Class JPEGQuality

java.lang.Object

com.twelvemonkeys.imageio.metadata.jpeg.JPEGQuality

public final class JPEGQuality
extends Object

Determines an approximate JPEG compression quality value from the quantization tables.

Version:

$Id: JPEGQuality.java,v 1.0 16.02.12 17:07 haraldk Exp$

Field Summary

Fields

Modifier and Type	Field	Description
(package private) static final int	DCT_SIZE_2
(package private) static final int	NUM_QUANT_TABLES

Constructor Summary

Constructors

Constructor	Description
JPEGQuality()

Method Summary

Modifier and Type	Method	Description
private static int	getJPEGQuality(int[][] quantizationTables)
static float	getJPEGQuality(List<JPEGSegment> segments)	Determines an approximate JPEG compression quality value from the quantization tables.
static float	getJPEGQuality(ImageInputStream input)	Determines an approximate JPEG compression quality value from the quantization tables.
static JPEGQTable[]	getQTables(List<JPEGSegment> segments)
private static int[][]	getQuantizationTables(List<JPEGSegment> dqtSegments)
static void	main(String[] args)

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

NUM_QUANT_TABLES

static final int NUM_QUANT_TABLES

See Also:

• Constant Field Values

DCT_SIZE_2

static final int DCT_SIZE_2

See Also:

• Constant Field Values

Constructor Details

JPEGQuality

public JPEGQuality()

Method Details

getJPEGQuality

public static float getJPEGQuality(List<JPEGSegment> segments)
                            throws IOException

Determines an approximate JPEG compression quality value from the quantization tables. The value will be in the range [0...1], where 1 is the best possible value.

Parameters:

segments - a list of JPEG segments containing the DQT quantization tables.

Returns:

a float in the range [0...1], representing the JPEG quality, or -1 if the quality can't be determined.

Throws:

IIOException - if a JPEG format error is found during parsing.

IOException - if an I/O exception occurs during parsing.

See Also:

• ImageWriteParam.setCompressionQuality(float)
• JPEG.DQT

getJPEGQuality

public static float getJPEGQuality(ImageInputStream input)
                            throws IOException

Determines an approximate JPEG compression quality value from the quantization tables. The value will be in the range [0...1], where 1 is the best possible value.

Parameters:

input - an image input stream containing JPEG data.

Returns:

a float in the range [0...1], representing the JPEG quality, or -1 if the quality can't be determined.

Throws:

IIOException - if a JPEG format error is found during parsing.

IOException - if an I/O exception occurs during parsing.

See Also:

• ImageWriteParam.setCompressionQuality(float)
• JPEG.DQT

getJPEGQuality

private static int getJPEGQuality(int[][] quantizationTables)
                           throws IOException

Throws:

IOException

getQTables

public static JPEGQTable[] getQTables(List<JPEGSegment> segments)
                               throws IOException

Throws:

IOException

getQuantizationTables

private static int[][] getQuantizationTables(List<JPEGSegment> dqtSegments)
                                      throws IOException

Throws:

IOException

main

public static void main(String[] args)
                 throws IOException

Throws:

IOException