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RGB-to-PNG 回顾

上一篇【手动生成一张 PNG 图片】根据【PNG 文件格式详解】一步一步地手动实现了将 RGB 数据生成了一张 PNG 图片。

有许多开源的 PNG 相关的库可以简化开发：

• svpng
• libattopng
• lodepng
• libpng

使用开源库的方式

svpng

Demo 例子:

void test_rgb(void) {unsigned char rgb[256 * 256 * 3], *p = rgb;
    unsigned x, y;
    FILE *file = fopen("/Users/staff/Desktop/svpng-rgb.png", "wb");
    // FILE *file = fopen("C:\\Users\\Administrator\\Desktop\\svpng-rgb.png", "wb+");
    for (y = 0; y < 256; y++)
        for (x = 0; x < 256; x++) {*p++ = (unsigned char)x;    /* R */
            *p++ = (unsigned char)y;    /* G */
            *p++ = 128;                 /* B */
        }
    svpng(file, 256, 256, rgb, 0);
    fclose(file);
}

Demo 例子:

void test_rgba(void) {unsigned char rgba[256 * 256 * 4], *p = rgba;
    unsigned x, y;
    FILE *file = fopen("/Users/staff/Desktop/svpng-rgba.png", "wb");
    // FILE *file = fopen("C:\\Users\\Administrator\\Desktop\\svpng-rgba.png", "wb+");
    for (y = 0; y < 256; y++)
        for (x = 0; x < 256; x++) {*p++ = (unsigned char)x;                /* R */
            *p++ = (unsigned char)y;                /* G */
            *p++ = 128;                             /* B */
            *p++ = (unsigned char)((x + y) / 2);    /* A */
        }
    svpng(file, 256, 256, rgba, 1);
    fclose(file);
}

自定义 rainbow -> PNG:

// 彩虹的七种颜色
uint32_t rainbowColors[] = {
        0XFF0000, // 红
        0XFFA500, // 橙
        0XFFFF00, // 黄
        0X00FF00, // 绿
        0X007FFF, // 青
        0X0000FF, // 蓝
        0X8B00FF  // 紫
};

uint8_t* getRainbowRGB24Data(uint8_t *rgb24Data, int width, int height) {for (int i = 0; i < width; ++i) {

        // 当前颜色
        uint32_t currentColor = rainbowColors[0];
        if(i < 100) {currentColor = rainbowColors[0];
        } else if(i < 200) {currentColor = rainbowColors[1];
        } else if(i < 300) {currentColor = rainbowColors[2];
        } else if(i < 400) {currentColor = rainbowColors[3];
        } else if(i < 500) {currentColor = rainbowColors[4];
        } else if(i < 600) {currentColor = rainbowColors[5];
        } else if(i < 700) {currentColor = rainbowColors[6];
        }
        // 当前颜色 R 分量
        uint8_t R = (currentColor & 0xFF0000) >> 16;
        // 当前颜色 G 分量
        uint8_t G = (currentColor & 0x00FF00) >> 8;
        // 当前颜色 B 分量
        uint8_t B = currentColor & 0x0000FF;

        for (int j = 0; j < height; ++j) {int currentPixelIndex = 3*(i*height + j);
            // 按 BGR 顺序写入一个像素 RGB24 到文件中
            rgb24Data[currentPixelIndex] = R;
            rgb24Data[currentPixelIndex+1] = G;
            rgb24Data[currentPixelIndex+2] = B;
        }
    }
    return rgb24Data;
}

void rainbow_rgb() {
    int width = 700, height = 700;
    uint8_t rgb24Data[width*height*3];
    FILE *file = fopen("/Users/staff/Desktop/svpng-rgb-rainbow.png", "wb");
    // FILE *file = fopen("C:\\Users\\Administrator\\Desktop\\svpng-rgb-rainbow.png", "wb+");

    getRainbowRGB24Data(rgb24Data, width, height);
    svpng(file, width, height, rgb24Data, 0);
    fclose(file);
}

libattopng

Demo 例子：

void test01() {#define RGBA(r, g, b, a) ((r) | ((g) << 8) | ((b) << 16) | ((a) << 24))
    libattopng_t* png = libattopng_new(250, 200, PNG_RGBA);
    int x, y;
    for (y = 0; y < 200; y++) {for (x = 0; x < 250; x++) {libattopng_set_pixel(png, x, y, RGBA(x & 255, y & 255, 128, (255 - ((x / 2) & 255))));
        }
    }

