转：Tiny Jpeg Decoder （JPEG解码程序） 源代码分析

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本文转自：http://blog.csdn.net/leixiaohua1020/article/details/12617079

Tiny Jpeg Decoder是一个可以用于嵌入式系统的JPEG解码器。也可以在Windows上编译通过。在此分析一下它部分的源代码，辅助学习JPEG解码知识。

通过TinyJpeg可以将JPEG（*.jpg）文件解码为YUV（*.yuv）或者RGB（*.tga）文件。

真正的解码开始于convert_one_image()函数：

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1. /**?
2. ?*?Load?one?jpeg?image,?and?decompress?it,?and?save?the?result.?
3. ?*/??
4. int?convert_one_image(LPVOID?lparam,const?char?*infilename,?const?char?*outfilename,?int?output_format)??
5. {??
6. ??FILE?*fp;??
7. ??unsigned?int?length_of_file;??
8. ??unsigned?int?width,?height;??
9. ??unsigned?char?*buf;??
10. ??struct?jdec_private?*jdec;??
11. ??unsigned?char?*components[3];??
12. ??
13. ??/*?Load?the?Jpeg?into?memory?*/??
14. ??fp?=?fopen(infilename,?"rb");??
15. ??if?(fp?==?NULL)??
16. ????exitmessage("Cannot?open?filename\n");??
17. ??length_of_file?=?filesize(fp);??
18. ??buf?=?(unsigned?char?*)malloc(length_of_file?+?4);??
19. ??if?(buf?==?NULL)??
20. ????exitmessage("Not?enough?memory?for?loading?file\n");??
21. ??fread(buf,?length_of_file,?1,?fp);??
22. ??fclose(fp);??
23. ??
24. ??/*?Decompress?it?*/??
25. ??//分配内存??
26. ??jdec?=?tinyjpeg_init();??
27. ??//传入句柄--------------??
28. ??jdec->dlg=(CSpecialVIJPGDlg?*)lparam;??
29. ??
30. ??if?(jdec?==?NULL)??
31. ????exitmessage("Not?enough?memory?to?alloc?the?structure?need?for?decompressing\n");??
32. ??//解头部??
33. ??if?(tinyjpeg_parse_header(jdec,?buf,?length_of_file)<0)??
34. ????exitmessage(tinyjpeg_get_errorstring(jdec));??
35. ??/*?Get?the?size?of?the?image?*/??
36. ??//获得图像长宽??
37. ??tinyjpeg_get_size(jdec,?&width,?&height);??
38. ??
39. ??snprintf(error_string,?sizeof(error_string),"Decoding?JPEG?image...\n");??
40. ??//解码实际数据??
41. ??if?(tinyjpeg_decode(jdec,?output_format)?<?0)??
42. ????exitmessage(tinyjpeg_get_errorstring(jdec));??
43. ??/*??
44. ???*?Get?address?for?each?plane?(not?only?max?3?planes?is?supported),?and?
45. ???*?depending?of?the?output?mode,?only?some?components?will?be?filled??
46. ???*?RGB:?1?plane,?YUV420P:?3?planes,?GREY:?1?plane?
47. ???*/??
48. ??tinyjpeg_get_components(jdec,?components);??
49. ??
50. ??/*?Save?it?*/??
51. ??switch?(output_format)??
52. ???{??
53. ????case?TINYJPEG_FMT_RGB24:??
54. ????case?TINYJPEG_FMT_BGR24:??
55. ??????write_tga(outfilename,?output_format,?width,?height,?components);??
56. ??????break;??
57. ????case?TINYJPEG_FMT_YUV420P:??
58. ??????//开始写入成YUV420P文件??
59. ??????write_yuv(outfilename,?width,?height,?components);??
60. ??????break;??
61. ????case?TINYJPEG_FMT_GREY:??
62. ??????//开始写入成灰度文件??
63. ??????write_pgm(outfilename,?width,?height,?components);??
64. ??????break;??
65. ???}??
66. ??
67. ??/*?Only?called?this?if?the?buffers?were?allocated?by?tinyjpeg_decode()?*/??
68. //modify?by?lei！??tinyjpeg_free(jdec);??
69. ??/*?else?called?just?free(jdec);?*/??
70. ??
71. ??free(buf);??
72. ??return?0;??
73. }??

tinyjpeg_init()用于初始化：

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1. /**?
2. ?*?Allocate?a?new?tinyjpeg?decoder?object.?
3. ?*?
4. ?*?Before?calling?any?other?functions,?an?object?need?to?be?called.?
5. ?*/??
6. struct?jdec_private?*tinyjpeg_init(void)??
7. {??
8. ??struct?jdec_private?*priv;??
9. ???
10. ??priv?=?(struct?jdec_private?*)calloc(1,?sizeof(struct?jdec_private));??
11. ??if?(priv?==?NULL)??
12. ????return?NULL;??
13. ??priv->DQT_table_num=0;??
14. ??return?priv;??
15. }??

