Color noise and how to get rid of it

Sigma 18-200mm f/3.5-6.3 DC OS for Canon

09/14/2005 09:00:03 PM · #1

Can anyone tell me if there is a way of getting rid of color noise that is allowed in basic editing? I have tried neat image and it just isn't doing it.

ElGordo

Canon EOS-400D Rebel XTi

09/14/2005 09:41:21 PM · #2

I believe this method is legal in Basic Editing but clarification from SC is needed:

Convert the image to LAB COLOR (Photoshop),
select each color channel separately and apply a gaussian blur to each. Do not blur the luminence channel!
Be careful to blur no more than is necessary to smudge out crisp color noise artifacts. Some channels may be nearly clean and others very noisy so use your judgement accordingly. When you are satisfied, convert the image back to RGB. You may not select any subpart of the image in this process but must use the entire image, because Basic Editing dictates that any filters applied must be applied to the entire image. There is also a restriction on what types of filters may be used. But noise reduction techniques are generally accepted in Basic Editing. Once again, be sure this method is acceptable to the SC before submitting an image processed this way in a Basic Challenge!

Edit to correct error!!

Message edited by author 2005-09-14 22:04:14.

kirbic

Canon EOS R5

Canon RF 24-70 f2.8 L IS

09/14/2005 09:54:00 PM · #3

Originally posted by ElGordo:

...Convert the image to CYMK (Photoshop)...

Gordon, did you mean convert to LAB color? The "L" channel is then the luminance (the one that shoudl remain unblurred). Yes, this is legalfor both advanced and basic, because in each case the blur is applied as noise reduction, not as an effect, and is applied to the entire image even though applied to individual channels.
This technique works because of how we see. We perceive detail in the luminance data, but some blurring of the color data has little effecdt on our perception of image sharpness :-)

ElGordo

Canon EOS-400D Rebel XTi

Sigma 18-200mm f/3.5-6.3 DC OS for Canon

09/14/2005 09:56:12 PM · #4

Thanks Kirbic! Yes, I did mean Lab color.

09/14/2005 09:57:15 PM · #5

Thankyou so much for the info, I will go and fix it up now. I really love the photograph but the few places that had a bit of visible noise was really getting to me. I will be sure to keep this info for future basic challenges too. Thanks again!

09/14/2005 10:11:43 PM · #6

The odd thing is,now that I am doing it, that the luminous channel is the only one that seems to have the noise/artifacts now. I tried putting the blur on it, but of course then I lost my sharpness. Any more ideas on how to tackle it?

dwoolridge

09/14/2005 10:26:56 PM · #7

You'll get much better results, depending on the type of noise, if you use Filter->Noise->Median instead of a gaussian blur. Gaussians will give you tonal bleed and you probably want to maintain colour contrast boundaries. You can be quite liberal with the radius setting.

Sigma 18-200mm f/3.5-6.3 DC OS for Canon

09/14/2005 10:31:43 PM · #8

Thanks dwoolridge, I will go give it a try.

ElGordo

Canon EOS-400D Rebel XTi

09/14/2005 10:47:37 PM · #9

DW's method has some merit. Using MEDIAN, small artifacts will be blended out of existance while larger objects will maintain some integrity. Gaussian blur has a similar effect but is not so dramatic as median.
If your noise is primarily in the luminence channel then I do not know of any method that would be permitted in Basic Editing to reduce that noise without degrading the sharpness of the image. But you might try using 'smart blur' in the luminence channel. This will reduce noise in broad areas while leaving edges mostly intact, but at the cost of some detail loss.