BGRABitmap to TImage fault

[schlueter550v]

Hello Lazarus Community,

this is my first post, and i hope i get good help. I am very new to Lazarus and ObjPascal, please be kind if i do simple stuff wrong.
To the Problem i have i found nothing in the Wiki nor the Forum.

I am currently doing experiments with BGRABitmap. I simply want to load an image from the clipboard and put it into a TBGRABitmap variable. Later i want to do something with this image, but in my test Code i want to show the TBGRABitmap variable in an Timage on the Form.

this is my current button function:

Code: Pascal  [Select][+][-]

1. procedure TForm1.btnClipboardClick(Sender: TObject);
2. var
3.   image : TBGRABitmap;
4.   pic : TPicture;
5. begin
6.   try
7.     try
8.       //initialize
9.       pic := TPicture.Create();
10.  
11.       if (Clipboard.HasFormat(PredefinedClipboardFormat(pcfBitmap))) then
12.        begin
13.          pic.LoadFromClipboardFormat(PredefinedClipboardFormat(pcfBitmap));
14.          image := TBGRABitmap.Create(pic.bitmap);
15.          Image1.Picture.Assign(image);
16.          Image2.Picture.Assign(pic.Bitmap);
17.        end
18.       else if (Clipboard.HasFormat(PredefinedClipboardFormat(pcfPicture))) then
19.        begin
20.          pic.LoadFromClipboardFormat(PredefinedClipboardFormat(pcfPicture));
21.          image := TBGRABitmap.Create(pic.Bitmap);
22.          Image1.Picture.Assign(image);
23.          Image2.Picture.Assign(pic.Bitmap);
24.        end;
25.     finally
26.       try
27.         pic.Free;
28.         //image.free
29.       except
30.         on E : Exception do ShowMessage(E.Message);
31.       end;
32.     end;
33.   except
34.     on E : Exception do ShowMessage(E.Message);
35.   end;
36. end;
37.  

Image1 on the Form looks corrupted, Image2 fine (see attachment). The Error appears in Windows, in Linux it works fine. What am i doing wrong?

[circular]

Hello,

The problem may come arise for different reasons.

If it is related to the the way TPicture stores the image, you could read the file directly:

Code: Pascal  [Select][+][-]

1. var stream: TStream;
2.        ...
3.        Stream := TMemoryStream.Create;
4.        Clipboard.GetFormat(Clipboard.Formats[i],Stream);
5.        Stream.Position := 0;
6.        image := TBGRABitmap.Create(Stream);
7.        if image.Empty then image.AlphaFill(255);  // you can try to always call AlphaFill
8.        Stream.Free;

If for some reason the alpha channel or alpha mask is not set properly (sometimes Windows writes inconsistent alpha in opaque bitmaps), then you could try:

Code: Pascal  [Select][+][-]

1.        pic.LoadFromClipboardFormat(PredefinedClipboardFormat(pcfBitmap));
2.        image := TBGRABitmap.Create(pic.bitmap);
3.        image.AlphaFill(255);  // fix alpha channel

Another thing that might help is to assign via a TBitmap copy:

Code: Pascal  [Select][+][-]

1. var copy: TBitmap;
2.        ...
3.        copy := image.MakeBitmapCopy(clNone);
4.        Image1.Picture.Assign(copy);
5.        copy.Free;

instead of:

Code: Pascal  [Select][+][-]

1.        Image1.Picture.Assign(image);

[schlueter550v]

Hello circular,

your way with loading the image from stream worked, but now something else occures.
If i have an image with alpha channel, i want to replace it with white, but somehow it turns black?

In my example i copied from Gimp. If i copy from Gimp to Lazpaint it works. If i copy then from Lazpaint to my Program it works too?