tinyjpeg_parse_header()用于解码JPEG文件头，可见函数前几句主要验证文件是否为JPEG文件：

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1. /**?
2. ?*?Initialize?the?tinyjpeg?object?and?prepare?the?decoding?of?the?stream.?
3. ?*?
4. ?*?Check?if?the?jpeg?can?be?decoded?with?this?jpeg?decoder.?
5. ?*?Fill?some?table?used?for?preprocessing.?
6. ?*/??
7. int?tinyjpeg_parse_header(struct?jdec_private?*priv,?const?unsigned?char?*buf,?unsigned?int?size)??
8. {??
9. ??int?ret;??
10. ????
11. ??/*?Identify?the?file?*/??
12. ??//0x?FF?D8??
13. ??//是否是JPEG格式文件？??
14. ??if?((buf[0]?!=?0xFF)?||?(buf[1]?!=?SOI))??
15. ????snprintf(error_string,?sizeof(error_string),"Not?a?JPG?file??\n");??
16. ??//是??
17. ??char?temp_str[MAX_URL_LENGTH];??
18. ??sprintf(temp_str,"0x?%X?%X",buf[0],buf[1]);??
19. ??//JPEG格式文件固定的文件头??
20. ??//begin指针前移2字节??
21. ??priv->stream_begin?=?buf+2;??
22. ??priv->stream_length?=?size-2;??
23. ??priv->stream_end?=?priv->stream_begin?+?priv->stream_length;??
24. ??//开始解析JFIF??
25. ??ret?=?parse_JFIF(priv,?priv->stream_begin);??
26. ??return?ret;??
27. }??

parse_JFIF()用于解析各种标签（SOF，SOS，DHT...）：

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1. //解各种不同的标签??
2. static?int?parse_JFIF(struct?jdec_private?*priv,?const?unsigned?char?*stream)??
3. {??
4. ??int?chuck_len;??
5. ??int?marker;??
6. ??int?sos_marker_found?=?0;??
7. ??int?dht_marker_found?=?0;??
8. ??const?unsigned?char?*next_chunck;??
9. ??
10. ??/*?Parse?marker?*/??
11. ??//在Start?of?scan标签之前??
12. ??while?(!sos_marker_found)??
13. ???{??
14. ?????if?(*stream++?!=?0xff)??
15. ???????goto?bogus_jpeg_format;??
16. ?????/*?Skip?any?padding?ff?byte?(this?is?normal)?*/??
17. ?????//跳过0xff字节??
18. ?????while?(*stream?==?0xff)??
19. ???????stream++;??
20. ?????//marker是跳过0xff字节后1个字节的内容??
21. ?????marker?=?*stream++;??
22. ?????//chunk_len是marker后面2个字节的内容（大端模式需要转换）??
23. ?????//包含自身，但不包含0xff+marker2字节??
24. ?????chuck_len?=?be16_to_cpu(stream);??
25. ?????//指向下一个chunk的指针??
26. ?????next_chunck?=?stream?+?chuck_len;??
27. ?????//各种不同的标签??
28. ?????switch?(marker)??
29. ??????{??
30. ???????case?SOF:??
31. ?????//开始解析SOF??
32. ?????if?(parse_SOF(priv,?stream)?<?0)??
33. ???????return?-1;??
34. ?????break;??
35. ?????//Define?quantization?table??
36. ???????case?DQT:??
37. ?????//开始解析DQT??
38. ?????if?(parse_DQT(priv,?stream)?<?0)??
39. ???????return?-1;??
40. ?????break;??
41. ???????case?SOS:??
42. ?????//开始解析SOS??
43. ?????if?(parse_SOS(priv,?stream)?<?0)??
44. ???????return?-1;??
45. ?????sos_marker_found?=?1;??
46. ?????break;??
47. ?????//Define?Huffman?table??
48. ???????case?DHT:??
49. ?????//开始解析DHT??
50. ?????if?(parse_DHT(priv,?stream)?<?0)??
51. ???????return?-1;??
52. ?????dht_marker_found?=?1;??
53. ?????break;??
54. ???????case?DRI:??
55. ?????//开始解析DRI??
56. ?????if?(parse_DRI(priv,?stream)?<?0)??
57. ???????return?-1;??
58. ?????break;??
59. ???????default:??
60. #if?TRACE_PARAM??
61. ????fprintf(param_trace,">?Unknown?marker?%2.2x\n",?marker);??
62. ????fflush(param_trace);??
63. #endif??
64. ?????break;??
65. ??????}??
66. ?????//解下一个segment??
67. ?????stream?=?next_chunck;??
68. ???}??
69. ??
70. ??if?(!dht_marker_found)?{??
71. #if?TRACE_PARAM??
72. ??????fprintf(param_trace,"No?Huffman?table?loaded,?using?the?default?one\n");??
73. ??????fflush(param_trace);??
74. #endif??
75. ????build_default_huffman_tables(priv);??
76. ??}??
77. ??
78. #ifdef?SANITY_CHECK??
79. ??if?(???(priv->component_infos[cY].Hfactor?<?priv->component_infos[cCb].Hfactor)??
80. ??????||?(priv->component_infos[cY].Hfactor?<?priv->component_infos[cCr].Hfactor))??
81. ????snprintf(error_string,?sizeof(error_string),"Horizontal?sampling?factor?for?Y?should?be?greater?than?horitontal?sampling?factor?for?Cb?or?Cr\n");??
82. ??if?(???(priv->component_infos[cY].Vfactor?<?priv->component_infos[cCb].Vfactor)??
83. ??????||?(priv->component_infos[cY].Vfactor?<?priv->component_infos[cCr].Vfactor))??
84. ????snprintf(error_string,?sizeof(error_string),"Vertical?sampling?factor?for?Y?should?be?greater?than?vertical?sampling?factor?for?Cb?or?Cr\n");??
85. ??if?(???(priv->component_infos[cCb].Hfactor!=1)???
86. ??????||?(priv->component_infos[cCr].Hfactor!=1)??
87. ??????||?(priv->component_infos[cCb].Vfactor!=1)??
88. ??????||?(priv->component_infos[cCr].Vfactor!=1))??
89. ????snprintf(error_string,?sizeof(error_string),"Sampling?other?than?1x1?for?Cr?and?Cb?is?not?supported");??
90. #endif??
91. ??
92. ??return?0;??
93. bogus_jpeg_format:??
94. #if?TRACE_PARAM??
95. ??fprintf(param_trace,"Bogus?jpeg?format\n");??
96. ??fflush(param_trace);??
97. #endif??
98. ??return?-1;??
99. }??

