was there ever a camera invariant all over the range? maybe an early sigma foveon?
May 4, 2023
150
-
-
Lots of CCD cameras were.
-
Especially the ones that applied no variable gain at all to the raw signal and counted on the raw converter to do the push.
-
I don't think that that is a helpful way of looking at the problem.
Invariant or not invariant at a particular ISO setting is - to some extent - a matter of judgement. Like if I showed you a yellowy-green Pantone color card, and asked you whether you you would call it yellow, or green, if forced to make a choice.
The question is: At a particular ISO setting, does (amplified) read noise dominate conversion noise?
A similar question is: At a particular ISO setting, is output noise significantly different from (amplified) read noise?Those are both slightly fuzzy questions.
If you're OK-ish with a noise model where amplified read noise adds in quadrature to conversion noise, then in black areas of the image we have:
(Recorded noise, in DN) = sqrt( (conversion noise, in DN)^2 + ( gain * (output referred read noise, in DN) )^2 )
Where "DN" means "Digital Numbers" - the numbers stored in a (lossless) RAW file.
Examples:
- If conversion noise is 1DN, and gain * output referred read noise is 1DN, recorded noise is sqrt(2)=1.414DN
- If conversion noise is 1DN, and gain * output referred read noise is 2DN, recorded noise is sqrt(5)=2.236DN
- If conversion noise is 1DN, and gain * output referred read noise is 3DN, recorded noise is sqrt(10)=3.162DN
...
As the gain increases, conversion noise has less and less effect, and the recorded noise becomes - arbitrarily - close to gain*(output referred read noise), regardless of what the conversion noise was at base ISO.To me, a camera is "ISOless" at a particular ISO if the recorded noise is - for practical purposes - equal to gain*(output referred read noise).
I just pulled up a noise-model spreadsheet I have, that says "ISOless" ("invariant") or "not ISOless" for a camera noise model, at different ISOs.
It seems that it says "ISOless" if gain*(output referred read noise) is more than 90% of the recorded noise (in black areas of the image, remember).
I could have chosen some other number, like 80% or 75%. But 10% or 30% would be silly.
...
The Aptina dual-gain thing has the effect of reducing read noise at (or above) the gain setting at which it turns on. Perhaps enough to make conversion noise significant again, so that the camera goes from being "ISOless" to "not ISOless" until the gain has increased sufficiently further.
We could have a camera that behaves like this:
- ISO 100: not ISOless
- ISO 200: ISOless
- ISO 400: ISOless
- ISO 800: not ISOless (Aptina thing kicks in).
- ISO 1600: ISOless
- ISO 3200: ISOless
- ISO 6400: ISOlessThat would mean that ISO 400, ISO 3200, and ISO6400 could be a bit pointless when capturing RAW images.
But the main thing is usually to try to capture as many photons as you can.
...
All uses of "ISO" above belong in scare quotes.
-
Both equations are fixed now.
-
Which tended to be MF cameras with no in-camera processing. Mostly the purpose of variable gain in those cameras was to do the multiplication operations in analog computing, which was much faster when working with 16-bit processors without single cycle barrel-shift multipliers. Lookup tables would have been an alternative, but they didn't have a lot of memory to spare either. That's why we should really be talking analog and digital multiplication ;-)
-
Allan or Bob: now that this thread now seems to have the Sony "a74" (whatever that is) as the gold standard for determining the best exposure for raw files, should it be now moved to the "Sony Camera" category ?!
As an owner of a camera that shoots and outputs raw only, I was initially interested ... but all this hot air about zebras and specific Sony settings is way off-topic, grump.
-
Assertions are not necessarily facts. In this case, for that to be true, the a7IV would have to be dramatically different from the a7, a7II, a7III, a7R, a7RII, a7RIII, a7RIV, a9, a9II, a7S, and a7SII, all of which I have tested.
-
Yes, most of the Sigma/Foveon non-Quattro cameras were thus, including my beloved SD9.
Much of the exposure hot air over on DPR was generated by those who were unable to cope with being able to clip "raw" data at any ISO ... as opposed to the higher the ISO, the more the raw data headroom., giving rise to the common "I always set ISO to 200".
Sigma experimented with an AFE in the DP2x and the SD15 and finally included one in all Quattro models. I guess that one AFE chip puts out less heat than three ADC chips.
Waiter: "more noise in your image, Sir?"
-
Not until you spell my name right πππ
I think the subject is still 'open' at the moment. Let's see how it develops.
Alan
-
Once a camera moves into someoneβs reality bubble it start behaving differently π.
-
I am not looking at anything - I am simply stating that camera's with dual gain sensors are NOT invariant - that was the whole point of what Aptina did - to break the mold and gain in S/N ...
they might be perfectly invariant in some range of nominal ISO values and thus you can call them partially invariant - no issues w/ that...
-
Oops ... apologies !!
Looks like the "a74" proponent is taking a break ...
-
Hasn't worked out that eccentric spelling is a sure telltale of denied former accounts.
-
"HLG Mode as a hack for perfect Raw exposure", www.dpreview.com/reviews/sony-a7r-mark-iii-review/4
For the record, based on my tests I disagree. -
Agreed. Never owned or tried a Sony, so my question was a bit tongue-in-cheek.
At least I now know that an "a74" is actually an Ξ±7 IV aka a Sony ILCE7M4.
-
thats what your not understanding. the camera shows extremally fine line clipping and so does fastraw its an identical match . you can take the raw into ACR and also fast raw and can not recover the blown high lights. ARE WE CLEAR NOW . you obviously dont play with your cameras much to draw your own conclusions.
-
Thats very poor on canons behalf .as i said live zebras finely tuned are un beatable for perfect "exposure evaluation" raw digger is not an exposure evaluation tool. in fact its useless in the field.
