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jmasin
Carpal Tunnel


Reged: 12/22/08

Loc: Murphy, TX (DFW)
LAB mode color noise reduction - it works! new
      #5639644 - 01/23/13 10:10 PM Attachment (38 downloads)

WOW, it works!

My apologies, I will not appropriately reference the original source, I've seen a few people mention this around the web, but I cannot recall exactly where (not all were AP references).

I tried this on my Rosette.

Here's a 1:1 crop (80% quality JPG to meet forum rules but no resize) of before and after performing a Gaussian Blur in photoshop on the (a) and (b) channels in LAB color mode. No other changes between left and right.

I guess the goal would be to not have this noise to start with, but given limited data, noise is a reality. This really did a nice job of reducing it a bit. Or, at least I think so, but I've been staring at it for a while... so open to "fresh" eyes/inputs.

Thanks!

Edited by jmasin (01/23/13 10:12 PM)


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JWalk
Pooh-Bah


Reged: 06/06/10

Loc: San Antonio, TX
Re: LAB mode color noise reduction - it works! new [Re: jmasin]
      #5639817 - 01/24/13 12:02 AM

WOW!! That looks really nice.

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jaddbd
professor emeritus


Reged: 05/18/05

Loc: Woodbine, MD
Re: LAB mode color noise reduction - it works! [Re: jmasin]
      #5639821 - 01/24/13 12:06 AM

Subtle, but effective (as it should be).

John D


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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: LAB mode color noise reduction - it works! new [Re: jaddbd]
      #5639893 - 01/24/13 01:10 AM

Looks good but what is the difference between doing
a Gaussian Blur in RGB & in LAB colour?


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Mike Wiles
scholastic sledgehammer


Reged: 02/04/09

Loc: Goodyear, AZ
Re: LAB mode color noise reduction - it works! new [Re: alpal]
      #5639897 - 01/24/13 01:15 AM

Quote:

Looks good but what is the difference between doing
a Gaussian Blur in RGB & in LAB colour?




By switching to LAB mode and doing the gaussian blur on just the A channel and the B channel, you effectively reduce the chrominance noise by blurring it. Because you're not applying the blur to the L-Luminance channel, there is no loss in sharpness of the image.

Mike


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Harel_Boren
Vendor-The Boren-Simon PowerNewt Astrograph


Reged: 03/15/09

Loc: Israel
Re: LAB mode color noise reduction - it works! new [Re: Mike Wiles]
      #5639924 - 01/24/13 01:44 AM

Quote:

Quote:

Looks good but what is the difference between doing
a Gaussian Blur in RGB & in LAB colour?




By switching to LAB mode and doing the gaussian blur on just the A channel and the B channel, you effectively reduce the chrominance noise by blurring it. Because you're not applying the blur to the L-Luminance channel, there is no loss in sharpness of the image.

Mike




Thanks Mike,
Wouldn't the same result be achieved by applying noise reduction to the color layer in lrgb?
Cheers,
Harel


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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: LAB mode color noise reduction - it works! new [Re: Mike Wiles]
      #5639939 - 01/24/13 01:59 AM

Quote:

Quote:

Looks good but what is the difference between doing
a Gaussian Blur in RGB & in LAB colour?




By switching to LAB mode and doing the gaussian blur on just the A channel and the B channel, you effectively reduce the chrominance noise by blurring it. Because you're not applying the blur to the L-Luminance channel, there is no loss in sharpness of the image.

Mike




Wow - you're right -
I just tried it on an RGB image & compared it to a LAB image where I had gone to channels & applied gaussian blur to each a & b layer separately.

I won't be applying blur to RGB images anymore.

You learn something every day.

thanks
Allan


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Mr_T
Pooh-Bah


Reged: 04/06/08

Loc: NJ
Re: LAB mode color noise reduction - it works! new [Re: alpal]
      #5640057 - 01/24/13 06:08 AM

You can also boost your color using the a and b channel only

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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: LAB mode color noise reduction - it works! new [Re: Mr_T]
      #5640078 - 01/24/13 06:38 AM

Quote:

You can also boost your color using the a and b channel only




I've been doing that for years but I never knew
about blurring noise with separate a & b LAB channels.


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vpcirc
Post Laureate


Reged: 12/09/09

Loc: Merced CA
Re: LAB mode color noise reduction - it works! new [Re: alpal]
      #5640105 - 01/24/13 07:11 AM

Hallas now reccomends doing it in camera raw. When you open the image in PS, use open as and choose camera raw. you have to select the save options then reopen it. It has very fine adjustments. For a detailed video, see his photoshop series 5 tutorial. I think it's $20

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jmasin
Carpal Tunnel


Reged: 12/22/08

Loc: Murphy, TX (DFW)
Re: LAB mode color noise reduction - it works! new [Re: Harel_Boren]
      #5640145 - 01/24/13 08:03 AM

Quote:


Thanks Mike,
Wouldn't the same result be achieved by applying noise reduction to the color layer in lrgb?
Cheers,
Harel




I would think so yes.

In this case all I had was an RGB image (actually a bicolor from Ha and Oiii and a synthetic G). I had no luminance only as it were.

I could have created one from the R(G)B, but it would have inherited the noise from the R(G)B image.

I did try treating the Ha as luminance but I did not care for the results with only a bicolor.


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Harel_Boren
Vendor-The Boren-Simon PowerNewt Astrograph


Reged: 03/15/09

Loc: Israel
Re: LAB mode color noise reduction - it works! new [Re: jmasin]
      #5640635 - 01/24/13 01:01 PM

Quote:

Quote:


Thanks Mike,
Wouldn't the same result be achieved by applying noise reduction to the color layer in lrgb?
Cheers,
Harel




I would think so yes.

In this case all I had was an RGB image (actually a bicolor from Ha and Oiii and a synthetic G). I had no luminance only as it were.

I could have created one from the R(G)B, but it would have inherited the noise from the R(G)B image.

I did try treating the Ha as luminance but I did not care for the results with only a bicolor.




I understand - indeed if all you had was a RGB then this is literally a breakthrough !

Thanks for sharing!

Cheers,
Harel


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jgraham
Postmaster
*****

Reged: 12/02/04

Loc: Miami Valley Astronomical Soci...
Re: LAB mode color noise reduction - it works! new [Re: Harel_Boren]
      #5640715 - 01/24/13 01:37 PM

For my RGB images (taken with an achromat and reseting the focus for each filter) I created a synthetic L by summing the R+G+B. The L was processed separately with the RGB layered on top of this. To smooth out the noise in the color data I applied a mild Gausian blur to the color layer. Blurring the color data is fairly common practice, I even do this with data from a color camera. This method has been around for quite a while. Still, a neat trick.

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Rick J
Postmaster
*****

Reged: 03/01/08

Loc: Mantrap Lake, MN
Re: LAB mode color noise reduction - it works! new [Re: jgraham]
      #5640993 - 01/24/13 04:24 PM

Lab color (note the a and b are lower case) offers a lot once you get the hang of it. I do nearly all my color work in Lab mode, only the initial combine and conversion back to RGB for the saved image take me out of it now. It has lots of power I can't duplicate in RGB mode. For instance pushing saturation can easily wipe detail or lower contrast in RGB but not if done right in Lab mode. Can be very useful in bringing out H alpha in galaxy images for instance. Learning Lab takes some effort but well worth it for me at least.

Rick


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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: LAB mode color noise reduction - it works! new [Re: Rick J]
      #5643063 - 01/25/13 06:01 PM

Thanks Jon - for starting this thread - some great tips
have come out of it which I'll use to improve my processing.


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