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How to change brightness and contrast in large bitmaps (2) (Views: 100)


Problem/Question/Abstract:

I have a Truecolor bitmap in TBitmap. Is there any fast coding to set the brightness?

Answer:

Add a fixed value and clip it to the range. I have used a LUT, which is faster for larger bitmaps. The range of Brightness is -255 (-100%) to 255 (+100%). You can use a 32 or 24 Bit calculation depending on the compiler setting ChangeBrightness24Bit.


procedure ChangeBrightness(Bitmap: TBitmap; Brightness: Integer);
var
  LUT: array[Byte] of Byte;
  v, i: Integer;
{$IFDEF ChangeBrightness24Bit}
  w, h, x, y: Integer;
  LineSize: LongInt;
  pLineStart: PByte;
{$ENDIF}
  p: PByte;
begin
  { create LUT }
  for i := 0 to 255 do
  begin
    v := i + Brightness;
    if v < 0 then
      v := 0
    else if v > 255 then
      v := 255;
    LUT[i] := v;
  end;

{$IFDEF ChangeBrightness24Bit}
  { edit bitmap }
  w := Bitmap.Width;
  h := Bitmap.Height - 1;
  Bitmap.PixelFormat := pf24Bit;
  pLineStart := PByte(Bitmap.ScanLine[h]);
  { pixel line is aligned to 32 Bit }
  LineSize := ((w * 3 + 3) div 4) * 4;
  w := w * 3 - 1;
  for y := 0 to h do
  begin
    p := pLineStart;
    for x := 0 to w do
    begin
      p^ := LUT[p^];
      Inc(p);
    end;
    Inc(pLineStart, LineSize);
  end;
{$ELSE}
  { edit bitmap }
  Bitmap.PixelFormat := pf32Bit;
  p := PByte(Bitmap.ScanLine[Bitmap.Height - 1]);
  for i := 0 to Bitmap.Width * Bitmap.Height - 1 do
  begin
    p^ := LUT[p^];
    Inc(p);
    p^ := LUT[p^];
    Inc(p);
    p^ := LUT[p^];
    Inc(p, 2);
  end;
{$ENDIF}
end;

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