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1 /* Copyright 2016 Google Inc. All Rights Reserved.
2    Author: zip753@gmail.com (Ivan Nikulin)
3 
4    Distributed under MIT license.
5    See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
6 */
7 
8 /* Tool for drawing diff PPM images between two input PGM images. Normally used
9    with backward reference histogram drawing tool. */
10 
11 #include <algorithm>
12 #include <cassert>
13 #include <cmath>
14 #include <cstdint>
15 #include <cstdio>
16 #include <cstdlib>  /* exit, EXIT_FAILURE */
17 #include <vector>
18 
19 #ifndef CHECK
20 #define CHECK(X) if (!(X)) exit(EXIT_FAILURE);
21 #endif
22 
ReadPGM(FILE * f,uint8_t *** image,size_t * height,size_t * width)23 void ReadPGM(FILE* f, uint8_t*** image, size_t* height, size_t* width) {
24   int colors;
25   CHECK(fscanf(f, "P5\n%lu %lu\n%d\n", width, height, &colors) == 3);
26   assert(colors == 255);
27   *image = new uint8_t*[*height];
28   for (int i = *height - 1; i >= 0; --i) {
29     (*image)[i] = new uint8_t[*width];
30     CHECK(fread((*image)[i], 1, *width, f) == *width);
31   }
32 }
33 
CalculateDiff(int ** diff,uint8_t ** image1,uint8_t ** image2,size_t height,size_t width)34 void CalculateDiff(int** diff, uint8_t** image1, uint8_t** image2,
35                    size_t height, size_t width) {
36   for (size_t i = 0; i < height; ++i) {
37     for (size_t j = 0; j < width; ++j) {
38       diff[i][j] = static_cast<int>(image1[i][j]) - image2[i][j];
39     }
40   }
41 }
42 
DrawDiff(int ** diff,uint8_t ** image1,uint8_t ** image2,size_t height,size_t width,FILE * f)43 void DrawDiff(int** diff, uint8_t** image1, uint8_t** image2,
44               size_t height, size_t width, FILE* f) {
45   int max = -1234;
46   int min = +1234;
47   for (size_t i = 0; i < height; ++i) {
48     for (size_t j = 0; j < width; ++j) {
49       if (max < diff[i][j]) max = diff[i][j];
50       if (min > diff[i][j]) min = diff[i][j];
51       int img_min = std::min(255 - image1[i][j], 255 - image2[i][j]);
52       if (max < img_min) max = img_min;
53     }
54   }
55 
56   int abs_max = -min;
57   if (abs_max < max) abs_max = max;
58 
59   fprintf(f, "P6\n%lu %lu\n%d\n", width, height, abs_max);
60 
61   uint8_t* row = new uint8_t[3 * width];
62   for (int i = height - 1; i >= 0; --i) {
63     for (int j = 0; j < width; ++j) {
64       int min_val = std::min(255 - image1[i][j], 255 - image2[i][j]);
65       int max_val = std::max(min_val, abs(diff[i][j]));
66       if (diff[i][j] > 0) { /* red */
67         row[3 * j + 0] = abs_max - max_val + diff[i][j];
68         row[3 * j + 1] = abs_max - max_val;
69         row[3 * j + 2] = abs_max - max_val + min_val;
70       } else { /* green */
71         row[3 * j + 0] = abs_max - max_val;
72         row[3 * j + 1] = abs_max - max_val - diff[i][j];
73         row[3 * j + 2] = abs_max - max_val + min_val;
74       }
75     }
76     fwrite(row, 1, 3 * width, f);
77   }
78   delete[] row;
79 }
80 
main(int argc,char * argv[])81 int main(int argc, char* argv[]) {
82   if (argc != 4) {
83     printf("usage: %s pgm1 pgm2 diff_ppm_path\n", argv[0]);
84     return 1;
85   }
86 
87   uint8_t **image1, **image2;
88   size_t h1, w1, h2, w2;
89 
90   FILE* fimage1 = fopen(argv[1], "rb");
91   ReadPGM(fimage1, &image1, &h1, &w1);
92   fclose(fimage1);
93 
94   FILE* fimage2 = fopen(argv[2], "rb");
95   ReadPGM(fimage2, &image2, &h2, &w2);
96   fclose(fimage2);
97 
98   if (!(h1 == h2 && w1 == w2)) {
99     printf("Images must have the same size.\n");
100     return 1;
101   }
102 
103   int** diff = new int*[h1];
104   for (size_t i = 0; i < h1; ++i) diff[i] = new int[w1];
105   CalculateDiff(diff, image1, image2, h1, w1);
106 
107   FILE* fdiff = fopen(argv[3], "wb");
108   DrawDiff(diff, image1, image2, h1, w1, fdiff);
109   fclose(fdiff);
110 
111   return 0;
112 }
113