UIImage Resize without loss of quality

Question

Im looking for an external library (or a method using Apple frameworks that doesn't destroy the quality) which will let me scale down images.

I have tried this 'simple-image-processing-library' but it only works for black and white - I don't know how to make it work for colour images. ( http://code.google.com/p/simple-iphone-image-processing/ )

I have tried Core Graphics, UIKit, the "trevor" ( http://vocaro.com/trevor/blog/2009/10/12/resize-a-uiimage-the-right-way/ ) method - which makes EXTREMELY blurry images and really I don't know what else I can do - I can't continue programming my app without getting at least half-decent image scaling working. I think interpolation is needed to get decent results.

Given the recent advances in iOS, I really hope someone can help me. This isn't a problem that only I am having, lots of other people seem to have the same problem, so if someone could solve it here, I'm sure if would appreciated by a very wide audience!

Thank you very much

Answer 1

My Answer:

OK - someone who actually answered my question originally then subsequently removed their answer, I'm really not sure why.

Here are three different approaches:

• Using Trevor's Category approach - I think this is terrible for preserving sharpness. It is more useful when you are trying to prevent jagged lines appearing.
• Using iOS5's Core Image support and the AffineTransform filter - the more advanced CILanczosScaleTransform is not available in iOS (as far as I am aware). Produces pretty bad results actually.
• Using MGImageUtilities' category - this seems to produce excellent results in scaling down. ( https://github.com/mattgemmell/MGImageUtilities )

Here is a screenshot of the four images. ENLARGE IT! : http://i.stack.imgur.com/M3DVE.jpg From Left->Right : Original, Trevor's, Core Image, MGIU.

Its amazing that the picture on the far right has about SIXTEEN times less memory usage than the picture on the left. Pretty much the same quality. On a small screen - always resize big images!