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