Dialling Down the Noise

posted August 22nd, 2016
I'd appreciate any advice on reducing noise in ACR. My (slightly out of date) version offers five sliders:

- luminance
- luminance detail
- luminance contrast
- colour
- colour detail

I've no idea what order to use these in, what they mean or how much to slide them. But trial and error isn't working well for me. I either end up with no effect or a waxwork effect. Point me to a good online tutorial if you know one. Thanks!
posted August 22nd, 2016
@jasperc Noise is typically reduced by blurring it away. So..

Color - color noise comprises those speckles of (typically) red and green that appear in dark areas. It is really nasty, so very digital, and should be seen to first. That's what the fourth slider does. You might note that most default raw conversions dial in some "color" noise reduction always. It occurs from random fluctuations in the "color" ( an R or a G or a B value, only one) signal per pixel in dark areas especially. If you are at all interested in understanding how digital cameras compute color of each pixel, yes "compute," a digital camera does not natively "see" the color of a pixel, google for "breyer filter" and "demosaicing" and you might see how random fluctuations in signal level at the pixel level might really screw up things, producing "color noise."

Color Detail slider tries to add back some detail that might have been blurred away with the first color slider. Unless really needed, leave it alone. I have never in my memory ever fiddled with it.

Then turn to "Luminance' slider. This will deal with the classic 'white" speckles often in the dark area, sometimes black in the light areas if you have pulled the highlights very low, in B&W sky conversions especially. Pull it to the right gradually. It's usually at 0 in preset raw conversions. "Luminance Detail" slider then will add back some detail (it will actually try to generate detail that might have been lost by the blurring of "luminance" slider. I usually try to leave it alone, at 0. Finally, "Luminance Contrast" will try to recover (interpolate really) added contrast that might have been blurred away by the previous two. Personally, I never touch it.

So bottom line, Color Noise and Luminance Noise sliders are the two I deal with almost exclusively. I leave the others alone. In my view, if I think I need them after the main two sliders have blurred away too much, then I would abandon the image.

Some other raw converters claim to more than just blur away noise, doing a real inspection of the raw file before starting and adjusting each pixel independently. DXO is one that claim they do this.

Does that help?

posted August 22nd, 2016
Thanks so much Frank. I've no doubt I'll be referring back to your explanation regularly and it gives me a really good idea as to where to start.
posted August 23rd, 2016
@jasperc Check specific forums about your camera for suggested default values. The ones I use in Lightroom for my OMD EM5 makes the Adobe default values seem like they weren't even trying.
posted August 23rd, 2016
I have found the noise reduction program in the Nik collection to be really good. Nik is free software.
posted August 23rd, 2016
@jasperc I agree with @lisainstpete - give the free NIK filter a go - I have found Dfine 2 on auto analysis works just fine 90% of the time - just one button & super fast. I also have the Topaz Denoise filter ($) which works well for really tough situations by adjusting individual settings as Frank as mentioned.
I find the noise reduction options in LR ( and ergo ACR) a little unrefined - great for baseline use & well exposed images, but risky for really high ISO or challenging shots.
posted August 24th, 2016
@ltodd @lisainstpete @fotoblah Thanks. This is super helpful!
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