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copied!<p>If you have two bitmaps to compare and you need to find a position of the first different pixel, you can iterate the bitmap rows, get the bitmap pixel array for each row of both bitmaps, compare them and if they don't match, find the horizontal position of a different pixel. In code it might look like this:</p> <pre><code>function CompareBitmaps(ABitmap1, ABitmap2: TBitmap; var ADiffPixel: TPoint): Boolean; var X, Y: Integer; Size: Integer; Pixels1, Pixels2: PByteArray; begin // first check if both bitmaps match in size and pixel format Result := (ABitmap1.PixelFormat = ABitmap2.PixelFormat) and (ABitmap1.Width = ABitmap2.Width) and (ABitmap1.Height = ABitmap2.Height); // if so, then... if Result then begin // assign the size of one pixel case ABitmap1.PixelFormat of pf24bit: Size := SizeOf(TRGBTriple); pf32bit: Size := SizeOf(TRGBQuad); else raise Exception.Create('Bitmap must be 24-bit or 32-bit format!'); end; // iterate all the bitmap rows for Y := 0 to ABitmap1.Height - 1 do begin // get pointer to pixel data array of the same row for both bitmaps Pixels1 := ABitmap1.ScanLine[Y]; Pixels2 := ABitmap2.ScanLine[Y]; // compare those pixel data arrays; if they differ, then... if not CompareMem(Pixels1, Pixels2, ABitmap1.Width * Size) then begin // return negative result Result := False; // assign vertical pixel position to the output ADiffPixel parameter ADiffPixel.Y := Y; // iterate the current row to find a different pixel; after it's found // the pixel's horizontal position is stored to the output ADiffPixel // parameter; the pixel array is treated as a byte array, so there's // need to be a division by the pixel size for X := 0 to ABitmap1.Width * Size - 1 do if (Pixels1[X] <> Pixels2[X]) then begin ADiffPixel.X := X div Size; Exit; end; end; end; end else raise Exception.Create('Bitmaps must match in size and pixel format!'); end; </code></pre> <p>And the example usage:</p> <pre><code>procedure TForm1.Button1Click(Sender: TObject); var PixelPos: TPoint; begin if CompareBitmaps(Image1.Picture.Bitmap, Image2.Picture.Bitmap, PixelPos) then ShowMessage('Bitmaps are the same!') else ShowMessage('Bitmaps are different! The first different pixel was found ' + 'at [' + IntToStr(PixelPos.X) + '; ' + IntToStr(PixelPos.Y) + '].'); end; </code></pre>

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