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Date Posted: 20:06:56 05/24/01 Thu
Author: wto
Subject: Re: problem in TDibGraphic.Assign
In reply to: Michel 's message, "Re: problem in TDibGraphic.Assign" on 07:37:18 05/23/01 Wed

Hi,
But I think a bitmap is DDB only when its pixelformat is
pfDevice, not pfCustom.

>
>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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