[-28] resolve darknet source image format conversion between RGB2YUV and YUV2RGB

This series darknet parse source code, as it relates to the RGB image, YUV, HSV format image.c, we will resolve image.c rgb_to_yuv involved in () function and yuv_to_rgb () function herein.

 

• RGB format converted to YUV format

 The corresponding function is as follows:

void rgb_to_yuv(image im)
{
    assert(im.c == 3);
    int i, j;
    float r, g, b;
    float y, u, v;
    for(j = 0; j < im.h; ++j){
        for(i = 0; i < im.w; ++i){
            r = get_pixel(im, i , j, 0);
            g = get_pixel(im, i , j, 1);
            b = get_pixel(im, i , j, 2);

            y = .299*r + .587*g + .114*b;
            u = -.14713*r + -.28886*g + .436*b;
            v = .615*r + -.51499*g + -.10001*b;

            set_pixel(im, i, j, 0, y);
            set_pixel(im, i, j, 1, u);
            set_pixel(im, i, j, 2, v);
        }
    }
}

 

• Converted RGB format YUV format

void yuv_to_rgb(image im)
{
    assert(im.c == 3);
    int i, j;
    float r, g, b;
    float y, u, v;
    for(j = 0; j < im.h; ++j){
        for(i = 0; i < im.w; ++i){
            y = get_pixel(im, i , j, 0);
            u = get_pixel(im, i , j, 1);
            v = get_pixel(im, i , j, 2);

            r = y + 1.13983*v;
            g = y + -.39465*u + -.58060*v;
            b = y + 2.03211*u;

            set_pixel(im, i, j, 0, r);
            set_pixel(im, i, j, 1, g);
            set_pixel(im, i, j, 2, b);
        }
    }
}

[References]

1. https://zhuanlan.zhihu.com/p/75735751