1 /*
2 * Copyright 2021 The LibYuv Project Authors. All rights reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11 #include <math.h>
12 #include <stdio.h>
13 #include <stdlib.h>
14 #include <string.h>
15
16 // This utility computes values needed to generate yuvconstants based on
17 // white point values.
18 // The yuv formulas are tuned for 8 bit YUV channels.
19
20 // See Also
21 // https://mymusing.co/bt601-yuv-to-rgb-conversion-color/
22
23 // BT.709 full range YUV to RGB reference
24 // R = Y + V * 1.5748
25 // G = Y - U * 0.18732 - V * 0.46812
26 // B = Y + U * 1.8556
27 // KR = 0.2126
28 // KB = 0.0722
29
30 // // Y contribution to R,G,B. Scale and bias.
31 // #define YG 16320 /* round(1.000 * 64 * 256 * 256 / 257) */
32 // #define YB 32 /* 64 / 2 */
33 //
34 // // U and V contributions to R,G,B.
35 // #define UB 113 /* round(1.77200 * 64) */
36 // #define UG 22 /* round(0.34414 * 64) */
37 // #define VG 46 /* round(0.71414 * 64) */
38 // #define VR 90 /* round(1.40200 * 64) */
39 //
40 // // Bias values to round, and subtract 128 from U and V.
41 // #define BB (-UB * 128 + YB)
42 // #define BG (UG * 128 + VG * 128 + YB)
43 // #define BR (-VR * 128 + YB)
44
main(int argc,const char * argv[])45 int main(int argc, const char* argv[]) {
46 if (argc < 3) {
47 printf("yuvconstants [KR] [KB]\n");
48 printf(" e.g. yuvconstants 0.2126 0.0722\n");
49 printf(" MC BT KR KB\n");
50 printf(" 1 BT.709 KR = 0.2126; KB = 0.0722\n");
51 printf(" 4 FCC KR = 0.30; KB = 0.11\n");
52 printf(" 6 BT.601 KR = 0.299; KB = 0.114\n");
53 printf(" 7 SMPTE 240M KR = 0.212; KB = 0.087\n");
54 printf(" 9 BT.2020 KR = 0.2627; KB = 0.0593\n");
55 return -1;
56 }
57 float kr = (float)atof(argv[1]);
58 float kb = (float)atof(argv[2]);
59 float kg = 1 - kr - kb;
60
61 float vr = 2 * (1 - kr);
62 float ug = 2 * ((1 - kb) * kb / kg);
63 float vg = 2 * ((1 - kr) * kr / kg);
64 float ub = 2 * (1 - kb);
65
66 printf("Full range\n");
67 printf("R = Y + V * %5f\n", vr);
68 printf("G = Y - U * %6f - V * %6f\n", ug, vg);
69 printf("B = Y + U * %5f\n", ub);
70
71 printf("KR = %4f; ", kr);
72 printf("KB = %4f\n", kb);
73 // printf("KG = %4f\n", kg);
74 // #define YG 16320 /* round(1.000 * 64 * 256 * 256 / 257) */
75 // #define YB 32 /* 64 / 2 */
76 //
77 // // U and V contributions to R,G,B.
78
79 printf("UB %-3.0f /* round(%f * 64 = %8.4f) */\n", round(ub * 64), ub, ub * 64);
80 printf("UG %-3.0f /* round(%f * 64 = %8.4f) */\n", round(ug * 64), ug, ug * 64);
81 printf("VG %-3.0f /* round(%f * 64 = %8.4f) */\n", round(vg * 64), vg, vg * 64);
82 printf("VR %-3.0f /* round(%f * 64 = %8.4f) */\n", round(vr * 64), vr, vr * 64);
83
84 vr = 255.f / 224.f * 2 * (1 - kr);
85 ug = 255.f / 224.f * 2 * ((1 - kb) * kb / kg);
86 vg = 255.f / 224.f * 2 * ((1 - kr) * kr / kg);
87 ub = 255.f / 224.f * 2 * (1 - kb);
88
89 printf("\nLimited range\n");
90 printf("R = (Y - 16) * 1.164 + V * %5f\n", vr);
91 printf("G = (Y - 16) * 1.164 - U * %6f - V * %6f\n", ug, vg);
92 printf("B = (Y - 16) * 1.164 + U * %5f\n", ub);
93
94 // printf("KG = %4f\n", kg);
95 // #define YG 16320 /* round(1.000 * 64 * 256 * 256 / 257) */
96 // #define YB 32 /* 64 / 2 */
97 //
98 // // U and V contributions to R,G,B.
99
100 printf("UB %-3.0f /* round(%f * 64 = %8.4f) */\n", round(ub * 64), ub, ub * 64);
101 printf("UG %-3.0f /* round(%f * 64 = %8.4f) */\n", round(ug * 64), ug, ug * 64);
102 printf("VG %-3.0f /* round(%f * 64 = %8.4f) */\n", round(vg * 64), vg, vg * 64);
103 printf("VR %-3.0f /* round(%f * 64 = %8.4f) */\n", round(vr * 64), vr, vr * 64);
104
105 return 0;
106 }
107