iphone - How do I desaturate a UIImage? -


is there easy way (or built-in library) in ios 5.x desaturate uiimage? here's how doing it:

cgcontextref context = uigraphicsgetcurrentcontext();     cgcontextsavegstate(context);      cgcontexttranslatectm(context, 0.0, self.bounds.size.height); // flip image right side     cgcontextscalectm(context, 1.0, -1.0);      cgcontextdrawimage(context, rect, self.image.cgimage);     cgcontextsetblendmode(context, kcgblendmodesaturation);     cgcontextcliptomask(context, self.bounds, image.cgimage); // restricts drawing within alpha channel     cgcontextsetrgbfillcolor(context, 0.0, 0.0, 0.0, desaturation);     cgcontextfillrect(context, rect);      cgcontextrestoregstate(context); // restore state reset blend mode

this seems bit more complicated expected. there simpler way this?

i thinking of core image, can't seem find concrete example on how desaturate image using that.

you can open source gpuimage framework using 2 or 3 lines of code:

uiimage *inputimage = [uiimage imagenamed:@"inputimage.png"];     gpuimagegrayscalefilter *grayscalefilter = [[gpuimagegrayscalefilter alloc] init]; uiimage *grayscaleimage = [grayscalefilter imagebyfilteringimage:inputimage];

(remembering release filter if not building using arc)

this reduces image luminance values, desaturating it. if want variable saturation / desaturation, can use gpuimagesaturationfilter. framework name indicates, filtering runs on gpu, , faster core image in every situation i've benchmarked on ios of 5.1.


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