    // FILE *file = fopen("/Users/staff/Desktop/libattopng-test-rgba.png", "wb");
    // FILE *file = fopen("C:\\Users\\Administrator\\Desktop\\libattopng-test-rgba", "wb+");
    libattopng_save(png, "/Users/staff/Desktop/libattopng-test-rgba.png");
    libattopng_destroy(png);
}

Demo 例子：

void test02() {#define RGBA(r, g, b, a) ((r) | ((g) << 8) | ((b) << 16) | ((a) << 24))
    // ceate palette image
    libattopng_t *png = libattopng_new(256, 256, PNG_PALETTE);
    uint32_t palette[] = {RGBA(0, 0, 0xff, 0xff), RGBA(0, 0xff, 0, 0x80), RGBA(0xff, 0, 0, 0xff), RGBA(0xff, 0, 0xff, 0x80)};
    // 4 colors: blue, green (50% alpha), red, cyan (50% alpha)
    libattopng_set_palette(png, palette, 4);

    int x, y;
    for (y = 0; y < 256; y++) {for (x = 0; x < 256; x++) {libattopng_set_pixel(png, x, y, (x % 16) / 4);
        }
    }
    // FILE *file = fopen("/Users/staff/Desktop/libattopng-test-rgba.png", "wb");
    // FILE *file = fopen("C:\\Users\\Administrator\\Desktop\\libattopng-test-rgba", "wb+");
    libattopng_save(png, "/Users/staff/Desktop/libattopng-test-palette.png");
    libattopng_destroy(png);
}

自定义 rainbow -> PNG:

// 彩虹的七种颜色
uint32_t rainbowColors[] = {
        0XFF0000, // 红
        0XFFA500, // 橙
        0XFFFF00, // 黄
        0X00FF00, // 绿
        0X007FFF, // 青
        0X0000FF, // 蓝
        0X8B00FF  // 紫
};


void testRainbow() {#define RGB(r, g, b) ((r) | ((g) << 8) | ((b) << 16))
    int width = 700, height = 700;
    // uint8_t rgb24Data[width*height*3];
    libattopng_t* png = libattopng_new(width, height, PNG_RGB);

    for (int i = 0; i < width; ++i) {

        // 当前颜色
        uint32_t currentColor = rainbowColors[0];
        if(i < 100) {currentColor = rainbowColors[0];
        } else if(i < 200) {currentColor = rainbowColors[1];
        } else if(i < 300) {currentColor = rainbowColors[2];
        } else if(i < 400) {currentColor = rainbowColors[3];
        } else if(i < 500) {currentColor = rainbowColors[4];
        } else if(i < 600) {currentColor = rainbowColors[5];
        } else if(i < 700) {currentColor = rainbowColors[6];
        }
        // 当前颜色 R 分量
        uint8_t R = (currentColor & 0xFF0000) >> 16;
        // 当前颜色 G 分量
        uint8_t G = (currentColor & 0x00FF00) >> 8;
        // 当前颜色 B 分量
        uint8_t B = currentColor & 0x0000FF;

        for (int j = 0; j < height; ++j) {int currentPixelIndex = 3*(i*height + j);
            // 按 BGR 顺序写入一个像素 RGB24 到文件中
            // rgb24Data[currentPixelIndex] = R;
            // rgb24Data[currentPixelIndex+1] = G;
            // rgb24Data[currentPixelIndex+2] = B;
            libattopng_set_pixel(png, j, i, RGB(R, G, B));
        }
    }

    // FILE *file = fopen("/Users/staff/Desktop/libattopng-rgb-rainbow.png", "wb");
    // FILE *file = fopen("C:\\Users\\Administrator\\Desktop\\libattopng-rgb-rainbow.png", "wb+");
    libattopng_save(png, "/Users/staff/Desktop/libattopng-rgb-rainbow.png");
    libattopng_destroy(png);

}

lodepng

Demo 例子：

void test01() {
    /*generate some image*/
    unsigned width = 512, height = 512;
    unsigned char* image = malloc(width * height * 4);
    unsigned x, y;
    for(y = 0; y < height; y++)
        for(x = 0; x < width; x++) {image[4 * width * y + 4 * x + 0] = 255 * !(x & y);
            image[4 * width * y + 4 * x + 1] = x ^ y;
            image[4 * width * y + 4 * x + 2] = x | y;
            image[4 * width * y + 4 * x + 3] = 255;
        }

    /*Encode the image*/
    // FILE *file = fopen("/Users/staff/Desktop/lodepng-test.png", "wb");
    // FILE *file = fopen("C:\\Users\\Administrator\\Desktop\\lodepng-test.png", "wb+");
    unsigned error = lodepng_encode32_file("/Users/staff/Desktop/lodepng-test.png", image, width, height);

