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Color to grayscale image

Dear Sirs:

How I can change an image (TBitMap or TJPEGImage) to grayscale. There is some functions API that do this.

Best regards.

DragonSlayer

something like this?

procedure GrayScale(b: TBitmap);
var
i, j, Colr : Integer;
sl : pRGBArray; // Scanline
begin
if b.PixelFormat <> pf24bit then begin
ShowMessage('Not a 24Bit color bitmap!');
Exit;
end;
for j:=0 to b.Height-1 do begin
sl := b.ScanLine[j];
for i:=0 to b.Width-1 do begin
Colr:=HiByte(sl[i].rgbtRed * 77 + sl[i].rgbtGreen * 151 +
sl[i].rgbtBlue * 28);
sl[i].rgbtRed := Colr;
sl[i].rgbtGreen := Colr;
sl[i].rgbtBlue := Colr;
end;
end;
end;

alternatively, look at
http://www.efg2.com/Lab/Library/UseNet/2002/0719.txt
http://www.efg2.com/Lab/Library/UseNet/1999/0311a.txt

for 256 colored bitmaps whereby you need to set the palette for it as well.

ASKER CERTIFIED SOLUTION

DragonSlayer

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pcsentinel

This gives a really good render

procedure MakeGrey(Bmp: TBitmap);
const
      GreyR = 11;
      GreyG = 59;
      GreyB = 30;
var
lx: integer;
ly: integer;
lc: longint;
begin
if Bmp.Empty then
Exit;
for lx := 0 to Bmp.Width do
begin
for ly := 0 to Bmp.Height do
begin
lc := Bmp.Canvas.Pixels[lx, ly];
lc := (GetRValue(lc) * GreyR + GetGValue(lc) * GreyG +
      GetBValue(lc) * GreyB) div (GreyR + GreyG + GreyB);
Bmp.Canvas.Pixels[lx, ly] := RGB(lc, lc, lc);
end;
end;
end;

call it with

MakeGrey(lBmp);

passing in the bitmap you want greyed

regards

DragonSlayer

You might want to use scanline instead of pixel (see my code above) because scanline is *much* faster, very noticable if you are working on a large bitmap.