Question

How to save a HBITMAP to JPEG and PNG file using Delphi 2007?

Asked by: tedz

I have a HBITMAP (and its Width, Height, Bitcount and pixeldata pointer). The bitmap is usually in 24 or 32 bpp color and have never a palette, but contain raw RGB data.

Now, how do I save this to JPG and PNG file using Delphi 2007 pro without using any other libraries other than the PNGImage unit (the TPNGObject component) and the standard Delphi libraries ?

Thank's!

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Asked On
2009-08-11 at 07:56:20ID24643352
Tags

HBITMAP JPEG PNG

Topic

Graphics and Delphi Programming

Participating Experts
1
Points
500
Comments
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Answers

 

by: lmiklePosted on 2009-08-11 at 13:27:13ID: 25073011

Try to assign HBitmap to TBitmap's handle and then convert it to jpeg (using jpeg unit) or png (using pngimage library).

uses jpeg;
 
function HBitmapToJpeg(AHandle : HBITMAP) : TJPEGImage;
var
  Bmp : TBitmap;
begin
  Result := Nil;
  Bmp := TBitmap.Create;
  Try
    Bmp.Handle := AHandle;
    Result := TJPEGImage.Create;
    Result.Assign(Bmp);
  Finally
    Bmp.Free;
  End;
end;

                                              
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by: tedzPosted on 2009-08-12 at 03:08:48ID: 25077179

Thank's, but this code seems to free the HBITMAP data.

If I am going to use the HBITMAP later to save to a PNG, I need to be able to continue using it.
If I write to the pixeldata afterwards, I get an AccessViolation

I tried setting Bmp.Handle := 0 before Free'ing the BMP, but that didn't help.

See code snippet for how I create the HBITMAP

  FillChar(FBMI, SizeOf(FBMI), #0);
 
  FBMI.bmiHeader.biSize := SizeOf(BITMAPINFOHEADER);
  FBMI.bmiHeader.biWidth := FWidth;
  FBMI.bmiHeader.biHeight := FHeight;
  FBMI.bmiHeader.biPlanes := 1;
  FBMI.bmiHeader.biBitCount := FBitCount;
  FBMI.bmiHeader.biCompression := BI_RGB;
  FBMI.bmiHeader.biSizeImage := FWidth * FHeight * BytesPerPixel;
 
  FBM := CreateDIBSection(0, FBMI, DIB_RGB_COLORS, FBuffer, 0, 0);

                                              
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by: tedzPosted on 2009-08-20 at 02:08:28ID: 25140444

So, this is still a problem:

I create a HBITMAP with CreateDIBSection, and I want to keep it for the duration of the application.

From time to time, I'd like to save this HBITMAP to PNG and JPEG.
I am aware of the TBitmap.Create / Assign trick used in the answer above.
However, this seems to free the memory for the DIB section, which I don't want.
I just basically want to save the raw RGB data to PNG and JPEG files without freeing the memory buffer.
I guess I could create another DIB and copy the data for each save, but isn't there a better solution?

 

by: tedzPosted on 2009-10-26 at 08:03:36ID: 31614242

Was not really what I was asking for.

Maybe it is impossible.

20120131-EE-VQP-002

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