Here is my code and in the attechment an example:

Code: Pascal  [Select][+][-]

1. procedure TForm1.btnFromClipboardClick(Sender: TObject);
2. var
3.   image : TBGRABitmap;
4.   stream : TMemoryStream;
5. begin
6.   try
7.     try
8.       //initialize
9.       stream := TMemoryStream.Create;
10.  
11.       if (Clipboard.HasFormat(PredefinedClipboardFormat(pcfBitmap))) then
12.        begin
13.          Clipboard.GetFormat(PredefinedClipboardFormat(pcfBitmap),stream);
14.          stream.Position := 0;
15.          image := TBGRABitmap.Create(stream);
16.          image.ReplaceTransparent(BGRAWhite);
17.          ShowMessage('bitmap');
18.          imgPreview.Picture.Bitmap.Assign(image.Bitmap);
19.          //scaleAndPreviewImage(image); // frees image
20.        end
21.       else if (Clipboard.HasFormat(PredefinedClipboardFormat(pcfPicture))) then
22.        begin
23.          Clipboard.GetFormat(PredefinedClipboardFormat(pcfPicture),stream);
24.          stream.Position := 0;
25.          image := TBGRABitmap.Create(stream);
26.          image.ReplaceTransparent(BGRAWhite);
27.          ShowMessage('picture');
28.          imgPreview.Picture.Bitmap.Assign(image.Bitmap);
29.          //scaleAndPreviewImage(image); // frees image
30.        end;
31.     except
32.       on E : Exception do ShowMessage(E.Message);
33.     end;
34.   finally
35.     try
36.       stream.Free;
37.     except
38.       on E : Exception do ShowMessage(E.Message);
39.     end;
40.   end;
41. end;

[schlueter550v]

Hello,

ok i got it. I've looked at the uclipboard.pas from LazPaint. I had to define A Clipboardformat for PNG.
It works, so i hope i've done everything correctly:

Code: Pascal  [Select][+][-]

1. implementation
2.  
3. {$R *.lfm}
4.  
5. var
6.   pngClipboardFormat : TClipboardFormat;
7.  
8. ...
9.  
10.  
11. procedure TForm1.btnFromClipboardClick(Sender: TObject);
12. var
13.   image : TBGRABitmap;
14.   stream : TMemoryStream;
15. begin
16.   try
17.     try
18.       //initialize
19.       stream := TMemoryStream.Create;
20.  
21.       if (Clipboard.HasFormat(PredefinedClipboardFormat(pcfBitmap))) AND (NOT(Clipboard.HasFormat(pngClipboardFormat))) then
22.        begin
23.          Clipboard.GetFormat(PredefinedClipboardFormat(pcfBitmap),stream);
24.          stream.Position := 0;
25.          image := TBGRABitmap.Create(stream);
26.          scaleAndPreviewImage(image); // frees image
27.        end;
28.       if (Clipboard.HasFormat(pngClipboardFormat)) then
29.        begin
30.          Clipboard.GetFormat(pngClipboardFormat,stream);
31.          stream.Position := 0;
32.          image := TBGRABitmap.Create;
33.          image.LoadFromStream(stream);
34.          //if image.Empty then image.AlphaFill(255);
35.          scaleAndPreviewImage(image); // frees image
36.        end;
37.     except
38.       on E : Exception do ShowMessage(E.Message);
39.     end;
40.   finally
41.     try
42.       stream.Free;
43.     except
44.       on E : Exception do ShowMessage(E.Message);
45.     end;
46.   end;
47. end;
48.  
49. ...
50.  
51. initialization
52.  
53. pngClipboardFormat := RegisterClipboardFormat({$IfDef WINDOWS}'PNG'{$Else}{$IfDef DARWIN}'public.png'{$Else}'image/png'{$EndIf}{$EndIf});
54.  
55.  

Now i only have Problems with Alpha Images from the Browser. I only think, is it possible to change the default background of TBGRABitmap.create to white instead of Black?

Best regards
schlueter550v

[winni]

Hi!

I have tested your code and the transparent pixel exist: Value 0/0/0/0.

The conversion from transparent results if you don't set the parameter opaque of BGRAbitmap.draw to false. So the correct way is

Code: Pascal  [Select][+][-]

1. BGRAbitmap.draw (Image1.canvas,0,0, false);

That's the whole secret.

Tested with Lin64, fpc 3.2, Laz 2.0.12.0

Winni

[winni]

Hmmmm

Draw with opaque =  false also fails.

The solution ist good old

Code: Pascal  [Select][+][-]

1. Image1.Canvas.CopyRect (MyRect, BGRAImage.Canvas,MyRect);

It respects the transparent pixels. Strange.

inni

[circular]

Maybe first fill the image canvas with white, then draw the image with transparency?

[circular]

I had to define A Clipboardformat for PNG.

