I have a slideshow using DisplayImage for drawing on a TPaintBox. Now I want to fade-in/fade-out images. How do I do that?
I tried something like Image.DrawAlpha(Image.BoundsRect, PaintBox.Canvas, 0, 0) in a loop where alphachannel values increases/decreased. It doesn't work.

Vampyre 0.26.4
FPC 2.4.1
WinXP sp3

Image.BoundsRect: 1920x1200
PaintBox.ClientRect: 682x633

CommonRect (103, 0, 682, 529)

Calling ImageCanvas.DrawStretchAlpha(Image.BoundsRect, ImageCanvas, CommonRect, rfBicubic)
results in a runtime error 201 in ImagingFormats.BuildMappingTable line 1611 SetLength(Result, DstWidth) because DstWidth has a negative value.

Do you have a quick fix please?

WinXP SP3, Lazarus 9.28.2, Vampyre 26.4
With demo LCLImager I converted a jpg file to A8R8G8B8 format and saved it as jng file. Windows explorer shows an incorrect file size of 0 KB (whereas file properties show the correct file size).

I have jpeg photo's which are converted to A8R8G8B8 because I need an alpha channel. In which extension should the resulting image be saved so quality is preserved best? Or should I convert to another format?