[fpc-pascal] Performance problems with Image Conversions

Michael Van Canneyt michael at freepascal.org
Sun Feb 24 12:43:27 CET 2013

On Sun, 24 Feb 2013, Sven Barth wrote:

> On 24.02.2013 11:44, Michael Van Canneyt wrote:
>>>      srcImg:=TFPMemoryImage.Create(0,0);
>> Do not use TFPMemoryImage. It is a catch-all memory format, not
>> optimized at all, using 64 bits for the images.
>> Instead, use e.g. TFPCompactImgRGBA8Bit if you need alpha or
>> TFPCompactImgRGB8Bit if you do not need Alpha.
> Nice, I did not know we have more compact image types available. O.o

If memory serves well, Mattias Gaertner made them.

>>>          dstImg:=TFPMemoryImage.Create(iX,iY);
>>>          dstImg.UsePalette:=false;
>>>          dstCanvas:=TFPImageCanvas.create(dstImg);
>>>          dstCanvas.StretchDraw(0,0,iX,iY,srcImg);
>> Phew, this is also a real killer.
>> Do not draw on a canvas with stretchdraw. That will be slow as well;
>> Rather, attempt to manipulate the image in memory by doing a stretch
>> directly.
>> Choose an algorithm which is fast. The default interpolation will result
>> in quite a lot of calculations.
> Maybe a collection of algorithms for in memory rescaling would be nice...

There are a lot of them, that is what the interpolations are for, but they 
work with a canvas. The case of rescaling an image and simply send the 
resulting image as a file was not foreseen at the time of writing.


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