That was an interesting article on "Global Chroma Noise Reduction in Photoshop". However, it sure seems like an overly complicated way to do it. Here's my alternative way...

1. Convert to Lab mode.
2. Select the Lightness channel.
3. Run your normal noise reduction tool(s) on this channel.
4. Select the "a" channel.
5. Hold down the <Ctrl> and select the "b" channel.
6. Run "Surface Blur" on the two color channels with a radius of 10 and a threshold of 10.

This process blurs the color channels. Any bits of chroma noise gets blurred into the surrounding colors. That's it!

OK, you probably should do your sharpening on the Lightness channel only while you are in Lab mode. You could run your noise reduction tool on the "a" and "b" channels, but that would be treating it like luminous noise and not chroma noise. It can help in some photos, but may not be needed. It won't hurt either.

Experiment with higher radius and threshold settings for the "Surface Blur" on the color channels. Doing so can give some nice soft colors without hurting the lightness sharpness. You might be surprised at how much blurring you can get away with.

This all works nicely in an Action assigned to an "F" key.

Clyde

Does anyone know if the Chroma reduction method discussed on the LL website has any relevance
to people who shoot in RAW and use either the Adobe RAW converter or Lightroom to reduce noise?

And If so what is the advantage of using the method in the article compared to using the raw processors or should it be considered to be used "in addition" to the raw processors?

I never used ACR for noise reduction because I found that my Noise Ninja was much better at reducing noise than ACR. Actually I don't use ACR for much at all. I sometimes will use the "auto" click to pull the histogram back inside the edges. Otherwise, I find my tools inside Photoshop to be more powerful and faster than those in ACR. If I get the histogram inside the edges, I know that I can edit in Photoshop without worrying about loosing data.

For example, I do a lot of my editing in Lab mode as it gives me a lot of easy and fast control over color and luminance that you can't get in any other mode. That is not available in ACR. I also use some plugins, like Noise Ninja, that do things better and faster than Photoshop or ACR. Also not available in ACR. I also do as much as possible with Actions; this is important in a pro environment with hundreds of pictures to edit. There are no Actions in ACR. There are also no layers in ACR and that answers your direct question.

I am also one of those Photoshop picture editors who isn't very concerned about loosing data. If I have the histogram inside the box, I know I have everything I possible can get from the RAW file. I also know that I'm very likely to edit it to intentionally loose some data. My goal is to make the picture better and I'm not silly enough to think that everything in my captured picture is needed to do that. Many times there are things in the picture that do not help to tell the story and I edit them out. Yes, that looses data, but who cares?

It seems to me that most people who do most of their correction in ACR have an obsession with loosing data from the RAW picture. To me that seems like keeping an eye on irrelevant technical information and forgetting that the goal is making the final picture tell the story.

My $0.02,
Clyde

Doesn't the blurring on the colour layers "smudge" the colour boundary and thereby lose sharpness?

For instance, it sounds as if the transition between eyelashes and skin would soften and the skin would pick up some "gray" from the lashes, or fine colour detail would be reduced even though the lightness (luminance?) contrast is maintained.

Andy

Good questions, but no. Almost all of what you see as sharpening is in the "L" channel. That's why you only sharpen it. The "a" and "b" channels don't have any lightness or gray information. They give nothing to the contrast that you use for seeing sharpness. Your eyelashes are almost completely in the "L" channel.

Take a look at these channels some time. You'll have a tough time figuring out what the shapes are in your photo. If the colors aren't one of the 4 extremes of the two axis (blue and yellow / magenta and green) and saturated you'll have a tough time even seeing anything at all. Well, as far as easily recognizable things go. I bet you can't even find the eyelashes in the "a" and "b" channels. After spending some time with these color only channels, you'll loose the concept of "color detail"; the "detail" is in the lightness and not in the color.

Also remember that "Surface Blur" looks for the edges and avoids them. It really only blurs the fields where everything is pretty much the same - based on the threshold setting. So, it would be blurring the inside of a big magenta field of color, but not the edges with the greens.

For fun and learning, try blurs other than "Surface Blur". These will blur the boundaries of colors. I think you will be surprised at how little these will affect the "sharpness" of your photo. Oh, you can really over do it and see what odd things you can get. That is why you use "Surface Blur" though; you don't want to blur the boundaries.

You will be surprised at how much blurring you can do with "Surface Blur" on the color channels. Where this really shines is with human skin. As you crank up the blur radius you will see some very nice softening of skin colors. My experience is that you can get a variety of effects at different levels - depending on the lighting. This can be a very nice tool for portraits of women. This is a benefit of this technique far beyond just getting rid of chroma noise.

So, give it a try and see what you can do with it.

Clyde

Impression is that the author is not aware of Photoshop HSL Blend modes.
Also, there might be no need to make a trip to Lab unless you want so.

Goto 16 bit if not already given
Despeckle filter -> Fade to Luminosity Blend mode w/reduced Opacity
Gaussian Blur -> Fade to Color Blend mode w/reduced Opacity
optionally done on a copy layer to combine with Masks
and followed by some re-sharpening

… as for a very basic approach and ignoring the Noise Reduction filter (since CS2 iirc)
which I think does something of that kind behind the scenes.

Peter

--

True on both accounts. There are a lot of ways to do the same thing in Photoshop.

There are many reasons why you might want to make a trip to Lab other than just chroma noise. One of the best Photoshop books I've ever read is this one:

http://www.amazon.com/Photoshop-LAB-Color-...05329866&sr=8-1

Clyde

I'll second the book recommendation!

http://makelightreal.com/category/one-action/ this link has some LAB color mode screencasts and tutuorials.