| /* HuffmanTable.java -- |
| Copyright (C) 2006 Free Software Foundation, Inc. |
| |
| This file is part of GNU Classpath. |
| |
| GNU Classpath is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2, or (at your option) |
| any later version. |
| |
| GNU Classpath is distributed in the hope that it will be useful, but |
| WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with GNU Classpath; see the file COPYING. If not, write to the |
| Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
| 02110-1301 USA. |
| |
| Linking this library statically or dynamically with other modules is |
| making a combined work based on this library. Thus, the terms and |
| conditions of the GNU General Public License cover the whole |
| combination. |
| |
| As a special exception, the copyright holders of this library give you |
| permission to link this library with independent modules to produce an |
| executable, regardless of the license terms of these independent |
| modules, and to copy and distribute the resulting executable under |
| terms of your choice, provided that you also meet, for each linked |
| independent module, the terms and conditions of the license of that |
| module. An independent module is a module which is not derived from |
| or based on this library. If you modify this library, you may extend |
| this exception to your version of the library, but you are not |
| obligated to do so. If you do not wish to do so, delete this |
| exception statement from your version. */ |
| |
| package gnu.javax.imageio.jpeg; |
| |
| import java.io.IOException; |
| |
| import javax.imageio.plugins.jpeg.JPEGHuffmanTable; |
| |
| |
| /** |
| * This Object construct a JPEGHuffmanTable which can be used to encode/decode |
| * a scan from a JPEG codec stream. The table must be initalized with either a |
| * BITS byte amount and a Huffman Table Value for decoding or a Huffman Size |
| * and Huffman Code table for encoding. |
| */ |
| public class HuffmanTable |
| { |
| public final static int HUFFMAN_MAX_TABLES = 4; |
| |
| private short[] huffcode = new short[256]; |
| private short[] huffsize = new short[256]; |
| private short[] EHUFCO; |
| private short[] EHUFSI; |
| private short[] valptr = new short[16]; |
| private short[] mincode = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, |
| -1,-1,-1}; |
| private short[] maxcode = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, |
| -1, -1, -1}; |
| private short[] huffval; |
| private short[] bits; |
| |
| static byte JPEG_DC_TABLE = 0; |
| static byte JPEG_AC_TABLE = 1; |
| |
| private short lastk = 0; |
| |
| public HuffmanTable(JPEGHuffmanTable table) |
| { |
| huffcode = table.getValues(); |
| bits = table.getLengths(); |
| } |
| |
| /** |
| * Generated from FIGURE C.1 - Generation of table of Huffman code sizes on |
| * ISO DIS 10918-1. Requirements and Guidelines |
| */ |
| private void generateSizeTable() |
| { |
| short index=0; |
| for(short i=0; i < bits.length ; i++) |
| { |
| for(short j=0; j < bits[i] ; j++) |
| { |
| huffsize[index] = (short) (i+1); |
| index++; |
| } |
| } |
| lastk = index; |
| } |
| |
| /** |
| * Generated from FIGURE C.2 - Generation of table of Huffman codes on |
| * ISO DIS 10918-1. Requirements and Guidelines |
| */ |
| private void generateCodeTable() |
| { |
| short k=0; |
| short si = huffsize[0]; |
| short code = 0; |
| for(short i=0; i < huffsize.length ; i++) |
| { |
| while(huffsize[k]==si) |
| { |
| huffcode[k] = code; |
| code++; |
| k++; |
| } |
| code <<= 1; |
| si++; |
| } |
| } |
| |
| /** |
| * Generated from FIGURE F.15 - Generation of decode table generation on |
| * ISO DIS 10918-1. Requirements and Guidelines |
| */ |
| private void generateDecoderTables() |
| { |
| short bitcount = 0; |
| for(int i=0; i < 16 ; i++) |
| { |
| if(bits[i]!=0) |
| valptr[i] = bitcount; |
| for(int j=0 ; j < bits[i] ; j++) |
| { |
| if(huffcode[j+bitcount] < mincode[i] || mincode[i] == -1) |
| mincode[i] = huffcode[j+bitcount]; |
| |
| if(huffcode[j+bitcount] > maxcode[i]) |
| maxcode[i] = huffcode[j+bitcount]; |
| } |
| if(mincode[i]!=-1) |
| valptr[i] = (short) (valptr[i] - mincode[i]); |
| bitcount += bits[i]; |
| } |
| } |
| |
| /** |
| * Generated from FIGURE C.3 - Generation of Order Codes and tables EHUFCO |
| * and EHUFSI from the ISO DIS 10918-1. Requirements and Guidelines |
| */ |
| public void orderCodes(boolean isDC) |
| { |
| EHUFCO = new short[isDC ? 15 : 255]; |
| EHUFSI = new short[isDC ? 15 : 255]; |
| |
| for (int p=0; p < lastk ; p++) |
| { |
| int i = huffval[p]; |
| if(i < 0 || i > EHUFCO.length || EHUFSI[i]!=0) |
| System.err.println("Error, bad huffman table."); |
| EHUFCO[i] = huffcode[p]; |
| EHUFSI[i] = huffsize[p]; |
| } |
| } |
| |
| /** |
| * Generated from FIGURE F.12 - Extending the sign bit of a decoded value in on |
| * ISO DIS 10918-1. Requirements and Guidelines<p> |
| * |
| * @param diff TODO |
| * @param t TODO |
| * @return TODO |
| */ |
| public static int extend(int diff, int t) |
| { |
| int Vt = (int)Math.pow(2,(t-1)); |
| if(diff<Vt) |
| { |
| Vt=(-1 << t)+1; |
| diff=diff+Vt; |
| } |
| return diff; |
| } |
| |
| /** |
| * Generated from FIGURE F.16 - Procedure for DECODE on |
| * ISO DIS 10918-1. Requirements and Guidelines<p> |
| * |
| * This function takes in a dynamic amount of bits and using the Huffman |
| * table returns information on how many bits must be read in to a byte in |
| * order to reconstruct said byte. |
| * |
| * @param JPEGStream the bits of the data stream. |
| */ |
| public int decode(JPEGImageInputStream JPEGStream) |
| throws IOException, JPEGException |
| { |
| int i=0; |
| short code = (short) JPEGStream.readBits(1); |
| while(code > maxcode[i]) |
| { |
| i++; |
| code <<= 1; |
| code |= JPEGStream.readBits(1); |
| } |
| int val = huffval[code+(valptr[i])]; |
| if(val < 0) |
| val = 256 + val; |
| return val; |
| } |
| } |