parse_SOF()用于解析SOF标签：

注意：其中包含了部分自己写的代码，形如：

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1. itoa(width,temp_str1,10);??
2. ??priv->dlg->AppendBInfo("SOF0","宽",temp_str1,"图像的宽度");??

?

这些代码主要用于在解码过程中提取一些信息，比如图像宽，高，颜色分量数等等

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1. static?int?parse_SOF(struct?jdec_private?*priv,?const?unsigned?char?*stream)??
2. {??
3. ??int?i,?width,?height,?nr_components,?cid,?sampling_factor;??
4. ??int?Q_table;??
5. ??struct?component?*c;??
6. #if?TRACE_PARAM??
7. ??fprintf(param_trace,">?SOF?marker\n");??
8. ??fflush(param_trace);??
9. #endif??
10. ??print_SOF(stream);??
11. ??
12. ??height?=?be16_to_cpu(stream+3);??
13. ??width??=?be16_to_cpu(stream+5);??
14. ??nr_components?=?stream[7];??
15. #if?SANITY_CHECK??
16. ??if?(stream[2]?!=?8)??
17. ????snprintf(error_string,?sizeof(error_string),"Precision?other?than?8?is?not?supported\n");??
18. ??if?(width>JPEG_MAX_WIDTH?||?height>JPEG_MAX_HEIGHT)??
19. ????snprintf(error_string,?sizeof(error_string),"Width?and?Height?(%dx%d)?seems?suspicious\n",?width,?height);??
20. ??if?(nr_components?!=?3)??
21. ????snprintf(error_string,?sizeof(error_string),"We?only?support?YUV?images\n");??
22. ??if?(height%16)??
23. ????snprintf(error_string,?sizeof(error_string),"Height?need?to?be?a?multiple?of?16?(current?height?is?%d)\n",?height);??
24. ??if?(width%16)??
25. ????snprintf(error_string,?sizeof(error_string),"Width?need?to?be?a?multiple?of?16?(current?Width?is?%d)\n",?width);??
26. #endif??
27. ??char?temp_str1[MAX_URL_LENGTH]={0};??
28. ??itoa(width,temp_str1,10);??
29. ??priv->dlg->AppendBInfo("SOF0","宽",temp_str1,"图像的宽度");??
30. ??itoa(height,temp_str1,10);??
31. ??priv->dlg->AppendBInfo("SOF0","高",temp_str1,"图像的高度");??
32. ??itoa(nr_components,temp_str1,10);??
33. ??priv->dlg->AppendBInfo("SOF0","颜色分量数",temp_str1,"图像的颜色分量数。一个字节，例如03，代表有三个分量，YCrCb");??
34. ??itoa(stream[2],temp_str1,10);??
35. ??priv->dlg->AppendBInfo("SOF0","精度",temp_str1,"图像的精度。一个字节，例如08，即精度为一个字节。");??
36. ??stream?+=?8;??
37. ??for?(i=0;?i<nr_components;?i++)?{??
38. ?????cid?=?*stream++;??
39. ?????sampling_factor?=?*stream++;??
40. ?????Q_table?=?*stream++;??
41. ?????c?=?&priv->component_infos[i];??
42. #if?SANITY_CHECK??
43. ?????c->cid?=?cid;??
44. ?????if?(Q_table?>=?COMPONENTS)??
45. ???????snprintf(error_string,?sizeof(error_string),"Bad?Quantization?table?index?(got?%d,?max?allowed?%d)\n",?Q_table,?COMPONENTS-1);??
46. #endif??
47. ?????c->Vfactor?=?sampling_factor&0xf;??
48. ?????c->Hfactor?=?sampling_factor>>4;??
49. ?????c->Q_table?=?priv->Q_tables[Q_table];??
50. ?????//------------??
51. ?????char?temp_str2[MAX_URL_LENGTH]={0};??
52. ?????sprintf(temp_str2,"垂直采样因子【%d】",i);??
53. ?????itoa(c->Hfactor,temp_str1,10);??
54. ?????priv->dlg->AppendBInfo("SOF0",temp_str2,temp_str1,"颜色分量信息：每个分量有三个字节，第一个为分量的ID，01：Y?02：U?03：V；第二个字节高位为水平采样因子，低位为垂直采样因子。");??
55. ?????sprintf(temp_str2,"水平采样因子【%d】",i);??
56. ?????itoa(c->Hfactor,temp_str1,10);??
57. ?????priv->dlg->AppendBInfo("SOF0",temp_str2,temp_str1,"颜色分量信息：每个分量有三个字节，第一个为分量的ID，01：Y?02：U?03：V；第二个字节高位为水平采样因子，低位为垂直采样因子。");??
58. ?????sprintf(temp_str2,"对应量化表ID【%d】",i);??
59. ?????itoa((int)Q_table,temp_str1,10);??
60. ?????priv->dlg->AppendBInfo("SOF0",temp_str2,temp_str1,"颜色分量信息：第三个字节代表这个分量对应的量化表ID，例如，Y对应的量化表ID索引值为00,而UV对应的量化表ID都为01，即它们共用一张量化表。");??
61. ????//-------------??
62. #if?TRACE_PARAM??
63. ?????fprintf(param_trace,"Component:%d??factor:%dx%d??Quantization?table:%d\n",??
64. ???????????cid,?c->Hfactor,?c->Hfactor,?Q_table?);??
65. ?????fflush(param_trace);??
66. #endif??
67. ??
68. ??}??
69. ??
70. ??
71. ??priv->width?=?width;??
72. ??priv->height?=?height;??
73. #if?TRACE_PARAM??
74. ??fprintf(param_trace,"<?SOF?marker\n");??
75. ??fflush(param_trace);??
76. #endif??
77. ??
78. ??return?0;??
79. }??

