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I have some photos shot in low light with a compact camera which exhibit significant chroma noise, which I’d like to correct as much as possible.

My searches turned up a technique called “chroma blur,” where, presumably, one or more color channels can be blurred to smooth out chroma noise. Unfortunately, I can’t locate this at all in Aperture 3.

There is mention of this on Apple Support and an example of its use, but both seem to be for Aperture 1. This part of the RAW adjustments is not present in Aperture 3, nor does it turn up when I search the manual.

From what I read, the available options in the RAW Fine Tuning adjustment can vary based on the camera and RAW file format. However, chroma blur seems like something that wouldn’t be dependent on specific RAW features, or even RAW in general.

I have two other techniques I’ve been using for reducing chroma noise:

  1. For splotchy noise, adjust the noisy channel’s luminance & saturation until it matches a surrounding area of flat color. Example:

    Example of chroma noise correction Cycle of: Original RAW image data (100% crop); yellow channel saturation increased to show noise; corrected image.

  2. For grainy noise on a flat-colored area, brush in a color adjustment which drops the noisy channel’s luminance. Example:

    Example of chroma noise reduction

While these two techniques seem viable, they both involve much more by-hand correction than I’d like, and chroma blur seems to require less. Is chroma blur hidden in Aperture 3 somewhere? What other techniques should I try to reduce chroma noise?

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3 Answers 3

I'd suggest downloading a free trial of Topaz Labs DeNoise (and you'll need the Fusion Express plug-in host for Aperture as well). The program is $US80, so it's probably not something you'd want to buy sight-unseen, but the trial is a full-feature 30-day deal (the only limit is the time). I was able to completely remove the noise from your images with a single click in both instances (although I've probable overdone it -- I used the "strongest" preset):

alt text

and:

alt text

You can tone down the de-noising process quite a bit and adjust the detail recovery levels to make a pretty good silkish purse out of the muddiest sow's ear.

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I will check it out, but it seems to be operating on luma noise, not chroma noise. The first shot you posted is mostly acceptable (though significantly softer than I’d like), but the second retains all the chroma noise of the original — even though the texture is smooth, it retains the same splotchy areas of over-saturated yellows as my original. –  ieure Jan 4 '11 at 6:14

You cannot do this inside Aperture. If you solve it with a plugin, a copy of your image will be created, wrecking havoc on a non-destructive workflow.

In Lightroom there are separate controls for noise reduction of luminance and chroma channels. Lightroom also gives more control overall over the de-noising process. This feature was one of the two (the other being lens distortion correction) that eventually made me move from Aperture to Lightroom.

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Not sure if this is what you mean or if it will help, but in Aperture 3, you can view more adjustment panels by clicking on 'Adjustments' in your inspector and then again on 'Adjustments right below that. You will notice that there is a Chromatic Aberration option. If I understand your problem correctly, this should help to fix it.

If you are ok with third party plugins, take a look at Nik Software they have some great plugins that help with stuff like this.

Apple support might be talking about Moire, which is a RAW edit, but that's about the closest thing to CA. Would you happen to have a URL to the Apple Support page?

Hope all of that helps!

Kevin

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Chroma noise is different from chromatic aberration. –  mattdm Dec 30 '10 at 14:36
    
I linked the Apple Support page in my question, and as mattdm points out, I’m asking about chroma noise, not chromatic aberration. I’ve used the CA adjustment a couple times, and have no issues with it. –  ieure Jan 4 '11 at 6:10

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