Chroma Noise Reduction

[tomczak]

I often have a problem with chroma noise in high ISO images - I find it more objectionable than the luminance noise. In AS, Noise Reduction tab, there is an option "blur chrominance only', which works fine. I can't use it in a workflow though as there is no AS widget. Is there another way? I tried to extract various channels, blur them, and then recombine the image, but with little success.

[den]

Maciej...

You might try experimenting with a Sharpen widget set to BilateralSharpen with initial settings: Amt=100; BR=5; BT=10; SF=20; and ST=1. Modify settings to suit your image content/dimensions. This does not address changing chorma noise to luminance but should significantly reduce the chorma noise, yet retain reasonable detail without introducing objectionable 'chroma splotches'...

25GaussianRGBNoise.jpg

25GaussianRGBNoise_reduced.jpg

...Edit1...
The above suggested initial BilateralSharpen settings seems to work well for reducing luma noise, reducing unwanted textures in skin image areas, etc... ...as well, again with slight adjustments for image content and dimensions, especially when used with an image area and/or texture mask.

[tomczak]

I've been experimenting with high-ISO chroma noise reduction some more. AS chroma-only blurring works well often, but it tends to soften the image sometimes (perhaps it's an illusion of making the image less grainy). The second tab in AS, the Speck Removal, sometimes can work even better in 1x1 pixel mode and the threshold adjusted properly, but it also tends to soften the image - unavoidably I think.

Canon Digital Photo Professional has a chroma noise slider which seems to work a little different - the end result is still grainy and appears sharp, but the high frequency saturation and hue variance between adjacent noisy pixels are reduced, making the noise less 'digital' and thus easier to look at (and such processing could be automated). Visually, the noise becomes less 'saturated' - it's still there but has a less 'Micky Mouse' appearance - small scale saturation variation are reduced without visually blurring the noise 'grain'. Am I right about it?

Also, is there a combination of techniques (widgets?) in PWP that could be set so that chroma noise can be isolated somehow and treated in a different way than using AS?

[tomczak]

Here is an example of what I'm trying to do. The only difference between the 3 crops is chroma noise.

A - no chroma noise reduction
B - chroma noise reduced in PWP - AS.
C - chroma noise reduced in DPP

The original blue/yellow multipixel blotches (A) become darker/lighter spots when PWP-AS (chrominance only) noise reduction is applied (B). DPP (C) chrominace noise slider reduced colour variance without touching the luminance noise.

What's the difference between these two methods? Is the difference the method of noise reduction or the chroma channel(s) separation?

Is there another way of dealing with the chroma noise in PWP? I tried blurring H or S channels, but went nowhere.

[tomczak]

I'm not sure if it's helpful, but I just looked at the same image in NeatImage, which can separate noise frequencies. The 'blue/yellow' blotches are v. low frequency, mostly in YCrCb-Cb channel or, a bit less decisively, in RGB-B channel.

[den]

Maciej... while this does not provide a direct PWP solution, it is a way to combine DPP preferences with PWP...

...I sometimes find that Canon's DPP colors are more preferably than those that can be easily achieved with PWP... so perhaps the the Extract/Combine channel substitutions described here...

http://www.dl-c.com/board/viewtopic.php ... 2307#p2307

...would be a way to obtain your preference for DPP Chroma Noise Reduction colors after taking into account the differing pixels dimensions between the PWP and DPP conversions and the needed off-set edge crops necessary for 1:1 registration.

[tomczak]

How does AS define 'chrominance' (a blur choice), and what are the two other colour channels?

The reason that I'm asking is that I think that AS is the only transformation that allows for chrominance extraction, which should be a good channel to handle colour noise, but I wonder what else can be done to chrominance blurring (larger radius?, median?) to better reduce this kind of colour noise.

[tomczak]

Does AS split the colours into YCrCb colour coordinates, and if so, would it make a difference if Cr and Cb channels could be blurred independently?

[tomczak]

Here is an article on PS manipulations in an attempt to reduce chroma noise only:

http://www.luminous-landscape.com/techn ... oise.shtml

If I understand it, the entire image, softened via medians and blurring, was composited with the unsoftened luminance of it, in 'colour' blending mode.

I'm not sure what the colour blending mode is, but it seems that some 'luma, chroma, hue' colour model (what is it?), different from HSV or HSL (what's the difference?), is used in which chroma and hue of one image is blended with luma of the other, with some provisions of handling maxed out values gracefully.

Is there a way of adopting this technique using the tools that PWP presently offers?

The best I came up with is to extract unblurred Luminance, then blur HSL-S and then replace HSL-L with unblurred Luminance. It sometimes seems to work.

[den]

As far as I know there is no PWP direct equivalent for a PhotoShop "Color Blend" or "Hue Blend" as described/illustrated here: http://www.adobetutorialz.com/articles/ ... -Photoshop.

The closest one might come in PWP is perhaps: (1) normalize an image's blurred H and S channels from its Lightness to a 50% tone and (2) Composite-Hard Light the result with the image's Luminance channel... recognizing that for the HSL color space model, the H and S plane is at a 50% tone and the Hard Light filter will brighten for any tone greater than 50% and darken for any tone less than 50%...

Let Img0 be the starting image...

1 to 1 image area_ori.jpg (47.31 KiB) Viewed 6903 times

(1) Extract Img0's Luminance channel, creating Img1

(2) Gaussian Blur Img0, creating Img2 [for the illustration, the blur was 10]

(3) Apply a HSL BrightnessCurve [0,50], [100,50], Amount = 100 to Img2, creating Img3

(4) Apply Composite-Hard Light where Input = Img3, Overlay = Img1, and Input/Overlay Amounts = 100; click OK, creating the reduced chroma image...

1 to 1 image_reducedChroma.jpg (47.87 KiB) Viewed 6907 times

The illustrations are 1:1 resolution 400x267 image area crops of a Panasonic DMC-GH2 converted RW2 file, whose ISO was 1250...

Composite-Soft Light will produce a softer ambience in step(4) if a preference.

This seems to work well for images in my files... How about yours???