parse_DHT()用于解析DHT标签：

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1. //解析DHT表??
2. static?int?parse_DHT(struct?jdec_private?*priv,?const?unsigned?char?*stream)??
3. {??
4. ??unsigned?int?count,?i,j;??
5. ??unsigned?char?huff_bits[17];??
6. ??int?length,?index;??
7. ??//------------------------------------------??
8. ??char?*temp;??
9. ??FILE?*fp;??
10. ??//------------------------------------------??
11. ??length?=?be16_to_cpu(stream)?-?2;??
12. ??//跳过length字段??
13. ??stream?+=?2;??/*?Skip?length?*/??
14. #if?TRACE_PARAM??
15. ??fprintf(param_trace,">?DHT?marker?(length=%d)\n",?length);??
16. ??fflush(param_trace);??
17. #endif??
18. ??
19. ??while?(length>0)?{??
20. ??????//跳过第1字节:??
21. ??????//Huffman?表ID号和类型，高?4?位为表的类型，0：DC?直流；1：AC交流??
22. ??????//低四位为?Huffman?表?ID。???
23. ?????index?=?*stream++;??
24. ??
25. ?????/*?We?need?to?calculate?the?number?of?bytes?‘vals‘?will?takes?*/??
26. ?????huff_bits[0]?=?0;??
27. ?????count?=?0;??
28. ??
29. ?????//不同长度?Huffman?的码字数量：固定为?16?个字节，每个字节代表从长度为?1到长度为?16?的码字的个数??
30. ?????for?(i=1;?i<17;?i++)?{??
31. ????huff_bits[i]?=?*stream++;??
32. ????//count记录码字的个数??
33. ????count?+=?huff_bits[i];??
34. ?????}??
35. #if?SANITY_CHECK??
36. ?????if?(count?>=?HUFFMAN_BITS_SIZE)??
37. ???????snprintf(error_string,?sizeof(error_string),"No?more?than?%d?bytes?is?allowed?to?describe?a?huffman?table",?HUFFMAN_BITS_SIZE);??
38. ?????if?(?(index?&0xf)?>=?HUFFMAN_TABLES)??
39. ???????snprintf(error_string,?sizeof(error_string),"No?more?than?%d?Huffman?tables?is?supported?(got?%d)\n",?HUFFMAN_TABLES,?index&0xf);??
40. #if?TRACE_PARAM??
41. ?????fprintf(param_trace,"Huffman?table?%s[%d]?length=%d\n",?(index&0xf0)?"AC":"DC",?index&0xf,?count);??
42. ?????fflush(param_trace);??
43. #endif??
44. #endif??
45. ??
46. ?????if?(index?&?0xf0?){??
47. ?????????//---------------------??
48. ?????????char?temp_str1[MAX_URL_LENGTH]={0};??
49. ?????????char?temp_str2[MAX_URL_LENGTH]={0};??
50. ?????????temp=(char?*)stream;??
51. ?????????//fp?=?fopen("DHT.txt",?"a+");??
52. ?????????//fwrite(temp,?16,?1,?fp);??
53. ?????????for(j=0;j<16;j++){??
54. ?????????????//fprintf(fp,"%d?",temp[j]);??
55. ?????????????sprintf(temp_str2,"%d?",temp[j]);??
56. ?????????????strcat(temp_str1,temp_str2);??
57. ?????????}??
58. ?????????//fprintf(fp,"\n-----------------------\n");??
59. ?????????//fclose(fp);??
60. ?????????//-----------------------------------------------------??
61. ?????????priv->dlg->AppendBInfo("DHT","定义霍夫曼表【交流系数表】",temp_str1,"Huffman表ID号和类型：1字节，高4位为表的类型，0：DC直流；1：AC交流?可以看出这里是直流表；低四位为Huffman表ID");??
62. ?????????//-----------------------------------------------------??
63. ????//交流霍夫曼表??
64. ???????build_huffman_table(huff_bits,?stream,?&priv->HTAC[index&0xf]);??
65. ?????}??
66. ?????else{??
67. ?????????//---------------------??
68. ?????????char?temp_str1[MAX_URL_LENGTH]={0};??
69. ?????????char?temp_str2[MAX_URL_LENGTH]={0};??
70. ?????????temp=(char?*)stream;??
71. ?????????//fp?=?fopen("DHT.txt",?"a+");??
72. ?????????//fwrite(temp,?16,?1,?fp);??
73. ?????????for(j=0;j<16;j++){??
74. ?????????????//fprintf(fp,"%d?",temp[j]);??
75. ?????????????sprintf(temp_str2,"%d?",temp[j]);??
76. ?????????????strcat(temp_str1,temp_str2);??
77. ?????????}??
78. ?????????//fprintf(fp,"\n-----------------------\n");??
79. ?????????//fclose(fp);??
80. ?????????//-----------------------------------------------------??
81. ?????????priv->dlg->AppendBInfo("DHT","定义霍夫曼表【直流系数表】",temp_str1,"Huffman表ID号和类型：1字节，高4位为表的类型，0：DC直流；1：AC交流?可以看出这里是直流表；低四位为Huffman表ID");??
82. ?????????//-----------------------------------------------------??
83. ?????????//直流霍夫曼表??
84. ???????build_huffman_table(huff_bits,?stream,?&priv->HTDC[index&0xf]);??
85. ?????}??
86. ??
87. ?????length?-=?1;??
88. ?????length?-=?16;??
89. ?????length?-=?count;??
90. ?????stream?+=?count;??
91. ??}??
92. #if?TRACE_PARAM??
93. ??fprintf(param_trace,"<?DHT?marker\n");??
94. ??fflush(param_trace);??
95. #endif??
96. ??return?0;??
97. }??

