Your interpretation is just plain wrong and unfortunately it's confusing others.
The truth is often confusing to people incapable of grasping it, but that is no excuse for propagating myths. The common ways of looking at things are often quite wrong. High ISOs, except in possibly a very small number of poorly designed cameras, do not add more noise to an image. They add less, or the same amount of noise, than lower ISOs. High-ISO images are generally noisier only because they dictate weaker exposures, to have the higher exposure index. Anyone who believes that higher ISOs "add" more noise to their images is incapable of coming consistently to accurate conclusions.
All you've demonstrated here is that under-exposing and post processing at low ISO gives more noise than correct exposures at a higher ISO without post processing.
Nonsense. There is no processing difference. The images are simply scaled to equal intensity; if you consider that "processing", you are very easily impressed.
That's no great surprise. There is a reason to strive for correct exposure in camera. It makes for the best picture. Even if you use RAW (which does give more leeway by recording more information but doesn't change your shutter speed or physical aperture).
Some people like to think of the "exposure triangle" with ISO, shutter speed and aperture at each corner. The trick is to get them all right in the first place. The minute you brighten one picture but not the other you're not playing on a level field.
Nonsense. Brightening an image is a meaningless, transparent operation, just like raising the volume on a stereo when switching from FM tuner to CD.
If higher ISOs were indeed less noisy, cameras would be built to default to higher ISOs rather than low ISOs.
This statement makes me wonder if you are agreeing to disagree, or if you even understand at all what you are disagreeing with. No one has suggested that higher ISOs, by default, give less noisy images. It is only when ISO is not dictating exposure, but rather, a variable trading SNR against headroom, that what Gabor is demonstrating is claimed to be true.
(In fact where the lower ISOs are below the base ISO of the sensor that's exactly how they work because the sensors don't do so well with dynamic range below their base ISO. My D90 defaults to ISO 200 not Lo 1)
That's just because the wells run out room for extra charge. I'm not one for substituting truth with simplicity, but sometimes simplicity is the truth, and this is it. Base ISO of a camera is simply determined by how much highlight headroom is decided to be enough, and the capacity of the wells. No electronic magic or gain issues ("do so well") involved here at all; the wells are filled, it's that simple (of course, the digitization process often clips slightly below sensor saturation). Most current DSLRs have maximum well capacities which allow a base ISO of 120 to 160 with a standard of 3.5 stops of highlights. Below that, there isn't enough capacity for 3.5 stops. I've seen a range of 2.5 to 4 stops of headroom in DSLRs by design.
In practical terms what you've shown (for a limited set of circumstances), is that if you have a choice between shooting low ISO and post processing,
What post-processing? You are weaving things into this which have no place or relevance. Processing was the same (basically, just demosaicing), except for the trivial, transparent act of arithmetic gain.
or higher ISO to get correct exposure, correct exposure with higher ISO will give you better results. But if you can shoot at lower ISO AND get correct exposures (eg. if you can control the light as with flash), that's preferable to both previous options. Correct exposure is king.
"Correct exposure" is an embarrassing term. It offers no concise meaning, and is open to interpretation. You have to shoot a scene, and there are lights in the shot which are much brighter than the ambient background and subject. no matter what exposure you choose, you will blow out a certain amount of detail in the bright lights. You want to have as much detail from the lights as possible. What is "correct exposure"?
You shoot a subject that is darker than the gray background. What is "proper exposure"? I know what optimal RAW exposure is; it is one where the gray background is just below clipping of the RAW (which would be an "over-exposure for a default JPEG). This could be at a low ISO for immobile subjects from a tripod; handheld or with subject motion, this may be at a high ISO with +2.6 or +3 EC. ISO 800 with +3 EC will give less read noise and the same shot noise as ISO 100 with 0 EC.
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John
- but we're talking about a few centimeters and the light source was on the ceiling
