is very good software for generating them, so
          future compatibility seems to be assured.



 I thank you for your time and consideration.

 Enjoy!



Sample 1: How to convert RGB to CMYK and back
=============================================

This is easy. Just use a transform between RGB profile to CMYK profile.


#include "lcms.h"


int main(void)
{

     cmsHPROFILE hInProfile, hOutProfile;
     cmsHTRANSFORM hTransform;
     int i;


     hInProfile  = cmsOpenProfileFromFile("sRGBColorSpace.ICM", "r");
     hOutProfile = cmsOpenProfileFromFile("MyCmyk.ICM", "r");



     hTransform = cmsCreateTransform(hInProfile,
                                           TYPE_RGB_8,
                                           hOutProfile,
                                           TYPE_CMYK_8,
                                           INTENT_PERCEPTUAL, 0);


     for (i=0; i < AllScanlinesTilesOrWatseverBlocksYouUse; i++)
     {
           cmsDoTransform(hTransform, YourInputBuffer,
                                      YourOutputBuffer,
                                      YourBuffersSizeInPixels);
     }



     cmsDeleteTransform(hTransform);
     cmsCloseProfile(hInProfile);
     cmsCloseProfile(hOutProfile);

     return 0;
}


And Back....? Same. Just exchange profiles and format descriptors:



int main(void)
{

     cmsHPROFILE hInProfile, hOutProfile;
     cmsHTRANSFORM hTransform;
     int i;


     hInProfile  = cmsOpenProfileFromFile("MyCmyk.ICM", "r");
     hOutProfile = cmsOpenProfileFromFile("sRGBColorSpace.ICM", "r");



     hTransform = cmsCreateTransform(hInProfile,
                                           TYPE_CMYK_8,
                                           hOutProfile,
                                           TYPE_RGB_8,
                                           INTENT_PERCEPTUAL, 0);


     for (i=0; i < AllScanlinesTilesOrWatseverBlocksYouUse; i++)
     {
           cmsDoTransform(hTransform, YourInputBuffer,
                                      YourOutputBuffer,
                                      YourBuffersSizeInPixels);
     }



     cmsDeleteTransform(hTransform);
     cmsCloseProfile(hInProfile);
     cmsCloseProfile(hOutProfile);

     return 0;
}


Sample 2: How to deal with Lab/XYZ spaces
==========================================

This is more elaborated. There is a Lab identity Built-In profile involved.


// Converts Lab(D50) to sRGB:

int main(void)
{

     cmsHPROFILE hInProfile, hOutProfile;
     cmsHTRANSFORM hTransform;
     int i;
     BYTE RGB[3];
     cmsCIELab Lab[..];


     hInProfile  = cmsCreateLabProfile(NULL);
     hOutProfile = cmsOpenProfileFromFile("sRGBColorSpace.ICM", "r");



     hTransform = cmsCreateTransform(hInProfile,
                                           TYPE_Lab_DBL,
                                           hOutProfile,
                                           TYPE_RGB_8,
                                           INTENT_PERCEPTUAL, 0);


     for (i=0; i < AllLabValuesToConvert; i++)
     {
           // Fill in the Float Lab

           Lab[i].L = Your L;
           Lab[i].a = Your a;
           Lab[i].b = Your b;
           
           cmsDoTransform(hTransform, Lab, RGB, 1);

           .. Do whatsever with the RGB values in RGB[3]
     }



     cmsDeleteTransform(hTransform);
     cmsCloseProfile(hInProfile);
     cmsCloseProfile(hOutProfile);

     return 0;
}




Annex A. About intents
============================================================================

  Charles Cowens gives to me a clear explanation about
  accomplished intents. Since it is very useful to understand how
  intents are internally implemented, I will reproduce here.


  AtoBX/BtoAX LUTs and Rendering Intents

  The ICC spec is pretty detailed about the LUTs and their
  varying meaning according to context in tables 20, 21, and 22
  in section 6.3. My reading of this is that even though there
  are 4 rendering intent selectors there are really 6 rendering
  styles:

                Relative Indefinite
                (Relative) Perceptual
                Relative Colorimetric
                (Relative) Saturation
                Absolute Indefinite
                Absolute Colorimetric

  If a device profile has a single-LUT or matrix:

   * Perceptual, Relative Colorimetric, Saturation selectors
     produce the same Relative Indefinite rendering style

   * Absolute Colorimetric selector produces an Absolute
     Indefinite rendering style derived from the single LUT or
     matrix, the media white point tag, and the inverse of a
     white point compensation method designated by the CMS

  If a device profile has 3 LUTs:

   * Perceptual, Relative Colorimetric, Saturation selectors
     produce the appropriate rendering styles using the 0, 1, and
     2 LUTs respectively

   * Absolute Colorimetric selector produces an Absolute
     Colorimetric rendering style derived from the Relative
     Colorimetric LUT (numbered "1"), the media white point tag,
     and the inverse of a white point compensation method
     designated by the CMS


 This would explain why perceptual is the default rendering style
 because a single-LUT profile's LUT is numbered "0".


Annex B Apparent bug in XYZ -> sRGB transforms
============================================================================

John van den Heuvel warns me about an apparent bug on
XYZ -> sRGB transforms. Ver 1.10 should minimize this effect.

The obtained results are visually OK, but numbers seems to be wrong.
It appears only when following conditions:

        a) You are using a transform from a colorspace with
           a gamut a lot bigger that output space, i.e. XYZ.
           Note than sRGB -> XYZ does work OK.

        b) You are using absolute colorimetric intent.

        c) You transform a color near gamut hull boundary

        d) The output profile is implemented as a matrix-shaper,
           i.e. sRGB.

        e) You are using precalculated device link tables.

The numbers lcms returns doesn't match closely that color, but other
perceptually close to the intended one.

It happens that since XYZ has a very big gamut, and sRGB a narrow
one on compared to XYZ, when lcms tries to compute the device link
between XYZ -> sRGB, got most values as negative RGB (out of gamut).
lcms assumes this is effectively out of gamut and clamps to 0.
Then, since (127, 0, 0) is just over gamut boundary (for example
(127, -1, -1) would be out of gamut), lcms does interpolate
wrongly, not between -n to n but between 0 to n.

I could put an If() in the code for dealing with such situation,
but I guess it is better not touch anything and document this
behaviour.

XYZ is almost never used as a storage space, and since most monitor
profiles are implemented as matrix shaper touching this would slow
down common operations. The solution is quite simple,
if you want to deal with numbers, then use cmsFLAGS_NOTPRECALC.
If you deal with images, let lcms optimize the transform.
Visual results should appear OK, no matter numbers doesn't match.


