Package com.drew.metadata.jpeg

Class HuffmanTablesDirectory

java.lang.Object

com.drew.metadata.Directory

com.drew.metadata.jpeg.HuffmanTablesDirectory

public class HuffmanTablesDirectory
extends Directory

Directory of tables for the DHT (Define Huffman Table(s)) segment.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	HuffmanTablesDirectory.HuffmanTable	An instance of this class holds a JPEG Huffman table.

Field Summary

Fields

Modifier and Type	Field	Description
static final int	TAG_NUMBER_OF_TABLES

Constructor Summary

Constructors

Constructor	Description
HuffmanTablesDirectory()

Method Summary

Modifier and Type	Method	Description
String	getName()	Provides the name of the directory, for display purposes.
int	getNumberOfTables()
HuffmanTablesDirectory.HuffmanTable	getTable(int tableNumber)
boolean	isOptimized()	The opposite of isTypical().
boolean	isTypical()	Evaluates whether all the tables in this HuffmanTablesDirectory are "typical" Huffman tables.

Methods inherited from class com.drew.metadata.Directory

addError, containsTag, getBoolean, getBooleanObject, getByteArray, getDate, getDate, getDate, getDescription, getDouble, getDoubleObject, getErrorCount, getErrors, getFloat, getFloatObject, getInt, getIntArray, getInteger, getLong, getLongObject, getObject, getParent, getRational, getRationalArray, getString, getString, getStringArray, getStringValue, getStringValueArray, getTagCount, getTagName, getTags, hasErrors, hasTagName, isEmpty, setBoolean, setByteArray, setDate, setDescriptor, setDouble, setDoubleArray, setFloat, setFloatArray, setInt, setIntArray, setLong, setObject, setObjectArray, setParent, setRational, setRationalArray, setString, setStringArray, setStringValue, setStringValueArray, toString

Methods inherited from class java.lang.Object

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

Field Details

TAG_NUMBER_OF_TABLES

public static final int TAG_NUMBER_OF_TABLES

See Also:

• Constant Field Values

Constructor Details

HuffmanTablesDirectory

public HuffmanTablesDirectory()

Method Details

getName

public String getName()

Description copied from class: Directory

Provides the name of the directory, for display purposes. E.g. Exif

Specified by:

getName in class Directory

Returns:

the name of the directory

getTable

public HuffmanTablesDirectory.HuffmanTable getTable(int tableNumber)

Parameters:

tableNumber - The zero-based index of the table. This number is normally between 0 and 3. Use getNumberOfTables() for bounds-checking.

Returns:

The HuffmanTablesDirectory.HuffmanTable having the specified number.

getNumberOfTables

public int getNumberOfTables()
                      throws MetadataException

Returns:

The number of Huffman tables held by this HuffmanTablesDirectory instance.

Throws:

MetadataException

isTypical

public boolean isTypical()

Evaluates whether all the tables in this HuffmanTablesDirectory are "typical" Huffman tables.

"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 all the tables in this HuffmanTablesDirectory are the predefined "typical" Huffman tables.

isOptimized

public boolean isOptimized()

The opposite of isTypical().

Returns:

Whether or not the tables in this HuffmanTablesDirectory are "optimized" - which means that at least one of them aren't one of the "typical" Huffman tables.