How to cut a PNG image

yueye232

Now there is a PNG image, which needs to be cut into several PNGs of equal size. Is there any good way?

rsq666

The memory data of the PNG image is divided into several equal memory blocks according to rows and columns.

yueye232

The problem is that I don’t know what the distribution of memory data is. How can I ensure that the memory blocks I keep are continuous squares?
Unless there is an array to record the arrangement of pixels of PNG in memory, so by recording png[][] you can get the corresponding block pixels for saving, and it also involves the PNG compression algorithm.

yangshuang

Convert it to BMP data, divide it into blocks, and then transfer it back.

What should the BMP data look like?

micjoy

png and bmp are similar, a large section of the head is all kinds of information of the picture, followed by the color data of each pixel (256-color palette, 24-bit ARGB), you can use GDI+

bitmap = new Bitmap(L"sample.png");
pixelFormat = bitmap->GetPixelFormat(); //such as PixelFormat24bppRGB, PixelFormat8bppIndexed
width = bitmap->GetWidth();
height = bitmap->GetHeight();

rect.X = 0;
rect.Y = 0;
rect.Width = width;
rect.Height = height;
bitmap->LockBits(rect, ImageLockModeWrite, pixelFormat, bitmapData); //Read the picture into bitmapData, and then you can operate

p = (byte *) bitmapData->Scan0; //bitmapData->Scan0 is the first pixel of the picture

You can deal with the above

micjoy

It’s OK to use GetPixel

ngacn123

Which prawn introduced in more detail?

yueye232

I finally used the CImage class to handle it, which is more convenient
But thank you very much for the algorithm provided bymicjoy~ I will considermicjoyalgorithm to write my own after finishing the current project with FMC! !