c代码不要库

以下是将JPEG图像转换为YUV格式的C代码，不依赖任何库：

#include <stdio.h>
#include <stdlib.h>

#define BLOCK_SIZE 8

// RGB转YUV的转换系数
#define R_Y_COEFF 0.299
#define G_Y_COEFF 0.587
#define B_Y_COEFF 0.114
#define R_U_COEFF -0.147
#define G_U_COEFF -0.289
#define B_U_COEFF 0.436
#define R_V_COEFF 0.615
#define G_V_COEFF -0.515
#define B_V_COEFF -0.100

// 定义RGB和YUV数据类型
typedef struct {
    unsigned char r;
    unsigned char g;
    unsigned char b;
} RGBPixel;

typedef struct {
    unsigned char y;
    unsigned char u;
    unsigned char v;
} YUVPixel;

// RGB转YUV
void RGBtoYUV(RGBPixel* rgb, YUVPixel* yuv) {
    yuv->y = (unsigned char)(rgb->r * R_Y_COEFF + rgb->g * G_Y_COEFF + rgb->b * B_Y_COEFF);
    yuv->u = (unsigned char)(rgb->r * R_U_COEFF + rgb->g * G_U_COEFF + rgb->b * B_U_COEFF + 128);
    yuv->v = (unsigned char)(rgb->r * R_V_COEFF + rgb->g * G_V_COEFF + rgb->b * B_V_COEFF + 128);
}

// 从文件中读取JPEG图像，返回RGB像素数组和图像宽度和高度
RGBPixel* readJPEG(const char* filename, int* width, int* height) {
    FILE* file = fopen(filename, "rb");
    if (!file) {
        printf("Failed to open file %s", filename);
        return NULL;
    }

    // 读取JPEG文件头
    unsigned char header[2];
    fread(header, 1, 2, file);
    if (header[0] != 0xFF || header[1] != 0xD8) {
        printf("Invalid JPEG file %s", filename);
        return NULL;
    }

    // 读取JPEG帧头
    unsigned char frameHeader[9];
    while (1) {
        fread(frameHeader, 1, 2, file);
        if (frameHeader[0] != 0xFF) {
            printf("Invalid JPEG file %s", filename);
            return NULL;
        }

        if (frameHeader[1] == 0xC0 || frameHeader[1] == 0xC2) {
            fread(frameHeader + 2, 1, 7, file);
            *height = (frameHeader[5] << 8) + frameHeader[6];
            *width = (frameHeader[7] << 8) + frameHeader[8];
            break;
        } else {
            fread(frameHeader + 2, 1, (frameHeader[2] << 8) + frameHeader[3] - 2, file);
        }
    }

    // 读取JPEG扫描头
    unsigned char scanHeader[12];
    while (1) {
        fread(scanHeader, 1, 2, file);
        if (scanHeader[0] != 0xFF) {
            printf("Invalid JPEG file %s", filename);
            return NULL;
        }

        if (scanHeader[1] == 0xDA) {
            fread(scanHeader + 2, 1, 10, file);
            break;
        } else {
            fread(scanHeader + 2, 1, (scanHeader[2] << 8) + scanHeader[3] - 2, file);
        }
    }

    // 读取JPEG数据并解码为RGB像素数组
    RGBPixel* rgbData = (RGBPixel*)malloc((*width) * (*height) * sizeof(RGBPixel));
    unsigned char block[64];
    int blockIndex = 0;
    int mcuCount = (*width + BLOCK_SIZE - 1) / BLOCK_SIZE * ((*height + BLOCK_SIZE - 1) / BLOCK_SIZE);
    for (int i = 0; i < mcuCount; i++) {
        // 解码一个8x8 DCT块
        for (int j = 0; j < 64; j++) {
            int byte;
            while ((byte = fgetc(file)) == 0xFF);  // 跳过填充字节
            block[j] = (unsigned char)byte;
        }

        // 将DCT块解码为RGB像素
        for (int j = 0; j < BLOCK_SIZE; j++) {
            for (int k = 0; k < BLOCK_SIZE; k++) {
                int x = (i % ((*width + BLOCK_SIZE - 1) / BLOCK_SIZE)) * BLOCK_SIZE + k;
                int y = (i / ((*width + BLOCK_SIZE - 1) / BLOCK_SIZE)) * BLOCK_SIZE + j;
                if (x >= *width || y >= *height) {
                    continue;
                }

                int blockValue = (int)block[j * BLOCK_SIZE + k];
                int r = blockValue + ((int)block[64 + j / 2 * BLOCK_SIZE / 2 + k / 2] - 128);
                int g = blockValue + ((int)block[64 + 256 / 4 + j / 2 * BLOCK_SIZE / 2 + k / 2] - 128);
                int b = blockValue + ((int)block[64 + 256 / 4 * 2 + j / 2 * BLOCK_SIZE / 2 + k / 2] - 128);
                rgbData[y * (*width) + x].r = (unsigned char)r;
                rgbData[y * (*width) + x].g = (unsigned char)g;
                rgbData[y * (*width) + x].b = (unsigned char)b;
            }
        }
    }

    fclose(file);
    return rgbData;
}

// 将YUV像素数组写入文件
void writeYUV(const char* filename, YUVPixel* yuvData, int width, int height) {
    FILE* file = fopen(filename, "wb");
    if (!file) {
        printf("Failed to open file %s", filename);
        return;
    }

    // 将YUV像素写入文件
    for (int i = 0; i < width * height; i++) {
        fwrite(&yuvData[i], sizeof(YUVPixel), 1, file);
    }

    fclose(file);
}

int main() {
    int width, height;
    RGBPixel* rgbData = readJPEG("input.jpg", &width, &height);
    if (!rgbData) {
        return 1;
    }

    // 将RGB像素转换为YUV像素
    YUVPixel* yuvData = (YUVPixel*)malloc(width * height * sizeof(YUVPixel));
    for (int i = 0; i < width * height; i++) {
        RGBtoYUV(&rgbData[i], &yuvData[i]);
    }

    // 将YUV像素写入文件
    writeYUV("output.yuv", yuvData, width, height);

    free(rgbData);
    free(yuvData);
    return 0;
}