CatMarley Loc: North Carolina

Better DR you mean. The resolution of detail is equal.

CatMarley Loc: North Carolina

If you say so . . . The word irrelevant is not absolute in this context, but relative only to its previous importance. The tonal manipulation of jpegs is a completely different procedure from manipulation of tone during conversion from raw data.

RRS Loc: Not sure

Cat, you say "just as in film days, only on the aperture and shutter speed" well the ASA of the film did determine what aperture and shutter speed you could use for a printable negative without having to pull or push your film. I shot weddings for over 25 years, film, and I didn't want to have to add extra time to get my proofs to a client. I shot Hasselblad's with numerous backs preloaded with different speed film to avoid excess grain, we didn't refer to it as noise or at least I didn't, back then. My question is why would anyone shooting RAW/JPEG want to shoot at ISO 200 and not be able to "chimp" a benefit with shooting digital. I can see it as a way to try and salvage a JPEG and I guess that if you aren't shooting professionally JPEG's for the speed of delivery then it could have a place. I seriously doubt that "SS" or any professional photographer shooting in JPEG would make such a serious blunder knowing the restraints of shooting in JPEG. I know some very serious SOOC photographers that are so meticulous that never have this problem. Thanks for bringing this up and your fine examples, very thought provoking and another trick to keep in your bag of tricks when PP.

rafael izakov

Dear CatMarley,
Please provide the data of your test, 1. Are you used MANUAL exposure for both images?
2. What you set for 1-st shot: ISO, F, shutter speed?
3. Same set for 2-d shot: ISO, F, shutter speed?

TriX Loc: Raleigh, NC

Well Cat (if I may call you that), I’ll give it a try.

While an in depth technical knowledge of the DSLR digitizing process isn’t necessary to take good photos, if you’re going to consider alternate exposure scenarios, it helps to understand what that really entails and the consequences. The idea of intentionally under exposing at base ISO and bringing up in post with an “ISO invariant” Camera with no adverse consequences is one of those, so let me explain.

Upon exposure, the sensor produces an array of analog data which is amplified (one element of ISO control) then digitized by an analog to digital converter (ADC). In modern cameras, the ADC outputs an array of digital values, typically at 12-14 bit resolution, which is then processed/demosaiced by the processor. The dynamic range of the camera is determined by the resolution of the ADC (I bit=1 stop=6.02 dB) and the noise produced by the entire signal chain - the sensor, amplifier and ADC. The noise floor limits the DR on the low end and saturation of the ADC (all bits =1) on the top end.

Let’s say your camera has a 14 bit ADC, which means it can theoretically resolve 16,383 levels (although the theoretical resolution is almost never actually realized due to noise and other anomalies). The output from the sensor is typically/often too low in value to completely use the entire 14 bits of the ADC, so the analog signal is then amplified by the amplifier, the gain of which is controlled by the ISO setting. The digital output of the ADC may also be multiplied by a constant at ISOs > 800, once the maximum amplifier gain has been utilized. In that case, the entire dynamic range of the system is utilized - almost all the 16K levels of the ADC are used. But what happens if you intentionally underexpose by 5 stops, essentially using no amplifier gain prior to the ADC? Now the ADC is using only 9 bits or 2048 levels of its range. Now if you later multiply that output in post to return to the full 14 bits or 16K of range, where does the extra data come from? (Remember we only have 2048 levels or 9 bits of actual data to work with). The answer is that it is interpolated - the missing levels are calculated as a value between the actual points - you cannot create data by multiplying data. The brightness of the shot may be the same, but the actual array of data only has a REAL maximum theoretical resolution of 9 bits - all the rest is interpolated data, and the subsequent demosaicing of the data is using interpolated data. This is very similar to using 8-bit PP as opposed to 16-bit and it potentially has similar consequences.

So the question becomes: you’ve just paid big $ for a high resolution imaging device - why intentionally limit that resolution to 5 bits lower resolution and then interpolating the missing data rather than use the full resolution of your system? Now if you’re trying to save a badly underexposed shot or need 1 or more stops of “headroom” in the highlights, then this is an available tool, but doesn’t make sense as a regular practice. If so, why not just buy a cheap camera with a 8 or 9 bit ADC and PP with an 8 bit package? Photos are often posted showing dramatic “saves” from dramatically underexposed shots, but what is rarely shown is the same shot (in raw, not 8 bit JPEG) correctly exposed and the associated histograms. When/if they are, you’ll note that the histograms are different, showing what is essentially a different greyscale or color pallet.

End of soapbox

RRS Loc: Not sure

Good morning Gene, what does this do to the practice of ETTR or with the newer cameras with 5 stops of DR. I may have to buy a Nikon D810 so I never blow out a white head on an eagle. It's nice to know that there is that much room to work with as to under exposures but aren't we still limited with headroom at the top. I will go out today and photograph an osprey and purposely under expose it and see what I can increase the exposure to in PP to bring out the highlights and see how much detail I can see with looking muddy, shooting a 1DXMKII. Good post, it makes me think a bit more.

RRS Loc: Not sure

It wouldn't change if you were shooting in the manual mode. It will change if shooting in aperture or shutter priority as that is a function of the camera.

drklrd Loc: Cincinnati Ohio

There is more detail in the bottom shot. Is that the one with ISO 1600?

selmslie Loc: Fernandina Beach, FL, USA

Not as dangerous as assuming that what you read here or elsewhere on the internet is correct without doing your own testing.

Lengthy arguments to support an un-tested opinion may be satisfying to the poster but it can be misleading and un-helpful.

What CatMarley has done is the right approach - to not trust what others have told her here on UHH but rather to perform her own experiment to test a hypothesis. That's also what I did a year and a half ago because I felt that I could not trust what I was hearing from some UHH "experts".

What we both have found is that, while many UH members know what they are talking about, there are many more who don't.

The only way to separate those who claim to know from those who actually do know the subject is to perform an experiment as we have each done.

Tim Hoover

ir·rel·e·vant
əˈreləvənt
adjective
not connected with or relevant to something.
synonyms:beside the point, immaterial, not pertinent, not germane, off the subject, unconnected, unrelated, peripheral, extraneous, inapposite, inapplicable

I have no idea what 'relatively irrelevant' would even mean.

Once an image is saved the tonal manipulation is independent of file type. JPEGs contain less information than raw files. That is the difference that is relevant to this discussion. However, that distinction is irrelevant to the discussion of ISO.

CatMarley Loc: North Carolina

If you are asking about the little foo dog, f stop and shutter speed on BOTH shots were the same f 5.6 and 1/60. ISO on the first shot was 1600 and the second was 200, so there was a 3 EV difference between them. The 200 shot was converted IN THE CAMERA to a jpg only boosting the EV by a factor of +3.

PGHphoto Loc: Pittsburgh, PA

I think the important thing to recognize is that while you CAN post process to reach an 'acceptable' image, why would you not limit the amount of PP and ensure the highest image quality up front ? You you admit, the IQ is not the same so why not get as close as possible to begin with ? To just shoot everything at 200 ISO, in my personal opinion is like saying "Why bother to make it perfect ?". Might as well just stick to an iPhone.

CatMarley Loc: North Carolina

The information is different in kind as well as amount. 8 ounces of vodka and one ounce of milk are different in more ways than one!

CatMarley Loc: North Carolina

How about "equal quality"? Because within certain limits, equal quality CAN be had. Outside those limits the quality falls off to acceptable, diminishing to awful. But that pretty well describes everything, doesn't it?

acreutz

Interesting...