    /*if there's an error, display it*/
    if(error) printf("error %u: %s\n", error, lodepng_error_text(error));

    free(image);
}

自定义 rainbow -> PNG:

// 彩虹的七种颜色
uint32_t rainbowColors[] = {
        0XFF0000, // 红
        0XFFA500, // 橙
        0XFFFF00, // 黄
        0X00FF00, // 绿
        0X007FFF, // 青
        0X0000FF, // 蓝
        0X8B00FF  // 紫
};


void testRainbow() {
    int width = 700, height = 700;
    uint8_t rgb24Data[width*height*3];

    for (int i = 0; i < width; ++i) {
        // 当前颜色
        uint32_t currentColor = rainbowColors[0];
        if(i < 100) {currentColor = rainbowColors[0];
        } else if(i < 200) {currentColor = rainbowColors[1];
        } else if(i < 300) {currentColor = rainbowColors[2];
        } else if(i < 400) {currentColor = rainbowColors[3];
        } else if(i < 500) {currentColor = rainbowColors[4];
        } else if(i < 600) {currentColor = rainbowColors[5];
        } else if(i < 700) {currentColor = rainbowColors[6];
        }
        // 当前颜色 R 分量
        uint8_t R = (currentColor & 0xFF0000) >> 16;
        // 当前颜色 G 分量
        uint8_t G = (currentColor & 0x00FF00) >> 8;
        // 当前颜色 B 分量
        uint8_t B = currentColor & 0x0000FF;

        for (int j = 0; j < height; ++j) {int currentPixelIndex = 3*(i*height + j);
            // 按 RGB 顺序写入一个像素 RGB24 到文件中
             rgb24Data[currentPixelIndex] = R;
             rgb24Data[currentPixelIndex+1] = G;
             rgb24Data[currentPixelIndex+2] = B;
        }
    }

    // FILE *file = fopen("/Users/staff/Desktop/lodepng-rgb-rainbow.png", "wb");
    // FILE *file = fopen("C:\\Users\\Administrator\\Desktop\\lodepng-rgb-rainbow.png", "wb+");
    unsigned error = lodepng_encode24_file("/Users/staff/Desktop/lodepng-rgb-rainbow.png", rgb24Data, width, height);
    if(error) printf("error %u: %s\n", error, lodepng_error_text(error));
}

libpng

Demo 例子：

void test01() {
    int width = 512, height = 512, bit_depth = 8;
    png_structp png_ptr;
    png_infop info_ptr;

    // FILE *file = fopen("C:\\Users\\Administrator\\Desktop\\libpng-test01.png", "wb+");
    FILE *png_file = fopen("/Users/staff/Desktop/libpng-test01.png", "wb");
    if (!png_file) {return ;}

    png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if(png_ptr == NULL) {printf("ERROR:png_create_write_struct/n");
        fclose(png_file);
        return ;
    }
    info_ptr = png_create_info_struct(png_ptr);
    if(info_ptr == NULL) {printf("ERROR:png_create_info_struct/n");
        png_destroy_write_struct(&png_ptr, NULL);
        return ;
    }
    png_init_io(png_ptr, png_file);
    png_set_IHDR(
            png_ptr,
            info_ptr,
            width,
            height,
            bit_depth,
            PNG_COLOR_TYPE_RGB_ALPHA,
            PNG_INTERLACE_NONE,
            PNG_COMPRESSION_TYPE_BASE,
            PNG_FILTER_TYPE_BASE);


    png_colorp palette = (png_colorp)png_malloc(png_ptr, PNG_MAX_PALETTE_LENGTH * sizeof(png_color));
    if (!palette) {fclose(png_file);
        png_destroy_write_struct(&png_ptr, &info_ptr);
        return ;
    }
    png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);
    png_write_info(png_ptr, info_ptr);
    png_set_packing(png_ptr);

    /*generate some image*/
    unsigned char* image = malloc(width * height * 4);
    unsigned x, y;
    for(y = 0; y < height; y++)
        for(x = 0; x < width; x++) {image[4 * width * y + 4 * x + 0] = 255 * !(x & y);
            image[4 * width * y + 4 * x + 1] = x ^ y;
            image[4 * width * y + 4 * x + 2] = x | y;
            image[4 * width * y + 4 * x + 3] = 255;
        }
    // 这里就是图像数据了
    png_bytepp rows = (png_bytepp)png_malloc(png_ptr, height * sizeof(png_bytep));
    for (int i = 0; i < height; ++i) {rows[i] = (png_bytep)(image + (i) * width * 4);
    }

    png_write_image(png_ptr, rows);

