Transparency...again

[loaded]

In the link, https://forum.lazarus.freepascal.org/index.php?topic=29498.0 The answer given by derek.john.eva is working.

[circular]

I am surprised by the result you get with BGRABitmap. Seems like black becomes transparent.

I suggest try:

Code: [Select]

procedure TMainForm.MakePng(screen:TBitmap;FileName: String; Trans: TColor);
var
  c: TBGRABitmap;
  xcolor: TBGRAPixel;
begin
  xcolor:= ColorToBGRA(trans,255);
  c := TBGRABitmap.Create(screen);
  c.ReplaceColor(color, BGRAPixelTransparent);
  c.ReplaceColor(clBlack, clBlackOpaque); // to fix black being transparent
  c.SaveToFile(FileName);
  c.free;
end;

[Eager]

Hi all. New user here, learning the ropes as I go along. 

I found myself having a similar need as the OP: I have a .bmp with a bunch of images against a fuchsia background, and I need to replace the fuchsia with transparency to produce a PNG file. 

I've been looking and searching over the past few days and finally got to BGRABitmap, but now I'm stuck with the issue of black getting replaced by a weird clear color.  Unfortunately the last suggestion by circular -replacing black with blackopaque- didn't work. Moreover, all my attempts to replace black with ANY color using ReplaceColor were fruitless.

But then I saved as a .bmp and it looked correct, only with no transparency. So I think I managed to narrow the problem - it happens when saving to a filename with the extension '.png'. So my guess is the issue may lie within the call to "savetofile"? That's as far as I got based on my current skill level. I'd like to keep using BGRABitmap as it seems pretty straightforward but I wonder if there's any easy solution to this behavior.

TIA for your help!

[winni]

Hi!

Maybe what you think is black in not pure black.

Pure black is 0/0/0 but the human eye cant distinguish it from 0/0/1 or even 5/5/5.

Load your original file into the Gimp and look what the color pipette tells you.

Winni

[winni]

Hi!

I made a little demo how to convert all colors near black to another color - here cssLawnGreen.

Play around with the constant trigger. The more you increase it the more you filter out some dark greys. The range is 0..255.
0 filters only pure black = 0/0/0. 255 replaces all pixels.

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button10Click(Sender: TObject);
2. const trigger = 20;
3. var i: Integer;
4.   bmp : TBgraBitmap;
5.   p: PBGRAPixel;
6.   kindOfBlack: Boolean;
7. begin
8.   bmp := TBGRAbitmap.create ('MyPicture.png');
9.   p := bmp.data;
10.   for i := 0 to bmp.NbPixels - 1 do
11.     begin
12.     KindOfBlack := (p^.red <= trigger) and (p^.green <= trigger) and (p^.blue <= trigger);
13.     if kindOfBlack then p^ := CSSLawnGreen;
14.     inc(p);
15.     end;
16.   bmp.invalidateBitmap;
17.   bmp.draw (Image1.canvas,0,0);
18.   bmp.saveToFile('LawnGreen.png');
19.   bmp.free;
20. end;
21.  
22.  

Perhaps this helps you.

Winni

[Eager]

Winni, you were right, there were "near black" pixels. The problem was right in front of me... *facepalm*

Thanks so much!