Mega Code Archive
Bmpcolourtogreyscale
<![CDATA[
UNTESTED code of someone else's that references
a lookup table to convert between colour and greyscale
values, and what do you find?
THE LOOKUP TABLE ISN'T THERE
procedure CursorBitMapGreyScale;
//Working with a pf8bit bitmap requires the use of a pByteArray
//to access each pixel in a scanline Row. With this palette
//definition in place, the rest of the palette solution is much
//like the pf24bit solution.
//This example only involves 182 shades of gray, so the limitation
//of 236 unique colors in a Windows' palette doesn't affect the image
//much.
var
Bitmap: TBitmap;
GrayBuffer: pByteArray; // ARRAY[0..BildWidth-1] OF BYTE;
GrayStream: TFileStream;
i: INTEGER;
j: INTEGER;
k: INTEGER;
LookupTable: ARRAY[0..255] OF BYTE;
Row: pByteArray; // Allocate buffer to read picture file
begin
GetMem(GrayBuffer, BildWidth);
TRY Bitmap := TBitmap.Create;
TRY Bitmap.PixelFormat := pf8bit;
Bitmap.Width := BildWidth;
Bitmap.Height := BildHeight;
Bitmap.Palette := DefineShadesOfGrayPalette;
GrayStream := TFileStream.Create('Gray.Stream', fmOpenRead);
TRY
FOR j := 0 TO BildHeight-1 DO
BEGIN
GrayStream.Read(GrayBuffer^, BildWidth);
Row := Bitmap.Scanline[j];
FOR i := 0 TO BildWidth-1 DO
BEGIN
Row[i] := LookupTable[ GrayBuffer[i] ]; // one byte per pixel
END
END; // Display image Image.Picture.Graphic := Bitmap;
// Save to file
Bitmap.SaveToFile('Graypf8bit.BMP');
FINALLY
GrayStream.Free;
END
FINALLY
Bitmap.Free;
END
FINALLY
FreeMem(GrayBuffer);
end;
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