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Date Posted: 07:42:31 11/27/00 Mon
Author: Michel
Subject: Re: Get DIB Failed
In reply to: James Wendell 's message, "Re: Get DIB Failed" on 11:40:23 11/14/00 Tue


Hi James,

I apologize for the delay. I had not noticed the change in the thread. The test program was simply a loop accumulating images in a list and destroying all the images when done:

procedure TForm1.Button1Click(Sender: TObject);
var
List : TUnOrderedList;

Graphic : TJpegGraphic;
Count : Integer;

begin
List := TUnOrderedList.Create( TObject, CompareLess );
try
Count := 0;

Stop := False;

while True do
begin
Graphic := TJpegGraphic.Create;

//Graphic.LoadFromFile( 'c:\temp\PA2500461.JPG' );
Graphic.LoadFromFile( 'c:\temp\thumb.jpg' );

List.Insert(Graphic);

Inc(Count);

Button1.Caption := IntToStr(Count);

Application.ProcessMessages;

if Stop then
begin
Button1.Caption := Button1.Caption + ' done';
break;
end;
end;

finally
List.Free;
end;
end;

An alternative to create a thumbnail viewer is to create a single image, and copy the thumbnails into it. This is how I will attempt it when I get around to it.

Independent of the size of the images, I also think creating a TImageScrollBox for each thumbnail uses a lot of Windows resources. Another idea could be to draw each thumb on a TPaintBox component, which does not have a window handle.

Best regards,

Michel

> I thank you for the testing and the response. Could
> you tell me HOW you loaded ONLY a RESIZED image with
> your test project? I think I was doing essentially
> just that with my Thumbnail program, and still cannot
> get past 20 to 30 images loaded sequentially. In
> effect, I was loading each full-size (2048x1536 JPEG)
> image as a TDibGraphic in memory (one only), resizing
> it to 112x112 for display as a thumbnail, and then
> displaying it in a TImageScrollBox. I then DESTROYED
> the original 2048x1536 TDibGraphic BEFORE I loaded the
> next image and repeated the process. So I should NEVER
> be using more resources than what are required to load
> ONE (1) full size image at a time, while maintaining
> the memory for previously loaded 112x112 thumbnails.
>
> I wonder how other thumbnail programs work, such as
> ACDSee and ImageExpert2000? I understand your argument
> about resource usage under Win9x and maybe Win2000
> (which I plan to try soon), but how do other vendors
> make thumbnails work properly? Perhaps freeing the
> TDibGraphic leaves some sort of residual memory usage
> (a memory leak?) or other anomaly.........
>
> I reecently tried another test using your sample demo
> program and the image (2048x1536) I sent you. Under
> Win98, if you load the image and then repeatedly
> lighten/darken the image while it is displayed, the
> SAME CreateDIBSection fail occurs. I think the error
> occurs here presumably because you are creating an
> "undo" image.

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