[RGlasel]

Instead it will be by the use of faster readout of the sensor, electronic shutter with much faster shutter speed and combined will averaging multiexposure for adding longer exposure time.

Definitely, the only limitation is the cost of implementing this in a convenient sized package that has the computing power to produce immediate results without sacrificing battery life. Or the photographer can use ND filters.

[Fogel70]

With faster shutter speed of electronic shutter, it will also help using wider apertures in bright light. And combined with multiexposure it will give the option of using both wider apertures and longer shutter speed in bright light.

---------- Post added 29-08-18 at 18:31 ----------

Definitely, the only limitation is the cost of implementing this in a convenient sized package that has the computing power to produce immediate results without sacrificing battery life. Or the photographer can use ND filters.

If needing to simulate more than 4-5 stops lower ISO than base ISO (16-32 exposures) then a ND filter might be a better option.

[normhead]

Have to say, after a brief gander, what he's talking about is that essentially, there is not ISO in digital. There is the base reading put out by the sensor, which is the same in every instance, and then there is baking done by the rest of the camera to create the effect of an ISO change for jpeg shooting. Why is it necessary to understand this... because for us film shooters, the only way to make a film faster was to increase the size of the grain. So, faster film was by definition, lower res. Larger grains but fewer of them.

Digital is different, you have the same number of pixel sites whether high or low ISO, the base exposure at the sensor level is taken at one value. All the camera does is change the mid point in a sort of internal "levels" way. That is relevant to jpeg export, because jpeg throws out the unused date that was made extraneous buy shifting the mid point.



And the shadow detail from the second. That is where the DR comes into play. In my experience, if you shoot at ISO 400 and achieve that look, in my experience, you will not be able to get the richness the original image has in the sky. The sky has to be properly exposed.

To prove ISO invariance he would have had to try and normalize both a 400 ISO image and a 100 ISO image and shown they were the same. He claims the simulated 400 ISO image is demonstrating ISO invariance, but to do that he should have used a 400 ISO image and tried to get the same result out of them.

No cameras are perfectly ISO invariant starting from base ISO; however, some are quite close, and many cameras become ISO invariant starting at a high enough ISO value (once the camera begins to “simulate” ISO values).

In his opening line he defines th parameters. Understanding those restrictions, when you understand you are only talking about ISO invariance when discussing what he calls, "Back end noise", the concept is pretty limited in use and application.

However, I often shoot base ISO at 2 under , 1under, even , 1 over and 2 stops over, in a sunset sequence. And from that perspective this is all nonsense. I can tell you without fear of contradiction, one of those exposures will give you the best image, although sometimes the exposure you need is half way between the two and 2 of the 5 will give you almost identical images.

So in my expereince, ISO invariance is irrelevant. What there is, on a given sensor there is a point at which the mid point on the curve is positioned at an optimal spot to produce the best image. But where that point is, is highly subjective, to the point where I've given up anticipating it. And that mid point is changed, not by the ISO but on how long the exposure time is and how much light is allowed to reach the sensor relative to the scene you are trying to capture.

So to mee the whole question of ISO invariance is subject to the absolute need to get the best exposure for your subject. How does ISO invariance help with that? Why are we talking about it. Where is the practical application. Especially since the changes are subjective. If you have a scene with 20 EV and you only can capture 15 of it, how long you expose lets you control whether you throw out the top five EV, the bottom 5 EV, or some combination of the two extremes. That is an aesthetic decision that has nothing to do with ISO invariance. And to me that to me is the issue. I'm not sure why ISO invariance is important, but to me, it's a non-issue. It doesn't address how to get a good image.

And much of what is explained in the linked article is irrelevant, because it's either over simplified, or irrelevant to the point., and because as admitted by the author, their are no ISO invariant cameras.

All you need to know is, that once your camera starts using digital enhancement, your post processor can do the same with raw files. But that's not true at all with in any circumstance with jpeg files. And it's not true where for aesthetic reasons you want more or less light than the camera can capture and use your exposure time to control the actual number of photons hitting each pixel site.

So, apart from the observable obvious, digital enhancement usually sucks, which can be explained other ways than a term as nebulous as "ISO invariance" I'm not seeing any useful application for this knowledge. It's like someone invented a topic for no apparent reason.

I find it interesting that you would imply if I did the work, I would think what you think. Well, I've done the work , many times on many images, and i don't think what you think. And the link you posted is neither peer reviewed nor technically relevant in all of it's information. I'd compare it to a guy quoting a bunch of accepted knowledge and trying to sneak a new concept into it, without doing the work he needed to do to prove his point. Especially since he says in his opening, it doesn't exist and provides no examples to show why he says that, even though if included, that would be the most valuable part of the article.

