Convert a picture to Gray

[fpauw]

I am trying to convert a color bitmap to a gray image.

The code works partly but The image is deformed. This only happens with BMP with a JPG it is ok
What do I miss.

Code: Pascal  [Select][+][-]

1.  
2. procedure TForm1.Button1Click(Sender: TObject);
3. Var
4.   ScanData: PRGBQuad;
5.   ValR, ValG, ValB: Byte;
6.   X, Y : Integer;
7.   Mono: Double;
8. begin
9.   if openpicturedialog1.Execute then
10.      Begin
11.        Image1.Picture.LoadFromFile(openpicturedialog1.FileName);
12.      end;
13.  
14.   Image7.Picture.Bitmap.Height := Image1.Height;
15.   Image7.Picture.Bitmap.Width := Image1.Width;
16.  
17.   For Y:=0 To Image1.Height-1 Do
18.   Begin
19.     ScanData := Image1.Picture.Bitmap.ScanLine[Y];
20.     For X:=0 To Image1.Width-1 Do
21.     Begin
22.       //   X, Y, TotalTime, DistCurve: Integer;Point to the pixel location
23.       // Get RGB value of the pixel
24.       ValR := ScanData^.rgbRed;
25.       ValG := ScanData^.rgbGreen;
26.       ValB := ScanData^.rgbBlue;
27.  
28.       //START Convert to gray
29.       mono := (0.2125 * ValR) + (0.7154 * ValG) + (0.0721 * ValB);
30.       Image7.Canvas.pixels[X,Y]:=StringToColor(IntToStr(Round(mono)*256*256+Round(mono)*256+Round(mono)));
31.  
32.       Inc(ScanData);
33.     end;
34.   end;
35. end;
36.  

[marcov]

Make sure your BMP is the good format, 24 or 32-bit RGB(A)?

[wp]

The code in lines 14 and 15 (of the posted code snippet) is not necessary and in my opinion the reason for the issue because it forces the bitmap size to be equal to the size of the Image control. Suppose you loaded a photo of 6000x4000 (24 MPixel) into a TImage of 100x100 then this code would truncate the photo to this tiny size - certainly not what you want.

[winni]

Hi!

What the hell do you code complicated stuff in line 30?

Simplify it

Code: Pascal  [Select][+][-]

1. Var monoByte : byte;
2.  
3. …....
4. MonoByte := round(0.2125 * ValR + 0.7154 * ValG + 0.0721 * ValB);
5. Image7.Canvas.pixels[X,Y]:= RBGtoColor(monoByte, monoByte,monoByte);
6.  

Winni

[wp]

Adjusting to the sensitivity of the eye on the three base colors? https://en.wikipedia.org/wiki/Grayscale

[lainz]

Adjusting to the sensitivity of the eye on the three base colors? https://en.wikipedia.org/wiki/Grayscale

He means line 30 , this line

Code: Pascal  [Select][+][-]

1. Image7.Canvas.pixels[X,Y]:=StringToColor(IntToStr(Round(mono)*256*256+Round(mono)*256+Round(mono)));

Replacing with

Code: Pascal  [Select][+][-]

1. Image7.Canvas.pixels[X,Y]:= RBGtoColor(monoByte, monoByte,monoByte);

[winni]

Thanx @lainz!

And @wp: I don't get you. I know that stuff described in wikipedia. Since 40 years.

Winni

[wp]

And @wp: I don't get you. I know that stuff described in wikipedia. Since 40 years.

Sorry. Careful reading is not by best strength...

[fpauw]

Make sure your BMP is the good format, 24 or 32-bit RGB(A)?

Thanks after converting the BMP to 32-bit the issue is gone!

[fpauw]

Hi!

What the hell do you code complicated stuff in line 30?

Simplify it

Code: Pascal  [Select][+][-]

1. Var monoByte : byte;
2.  
3. …....
4. MonoByte := round(0.2125 * ValR + 0.7154 * ValG + 0.0721 * ValB);
5. Image7.Canvas.pixels[X,Y]:= RBGtoColor(monoByte, monoByte,monoByte);
6.  

Winni

Thanks I tried this but than I get

unit1.pas(63,35) Error: Identifier not found "RBGtoColor"

[lucamar]

Thanks I tried this but than I get

unit1.pas(63,35) Error: Identifier not found "RBGtoColor"

Because it is RGBToColor(), not RBGToColor(). A simple typo

[fpauw]

Thanks I tried this but than I get

unit1.pas(63,35) Error: Identifier not found "RBGtoColor"

Because it is RGBToColor(), not RBGToColor(). A simple typo

Thanks It works

[fpauw]

Now I try to speed it up with writing it back with a ScanLine. But than I get the error "Raised exception class 'External:SIGSEGV"

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. Var
3.   ScanData, ResultData: PRGBQuad;
4.   ValR, ValG, ValB: Byte;
5.   X, Y: Integer;
6.   monoByte : byte;
7. begin
8.   if openpicturedialog1.Execute then
9.      Begin
10.        Image1.Picture.LoadFromFile(openpicturedialog1.FileName);
11.      end;
12.  
13.   Image7.Picture.Bitmap.Height := Image1.Height;
14.   Image7.Picture.Bitmap.Width := Image1.Width;
15.  
16.   For Y:=0 To Image1.Height-1 Do
17.   Begin
18.     ScanData := Image1.Picture.Bitmap.ScanLine[Y];
19.     ResultData := Image7.Picture.Bitmap.ScanLine[Y];
20.     For X:=0 To Image1.Width-1 Do
21.     Begin
22.       //   X, Y, TotalTime, DistCurve: Integer;Point to the pixel location
23.       // Get RGB value of the pixel
24.       ValR := ScanData^.rgbRed;
25.       ValG := ScanData^.rgbGreen;
26.       ValB := ScanData^.rgbBlue;
27.  
28.       MonoByte := round(0.2125 * ValR + 0.7154 * ValG + 0.0721 * ValB);
29.  
30.       ResultData^.rgbRed   :=monoByte;
31.       ResultData^.rgbGreen :=monoByte;
32.       ResultData^.rgbBlue  :=monoByte;
33.  
34.       Inc(ScanData);
35.       Inc(ResultData);
36.     end;
37.   end;
38. end;
39.  

[wp]

Setting width and height of the destination bitmap (Image7.Picture.Bitmap) equal to the size of the source control (Image1) is not correct because the source bitmap (Image1.Picture.Bitmap, or more general: Image1.Picture) may have a different size than the source control.

Try this instead of lines 13 and 14:

Code: Pascal  [Select][+][-]

1. Image7.Picture.Bitmap.Width := Image1.Picture.Width;
2. Image7.Picture.Bitmap.Height := Image1.Picture.Height;
3.  
4. // or: combine both in
5. Image7.Picture.Bitmap.SetSize(Image1.Picture.Width, Image1.Picture.Height);

[fpauw]

Setting width and height of the destination bitmap (Image7.Picture.Bitmap) equal to the size of the source control (Image1) is not correct because the source bitmap (Image1.Picture.Bitmap, or more general: Image1.Picture) may have a different size than the source control.

Clear Thanks!

But I have still the  "Raised exception class 'External:SIGSEGV" error...