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Trouble with Color Noise Correction

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  #1  
Old 05-29-2003, 11:12 AM
Jeff F Jeff F is offline
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Trouble with Color Noise Correction

In chapter 4 of Richard's book, he lists the steps he used to correct the noise in the vince.psd file. Looking at the before and after images in the color pages shows a marked improvement to the most casual observer. The problem is I cannot reproduce his results. I've blurred that color layer like there's no tomorrow, but in the end with the before and after images side-by-side, if I didn't know better I'd think they were identical. He doesn't mention what radius he used in the Gaussian Blur step, so I've tried many combinations to no avail. To my untrained eye, the luminosity layer appears to have about as much noise in it as the color layer after they're split, but there's no mention of a correction to the luminosity layer in the book. Has anyone else tried this unsuccessfully or know what I may be missing?

Thanks in advance,
Jeff
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Old 05-29-2003, 04:58 PM
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Richard_Lynch Richard_Lynch is offline
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You probably will not SEE the same results as appear in the color section with just a single application of the noise reduction. This is partially due to printing in process color on an offset press and comparing it to what you see on your monitor -- monitors tend to be a bit more exacting (and minus one color conversion). At the same time, I am sure I did a few additional things to the images in the color section to show results -- almost a necessary evil in a book

You'll notice at a glance that the after image in the color section is lighter and a bit more saturated...The idea of the color section to me was probably more to show what can be done with several applications of the techniques in the book rather than just showing what occurred in B&W with denoise only. It was at the wrong point in the book to go on about additional corrections and I believe my intent (originally) was to supply the full-blown correction on the CD -- it's quite a tangle keeping all the things I want to get in a book together, and that was an oversight.

If you open the image and do the separation and really look at the Blue channel, then flatten, apply denoise and look again, I think you'll be amazed at the difference. The noise in the Luminosity can be quelled a bit using a curve application (you'll want to drag out those highlights and shadows) and there will be something you'll want to accomplish with Hue/Saturation. You might also use a luminosity mask to mask the Luminosity channel and try to apply some blur in the mid-tone.

I see how that might appear to be cheating, and it wasn't at all the intent -- otherwise I'd never admit it. My goal in the section in Chapter 4 was to work with a concrete example of how Luminosity and color could be used to an advantage -- getting off into the rest of the corrections would have been a tangent. Interesting to some, and valuable, I agree. My goal in the color section, was to give you a good look at what can be accomplished. That leads to some things sliding by in the technique. However, and in defense of the tactic, too much of one image can get pretty boring. For the sake of interest and moving the reader along, I wanted to get through general technique to enable the later, more involved projects. Perhaps in a later version of the book I'll get a few more pages, and this can be expanded.

If you'd like to have a look at the layered correction, I can dig it up...I don't have it on hand right here as this is not my writing workstation. I'd need your email...

Let me know.
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Old 05-29-2003, 05:30 PM
Jeff F Jeff F is offline
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Thanks Richard,

It's nice to know your purpose for the color section of your book; now I won't get wrapped around the axle trying to get all of my results to mirror yours exactly. I will email you soon with my email address because I would appreciate you sending me the layered copy of the after image when you come across it. When I get into a subject that interests me, there's rarely a such thing as too much information.

Another related question came to me while reading your reply. Is it possible to "Split Luminosity" followed by "Split RGB" on the color layer? In my mind, this would allow you to eliminate the noise in the isolated blue channel without affecting the luminosity one iota, if desired. If this is covered later in the book, just tell me to keep reading. I'm only on Chapter 4, after all.

Thanks again,
Jeff
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Old 05-29-2003, 09:38 PM
Susan S. Susan S. is offline
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Jeff- by trial and error i've found that I get a better result in chromanoise reduction by blurring the color layer several times using a radius of 2 to 3 pixels - any more than that and the colour seems to start to bleed into places that it isn't wanted. it makes a Big difference over just applying a correction once.

Richard, thanks for the tips on reducing noise in the luminosity channel too, that's useful. Noise reduction is one of my current preoccupations - I was going to buy a better camera, but my gas furnace blew up, and the family weren't that keen on shivering in the cold! Now the idea of splitting the colour layer into RGB and applying denoise to that and remerging sounds interesting. It always does seem like the blue channel that has most of the noise. Jeff, you are asking some most interesting questions....(and getting through the book much more quickly than i did - I must confess that I still haven't worked in detail through all of the examples - i've been sidetracked by other things. I really must get back to it)
Susan S.
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Old 05-29-2003, 10:07 PM
Jeff F Jeff F is offline
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Susan,

Thanks for chiming in with the 2-3 pixel radius technique on the noise reduction. I played around with it last night for a little while trying to reproduce Richard's results. However, I was operating under the apparently false assumption that one full blown correction was better (or at least less lossy) than several smaller adjustments. I will definately try it your way now.

