Title: How to do a 2D Convolution on an Image
uses
Graphics, Windows;
type
TRGBTripleArray = array[0..10000] of TRGBTriple;
PRGBTripleArray = ^TRGBTripleArray;
T3x3FloatArray = array[0..2] of array[0..2] of Extended;
implementation
function Convolve(ABitmap: TBitmap; AMask: T3x3FloatArray;
ABias: Integer): TBitmap;
var
LRow1, LRow2, LRow3, LRowOut: PRGBTripleArray;
LRow, LCol: integer;
LNewBlue, LNewGreen, LNewRed: Extended;
LCoef: Extended;
begin
LCoef := 0;
for LRow := 0 to 2 do
for LCol := 0 to 2 do
LCoef := LCoef + AMask[LCol, LRow];
if LCoef = 0 then LCoef := 1;
Result := TBitmap.Create;
Result.Width := ABitmap.Width - 2;
Result.Height := ABitmap.Height - 2;
Result.PixelFormat := pf24bit;
LRow2 := ABitmap.ScanLine[0];
LRow3 := ABitmap.ScanLine[1];
for LRow := 1 to ABitmap.Height - 2 do
begin
LRow1 := LRow2;
LRow2 := LRow3;
LRow3 := ABitmap.ScanLine[LRow + 1];
LRowOut := Result.ScanLine[LRow - 1];
for LCol := 1 to ABitmap.Width - 2 do
begin
LNewBlue :=
(LRow1[LCol - 1].rgbtBlue * AMask[0,0]) + (LRow1[LCol].rgbtBlue * AMask[1,0]) +
(LRow1[LCol + 1].rgbtBlue * AMask[2,0]) +
(LRow2[LCol - 1].rgbtBlue * AMask[0,1]) + (LRow2[LCol].rgbtBlue * AMask[1,1]) +
(LRow2[LCol + 1].rgbtBlue * AMask[2,1]) +
(LRow3[LCol - 1].rgbtBlue * AMask[0,2]) + (LRow3[LCol].rgbtBlue * AMask[1,2]) +
(LRow3[LCol + 1].rgbtBlue * AMask[2,2]);
LNewBlue := (LNewBlue / LCoef) + ABias;
if LNewBlue 255 then
LNewBlue := 255;
if LNewBlue 0 then
LNewBlue := 0;
LNewGreen :=
(LRow1[LCol - 1].rgbtGreen * AMask[0,0]) + (LRow1[LCol].rgbtGreen * AMask[1,0]) +
(LRow1[LCol + 1].rgbtGreen * AMask[2,0]) +
(LRow2[LCol - 1].rgbtGreen * AMask[0,1]) + (LRow2[LCol].rgbtGreen * AMask[1,1]) +
(LRow2[LCol + 1].rgbtGreen * AMask[2,1]) +
(LRow3[LCol - 1].rgbtGreen * AMask[0,2]) + (LRow3[LCol].rgbtGreen * AMask[1,2]) +
(LRow3[LCol + 1].rgbtGreen * AMask[2,2]);
LNewGreen := (LNewGreen / LCoef) + ABias;
if LNewGreen 255 then
LNewGreen := 255;
if LNewGreen 0 then
LNewGreen := 0;
LNewRed :=
(LRow1[LCol - 1].rgbtRed * AMask[0,0]) + (LRow1[LCol].rgbtRed * AMask[1,0])
+ (LRow1[LCol + 1].rgbtRed * AMask[2,0]) +
(LRow2[LCol - 1].rgbtRed * AMask[0,1]) + (LRow2[LCol].rgbtRed * AMask[1,1])
+ (LRow2[LCol + 1].rgbtRed * AMask[2,1]) +
(LRow3[LCol - 1].rgbtRed * AMask[0,2]) + (LRow3[LCol].rgbtRed * AMask[1,2])
+ (LRow3[LCol + 1].rgbtRed * AMask[2,2]);
LNewRed := (LNewRed / LCoef) + ABias;
if LNewRed 255 then
LNewRed := 255;
if LNewRed 0 then
LNewRed := 0;
LRowOut[LCol - 1].rgbtBlue := trunc(LNewBlue);
LRowOut[LCol - 1].rgbtGreen := trunc(LNewGreen);
LRowOut[LCol - 1].rgbtRed := trunc(LNewRed);
end;
end;
end;
// example use
// edge detection
procedure TForm1.Button1Click(Sender: TObject);
var
LMask: T3x3FloatArray;
begin
LMask[0,0] := -1;
LMask[1,0] := -1;
LMask[2,0] := -1;
LMask[0,1] := -1;
LMask[1,1] := 8;
LMask[2,1] := -1;
LMask[0,2] := -1;
LMask[1,2] := -1;
LMask[2,2] := -1;
Image1.Picture.Bitmap := Convolve(Image1.Picture.Bitmap, LMask, 0);
end;