Re: most efficient way to string CIFilters together?

FROM : Jean-Daniel Dupas
DATE : Sat May 03 22:33:33 2008

Le 3 mai 08 à 20:06, Josh Burnett a écrit :

> In a photography app, I'm chaining a series of CIFilters together to 
> process the image.  I'm able to do the chain just fine, but I'm only 
> using a few filters at the moment.  As I increase the length of this 
> chain, am I going to run into performance issues?  Here's my code:
>
> exposureFilter  = [CIFilter filterWithName: @"CIExposureAdjust"
>     keysAndValues:
>         @"inputImage", inputImage,
>         @"inputEV", [NSNumber numberWithFloat: exposureValue],
>         nil];
> outputImage = [exposureFilter valueForKey: @"outputImage"];
> [exposureFilter retain];
>
> zoomFilter  = [CIFilter filterWithName: @"CILanczosScaleTransform"
>     keysAndValues:
>         @"inputImage", outputImage,
>         @"inputScale", [NSNumber numberWithFloat: mappedZoom],
>         @"inputAspectRatio", [NSNumber numberWithFloat: 1.0],
>         nil];
> outputImage = [zoomFilter valueForKey: @"outputImage"];
> [zoomFilter retain];
>
>
> Obviously, it's easy to continue to add to this chain.  Is this the 
> most efficient way to string multiple filters together?  I can 
> probably use Quartz Composer to create a single image unit that does 
> all of the processing.  Would that be any more efficient, or would 
> it be essentially the same result?
>
> Thanks,
>
> Josh


On Mac OS 10.5, there is a class designed to create and store filter 
chain (CIFilterGenerator). You may have a look at it.
You also have to know that the filter is not computed when you call 
[valueForKey:@"outputImage"] but when you try to access the final 
outputImage content (to display it for example). Even if this is not 
obvious as you have to create a new image instance for each filter, 
Core Image optimize the image processing. So creating a single image 
unit would probably not be more efficient.