Re: Newbie: Chaining CIFilters together?

Subject: Re: Newbie: Chaining CIFilters together?
From: Troy Stephens <email@hidden>
Date: Tue, 24 May 2005 11:51:01 -0700

On May 23, 2005, at 8:16 PM, M. Carlson wrote:

Okay, it's probably a case of RTFM, but I can't figure how to chain CIFilters for combined effects.

There is a sample project, CIExposureSample, under Developer > Examples > Quartz > Core Image. I can replace the CIExposureAdjust filter with CIHueAdjust, for instance, and it works fine. But if I try to make the output of one CIFilter become the input of another, like:

selectedImage = [CIImage imageWithContentsOfURL: ...
hueFilter = [CIFilter filterWithName:@"CIHueAdjust"
keysAndValues:@"inputImage",selectedImage,nil];
expFilter = [CIFilter filterWithName:@"CIExposureAdjust"
keysAndValues:@"inputImage",[hueFilter valueForKey:@"outputImage"],nil];
[context drawImage:[ expFilter valueForKey: @"outputImage"] ...

This does not seem to work. Apparently, I don't quite get the paradigm used.
Thanks for any pointers.

--M

You've got the right approach, but perhaps your hueFilter isn't yet fully configured at the point where you're asking for its "outputImage"?

A gotcha that may be biting you is that each time you change one or more of a filter's parameters, its "outputImage" actually changes identity ([theFilter valueForKey:@"outputImage"] subsequently returns a different pointer value).

Your "hueFilter" has some other parameters, which presumably you're setting later on in your code (maybe individually, or via a [hueFilter setDefaults] message). After you change those values, it's necessary to re-establish the connection between filters, since the hueFilter will now return a different "outputImage" instance:

[expFilter setValue:[hueFilter valueForKey:@"outputImage"] forKey:@"inputImage"];

Troy Stephens

Cocoa Frameworks

Apple Computer, Inc.

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