如果不使用规定的YUV2RGB 转换矩阵来转换可能会造成overflkow

#include <stdio.h>

static const float matrix_rgb2yuv_709[] = {
    0.2126, 0.7152, 0.0722,
    - 0.1146, -0.3854, 0.5000,
    0.5000, -0.4542, -0.0458
};

static const float matrix_rgb2yuv_709_invert[] = {
    1, 0, 1.5747,
    1, -0.1873, -0.4682,
    1, 1.8556, 0
};

static const float matrix_rgb2yuv_ntsc[] = {
    0.2989, 0.5866, 0.1145,
    -0.1688, -0.3312, 0.5000,
    0.5000, -0.4184, -0.0816
};

static const float matrix_rgb2yuv_ntsc_invert[] = {
    1, 0, 1.4022,
    1, -0.3456, -0.7145,
    1, 1.7710, 0
};

void mul32f_3x3(const float* matrix, float* in, float* out)
{
    out[0] = matrix[0] * in[0] + matrix[1] * in[1] + matrix[2] * in[2];
    out[1] = matrix[3] * in[0] + matrix[4] * in[1] + matrix[5] * in[2];
    out[2] = matrix[6] * in[0] + matrix[7] * in[1] + matrix[8] * in[2];
}

int check_if_overflow()
{
    for (int i = 0; i < 256; i+=255) {
        for (int j = 0; j < 256; j+=255) {
            for (int k = 0; k < 256; k+=255) {
                float src[] = { i/255.0,j/255.0,k/255.0 };
                //float src[] = { 0/255.0,255/255.0,0/255.0 };
                float srcyuv[3], dstrgb[3];
                mul32f_3x3(matrix_rgb2yuv_709, src, srcyuv);
                mul32f_3x3(matrix_rgb2yuv_ntsc_invert, srcyuv, dstrgb);
                if (dstrgb[0] < -0.1 || dstrgb[1] < -0.1 || dstrgb[2] < -0.1) {
                    printf("srcyuv:%.4f %.4f %.4f dstrgb:%.4f %.4f %.4f\n", 
                        srcyuv[0], srcyuv[1], srcyuv[2], dstrgb[0], dstrgb[1], dstrgb[2]);
                    //return -1;
                }
            }
        }
    }
    return 0;
}

int main()
{
    return check_if_overflow();
}

 

output

srcyuv:0.2126 -0.1146 0.5000 dstrgb:0.9137 -0.1050 0.0096
srcyuv:0.2848 0.3854 0.4542 dstrgb:0.9217 -0.1729 0.9673