Package com.drew.metadata.jpeg

Class HuffmanTablesDirectory.HuffmanTable

java.lang.Object

com.drew.metadata.jpeg.HuffmanTablesDirectory.HuffmanTable

Enclosing class:

HuffmanTablesDirectory

public static class HuffmanTablesDirectory.HuffmanTable
extends Object

An instance of this class holds a JPEG Huffman table.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static enum	HuffmanTablesDirectory.HuffmanTable.HuffmanTableClass

Constructor Summary

Constructors

Constructor	Description
HuffmanTable(HuffmanTablesDirectory.HuffmanTable.HuffmanTableClass tableClass, int tableDestinationId, byte[] lengthBytes, byte[] valueBytes)

Method Summary

Modifier and Type	Method	Description
byte[]	getLengthBytes()
HuffmanTablesDirectory.HuffmanTable.HuffmanTableClass	getTableClass()
int	getTableDestinationId()
int	getTableLength()
byte[]	getValueBytes()
boolean	isOptimized()	The opposite of isTypical().
boolean	isTypical()	Evaluates whether this table is a "typical" Huffman table.

Methods inherited from class java.lang.Object

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

Constructor Details

HuffmanTable

public HuffmanTable(HuffmanTablesDirectory.HuffmanTable.HuffmanTableClass tableClass,
 int tableDestinationId,
 byte[] lengthBytes,
 byte[] valueBytes)

Method Details

getTableLength

public int getTableLength()

Returns:

The table length in bytes.

getTableClass

public HuffmanTablesDirectory.HuffmanTable.HuffmanTableClass getTableClass()

Returns:

The HuffmanTablesDirectory.HuffmanTable.HuffmanTableClass of this table.

getTableDestinationId

public int getTableDestinationId()

Returns:

the the destination identifier for this table.

getLengthBytes

public byte[] getLengthBytes()

Returns:

A byte array with the L values for this table.

getValueBytes

public byte[] getValueBytes()

Returns:

A byte array with the V values for this table.

isTypical

public boolean isTypical()

Evaluates whether this table is a "typical" Huffman table.

"Typical" has a special meaning in this context as the JPEG standard (ISO/IEC 10918 or ITU-T T.81) defines 4 Huffman tables that has been developed from the average statistics of a large set of images with 8-bit precision. Using these instead of calculating the optimal Huffman tables for a given image is faster, and is preferred by many hardware encoders and some hardware decoders.

Even though the JPEG standard doesn't define these as "standard tables" and requires a decoder to be able to read any valid Huffman tables, some are in reality limited decoding images using these "typical" tables. Standards like DCF (Design rule for Camera File system) and DLNA (Digital Living Network Alliance) actually requires any compliant JPEG to use only the "typical" Huffman tables.

This is also related to the term "optimized" JPEG. An "optimized" JPEG is a JPEG that doesn't use the "typical" Huffman tables.

Returns:

Whether or not this table is one of the predefined "typical" Huffman tables.

isOptimized

public boolean isOptimized()

The opposite of isTypical().

Returns:

Whether or not this table is "optimized" - which means that it isn't one of the "typical" Huffman tables.