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Date Posted: 18:37:09 10/23/00 Mon
Author: Michel
Subject: Re: TImageScrollBox Zooming
In reply to: Bill Miller 's message, "TImageScrollBox Zooming" on 18:06:43 10/23/00 Mon

Hi Bill,

Yes, I have noticed this before.

It occurs with the Windows API StretchDiBits call in TResizeTransform, when the image

becomes too large. It is definitely dependent on image format. For example I was able to

resize a 256 color image to 999%, but the same image in true color gave a black rectangle at
900%. This is not much I can do about this. I also is probably related to the OS and video

as are many issues with large image sizes. I could change the code to raise an exception,

but that may be more disruptive.

Best regards,


> In some testing here it looks like
> TImageScrollBox.ZoomPercent may be failing at 400-800
> percent depending on the size of the image in the
> component. With a small 40x40 pixel image I can set
> ZoomPercent to over 800 percent, but with a 1024 x 768
> image I can only reach about 400 percent.
> After I reach these levels depending on the size of
> the image in the TImageScrollBox, the image appears to
> be entirely black. No error messages are produced.
> Has this been reported before?
> I thought it might be a memory problem but it does not
> seem to make a difference if running the compiled
> application stand-alone or from the IDE. I guess it
> could also be the video card...
> The test computer is running Delphi 5, patch 2 with
> 128 megs ram.
> Regards
> Bill

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