parse_DQT()用于解析DQT标签：

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1. //解析Define?quantization?table??
2. static?int?parse_DQT(struct?jdec_private?*priv,?const?unsigned?char?*stream)??
3. {??
4. ??int?qi;??
5. ??float?*table;??
6. ??const?unsigned?char?*dqt_block_end;??
7. ??
8. //------------------------------------------------??
9. ????int?j,k;??
10. ????char?*temp;??
11. ????FILE?*fp;??
12. //------------------------------------------------??
13. #if?TRACE_PARAM??
14. ??fprintf(param_trace,">?DQT?marker\n");??
15. ??fflush(param_trace);??
16. #endif??
17. ??//该Segment末尾??
18. ??dqt_block_end?=?stream?+?be16_to_cpu(stream);??
19. ??//跳过标签length（2字节）??
20. ??stream?+=?2;??/*?Skip?length?*/??
21. ??//没到末尾??
22. ??while?(stream?<?dqt_block_end)??
23. ???{??
24. ????//跳过该Segment的第1个字节,QT信息??
25. ????//precision:?00??(Higher?4?bit)??
26. ????//index:?00??(Lower?4?bit)???
27. ????//qi取1，第1张量化表（例如，亮度表），取2，第2张量化表（例如，色度表）??
28. ?????qi?=?*stream++;??
29. #if?SANITY_CHECK??
30. ?????if?(qi>>4)??
31. ???????snprintf(error_string,?sizeof(error_string),"16?bits?quantization?table?is?not?supported\n");??
32. ?????if?(qi>4)??
33. ???????snprintf(error_string,?sizeof(error_string),"No?more?4?quantization?table?is?supported?(got?%d)\n",?qi);??
34. #endif??
35. ?????//table指向jdec_private的Q_tables数组，为了在其中写入数据??
36. ?????table?=?priv->Q_tables[qi];??
37. ?????//注意：一次搞定整张！写入??
38. ?????//需要对数值进行变换！cos(k*PI/16)?*?sqrt(2)??
39. ?????//这样才能得到离散余弦变换的系数??
40. ?????build_quantization_table(table,?stream);??
41. //----------------------------------------------------------??
42. ??
43. ????????temp=(char?*)stream;??
44. ????????//fp?=?fopen("DQT.txt",?"a+");??
45. ????????//fwrite(temp,?64,?1,?fp);??
46. ????????char?temp_str1[MAX_URL_LENGTH]={0};??
47. ????????char?temp_str2[MAX_URL_LENGTH]={0};??
48. ????????for(j=0;j<64;j++){??
49. ????????????sprintf(temp_str2,"%d?",temp[j]);??
50. ????????????strcat(temp_str1,temp_str2);??
51. ????????????//fprintf(fp,"%d?",temp[j]);??
52. ????????}??
53. ????????//计数??
54. ????????char?temp_str3[MAX_URL_LENGTH]={0};??
55. ????????sprintf(temp_str3,"量化表【%d】",priv->DQT_table_num);??
56. ????????priv->dlg->AppendBInfo("DQT",temp_str3,temp_str1,"JPEG格式文件的量化表，一般来说第一张是亮度的，后面是色度的");??
57. ????????priv->DQT_table_num++;??
58. ????????//fprintf(fp,"\n-----------------------\n");??
59. ????????//fclose(fp);??
60. #if?TRACE_PARAM??
61. ????????for(j=0;j<8;j++){??
62. ????????????for(k=0;k<8;k++){??
63. ????????????????fprintf(param_trace,"%d?",temp[j*8+k]);??
64. ????????????}??
65. ????????????fprintf(param_trace,"\n");??
66. ????????}??
67. ????????fprintf(fp,"\n-----------------------\n");??
68. ?????fflush(param_trace);??
69. #endif??
70. //----------------------------------------------------------??
71. ?????//完事了！??
72. ?????stream?+=?64;??
73. ???}??
74. #if?TRACE_PARAM??
75. ??fprintf(param_trace,"<?DQT?marker\n");??
76. ??fflush(param_trace);??
77. #endif??
78. ??return?0;??
79. }??

其他标签的解析不一一列举。

?