    // delete[] rows;
    png_write_end(png_ptr, info_ptr);

    png_free(png_ptr, palette);
    palette=NULL;
    png_destroy_write_struct(&png_ptr, &info_ptr);
    fclose(png_file);
}

自定义 rainbow -> PNG:

// 彩虹的七种颜色
uint32_t rainbowColors[] = {
        0XFF0000, // 红
        0XFFA500, // 橙
        0XFFFF00, // 黄
        0X00FF00, // 绿
        0X007FFF, // 青
        0X0000FF, // 蓝
        0X8B00FF  // 紫
};

uint8_t* getRainbowRGB24Data(uint8_t *rgb24Data, int width, int height) {for (int i = 0; i < width; ++i) {
        // 当前颜色
        uint32_t currentColor = rainbowColors[0];
        if(i < 100) {currentColor = rainbowColors[0];
        } else if(i < 200) {currentColor = rainbowColors[1];
        } else if(i < 300) {currentColor = rainbowColors[2];
        } else if(i < 400) {currentColor = rainbowColors[3];
        } else if(i < 500) {currentColor = rainbowColors[4];
        } else if(i < 600) {currentColor = rainbowColors[5];
        } else if(i < 700) {currentColor = rainbowColors[6];
        }
        // 当前颜色 R 分量
        uint8_t R = (currentColor & 0xFF0000) >> 16;
        // 当前颜色 G 分量
        uint8_t G = (currentColor & 0x00FF00) >> 8;
        // 当前颜色 B 分量
        uint8_t B = currentColor & 0x0000FF;

        for (int j = 0; j < height; ++j) {int currentPixelIndex = 3*(i*height + j);
            // 按 BGR 顺序写入一个像素 RGB24 到文件中
            rgb24Data[currentPixelIndex] = R;
            rgb24Data[currentPixelIndex+1] = G;
            rgb24Data[currentPixelIndex+2] = B;
        }
    }
    return rgb24Data;
}

void testRainbow() {
    int width = 700, height = 700, bit_depth = 8;
    uint8_t rgb24Data[width*height*3];
    png_structp png_ptr;
    png_infop info_ptr;

    // FILE *file = fopen("C:\\Users\\Administrator\\Desktop\\libpng-rgb-rainbow.png", "wb+");
    FILE *png_file = fopen("/Users/staff/Desktop/libpng-rgb-rainbow.png", "wb");
    if (!png_file) {return ;}

    png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if(png_ptr == NULL) {printf("ERROR:png_create_write_struct/n");
        fclose(png_file);
        return ;
    }
    info_ptr = png_create_info_struct(png_ptr);
    if(info_ptr == NULL) {printf("ERROR:png_create_info_struct/n");
        png_destroy_write_struct(&png_ptr, NULL);
        return ;
    }
    png_init_io(png_ptr, png_file);
    png_set_IHDR(
            png_ptr,
            info_ptr,
            width,
            height,
            bit_depth,
            PNG_COLOR_TYPE_RGB,
            PNG_INTERLACE_NONE,
            PNG_COMPRESSION_TYPE_BASE,
            PNG_FILTER_TYPE_BASE);


    png_colorp palette = (png_colorp)png_malloc(png_ptr, PNG_MAX_PALETTE_LENGTH * sizeof(png_color));
    if (!palette) {fclose(png_file);
        png_destroy_write_struct(&png_ptr, &info_ptr);
        return ;
    }
    png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);
    png_write_info(png_ptr, info_ptr);
    png_set_packing(png_ptr);

    getRainbowRGB24Data(rgb24Data, width, height);
    // 这里就是图像数据了
    png_bytepp rows = (png_bytepp)png_malloc(png_ptr, height * sizeof(png_bytep));
    for (int i = 0; i < height; ++i)
    {rows[i] = (png_bytep)(rgb24Data + (i) * width * 3);
    }

    png_write_image(png_ptr, rows);

    // delete[] rows;
    png_write_end(png_ptr, info_ptr);

    png_free(png_ptr, palette);
    palette=NULL;
    png_destroy_write_struct(&png_ptr, &info_ptr);
    fclose(png_file);
}

Congratulations!

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代码：
13-rgb-to-png-library

参考资料：

如何把图片数据流使用 libpng 保存成 png 图片

PNG 格式学习以及使用 libpng 解析

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