//-------------------------------------------------------------------------- // Program to pull the information out of various types of EXIF digital // camera files and show it in a reasonably consistent way // // This module handles guessing of jpeg quality from quantization table // // Using code from Andy Spiegl //-------------------------------------------------------------------------- #include "jhead.h" // for the DQT marker -- start -- // Sample quantization tables from JPEG spec --- only needed for // guesstimate of quality factor. Note these are in zigzag order. static int std_luminance_quant_tbl[64] = { 16, 11, 12, 14, 12, 10, 16, 14, 13, 14, 18, 17, 16, 19, 24, 40, 26, 24, 22, 22, 24, 49, 35, 37, 29, 40, 58, 51, 61, 60, 57, 51, 56, 55, 64, 72, 92, 78, 64, 68, 87, 69, 55, 56, 80, 109, 81, 87, 95, 98, 103, 104, 103, 62, 77, 113, 121, 112, 100, 120, 92, 101, 103, 99 }; static int std_chrominance_quant_tbl[64] = { 17, 18, 18, 24, 21, 24, 47, 26, 26, 47, 99, 66, 56, 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, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99 }; static int *deftabs[2] = { std_luminance_quant_tbl, std_chrominance_quant_tbl }; // jpeg_zigzag_order[i] is the zigzag-order position of the i'th element // of a DCT block read in natural order (left to right, top to bottom). static int jpeg_zigzag_order[64] = { 0, 1, 5, 6, 14, 15, 27, 28, 2, 4, 7, 13, 16, 26, 29, 42, 3, 8, 12, 17, 25, 30, 41, 43, 9, 11, 18, 24, 31, 40, 44, 53, 10, 19, 23, 32, 39, 45, 52, 54, 20, 22, 33, 38, 46, 51, 55, 60, 21, 34, 37, 47, 50, 56, 59, 61, 35, 36, 48, 49, 57, 58, 62, 63 }; // for the DQT marker -- end -- //-------------------------------------------------------------------------- // Process an DQT (Define Quantization Table) marker. // // Code mostly "stolen" from jpegdump: // Copyright (c) 1992 Handmade Software, Inc. // by Allan N. Hessenflow // // We want to print out the "Approximate quality factor" //-------------------------------------------------------------------------- // // The numbers printed in the `Approximate quality factor' line are as follows: // Quality: an estimate of the quality factor used when cjpeg was run. // Scaling factor (scale): mean ratio between quantization table entries // and JPEG sample table entries, times 100. // Variance (var): squared standard deviation of the above ratio. // If this is larger than about 2, then the table is not a simple // multiple of the standard's sample table, so the file was NOT // generated by cjpeg and the quality estimate is dubious. //-------------------------------------------------------------------------- void process_DQT (const uchar * Data, int length) { int a; int c; int tableindex, coefindex, row, col; unsigned int table[64]; int *reftable = NULL; double cumsf = 0.0, cumsf2 = 0.0; int allones = 1; a=2; // first two bytes is length while (a1){ printf("DQT: table %d precision %d\n", tableindex, (c>>4) ? 16 : 8); } if (tableindex < 2){ reftable = deftabs[tableindex]; } // Read in the table, compute statistics relative to reference table for (coefindex = 0; coefindex < 64; coefindex++) { unsigned int val; if (c>>4) { register unsigned int temp; temp=(unsigned int) (Data[a++]); temp *= 256; val=(unsigned int) Data[a++] + temp; } else { val=(unsigned int) Data[a++]; } table[coefindex] = val; if (reftable) { double x; // scaling factor in percent x = 100.0 * (double)val / (double)reftable[coefindex]; cumsf += x; cumsf2 += x * x; // separate check for all-ones table (Q 100) if (val != 1) allones = 0; } } // If requested, print table in normal array order if (ShowTags>2){ for (row=0; row<8; row++) { printf(" "); for (col=0; col<8; col++) { printf("%5u ", table[jpeg_zigzag_order[row*8+col]]); } printf("\n"); } } // Print summary stats if (reftable) { // terse output includes quality double qual, var; cumsf /= 64.0; // mean scale factor cumsf2 /= 64.0; var = cumsf2 - (cumsf * cumsf); // variance if (allones){ // special case for all-ones table qual = 100.0; }else if (cumsf <= 100.0){ qual = (200.0 - cumsf) / 2.0; }else{ qual = 5000.0 / cumsf; } if (ShowTags>1) printf(" "); if (ShowTags){ printf("Approximate quality factor for qtable %d: %.0f (scale %.2f, var %.2f)\n", tableindex, qual, cumsf, var); } else { if (tableindex == 0){ ImageInfo.QualityGuess = (int)(qual+0.5); } } } } } //-------------------------------------------------------------------------- // Process an DHT (Define Huffmann Tables) marker. // // Code mostly "stolen" from jpegdump: // Copyright (c) 1992 Handmade Software, Inc. // by Allan N. Hessenflow //-------------------------------------------------------------------------- void process_DHT (const uchar * Data, int length) { int a, i; int c, c2; unsigned char huff[16]; if (ShowTags>1){ printf("DHT (length %d bytes)\n", length); } a=2; // first two bytes is length while (a1){ printf(" table %d\n", c); } for (i=0; i<16; i++) { huff[i]=(unsigned char) Data[a++]; } for (i=0; i<16; i++) { if (ShowTags>2){ printf(" bits %2d (codes=%3u) ", i+1, (unsigned int) huff[i]); } while (huff[i]--) { c2 = Data[a++]; if (ShowTags>2){ printf(" $%02x ", c2); } } if (ShowTags>2){ printf("\n"); } } } }