Indeed, some programs use PNG as clipboard format.

[winni]

Hi!

Gimp for example uses PNG as Clipboard format.

The problems drawing the BGRAbitmap from the Clipboard stream:

Code: Pascal  [Select][+][-]

1. Bmp.draw (Image.canvas, 0,0);
2.  

draws the transparent pixels as black, even if you fill the Image with some color.

Code: Pascal  [Select][+][-]

1. Bmp.draw (Image.canvas,0,0,false);

draws  nothing if you fill the image before with a color.

Code: Pascal  [Select][+][-]

1. Image.canvas.CopyRect (Arect, Bmp.canvas,ARect);

does the job including respecting transparency.

The transparent pixel exist as 0/0/0/0. That is not the reason.

Talking about Linux.

Winni

[schlueter550v]

Hello,

i tried the following now, but it did no change. Im not even sure if i used the CopyRect correct?
The image background keeps black on Windows:

Code: Pascal  [Select][+][-]

1. if (Clipboard.HasFormat(PredefinedClipboardFormat(pcfBitmap))) AND (NOT(Clipboard.HasFormat(pngClipboardFormat))) then
2.        begin
3.          Clipboard.GetFormat(PredefinedClipboardFormat(pcfBitmap),stream);
4.          stream.Position := 0;
5.          image := TBGRABitmap.Create(stream);
6.          imgPreview.Canvas.CopyRect(Rect(0,0,image.Width,image.Height),image.Canvas,Rect(0,0,image.Width,image.Height));
7.          //scaleAndPreviewImage(image); // frees image
8.        end;

How to check if those pixels are actual transparent?

Best Regards
schlueter550v

[winni]

Hi!

First fill the imgPreview with a color. Otherwise the color is by default black. So the copyrect respects the transparency but the background is black.

Check the values of a pixel:

Code: Pascal  [Select][+][-]

1. Const LE=LineEnding;
2. var px : TBGRApixel;
3. s : string;
4. ...
5. px := Image.GetPixel(x,y);
6. s := IntToStr(px.red)+LE+IntToStr(px.green)+LE+IntToStr(px.blue)+
7.               LE +IntToStr(px.alpha);
8. showMessage (s);                
9. ....
10.  

If a pixel is transparent it should show 0/0/0/0

Winni

[schlueter550v]

Hello winni,

i tried your suggestion:

Code: Pascal  [Select][+][-]

1. if (Clipboard.HasFormat(PredefinedClipboardFormat(pcfBitmap))) AND (NOT(Clipboard.HasFormat(pngClipboardFormat))) then
2.        begin
3.          Clipboard.GetFormat(PredefinedClipboardFormat(pcfBitmap),stream);
4.          stream.Position := 0;
5.          image := TBGRABitmap.Create(stream);
6.          //image.LoadFromStream(stream, reader,[loBmpAutoOpaque]);
7.          px := image.GetPixel(3,1);
8.          s :=  IntToStr(px.red) + ' ' + IntToStr(px.green) + ' ' + IntToStr(px.blue) + ' ' + IntToStr(px.alpha);
9.          ShowMessage(s);
10.          scaleAndPreviewImage(image); // frees image
11.        end;
12.  

But somehow i get 0 0 0 255 from that Pixel, which definetly should be transparent.
I also tried to fill the complete Canvas (250x250) white and put the image (200x200) with CopyRect on it.
The (200x200) area background is black from the image, and the rest of the Canvas space is white.
Im talking about a Win 10 System.


Some more ideas??


Best Regards

schlueter550v

[winni]

Hi!

The RGBA value 0/0/0/255 is black.

The value x/x/x/0  is transparent.


It seems that Windows behaves different from gtk2.
We should wait for  circular to give us an answer.

Winni

[circular]

@schlueter550v

In your latest example, you read the BMP format, not PNG. On Windows, BMP clipboard is almost always opaque.

[schlueter550v]

Hello,

so you suggest to use another Clipboardformat than pcfBitmap? But if i copy my PNG Picture from Firefox the Clipboard shows no PNG???
Or do i have to use that very long code from LazPaints uclipboard.pas' functions where some data is obtained from HTML? Is it possible to "use" this unit in uses?

In the attachment is an example of an PNG copied in Firefox. If i do it in IE or Edge it looks again different.