Processing large images with Delphi for saving as .jpeg

Question

In Delphi 7, I have a library that uses the TCanvas component to output some information. The resulting image is about 4800*6000 pixels and I would like to print it and save it as .jpeg.

To achieve this, I created a TBitmap and gave its Canvas as parameter to the library and then I assigned the bitmap to the jpeg. Apparently, this is taking too much memory, because I am getting an exception when trying to set the bitmap's width and height, saying "Not enough storage is available to process this command."

// output to printer
Printer.BeginDoc();
doPrint(Printer.Canvas);
Printer.EndDoc();

// output in bmp.Canvas
bmp := TBitmap.Create;
bmp.Width := Printer.PageWidth;
bmp.Height := Printer.PageHeight; // <- BAM! Exception!
doPrint(bmp.Canvas);

// save as jpeg
jpg := TJPEGImage.Create;
jpg.Assign(bmp);
jpg.SaveToFile('...');

// free
bmp.Free();
jpg.Free();

What am I doing wrong? Could I save Printer.Canvas directly as a .jpeg file?

Edit: Updated image size approximation from 2000*2000 to 4800*6000

Answer 1

Delphi's TBitmap class has problems handling such large bitmaps. And no, you cannot save a TCanvas directly to a .jpg file.

Answer 2

I tried the following code on my machine (Windows XP, Delphi 2006), and did not receive any exceptions. What OS are you using?

  procedure TForm3.Button3Click(Sender: TObject);
  var
     bmp : TBitmap;
  begin
     bmp := TBitmap.Create;
     bmp.PixelFormat := pf32bit;
     bmp.Width := 6000;
     bmp.Height := 4800;
     bmp.Free;
  end;

Answer 3

you should be able to process large bitmaps using TBitmap32 from Graphic32 (http://www.graphics32.org/wiki/)

Answer 4

As mghie said: It depends a lot on your system see EFGs computer lab on large bitmaps

Answer 5

You should set the pixelformat for the bmp to something before sizing up the bmp, as Ben Ziegler suggests. This makes all the difference.

Answer 6

Try to set PixelFormat to pf32bit or pf24bit (as in example by Ben Ziegler), in most cases this PixelFormat does the trick (as I remember, it was mainly on XP). You can find more info here.

Answer 7

Not sure if this will work or help. But we created a function which will save a component to a jpeg:

    function SaveComponentToJPeg(mControl: TWinControl): TJpegImage;
    var
      bmp: TPicture;
      jpg : TJpegImage;
      dc: HDC;
      wnd: HWND;
      Params: array[0..255] of Char;

    begin
      bmp:=TPicture.Create;
      jpg := TJpegImage.create;
      try
        bmp.Bitmap.Width  := mControl.Width  - 05;  // Deduct for border.
        bmp.Bitmap.Height := mControl.Height -05;  // Deduct for border.
        wnd               := mControl.Handle;  //ctiveWindow;
        dc                := GetDc(wnd);
        BitBlt(bmp.Bitmap.Canvas.Handle,0,0,bmp.Width,bmp.Height,dc,0,0,SrcCopy);
        ReleaseDc(wnd, dc);
        jpg.assign(bmp.bitmap);
        result := jpg
      finally
        bmp.Free;
      end;
    end;