真正的解码数据开始于tinyjpeg_decode()函数：

注意：本代码中包含部分自己写的代码，用于提取DCT系数表，解码后亮度数据表等数据。

[cpp] view plaincopy

1. /**?
2. ?*?Decode?and?convert?the?jpeg?image?into?@pixfmt@?image?
3. ?*解码函数?
4. ?*?Note:?components?will?be?automaticaly?allocated?if?no?memory?is?attached.?
5. ?*/??
6. int?tinyjpeg_decode(struct?jdec_private?*priv,?int?pixfmt)??
7. {??
8. ??unsigned?int?x,?y,?xstride_by_mcu,?ystride_by_mcu;??
9. ??unsigned?int?bytes_per_blocklines[3],?bytes_per_mcu[3];??
10. ??decode_MCU_fct?decode_MCU;??
11. ??const?decode_MCU_fct?*decode_mcu_table;??
12. ??const?convert_colorspace_fct?*colorspace_array_conv;??
13. ??convert_colorspace_fct?convert_to_pixfmt;??
14. ??
15. ??//-------------------------------------------??
16. ????FILE?*fp;??
17. ????char?*temp;??
18. ????int?j,k;??
19. ??//-------------------------------------------??
20. ??
21. ??if?(setjmp(priv->jump_state))??
22. ????return?-1;??
23. ??
24. ??/*?To?keep?gcc?happy?initialize?some?array?*/??
25. ??bytes_per_mcu[1]?=?0;??
26. ??bytes_per_mcu[2]?=?0;??
27. ??bytes_per_blocklines[1]?=?0;??
28. ??bytes_per_blocklines[2]?=?0;??
29. ??
30. ??decode_mcu_table?=?decode_mcu_3comp_table;??
31. ??switch?(pixfmt)?{??
32. ?????case?TINYJPEG_FMT_YUV420P:??
33. ???????colorspace_array_conv?=?convert_colorspace_yuv420p;??
34. ???????if?(priv->components[0]?==?NULL)??
35. ?????priv->components[0]?=?(uint8_t?*)malloc(priv->width?*?priv->height);??
36. ???????if?(priv->components[1]?==?NULL)??
37. ?????priv->components[1]?=?(uint8_t?*)malloc(priv->width?*?priv->height/4);??
38. ???????if?(priv->components[2]?==?NULL)??
39. ?????priv->components[2]?=?(uint8_t?*)malloc(priv->width?*?priv->height/4);??
40. ???????bytes_per_blocklines[0]?=?priv->width;??
41. ???????bytes_per_blocklines[1]?=?priv->width/4;??
42. ???????bytes_per_blocklines[2]?=?priv->width/4;??
43. ???????bytes_per_mcu[0]?=?8;??
44. ???????bytes_per_mcu[1]?=?4;??
45. ???????bytes_per_mcu[2]?=?4;??
46. ???????break;??
47. ??
48. ?????case?TINYJPEG_FMT_RGB24:??
49. ???????colorspace_array_conv?=?convert_colorspace_rgb24;??
50. ???????if?(priv->components[0]?==?NULL)??
51. ?????priv->components[0]?=?(uint8_t?*)malloc(priv->width?*?priv->height?*?3);??
52. ???????bytes_per_blocklines[0]?=?priv->width?*?3;??
53. ???????bytes_per_mcu[0]?=?3*8;??
54. ???????break;??
55. ??
56. ?????case?TINYJPEG_FMT_BGR24:??
57. ???????colorspace_array_conv?=?convert_colorspace_bgr24;??
58. ???????if?(priv->components[0]?==?NULL)??
59. ?????priv->components[0]?=?(uint8_t?*)malloc(priv->width?*?priv->height?*?3);??
60. ???????bytes_per_blocklines[0]?=?priv->width?*?3;??
61. ???????bytes_per_mcu[0]?=?3*8;??
62. ???????break;??
63. ??
64. ?????case?TINYJPEG_FMT_GREY:??
65. ???????decode_mcu_table?=?decode_mcu_1comp_table;??
66. ???????colorspace_array_conv?=?convert_colorspace_grey;??
67. ???????if?(priv->components[0]?==?NULL)??
68. ?????priv->components[0]?=?(uint8_t?*)malloc(priv->width?*?priv->height);??
