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[OM] Raw is ???? & ISO invariance [was GX85 Clarity Slider]

Subject: [OM] Raw is ???? & ISO invariance [was GX85 Clarity Slider]
From: Moose <olymoose@xxxxxxxxx>
Date: Sat, 31 Aug 2019 22:18:13 -0700
On 8/30/2019 3:23 PM, Mike Gordon via olympus wrote:
<<<If one uses ACR (LR or PS), distortion correction is not optional.

Yes, no option using ACR to turn off use of metadata corrections.  I haven't 
reviewed this in a couple years.  Some corrections in metadata also include CA 
and vignetting.  Starting 2014 or slightly before, Panny lenses on Panny bodies 
began including  the CA correction metadata.  DXO does NR on the RAW data 
pre-conversion, but that is fully user controlled.  Not clear how clarity could 
be applied pre-conversion though some other aspects of the image are baked into 
the RAW files:


https://theonlinephotographer.typepad.com/the_online_photographer/2012/10/raw-is-not-raw.html

While this essay is a great resource, the title is a little misleading. Raw is indeed Raw, but useless until converted into something else. The point is, I think, that the process is more interpretation than conversion. This is rather obvious if one uses different converters on the same Raw file. I can see people wanting to know which conversion is the CORRECT one, but the answer is both none, as there is no inherent converted result in the Raw file, and all.

The interesting thing that's happened since this essay is improvements in sensor systems such that some cameras may be said to be ISO Invariant (over some range of ISOs). That is to say, the result of shooting at ISO 1600 is identical in shadows/noise to shooting at ISO 200 and increasing luminosity by three stops in processing.

Quite remarkable is that this is true of some 1" sensor systems, such as the 
Sony RX100 and Panny ZS200:

"The ZS200's sensor is essentially ISO invariant, so you can (in most instances) shoot at base ISO and increase the brightness several stops while processing the Raw image, with a minimal noise penalty. By keeping the ISO low the camera captures additional highlight data instead of 'throwing it away' at higher sensitivities by amplifying the signal. You can see similar results from the Sony RX100 IV, which has a more modern CMOS sensor. In turn, this gives some scope for underexposing a low ISO setting to protect highlights, then brightening later."

They don't mention it, but this also means it will generally be possible to 
underexpose to maintain usable shutter speeds.

This change makes some of the conclusions of Ctein's tests rather moot, as one may choose exposure arbitrarily and adjust "exposure point" and curve later, with no IQ penalty.

Invariably Moose

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