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JPEGHuffmanTable.javaAPI DocJava SE 5 API8729Fri Aug 26 14:54:40 BST 2005com.sun.image.codec.jpeg

JPEGHuffmanTable

public class JPEGHuffmanTable extends Object
A class to encapsulate a JPEG Huffman table.

Note that the classes in the com.sun.image.codec.jpeg package are not part of the core Java APIs. They are a part of Sun's JDK and JRE distributions. Although other licensees may choose to distribute these classes, developers cannot depend on their availability in non-Sun implementations. We expect that equivalent functionality will eventually be available in a core API or standard extension.

Fields Summary
private static final int
HUFF_MAX_LEN
The maximum number of symbol lengths (max symbol length in bits = 16)
private static final int
HUFF_MAX_SYM
the maximum number of symbols
private short[]
lengths
bits[k] = number of symbols with length k bits
private short[]
symbols
Symbols in order of increasing length
public static final JPEGHuffmanTable
StdDCLuminance
Standard Huffman table ( JPEG standard section K.3 )
public static final JPEGHuffmanTable
StdDCChrominance
Standard Huffman table ( JPEG standard section K.3 )
public static final JPEGHuffmanTable
StdACLuminance
Standard Huffman table ( JPEG standard section K.3 )
public static final JPEGHuffmanTable
StdACChrominance
Standard Huffman table ( JPEG standard section K.3 )
Constructors Summary
private JPEGHuffmanTable()
Private constructor used to construct the Standard Huffman tables

	 
		short lengths[] =  { // 0-base
			0, 0, 2, 1, 2, 4, 4, 3, 4, 7, 5, 4, 4, 0, 1, 2, 0x77 };
		short symbols[] = { 
			0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21,
			0x31, 0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71,
			0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91,
			0xa1, 0xb1, 0xc1, 0x09, 0x23, 0x33, 0x52, 0xf0,
			0x15, 0x62, 0x72, 0xd1, 0x0a, 0x16, 0x24, 0x34,
			0xe1, 0x25, 0xf1, 0x17, 0x18, 0x19, 0x1a, 0x26,
			0x27, 0x28, 0x29, 0x2a, 0x35, 0x36, 0x37, 0x38,
			0x39, 0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
			0x49, 0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
			0x59, 0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
			0x69, 0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,
			0x79, 0x7a, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
			0x88, 0x89, 0x8a, 0x92, 0x93, 0x94, 0x95, 0x96,
			0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5,
			0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4,
			0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3,
			0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2,
			0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda,
			0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9,
			0xea, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,
			0xf9, 0xfa };
			
		StdACChrominance.lengths = lengths;
		StdACChrominance.symbols = symbols;
		StdACChrominance.checkTable();
	
		lengths = null;
		symbols = null;
public JPEGHuffmanTable(short[] lengths, short[] symbols)
Creates a Huffman Table and initializes it.

param
lengths lengths[k] = # of symbols with codes of length k bits; lengths[0] is ignored
param
symbols symbols in order of increasing code length
exception
IllegalArgumentException if the length of lengths is greater than 17
exception
IllegalArgumentException if the length of symbols is greater than 256
exception
IllegalArgumentException if any of the values in lengths or symbols is less than zero

		if ( lengths.length > HUFF_MAX_LEN )
			throw new IllegalArgumentException( "lengths array is too long" );
		for (int i=1; i < lengths.length; i++)
			if (lengths[i] < 0)
				throw new IllegalArgumentException
					( "Values in lengths array must be non-negative." );

		
		if ( symbols.length > HUFF_MAX_SYM )
			throw new IllegalArgumentException( "symbols array is too long" );
		for (int i=0; i < symbols.length; i++)
			if (symbols[i] < 0)
				throw new IllegalArgumentException
					( "Values in symbols array must be non-negative." );
		
		this.lengths = new short[lengths.length];
		this.symbols = new short[symbols.length];
		
		System.arraycopy( lengths, 0, this.lengths, 0, lengths.length );
		System.arraycopy( symbols, 0, this.symbols, 0, symbols.length );

		checkTable();
Methods Summary
private voidcheckTable()
This checks that the table they gave us isn't 'illegal' It checks that the symbol length counts are possible, and that they gave us at least enough symbols for the symbol length counts. Eventually this might check that there aren't duplicate symbols.

		int numVals=2;
		int sum=0;
		for (int i=1; i<lengths.length; i++) {
			sum     += lengths[i];
			numVals -= lengths[i];
			numVals *= 2;
		}

		//System.out.println("NumVals: " + numVals);
		//System.out.println("Sum: " + sum + " Symbols: " + symbols.length);

		if (numVals < 0) 
			throw new IllegalArgumentException
				("Invalid Huffman Table provided, lengths are incorrect.");

		// I'll let them go if they gave us 'extra' symbols...
		if (sum > symbols.length)
			throw new IllegalArgumentException
				("Invalid Huffman Table provided, not enough symbols.");
public short[]getLengths()
Return a copy of the array containing the number of symbols for each length in the Huffman table.

return
A short array where array[k] = # of symbols in the table of length k. array[0] is unused

		short[] ret = new short[ lengths.length];
		System.arraycopy( lengths, 0, ret, 0, lengths.length);
		return ret;
public short[]getSymbols()
Return an array containing the Huffman symbols arranged by increasing length. To make use of this array you must refer the the lengths array.

return
A short array of Huffman symbols

		short[] ret = new short[symbols.length];
		System.arraycopy( symbols, 0, ret, 0, symbols.length);
		return ret;