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Date Posted: 07:37:18 05/23/01 Wed
Author: Michel
Subject: Re: problem in TDibGraphic.Assign
In reply to: Michel 's message, "Re: problem in TDibGraphic.Assign" on 17:45:47 05/22/01 Tue


Hi,

I have looked at the latest code base (1.1), and the handle type is only set to bmDDB, to handle 16 bit bitmaps which are very rare:

else if (Source is TBitmap) then
begin
{ AssignFromBitmapHandle reads the X and Y resolutions }

{ MB Oct 28, 1999. The AssignFromBitmapHandle works with a device
dependent bitmap. This is required to load 16 bit bitmaps, in order
to convert them to 24 bits using the GetDIB function. For an example,
see ..\En\QAtests\Tomcat16.bmp

MB Jan 17, 2001. After testing assigning a 24 bit
TBitmap to a TBitmapGraphic, then perform a color conversion to 256
colors, and saving the new bitmap, with bmDDB the quality is not
as good. The sample project is in ..\en\qatests\TBitmap assign and 8 bit\

The only way to distinguish when to use bmDDB or mbDIB is to use the
PixelFormat property. With the 16 bit bitmap test case, the pixel format
is pfCustom }

if TBitmap(Source).PixelFormat = pfCustom then
TBitmap(Source).HandleType := bmDDB
else
TBitmap(Source).HandleType := bmDib;

Self.AssignFromBitmapHandle(TBitmap(Source).Handle);
end

Best regards,

Michel

>
>Hi,
>
>I suggested using TBitmapGraphic as a workaround. If a
>lot of your code is based on TBitmap, this may not be
>a good idea.
>
>I will be looking at this tomorrow. I need to find the
>orginal image for which the original fix was
>introduced, and make sure I don't fix one problem and
>introduce another.
>
>Best regards,
>
>Michel
>
>>Hi,
>> Thank you very much for your reply. You suggest me
>>to
>>use TBitmapGraphic instead of TBitmap. But there is a
>>problem: I have wrotten a bundle of graphic classes
>>inherited from TBitmap. How should I process these
>>classes,
>>can you give me a solution?
>>
>>>
>>>Hi,
>>>
>>>The handle type was changed to workaround a problem
>>>when assigning 16 bit bitmaps. I'll have to look into
>>>this in more detail before I do a change.
>>>
>>>As a workaround, you may try loading your bitmap in a
>>>TBitmapGraphic instead of a TBitmap.
>>>
>>>Best regards,
>>>
>>>Michel
>>>
>>>>you use following code in TDibGraphic.Assign:
>>>>
>>>> if (Source is TBitmap) then
>>>> begin
>>>> { AssignFromBitmapHandle reads the X and Y
>>>>resolutions }
>>>>
>>>> { MB Oct 28, 1999. The
>AssignFromBitmapHandle
>>>>works with a device
>>>> dependent bitmap. This is required to load
>>>>16 bit bitmaps, in order
>>>> to convert them to 24 bits using the
>GetDIB
>>>>function. }
>>>> TBitmap(Source).HandleType := bmDDB;
>>>>
>>>>
>>>>Self.AssignFromBitmapHandle(TBitmap(Source).Handle);
>>>> end
>>>>
>>>>I don't know why you select to change the HandleType
>>>>of the
>>>>source bitmap since usually it is considered as a
>>>>constant one and will not be changed in a
>>>>AnotherGraphic.Assign(SourceBitmap) operation?

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