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Topic # 172055 10-May-2015 13:26
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I have never asked this question so today I will.

Why does the ACR/LR apply Colour Noise Reduction to all images, even at ISO 100?

I am guessing there is a very technical answer about signal-noise ratio / patterns and digital sensors but I can't find it on google.

Thanks




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  Reply # 1301453 10-May-2015 14:50
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Probably because it helps most images and negatively affects very few.

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  Reply # 1301479 10-May-2015 15:20
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I don't think the answer is too technical.
It's probably just that it's a default setting, as ACR can't read all the metadata in raw file formats, so doesn't or can't convert the raw file based on in-camera settings. If you open a *nef raw file using Nikon software, then the initial conversion will be done using the in-camera settings for sharpening, noise reduction, lens distortion correction, CA correction, d-lighting, saturation etc etc.
ACR applies sharpening by default (which should normally be the last operation in an editing process - not at the start).  It also can't read camera white balance setting correctly - looking at an *nef file shot with AWB on, ACR has applied a wb of 4500, Nikon software tells me that the camera had set the wb at 4650.  I understand that this has been an ongoing gripe, as the wb metadata in Nikon raw files is encrypted.

 
 
 
 


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  Reply # 1301571 10-May-2015 19:25
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From what I remember color noise reduction normally does not effect image quality in negatives ways, unlike Luminosity based noise reduction which softens the image a lot. I'm assuming the apply some automatically to all images as that amount may get rid of most random colour noise that comes from reading the sensor at an ISO?





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  Reply # 1301764 11-May-2015 10:08
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RileyB: From what I remember color noise reduction normally does not effect image quality in negatives ways, unlike Luminosity based noise reduction which softens the image a lot. I'm assuming the apply some automatically to all images as that amount may get rid of most random colour noise that comes from reading the sensor at an ISO?


All noise reduction loses image data - so there is an effect on image quality, even if the trade-off may be "worth it".   
If you were to take a photo of something which consisted of nothing but a facsimile of a noise pattern, then applied noise reduction to the photo you took, you'd eventually end up with a photo showing nothing at all - as you'd have lost all (real - in this hypothetical example) image data.

I don't think that it matters much what ACR defaults to, as the biggest point for shooting raw is so that you can make such adjustments as part of raw conversion.  You can adjust the sliders in ACR to apply whatever noise reduction level you want - and if you don't make adjustments and just go with the default conversion settings for everything, then you're losing much of the advantage from shooting raw over shooting jpeg in the first place.  



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  Reply # 1301949 11-May-2015 13:45
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so looks like nobody knows (why LR/ACR defaults to 25)! how strange on GZ ;p
my guess would be that there is always random colour noise from the digital sensor which needs to be eliminated

anyway, i have tested in the past and 0-25 colour noise reduction makes no difference to picture quality at 100%, 200%, 300%, 400%!
but with anything under 15 for ISO 100 you get random colour noise patterns only visible at 300%+, and anything under 25 at ISO 12800 you get randow colour noise patterns visible all the time

now this is for a Canon sensor with an AA filter with known dreaded vertical colour noise stripes - which reminds me need to challenge canon and send more nasty emails

i might do more formal testing when i have time ... with raw files from Nikon with AA filter, Nikon with no AA filter :D




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  Reply # 1301973 11-May-2015 14:21
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You won't see any image quality reduction as outside of theoretical photos (who would photograph something that actually had random colour noise in it at a pixel size level, and if you did it would look bad with or without colour noise reduction because of the random colour noise from the sensor), 25 would be the level that the soft engineers believe to get rid of most random colour noise from most cameras. There is a lot of stuff going on that you don't see like hot pixel removal etc, if you looked 1:1 at a raw image with nothing but a bayer filter applies, it would probably look pretty bad.

If you don't want Color NR turned on, you should be able to cancel it out at import with the "Apply During Import" develop settings by creating a pre set with the slider at 0

You'll also find it sharpens by 25 at a radius of 1 and detail mask of 25, and probably some other stuff too.





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  Reply # 1305353 14-May-2015 18:33
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RileyB:25 would be the level that the soft engineers believe to get rid of most random colour noise from most cameras.


Ummm, there are about a million different cameras out there, each with about a million different possible settings, so that makes about a billion to one chance that adobe's software geeks got the right default setting.
OK - I'm exaggerating about the billion...
Another guess is that the colour noise reduction setting is a legacy from Pixmantic - who made RawShooter software.  I used to use that with a camera which was prone to generate moire from the RawShooter demoisaicing - the colour noise reduction was effective at reducing that.
TBH, the terms "luma" and "chroma" for noise / noise reduction are a bit obscure, as each raw pixel is either red, blue, or green.
 

RileyB:25
You'll also find it sharpens by 25 at a radius of 1 and detail mask of 25, and probably some other stuff too.


This is probably a case of Adobe's marketing department in action.  As I said above, sharpening should be the last operation in post-processing workflow - and carried out relative to image output size.  That's post-processing 101.  I expect adobe's software geeks should know this.  There's no no point applying 1px radius USM to a 50mp file you're going to print at 6x4 or display at typical web resolution. 
But if Adobe defaulted to zero sharpening of raw files, no doubt pixel peepers with poor knowledge and loud mouths would whine on forums about how ACR produces "soft images" - especially compared to camera maker supplied raw conversion software which typically applies sharpening at the same level as applied to in-camera jpegs - based on camera settings.



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  Reply # 1305361 14-May-2015 18:49
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I think bring the sharpening defaults in the picture puts perspective into the colour noise reduction defaults

The former to cater for the users of lowest common denominators. The latter for sensors of lowest common denominators (unfortunately the current flagship prosumer canon has such a sensor - nevermind I learn to work around it ... )

Thanks makes all the sense now




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  Reply # 1305362 14-May-2015 18:51
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Fred99:
TBH, the terms "luma" and "chroma" for noise / noise reduction are a bit obscure, as each raw pixel is either red, blue, or green.
 


I guess they refer to different patterns of noise that is picked up by the algorithms, and caused by very different phenomenons (I read the science of it somewhere but it was over the top of my head)




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