To be honest, I'm working through the book examples in depth purely as a way to understand it (inside out if possible). Other than some very basic levels adjustment and some red-eye correction, I've not been seriously into photo correction before now. But now with the more pictures I capture with my digital, I getting to be more discrimminating and critical of how they look raw. Anyway, I want to learn as much as a hobbyist can about this field.

By the way, it's been over 30 degrees C here in the Mojave Desert all week, so bring the family up here and buy that new camera -- I promise there'll be no shivering!

Thanks,
Jeff
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Old 05-29-2003, 10:21 PM
Susan S. Susan S. is offline
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Jeff - you pay the airfare and I'll be there!! (I'm in Australia - and it was 20 degrees C today, so i can't complain too much, although three degrees C first thing this morning was a bit nippy!). If I lived in the US I would already have bought the new camera - I have to pay between thirty and fifty per cent extra on US prices here. (but i prefer to have a warranty so I'm not game to import)

I often find, particularly with adjustments that require blurring that several small increments can be better than a one shot large blur. Obviously the less blurring the better, as it's all destroying data from the original image. You certainly do need to check and compare with the original. (and remember to work on a duplicate! - I've been caught a couple of times by that, but haven't destroyed anthing valuable).
Susan S.
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Old 05-30-2003, 04:09 AM
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Richard_Lynch Richard_Lynch is offline
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Quote:
Is it possible to "Split Luminosity" followed by "Split RGB" on the color layer?
Jeff, try the RGBL separation. If you are new to this and these are the questions you are asking, you'll pick it up pretty quickly. The idea of RGBL is pretty new, and as you say (I believe it does in the book too) offers the advantage of using RGB for color and luminosity for tone control.

Susan, using the blend mask techniques to isolate specific areas where noise occurs, you can really target exactly those tonal ranges where the problems occur.

If people bought big books, I'd have written one covering all this stuff more extensively! I'm glad to see this kind of question here.
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Old 05-30-2003, 06:58 AM
Susan S. Susan S. is offline
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Thnks Richard. I've been working in that direction. While I can improve matters I'm rapidly coming to the conclusion that I really do need a new camera!! (and I buy thick books, when I can get them - if they are any good that is - but a lot of the doorstop - size books that I've looked at seem to be best off used for that purpose..)

The RGBL separation is one I haven't played with yet - but I will now. I was trying to get my head around the way it works. At first sight I couldn't see that the luminosity layer would add anything to the mix, as the three colour layers clearly add up to the total image already, but it obviously does as otherwise you wouldn't have put it in there! ... Now it makes a bit more sense as it does indeed seem to act exactly like a split of the colour layers from a luminosity/colour separation. I'm still a bit befuzzled as to why it works like that - I still haven't quite got straight the interaction of multiple layers in different blending modes. When I've got just two layers I can usually predict what is going to happen, but multiple layers like that are still a bit tough.

Susan S.
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Old 05-30-2003, 07:33 AM
Stephen M Stephen M is offline
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These resources are for the full version, but users of PSE may find some benefit to them...

* For more on LAB mode in general (luminance and color blend modes are similar but not the exactly the same):

http://members.ozemail.com.au/~binar...V_links.html#L

* Luminance masks or layer blend data:

http://members.ozemail.com.au/~binar...litymasks.html

* On colour component noise cleaning:

http://members.ozemail.com.au/~binar...ctremoval.html

* Grain and noise info:

http://members.ozemail.com.au/~binar...V_links.html#G

* For more on layer blending, see these RP forum link:

http://www.retouchpro.com/forums/sho...&threadid=4492


Sincerely,

Stephen Marsh.
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  #10  
Old 05-30-2003, 11:32 AM
Jeff F Jeff F is offline
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Richard,

Thanks again for the RGBL information. I just finished Chapter 4 last night, and you mention it in there near the end. I just need to be more patient it seems. I haven't had a chance to play with it yet, but rest assured I will. It's too bad your publisher won't let you do abridged and unabridged versions of the book. If Amazon charged me shipping by the pound for the books I've bought, I couldn't afford them. Until the long version comes out, I'll be here trying to pick your brain.

Stephen,

I appreciate the links you replied with. They look to be chocked full of good information.

Susan,

I'm with you on the whole "multiple layers with different blending modes" business. I really have to stop and carefully work my way through, and many times I have to go back and look up what exactly the blending modes do because I haven't really worked with them much. Oh, and if I had the kind of money they charge for airfare between Australia and the US, I'd just send it to you and you could probably get several nice cameras plus the full version of Photoshop.

Thanks to all,
Jeff
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