Question

I got a problem with Lockbits. I’m searching black pixels, and because it does not seem right, I’m using a WindowPopup to print the colors of every pixel, but it’s like my program is using another picture.

alt text http://i208.photobucket.com/albums/bb91/Savaronna/pixel-1.jpg?t=1234874238

I marked the first found black pixel red. As you can see there are several other pixels that should match too. What am I doing wrong?

This is my script, do I oversee something?

Bitmap b = this.TableListBMP; BitmapData bmpData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height),                                 ImageLockMode.ReadWrite,                                  PixelFormat.Format32bppPArgb);  int stride = bmpData.Stride; IntPtr Scan0 = bmpData.Scan0;  unsafe {   byte * p = (byte *)(void *)Scan0;     int nOffset = bmpData.Stride - b.Width*4;       int xOffset, yOffset;    for(int y=5; y<b.Height; ++y)   {     for(int x=1; x<b.Width; ++x)     {       MessageBox.Show(         string.Format('x={0}, y={1}, ARGB={2},{3},{4},{5}',           x, y,           Convert.ToString(p[(y*stride)+(x*4)]),           Convert.ToString(p[(y*stride)+(x*4)+1]),           Convert.ToString(p[(y*stride)+(x*4)+2]),           Convert.ToString(p[(y*stride)+(x*4)+3])));       p +=4;     }     // EDIT: This line should be removed     p += nOffset;   } } b.UnlockBits(bmpData); 

Answer 1

If you are using offsets such as p[((y)*stride)+((x)*4)], you probably shouldn’t be increasing p at all? Surely you’ve already handled that (x and y) with the multiplication? Also, bmpData.Stride - b.Width*4 is not (as far as I can see) a meaningful number… the stride is the rows size including padding.

Either remove the ‘p += ...‘ code, or change the offset algorithm. At the moment you are skipping data (bad) and accessing data outside of the object (very bad).