C# image pixel colors how to sorting ?

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C#

sorting

color

image

I got a tool from elsewhere

It can list the pixel values used by the image

i try to imitate it

I use the memory method to extract image pixel colors values and remove duplicate values, but I can't achieve its sorting effect.

Pixel Sort Sample Image URL:https://drive.google.com/file/d/1EdY_JPmU_wfUFuw2202Yq64ocInLabUR/view?usp=share_link

Arranged from top to bottom (5 pictures result)

What I have tried:

BitmapData bitmapData = bitmap.LockBits(new Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
            int stride = bitmapData.Stride; 
            IntPtr iptr = bitmapData.Scan0;  
            int DataBytes = stride * bitmap.Height;  
            byte[] Data = new byte[DataBytes];
            Marshal.Copy(iptr, Data, 0, DataBytes);
            bitmap.UnlockBits(bitmapData);