[linux]使用libpng库将数据生成为png图像文件

一、需求

将一段图像数据生成为png图像。

二、方案

使用libpng库，新建png图像文件，将数据按格式写入到文件内。

三、源码

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

void write_png_file(char* filename, int width, int height, png_bytep* row_pointers) {
    FILE* fp = fopen(filename, "wb");
    if (!fp) {
        printf("Error opening file %s for writing\n", filename);
        return;
    }

    png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!png_ptr) {
        printf("Error creating PNG write structure\n");
        fclose(fp);
        return;
    }

    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr) {
        printf("Error creating PNG info structure\n");
        png_destroy_write_struct(&png_ptr, NULL);
        fclose(fp);
        return;
    }

    if (setjmp(png_jmpbuf(png_ptr))) {
        printf("Error during PNG writing\n");
        png_destroy_write_struct(&png_ptr, &info_ptr);
        fclose(fp);
        return;
    }

    png_init_io(png_ptr, fp);

    png_set_IHDR(png_ptr, info_ptr, width, height, 8, PNG_COLOR_TYPE_RGBA, PNG_INTERLACE_NONE,
                 PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);

    png_write_info(png_ptr, info_ptr);

    png_write_image(png_ptr, row_pointers);

    png_write_end(png_ptr, NULL);

    png_destroy_write_struct(&png_ptr, &info_ptr);

    fclose(fp);
}

int main() {
    int width = 256;
    int height = 256;

    png_bytep* row_pointers = (png_bytep*)malloc(sizeof(png_bytep) * height);
    for (int y = 0; y < height; y++) {
        row_pointers[y] = (png_byte*)malloc(sizeof(png_byte) * width * 4);
        for (int x = 0; x < width; x++) {
            png_byte* pixel = &(row_pointers[y][x * 4]);
            pixel[0] = x % 256;         // Red
            pixel[1] = y % 256;         // Green
            pixel[2] = (x + y) % 256;   // Blue
            pixel[3] = 255;             // Alpha
        }
    }

    write_png_file("output.png", width, height, row_pointers);

    for (int y = 0; y < height; y++) {
        free(row_pointers[y]);
    }
    free(row_pointers);

    return 0;
}

四、编译

gcc编译指令：

依据环境不同，指令内容会有小幅变化。指令编译的各参数解析详见下文：

[linux]使用libqrencode库生成二维码数据https://evenurs.blog.csdn.net/article/details/135655176?spm=1001.2014.3001.5502

Evenurs@admin-PowerEdge-T630-212:~/f1c100s/dev/f1c100s/tina$ /home/Evenurs/f1c100s/dev/f1c100s/tina/prebuilt/gcc/linux-x86/arm/toolchain-sunxi-arm9-musl/toolchain/bin/arm-openwrt-linux-muslgnueabi-gcc -I /home/Evenurs/f1c100s/dev/f1c100s/tina/out/c200s-F1C200s/compile_dir/target/libpng-1.2.56/ -I /home/Evenurs/f1c100s/dev/f1c100s/tina/out/c200s-F1C200s/compile_dir/target/zlib-1.2.8/ data2png.c -o data2png -L /home/Evenurs/f1c100s/dev/f1c100s/tina/out/c200s-F1C200s/compile_dir/target/libpng-1.2.56/.libs/ -L /home/Evenurs/f1c100s/dev/f1c100s/tina/out/c200s-F1C200s/compile_dir/target/zlib-1.2.8/ -lpng -lz 

编译结果：

arm-openwrt-linux-muslgnueabi-gcc.bin: warning: environment variable 'STAGING_DIR' not defined
arm-openwrt-linux-muslgnueabi-gcc.bin: warning: environment variable 'STAGING_DIR' not defined
arm-openwrt-linux-muslgnueabi-gcc.bin: warning: environment variable 'STAGING_DIR' not defined

五、通过adb push烧录

详细烧录步骤参考下文：

【adb】adb push命令 向设备传输文件https://evenurs.blog.csdn.net/article/details/128940198?spm=1001.2014.3001.5502

六、linux下运行

root@TinaLinux:/# chmod -R 777 ./data2png
root@TinaLinux:/# ./data2png
root@TinaLinux:/# ls
bin          hello        overlay      qrencode     sbin         var
data2png     lib          proc         rdinit       sys          www
dev          mnt          pseudo_init  rom          tmp
etc          output.png   qrcode.png   root         usr
root@TinaLinux:/# exit

C:\Users\Evenurs>adb pull /output.png D:\work\temp
/output.png: 1 file pulled. 0.0 MB/s (855 bytes in 0.019s)

C:\Users\Evenurs>

七、结果检查

图像生成算法：

for (int y = 0; y < height; y++) {
        row_pointers[y] = (png_byte*)malloc(sizeof(png_byte) * width * 4);
        for (int x = 0; x < width; x++) {
            png_byte* pixel = &(row_pointers[y][x * 4]);
            pixel[0] = x % 256;         // Red
            pixel[1] = y % 256;         // Green
            pixel[2] = (x + y) % 256;   // Blue
            pixel[3] = 255;             // Alpha
        }
    }

png图像：

?八、结论

可以通过libpng将数据直接转为png图像文件。