Resizing an animated GIF is not as simple as it might first seem. There are some key considerations to take into account:
- Each frame must be independently resized.
- The offset of the frame must also be adjusted by the X and Y ratio. We must account for offsets that don't line up exactly. For example, if you are resizing by 0.5 and one offset is 71 ... the resulting offset will not line up with the rest of the image.
- Almost all animated GIF's use transparency for optimization. The transparent palette index must be retained. Any interpolation will give the edges of transparent areas a strange colored border.
- Resizing the image significantly larger results in a blocky image due to the nearestneighbor resizing which uses no interpolation.
The attached project contains an updated version of the previous project using DotImage 11.2 in Visual Studio 2012 (though the code should work fine in any DotImage 9.0 and above).
Original Article:
Q10086 - INFO: Resize an animated GIF using DotImage