How to create a solid mask from a semi-transparent Bitmap?

Question

I want to create the image on the right from the one on the left.

And I have the following structure:

var
  Image, Mask : TBitmap;
begin
  Mask := TBitmap.Create;
  Image := TBitmap.Create;
  Image.LoadFromFile('Yoshi.png');

// Criação da máscara aqui

end; 

The result I seek must transform Mask in the image on the right to be shown in a form. Does anyone know what kind of method should I use? Mess directly with pixels? Or maybe there’s another way through canvas? Whoever has any idea, send it down.

Answer 1

Sorry for the delay to attend, I’ve been very busy. It seems that we have lacked a little research.

If the ideal is to work with PNG for the sake of transparency, then work with Bitmap is not correct.

In fact, from the Delphi 2009 with the introduction of Unicode it has become possible to work with several other types of images, including the PNG.

Here’s a question on Soen about the TPNGImage: how-do-i-get-pngs-to-work-in-d2009

@Guill, you yourself dealt with the Tpngimage type in your question:How to load semi-transparent PNG via a memory stream?.

Anyway, my humble method of treating that image:

procedure TMainForm.btnCriarMascaraClick(Sender: TObject);
var
  png: TPNGImage;
  x,y: TColor;
begin
  png := TPNGImage.Create;
  try
    png.Assign(imgOrig.Picture);

    for x := 0 to pred(png.Width) do
      for y := 0 to pred(png.Height) do
      begin
        if png.Pixels[x,y] <> png.TransparentColor then
        begin
          png.Pixels[x,y] := clLime;
        end;
      end;

    ImgDest.Picture.Assign(png);
  finally
    png.Free;
  end;
end;

Next up, the result!

It is necessary to have the unit pngimage. In XE3 is in Vcl.Imaging.pngimage. However, if you load the image at desing time, the Delphi IDE itself already adds a reference to it.

Answer 2

A possible solution:

var
  Image, Mask : TBitmap;
  i,j,Color   : LongWord;
  rowI, rowM  : pRGBQuadArray;

begin
   Color := $FF0000;

   Image := TBitmap.Create;
   Image.LoadFromFile('Yoshi.png');

   Mask := TBitmap.Create;
   Mask.PixelFormat := pf32bit;
   Mask.Width  := Image.Width;
   Mask.Height := Image.Height;
   FOR j := 0 TO Mask.Height-1 DO
   begin
      rowM := Mask.Scanline[j];
      rowI := Mask.Scanline[j];
      FOR i := 0 TO Mask.Width-1 DO
      begin       
         rowM[i] := ( rowI[i] and $FF000000 ) + Color;
      end;
   end;
   // ...use a máscara...
end;

It pays to include a test to make sure that Image is also pf32bit before creating the mask.

Answer 3

Try using the Canvas and Fillrect property.

Something like:

procedure CreateBitmapSolidColor(Width,Height:Word;Color:TColor;const FileName : TFileName);
var
 bmp : TBitmap;
begin
 bmp:=TBitmap.Create;
 try
   bmp.PixelFormat:=pf24bit;
   bmp.Width:=Width;
   bmp.Height:=Height;
   bmp.Canvas.Brush.Color := Color;
   bmp.Canvas.FillRect(Rect(0,0,Height, Width));
   bmp.SaveToFile(FileName);
 finally
   bmp.Free;
 end;
end;

https://stackoverflow.com/questions/5414929/how-i-create-bmp-files-bitmaps-of-a-single-color-using-delphi