69. ???????bytes_per_blocklines[0]?=?priv->width;??
70. ???????bytes_per_mcu[0]?=?8;??
71. ???????break;??
72. ??
73. ?????default:??
74. #if?TRACE_PARAM??
75. ?????????fprintf(param_trace,"Bad?pixel?format\n");??
76. ?????????fflush(param_trace);??
77. #endif??
78. ???????return?-1;??
79. ??}??
80. ??
81. ??xstride_by_mcu?=?ystride_by_mcu?=?8;??
82. ??if?((priv->component_infos[cY].Hfactor?|?priv->component_infos[cY].Vfactor)?==?1)?{??
83. ?????decode_MCU?=?decode_mcu_table[0];??
84. ?????convert_to_pixfmt?=?colorspace_array_conv[0];??
85. #if?TRACE_PARAM??
86. ?????fprintf(param_trace,"Use?decode?1x1?sampling\n");??
87. ?????fflush(param_trace);??
88. #endif??
89. ??}?else?if?(priv->component_infos[cY].Hfactor?==?1)?{??
90. ?????decode_MCU?=?decode_mcu_table[1];??
91. ?????convert_to_pixfmt?=?colorspace_array_conv[1];??
92. ?????ystride_by_mcu?=?16;??
93. #if?TRACE_PARAM??
94. ?????fprintf(param_trace,"Use?decode?1x2?sampling?(not?supported)\n");??
95. ?????fflush(param_trace);??
96. #endif??
97. ??}?else?if?(priv->component_infos[cY].Vfactor?==?2)?{??
98. ?????decode_MCU?=?decode_mcu_table[3];??
99. ?????convert_to_pixfmt?=?colorspace_array_conv[3];??
100. ?????xstride_by_mcu?=?16;??
101. ?????ystride_by_mcu?=?16;??
102. #if?TRACE_PARAM???
103. ?????fprintf(param_trace,"Use?decode?2x2?sampling\n");??
104. ?????fflush(param_trace);??
105. #endif??
106. ??}?else?{??
107. ?????decode_MCU?=?decode_mcu_table[2];??
108. ?????convert_to_pixfmt?=?colorspace_array_conv[2];??
109. ?????xstride_by_mcu?=?16;??
110. #if?TRACE_PARAM??
111. ?????fprintf(param_trace,"Use?decode?2x1?sampling\n");??
112. ?????fflush(param_trace);??
113. #endif??
114. ??}??
115. ??
116. ??resync(priv);??
117. ??
118. ??/*?Don‘t?forget?to?that?block?can?be?either?8?or?16?lines?*/??
119. ??bytes_per_blocklines[0]?*=?ystride_by_mcu;??
120. ??bytes_per_blocklines[1]?*=?ystride_by_mcu;??
121. ??bytes_per_blocklines[2]?*=?ystride_by_mcu;??
122. ??
123. ??bytes_per_mcu[0]?*=?xstride_by_mcu/8;??
124. ??bytes_per_mcu[1]?*=?xstride_by_mcu/8;??
125. ??bytes_per_mcu[2]?*=?xstride_by_mcu/8;??
126. ??
127. ??/*?Just?the?decode?the?image?by?macroblock?(size?is?8x8,?8x16,?or?16x16)?*/??
128. ??//纵向??
129. ??for?(y=0;?y?<?priv->height/ystride_by_mcu;?y++)??
130. ???{??
131. ?????//trace("Decoding?row?%d\n",?y);??
132. ?????priv->plane[0]?=?priv->components[0]?+?(y?*?bytes_per_blocklines[0]);??
133. ?????priv->plane[1]?=?priv->components[1]?+?(y?*?bytes_per_blocklines[1]);??
134. ?????priv->plane[2]?=?priv->components[2]?+?(y?*?bytes_per_blocklines[2]);??
135. ?????//横向（循环的写法还不一样？）??
136. ?????for?(x=0;?x?<?priv->width;?x+=xstride_by_mcu)??
137. ??????{??
138. ????????decode_MCU(priv);??
139. ????????convert_to_pixfmt(priv);??
140. ??
141. //DCT系数-----------------------------------------------------------??
142. ????????//temp=(char?*)priv->component_infos->DCT;??
143. ????????//if(y==4&&x==xstride_by_mcu*3){??
144. ????????if(priv->dlg->m_vijpgoutputdct.GetCheck()==1){??
