From: Ignacio Alvarez <ice30@son1.telmex.net.mx>
Subject: Re: Generation of 24-bit colour memory-bitmap with computer running  lower colour-depth
Date: 12 Apr 1999 00:00:00 GMT
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To: Thomas Munk <tmunk@post1.tele.dk>
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I've encountered the same problems, and found a solution.

When you're in 256 color mode, and you resize a TBitmap, a palette is always
created (even if PixelFormat = pf24Bit). So when you save a modified 24Bit
bitmap to disk, the unnecessary palette is saved too.

Apparently, Delphi can read this corrupt bitmap, but other programs that
expect a standard bitmap, display it all wrong.

The solution is to set the Palette to 0 before saving it (i.e.
Bitmap.Palette:= 0).


Thomas Munk wrote:

> Hello Delphi-group
>
> I was wondering if someone could give me some guidelines for handling the
> following job in Delphi 3:
>
> I want my program to generate one bitmap containing several thumbnails of
> other bitmaps. This final thumb-bitmap should be 24-bit colours, no matter
> what colour-depth the computer runs at generation time. The bitmaps to be
> thumbnailed are both 24-bit and other depths. What I do today is this:
>
> - B:=TBitmap.Create
> - B.PixelFormat:=pf24bit;
> - Set B.Width and B.Height to 500 x 480
> - Putting in the small thumbnails with B.Canvas.Draw
> - Maybe assigning B.Width and/or B.Height smaller values
> - B.SaveToFile
>
> I works allright most of the time, but here's my problem: If the computer
> runs less than 24-bit colour-depth and I assign smaller values to the
> bitmap's width and height the saved image goes crazy. With 'crazy' I mean
> wrong (blue-like) colours and image pushed half left or right. If I don't
> touch the width/height all seems right OR if the computer runs at 24-bit
> depth it's allright to adjust the width/height.
>
> Am I doing this the complete wrong way?
>
> Thomas