jpeg图像质量参数及icc信息提取

图像编码算法都有相应的质量参数，如hevc编码中的qp值（值越大，压缩率越高），jpeg中的quality（对应到DCT变换后的量化程度）。最近看了看如何根据jpeg图像中的量化文件统计其quality参数，记录下过程。

jpeg文件中可以携带icc颜色配置信息，这个参数告诉显示器用什么色域来显示图像，如下图文件中包含了Adobe RGB色彩描述文件，icc文件大小通常为几百个字节，嵌入在APP2 marker（0xe2）中。

我的环境：linux centos、libjpeg turbo库
Talk is cheap, Show me your code…

#include <stdio.h>
#include <math.h>#include "jpeglib.h"
#include <setjmp.h>
#include "turbojpeg.h"
#include "cdjpeg.h"//标准亮度分量量化表
static const unsigned int std_luminance_quant_tbl[DCTSIZE2] = {16,  11,  10,  16,  24,  40,  51,  61,12,  12,  14,  19,  26,  58,  60,  55,14,  13,  16,  24,  40,  57,  69,  56,14,  17,  22,  29,  51,  87,  80,  62,18,  22,  37,  56,  68, 109, 103,  77,24,  35,  55,  64,  81, 104, 113,  92,49,  64,  78,  87, 103, 121, 120, 101,72,  92,  95,  98, 112, 100, 103,  99
};//标准色度分量量化表
static const unsigned int std_chrominance_quant_tbl[DCTSIZE2] = {17,  18,  24,  47,  99,  99,  99,  99,18,  21,  26,  66,  99,  99,  99,  99,24,  26,  56,  99,  99,  99,  99,  99,47,  66,  99,  99,  99,  99,  99,  99,99,  99,  99,  99,  99,  99,  99,  99,99,  99,  99,  99,  99,  99,  99,  99,99,  99,  99,  99,  99,  99,  99,  99,99,  99,  99,  99,  99,  99,  99,  99
};const char *subsampName[TJ_NUMSAMP] = {"4:4:4", "4:2:2", "4:2:0", "Grayscale", "4:4:0", "4:1:1"
};const char *colorspaceName[TJ_NUMCS] = {"RGB", "YCbCr", "GRAY", "CMYK", "YCCK"
};//读取JPG文件的质量参数
int ReadJpegInfo(const char *filename, char *icc_filename)
{FILE * infile = fopen(filename, "rb");fseek(infile,0,SEEK_END);       //把文件指针移到文件末尾size_t sz = ftell(infile);      //获取文件指针相对文件首的偏移数fseek(infile,0,SEEK_SET);       //把文件指针移到文件头unsigned char* buffer = new unsigned char[sz];fread(buffer,1,sz,infile);fclose(infile);//如果不是JPG格式的文件返回-1if(buffer==NULL || sz <= 2 || 0xFF != (unsigned char)buffer[0] || 0xD8 != (unsigned char)buffer[1]){return -1;}struct jpeg_decompress_struct cinfo;struct jpeg_error_mgr jerr;cinfo.err = jpeg_std_error(&jerr);jpeg_create_decompress(&cinfo);jpeg_mem_src(&cinfo,(unsigned char*)buffer, sz);jpeg_save_markers(&cinfo, JPEG_APP0 + 2, 0xFFFF);jpeg_read_header(&cinfo, TRUE);int tmp_quality = 0;int linear_quality = 0;const int aver_times = 64;int times = 0;int aver_quality = 0;long temp1 = 0;long temp2 = 0;//get jpeg file infoint src_width = cinfo.image_width;int src_height = cinfo.image_height;//int jpegSubsamp = getSubsamp(cinfo);//int jpegHorSamp = cinfo.h_samp_factor;//int jpegVerSamp = cinfo.v_samp_factor;int jpegColorspace = 1;     //defaultswitch (cinfo.jpeg_color_space) {case JCS_GRAYSCALE:  jpegColorspace = TJCS_GRAY;  break;case JCS_RGB:        jpegColorspace = TJCS_RGB;  break;case JCS_YCbCr:      jpegColorspace = TJCS_YCbCr;  break;case JCS_CMYK:       jpegColorspace = TJCS_CMYK;  break;case JCS_YCCK:       jpegColorspace = TJCS_YCCK;  break;default:             jpegColorspace = -1;  break;}printf("Input Image:  %d x %d pixels, %s colorspace\n", src_width, src_height, colorspaceName[jpegColorspace]);//量化表反推，取平均值for(int i = 0; i < DCTSIZE2; i++){temp1 = cinfo.quant_tbl_ptrs[0]->quantval[i];temp2 = cinfo.quant_tbl_ptrs[1]->quantval[i];printf("DCTQUA1[%d] = %ld, DCTQUA2[%d] = %ld\n", i, temp1, i, temp2);if(temp1 < 32767L && temp1 > 0){linear_quality = ceil((float)(temp1 * 100L - 50L)/std_luminance_quant_tbl[i]);     //100L表示long intif(linear_quality == 1) tmp_quality = 1;else if(linear_quality == 100) tmp_quality = 50;else if(linear_quality > 100)tmp_quality = ceil((float)5000 / linear_quality);elsetmp_quality = 100 - ceil((float)linear_quality/2);aver_quality += tmp_quality;times++;if(aver_times == times){aver_quality = aver_quality / aver_times;break;}}}if (icc_filename != NULL) {FILE *icc_file;JOCTET *icc_profile;unsigned int icc_len;if ((icc_file = fopen(icc_filename, "wb")) == NULL) {printf("can't open %s\n", icc_filename);}if (jpeg_read_icc_profile(&cinfo, &icc_profile, &icc_len)) {printf("icc_len = %d\n", icc_len);if (fwrite(icc_profile, icc_len, 1, icc_file) < 1) {printf("can't read ICC profile from %s\n", icc_filename);free(icc_profile);fclose(icc_file);}free(icc_profile);fclose(icc_file);}else{printf("no icc file found\n");}//else if (cinfo.err->msg_code != JWRN_BOGUS_ICC)//    printf("no ICC profile data in JPEG file\n");}jpeg_destroy_decompress(&cinfo);return aver_quality;
}
// g++ -L /opt/libjpeg-turbo/lib64 -lturbojpeg -ljpeg get_jpg_quality.cpp -o quality
// ./quality xxx.jpg
int main(int argc, char **argv)
{if(argc != 2){printf("parameter number should set to 2\n");return -1;}char icc_filename[100] = {0};sprintf(icc_filename, "%s.icc", argv[1]);printf("quality: %d\n", ReadJpegInfo(argv[1], icc_filename));return 0;
}

运行结果如下，计算得到quality为92.

参考
[1] libjpeg-turbo/libjpeg-turbo

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