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Author Topic: Luminance and noise  (Read 3116 times)
Bill Jaynes
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« on: January 27, 2010, 10:49:08 PM »
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From time to time, after bringing an image from ACR to PShop, I'll notice some really rough noise in a sky. My 5D has been pretty good at keeping that to a minimum. So, for a while, it was just a bogey. Tonight I finally found it, in ACR. If I ran up the luminance slider for yellow, grey clouds would start looking like Rodinal on steroids. So, not knowing really what that slider does, I'll use it more cautiously. What I was after, in so much ranch land scenery, was a way to control yellow so it was there but not so dominant; a way to lighten it the way you can in PShop in the saturation panel. Clearly Luminance must be a different animal. Didn't think it would be like patching out in a gravel parking lot!
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stamper
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« Reply #1 on: January 28, 2010, 05:25:52 AM »
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Quote from: Bill Jaynes
From time to time, after bringing an image from ACR to PShop, I'll notice some really rough noise in a sky. My 5D has been pretty good at keeping that to a minimum. So, for a while, it was just a bogey. Tonight I finally found it, in ACR. If I ran up the luminance slider for yellow, grey clouds would start looking like Rodinal on steroids. So, not knowing really what that slider does, I'll use it more cautiously. What I was after, in so much ranch land scenery, was a way to control yellow so it was there but not so dominant; a way to lighten it the way you can in PShop in the saturation panel. Clearly Luminance must be a different animal. Didn't think it would be like patching out in a gravel parking lot!

Are you sure it is noise and not posterization? Can you not use the saturation tab to cool down the yellow? In Photoshop selective colour would be helpful?
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Tim Lookingbill
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« Reply #2 on: January 28, 2010, 12:03:49 PM »
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Assuming you're referring to the yellow Luminance slider in the HSL panel, I would suggest you reduce saturation using the Saturation slider.

I do this on the blue channel when shadows get to looking overly blue as they often do shooting a white subject lit on one side by a low sun with the canopy of the blue sky accentuating a blue cast in the shadows.

I'm not clearly understanding how you're seeing yellow in a blue sky, but I'ld also suggest you might also adjust to the right the Tint slider in the Color Temp section toward magenta. Sometimes I get sky's that look like they have yellow when in fact they have too much green.

Also the Color noise slider (right under the Luminance noise slider) in the Sharpening panel in ACR will desaturate/equalize color noise in areas such as yours. That sounds more of what you want anyway over the suggestions I mentioned above.
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Philmar
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« Reply #3 on: January 28, 2010, 03:57:38 PM »
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Quote from: tlooknbill
I'm not clearly understanding how you're seeing yellow in a blue sky

Maybe the yellow is in the cloud/light cloud of skies where the white balance has agressively been pushed to the yellower end of that slider (perhaps because it is more pleasing for the non-sky portion?)
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Panopeeper
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« Reply #4 on: January 28, 2010, 08:42:45 PM »
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Quote from: Bill Jaynes
If I ran up the luminance slider for yellow, grey clouds would start looking like Rodinal on steroids. So, not knowing really what that slider does, I'll use it more cautiously
Earlier I used the HSL adjustments for a while, but then I noticed, that it can introduce posterisation and/or noise. The reason is, that the adjustment is affecting only pixels with color satisfying the selection of the adjustment; this can lead to make those pixels more "outstanding". Only slight adjustments should be done this way.
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Gabor
Bill Jaynes
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« Reply #5 on: January 29, 2010, 08:05:49 PM »
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Quote from: Panopeeper
Earlier I used the HSL adjustments for a while, but then I noticed, that it can introduce posterisation and/or noise. The reason is, that the adjustment is affecting only pixels with color satisfying the selection of the adjustment; this can lead to make those pixels more "outstanding". Only slight adjustments should be done this way.
Thanks,
That sounds like what I'm seeing. I didn't mean to mislead about the yellow; it just happened that in one image, cranking yellow luminance, yes, made those pixels more "outstanding". I just needed to be aware of it so I didn't end up finishing the image and then noticing these issues too late.
Bill
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Best regards,
Bill Jaynes
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