CIMG中的Append图像并保存在stb_image_write中不起作用

Question

I am using stb_image stb_image_write and CImg with following code

    int width, height, bpp;
    img = stbi_load(imgPath, &width, &height, &bpp, 3);

    CImg<unsigned char> cimg(img, width, height, 1, bpp);
    CImg<unsigned char> wimg(width, 10, 1, 3, 0);
    cimg.append(wimg,'y');
    cimg.display();

    stbi_write_png("save.png", width, height, 3, cimg, width * 3);

It simply creating black line with 10 pixel and appending to bottom of image when I display this it works fine but when I save it showing distorted

I need to add border at bottom am I doing something wrong or any better way to do it?

Original

Saved

Below code works fine read image with stb do some change in cimg and save with stb it overlay small image to big one

    int width, height, bpp;
    int width2, height2, bpp2;

    CImg<unsigned char> gradient(img1, bpp, width, height, 1);
    CImg<unsigned char> overlay(img2, bpp2, width2, height2, 1);

    CImg<unsigned char> gradient(img1, width, height, bpp, 1);
    CImg<unsigned char> overlay(img2, width2, height2, bpp2, 1);
    gradient.draw_image(0, 0, overlay);
    stbi_write_png("gradient.png", width, height, 3, gradient, width * 3);

Overlay

Answer 1

Ok I got it worked as mentioned by Mark Setchell in comments about interleave so I have to permute the buffer structure as mentioned in below post

CImg library creates distorted images on rotation

so if I need to used these three libs than my code would be as below

int width, height, bpp;
    setHeader();

    img = stbi_load(imgPath, &width, &height, &bpp, 3);
    
    //Load with stb type
    CImg<unsigned char> cimg(img, bpp, width, height, 1);
    
    //Convert cimg type
    cimg.permute_axes("yzcx");

    //Can work with all type of cimg functions
    CImg<unsigned char> wimg(width, 10, 1, 3, 0);
    cimg.append(wimg,'y');
    
    //Convert back to stb type to save
    cimg.permute_axes("cxyz");
    stbi_write_png("save.png", width, height+10, 3, cimg, width * 3);