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fkaelberer 2014-03-11 09:14:59 +01:00
parent 7b5b5178ef
commit 2c8b776687
1 changed files with 13 additions and 2 deletions
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15
src/core/arithmetic_decoder.js
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@ -17,8 +17,16 @@
'use strict'; 'use strict';
// Annex E. Arithmetic Coding /* This class implements the QM Coder decoding as defined in
* JPEG 2000 Part I Final Committee Draft Version 1.0
* Annex C.3 Arithmetic decoding procedure
* available at http://www.jpeg.org/public/fcd15444-1.pdf
*
* The arithmetic decoder is used in conjunction with context models to decode
* JPEG2000 and JBIG2 streams.
*/
var ArithmeticDecoder = (function ArithmeticDecoderClosure() { var ArithmeticDecoder = (function ArithmeticDecoderClosure() {
// Table C-2
var QeTable = [ var QeTable = [
{qe: 0x5601, nmps: 1, nlps: 1, switchFlag: 1}, {qe: 0x5601, nmps: 1, nlps: 1, switchFlag: 1},
{qe: 0x3401, nmps: 2, nlps: 6, switchFlag: 0}, {qe: 0x3401, nmps: 2, nlps: 6, switchFlag: 0},
@ -69,6 +77,7 @@ var ArithmeticDecoder = (function ArithmeticDecoderClosure() {
{qe: 0x5601, nmps: 46, nlps: 46, switchFlag: 0} {qe: 0x5601, nmps: 46, nlps: 46, switchFlag: 0}
]; ];
// C.3.5 Initialisation of the decoder (INITDEC)
function ArithmeticDecoder(data, start, end) { function ArithmeticDecoder(data, start, end) {
this.data = data; this.data = data;
this.bp = start; this.bp = start;
@ -86,6 +95,7 @@ var ArithmeticDecoder = (function ArithmeticDecoderClosure() {
} }
ArithmeticDecoder.prototype = { ArithmeticDecoder.prototype = {
// C.3.4 Compressed data input (BYTEIN)
byteIn: function ArithmeticDecoder_byteIn() { byteIn: function ArithmeticDecoder_byteIn() {
var data = this.data; var data = this.data;
var bp = this.bp; var bp = this.bp;
@ -111,6 +121,7 @@ var ArithmeticDecoder = (function ArithmeticDecoderClosure() {
this.clow &= 0xFFFF; this.clow &= 0xFFFF;
} }
}, },
// C.3.2 Decoding a decision (DECODE)
readBit: function ArithmeticDecoder_readBit(contexts, pos) { readBit: function ArithmeticDecoder_readBit(contexts, pos) {
// contexts are packed into 1 byte: // contexts are packed into 1 byte:
// highest 7 bits carry cx.index, lowest bit carries cx.mps // highest 7 bits carry cx.index, lowest bit carries cx.mps
@ -154,7 +165,7 @@ var ArithmeticDecoder = (function ArithmeticDecoderClosure() {
cx_index = nmpsIcx; cx_index = nmpsIcx;
} }
} }
// renormD; // C.3.3 renormD;
do { do {
if (this.ct === 0) { if (this.ct === 0) {
this.byteIn(); this.byteIn();