145. ????????????fp?=?fopen("DCT系数表.txt",?"a+");??
146. ????????????//fwrite(temp,64,1,fp);??
147. ????????????fprintf(fp,"第%d行，第%d列\n",y,x/xstride_by_mcu);??
148. ????????????for(j=0;j<64;j++){??
149. ????????????fprintf(fp,"%d?",priv->component_infos[cY].DCT[j]);??
150. ????????????}??
151. ????????????fprintf(fp,"\n");??
152. ????????????fclose(fp);??
153. ????????}??
154. #if?TRACE_PARAM??
155. ????????fprintf(param_trace,"\n第3行，第4列\n");??
156. ????????for(j=0;j<8;j++){??
157. ????????????for(k=0;k<8;k++){??
158. ????????????????fprintf(param_trace,"%d?",priv->component_infos[cY].DCT[j*8+k]);??
159. ????????????}??
160. ????????????fprintf(param_trace,"\n");??
161. ????????}??
162. ????????fprintf(fp,"\n-----------------------\n");??
163. ????????fflush(param_trace);??
164. #endif??
165. ????????//}??
166. ??
167. //解码后系数（Y）---------------------------------------------------??
168. ????????//temp=(char?*)priv->Y;??
169. ????????//if(y==4&&x==xstride_by_mcu*3){??
170. ????????if(priv->dlg->m_vijpgoutputy.GetCheck()==1){??
171. ????????????fp?=?fopen("解码后Y系数表.txt",?"a+");??
172. ????????????//fwrite(temp,64*4,1,fp);??
173. ????????????fprintf(fp,"第%d行，第%d列\n",y,x/xstride_by_mcu);??
174. ????????????for(j=0;j<64*4;j++){??
175. ????????????fprintf(fp,"%d?",priv->Y[j]);??
176. ????????????}??
177. ????????????fprintf(fp,"\n");??
178. ????????????fclose(fp);??
179. ????????}??
180. #if?TRACE_PARAM??
181. ????????fprintf(param_trace,"第3行，第4列\n");??
182. ????????for(j=0;j<8;j++){??
183. ????????????for(k=0;k<8;k++){??
184. ????????????????fprintf(param_trace,"%d?",priv->Y[j*8+k]);??
185. ????????????}??
186. ????????????fprintf(param_trace,"\n");??
187. ????????}??
188. ????????fprintf(fp,"\n-----------------------\n");??
189. ????????fflush(param_trace);??
190. #endif??
191. ????????//}??
192. ??
193. //------------------------------------------------------------------??
194. ????????priv->plane[0]?+=?bytes_per_mcu[0];??
195. ????????priv->plane[1]?+=?bytes_per_mcu[1];??
196. ????????priv->plane[2]?+=?bytes_per_mcu[2];??
197. ??
198. ????????if?(priv->restarts_to_go>0)??
199. ?????????{??
200. ???????????priv->restarts_to_go--;??
201. ???????????if?(priv->restarts_to_go?==?0)??
202. ????????????{??
203. ??????????????priv->stream?-=?(priv->nbits_in_reservoir/8);??
204. ??????????????resync(priv);??
205. ??????????????if?(find_next_rst_marker(priv)?<?0)??
206. ????????????return?-1;??
207. ????????????}??
208. ?????????}??
209. ??????}??
210. ???}??
211. #if?TRACE_PARAM??
212. ??fprintf(param_trace,"Input?file?size:?%d\n",?priv->stream_length+2);??
213. ??fprintf(param_trace,"Input?bytes?actually?read:?%d\n",?priv->stream?-?priv->stream_begin?+?2);??
214. ??fflush(param_trace);??
215. #endif??
216. ??
217. ??return?0;??
218. }??

转：Tiny Jpeg Decoder （JPEG解码程序） 源代码分析

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原文地址：http://www.cnblogs.com/xkfz007/p/4511490.html