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Date Posted: 07:41:49 05/25/01 Fri
Author: Michel
Subject: Re: problem in TDibGraphic.Assign
In reply to: wto 's message, "Re: problem in TDibGraphic.Assign" on 20:06:56 05/24/01 Thu


Hi,

I believe that is the case. The handle type is changed to DDB when the format is pfCustom. I am not sure how to workaround this. I know ideally, the handle type of the source TBitmap should not change, but this was necessary to properly handle 16 bit bitmaps.

I will do more investigating on this. Does the latest version,

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

improve your situation?

Best regards,

Michel

>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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