学步园

在网上看到一个开源项目的代码，写的非常整洁，易懂，特此记录下来，网址忘了，还望见谅！！

#include <math.h>
#include <stdint.h>
 
#define ALIGN_2K(x) ((x + 2047) & ~ 2047)
struct Buffer {
    void * data;
    size_t size;
    size_t width, height;
};
 
static int convertRGB888toRGB565(struct Buffer src, struct Buffer dst);
static int convertRGB888toYCbCr420SP(struct Buffer src, struct Buffer dst);
 
int main() {
    struct Buffer src, dst;
 
    FILE * in = fopen("input.yuv", "rb");
    FILE * out = fopen("output.yuv", "wb");
    int width = 800;
    int height = 480;
    uint8_t *srcData = malloc(width * height * 3);
    uint8_t *dstData = malloc(width * height + ALIGN_2K(width * height));
    fread(srcData, width * height * 3, 1, in);
 
    src.data = srcData;
    src.size = width * height * 3;
    src.width = WIDTH;
    src.height = HEIGHT;
 
    dst.data = dstData;
    dst.size = width * height + ALIGN_2K(width * height);
    dst.width = WIDTH;
    dst.height = HEIGHT;
    
    convertRGB888toYCbCr420SP(src, dst);
 
    fwrite(dstData, width * height + ALIGN_2K(width * height), 1, out);
 
    free(srcData);
    free(dstData);
    fclose(in);
    fclose(out);
 
    return 0;
 
 
}
 
static int convertRGB888toRGB565(struct Buffer src, struct Buffer dst) {
    uint8_t *srcData, *dstData;
 
    srcData = (uint8_t *)src.data;
    dstData = (uint8_t *)dst.data;
 
    for (int c = 0, i = 0; c < src.width * src.height;) {
            //scale down each component to 5 or 6 bits
            uint8_t r, g, b;
            r = srcData[c++];
            g = srcData[c++];
            b = srcData[c++];
            r = (uint8_t)((srcData[c++]/255.0)*31); //R component
            g = (uint8_t)((srcData[c++]/255.0)*63); //G component
            b = (uint8_t)((srcData[c++]/255.0)*31); //B component
            dstData[i++] = ((r & 0x1f) << 3) | ((g >> 3) & 0x7); //R (5 bits) +  G (upper 3 bits)
            dstData[i++] = ((g & 0x7) << 5) | (b & 0x1f); //G (lower 3 bits) + B (5 bits)
    }
 
    return 0;
}
 
 
static int convertRGB888toYCbCr420SP(struct Buffer src, struct Buffer dst) {
    uint8_t *srcData, *dstData;
 
    srcData = (uint8_t *)src.data;
    dstData = (uint8_t *)dst.data;
 
    //derive the luma
    for (int c = 0, i = 0, j = 0; c < src.width * src.height * 3;) {
        uint8_t r, g, b;
        r = srcData[c++];
        g = srcData[c++];
        b = srcData[c++];
        //stolen from wikipedia
        uint8_t y, cb, cr;
 
        y = (uint8_t)(16 + (65.481 * r + 128.553 * g + 24.966 * b)/256);
        cb = (uint8_t)(128 + (-37.979 * r - 74.203 * g + 112 * b)/256);
        cr = (uint8_t)(128 + (112 * r - 93.786 * g - 18.214 * b)/256);
        dstData[i++] = y;
        (dstData + ALIGN_2K(src.width * src.height))[j++] = cb;
        (dstData + ALIGN_2K(src.width * src.height))[j++] = cr;
    }
    return 0;
}