Have you missed all of the drama surrounding Tony Northrup and his ISO claims? Let's take one final look.
Last week, Tony Northrup released an interesting video on ISO. In this video, Tony makes a few interesting claims; some were known by me, and one, in particular, was new to me. Since this video came out, the photography industry has been in a major debate about what Tony said and if it is partially incorrect. You can watch the entire video here:
Patrick showed me Tony's video, and I wanted to put two of the claims to the test. One claim was that ISO numbers may have been purposefully skewed by camera brands to make it appear that newer camera models have better ISO performance than older models. The second claim was that (in some cameras) you can get similar image quality from shooting a raw image at ISO 100 and raising the exposure in post versus choosing a higher ISO in camera. You can watch this video here:
Then, Dave McKeegan created a video claiming that Tony was spreading false information about ISO and that Fstoppers (Lee Morris) basically agreed with everything Tony said. You can watch this video here:
If you would like to go down the rabbit hole of ISO, Noise, and ISO invariance, I highly suggest reading this article on Photography Life. The only thing that I can point to that we may have gotten wrong by failing to mention it is that some noise can be produced by "Back-end read noise" (although I do mention it without knowing the technical name of it at 5:15 in our mythbusting video). This is the type of noise that Dave Mckeegan mentions in his video. Tony didn't mention this directly, and although I didn't mention it by name, I did point out some extra artifacts found on the image boosted in software rather than the camera.
Not all cameras are ISO invariant, but the ones that are or the ones that are very close may be capable of similar image quality when boosting exposures in post; we certainly proved that with the D850. The key here is that "back-end read noise" has gotten so clean in some cameras that it's hard to see a difference when comparing high-ISO photographs versus exposure-boosted photographs.
Well our curiosity got the better of us again, and we decided to make a second video. In this video, we test seven different raw processors to see which one could boost an underexposed raw file four stops and produce the best-looking file without noise reduction or sharpening enabled.
In the end, we found that Capture One may have produced the best-looking file without noise reduction or sharpening, but once you start adding those in, you can get almost identical looking files out of any of the programs.
So, what have we learned? Some, not all cameras are ISO invariant, which means in theory, you should be able to boost exposure in post and get identical noise to a correctly exposed image shot at a higher ISO. But, back-door read noise will introduce some noise when you do this. But, back-door read noise has become so insignificant in some cameras that it may not be worth worrying about.
So, should you walk around snapping black pictures and then raising the exposure in post? No, that would be stupid. Can we be done now?
Look at some of the Dutch Master's paintings (Rijksmuseum perhaps the best place) and the level of detail in the shadows. And lights. The dynamic range of these is nearly infinite - it's only our eye's ability to distinguish. With current cameras we still can't reproduce the images that they were creating 300 years ago.
For what I'd like to be able to do with photography I'm OK w/ pixel peeping and finding ways to push (pun both intended and not) the images our current technology can produce to achieve better fine detail. If I can expose a bit one way or the other to get the details I want and then fix the exposure later I'm all for that.
For many forms of photography this isn't worth much or anything but just because that is the case doesn't mean that it's useless for everyone. Just because there's an impossible to climb mountain in Senegal doesn't mean that I can't ride my bicycle one flat mile to the local pub for a pint.
This may be a stupid question, but how do Nikon and Canon and Red and Black Magic create ISO in a digital camera? In film it was a difference in the emulsion. That's easy to understand. The sensor in a digital camera doesn't change? It sees what it sees? Do they read it differently for different ISO"s? Or do they always get the exact same digital bits from each pixel and they are manipulating those bits in firmware to produce a RAW file of xxx ISO?
The sensor array, aka pixels, sees what they see but before converting to digital data different sensors have different strategies to increase the response. Most often and the simplest case is pure analog amplification of the signal out from the pixel semiconductor, stored in a capacitance, before the ADC. Approx. 6dB in analog gain before ADC is one stop of exposure, since it doubles the analog signal and therefor the digital data value. An analoge amplification is preferable since it does not have a linear relative noise response which digital gain has.