I'm a great fan of science, pop science like this, not so much.
My objection is not that it's not a thing, my objection is that, it's a worthless thing.

Relevant to the the notion of ISO invariance when you use 400 ISO you use a 4 time less light hitting the sensor than you would at 100 ISO. IN a simple system that will cost you two stops of dynamic range. Claiming ISO invariance is to claim that this does not effect not he final image, noise etc.

Nonsense.

Very interesting topic though. As long as you remember, Low ISO means more light hits the sensor, less ISO means less light hits the sensor, and that you can have too much or too little light hitting the sensor for the image you are trying to create, so you understand the limitations of Invariance, it could be useful for some people, I'm just having trouble thinking of who it might be and for what application.

The fundamentals, expose properly, use the lowest possible ISO, use high ISO to shorten shutter speed, not increase IQ, and as far as i can tell, Invariance makes little difference to what you need to think about.

[MossyRocks]

For diffusing water and ghosting crowds, interval composite (set to "average") can be a decent solution.

I saw this the other day over in the critique forum here. I had read about that feature when I got my camera but never payed attention to it. I will try it out the next time I go shoot a waterfall as I am curious how it turns out over how I currently do similar things. I expect the various mode all produce different artifacts with average being the one closest to what I currently do. Additive and brightest would be the most interesting to play with.

Currently to achieve this type of functionality I do normal image stacking like I was going to do a super resolution image but then just scale it back down to the smaller size and apply only a very mild sharpening before down sampling. Even shooting off a tripod there always seems to be a slight variation in alignment so a 2x or 3x upscaling, align, blend, flatten, crop 5-10 pixels from each side, slight sharpen and down sample works great.

If wanting to reduce noise this way remember that it reduces at best by 1/squareroot of the number of images assuming you have a truly random noise which isn't the case with digital cameras (there is systematic noise in the system). So 4 images gives you a theoretical 1/2 the noise, 16 give a theoretical 1/4 the noise and 100 images gives a theoretical 1/10 the noise. Keep in mind that if you are already shooting at the base ISO you will very quickly push both the random and systematic noise below the 16 bpc that your final working image will be in. Surprisingly this same 1/sqrt(n) type rule also works for upping the spacial resolution but there you theory and reality diverge much quicker. So in theory 4 shots under ideal circumstances can give you a 2x increase in spacial resolution (4x total pixel count), and this is what pixel shift is doing. Pixel shift does a much better job of getting to the ideal than myself working manually. because of this when I do shots like that I will typically take a buffer full of them and stack them all. By doing this it also helps reduce the jaggedness that can crop in when enlarging and stacking only a few shots.

Since you just want the lower the effective ISO the math becomes much easier. If you want the equivalent of ISO 50 just take 2 shots at ISO 100 and stack, 4 shots gets you ISO 25, 10 gets ISO 10, and so one. This can be generalized as (Base ISO)/(Desired ISO)=(number of shots needed at base ISO). I would suggest following the super resolution method described above and then down sampling to the original scale as you will reap the greatest benefits.

I would think doing this in the computer would produce better results given the power budget and limited resources that the camera has but it would be an interesting comparison.

[Scintilla]

Norm -- You seem to be coming at this from the angle of there being no advantage to shooting ISO 400 instead of ISO 100 pushed 2 stops. But no discussion of ISO invariance I've seen has ever argued otherwise.


Rather, the value of ISO invariance is supposed to be in being able to shoot at the lower ISOs and push without any noise penalty, so that you can retain any highlights that might have been lost (in the raw and not just the JPEG, because the ISO setting is (in most cameras?) effected via an analog gain stage) at higher ISOs.
This might not matter much to you or me shooting sunsets, where the highlights are critical and shadow detail is a nice-to-have. But I imagine this would be important to people shooting night scenes where much of the detail is in the shadows, so shadows are critical and unclipped highlights are a nice-to-have. Or maybe astrophotography?

[MossyRocks]

Or maybe astrophotography?

For astrophotography we blast away and stack images. Usually cranking up the ISO to get the slight benefit that the analogue low noise signal amp before the A2D converter provides over just boosting digitally after going through the A2D converter. Then toss in some dark and bias frames to help with the random and systematic noise.

[normhead]

Rather, the value of ISO invariance is supposed to be in being able to shoot at the lower ISOs and push without any noise penalty, so that you can retain any highlights that might have been lost (in the raw and not just the JPEG, because the ISO setting is (in most cameras?)

Ya, if you read my post about bracketing up to 5 EV, you'd see that practice has always been true. So I still don't see the need for ISO invariance. Methods of achieving the optimum exposure make more sense. You set ISO 100, you bracket, you pick out the best exposure. Easy peasy. As far as I can tell ISO invariance is way more complicated than it needs to be, and it's along explanation of very simple content. The discussion on here where people are waltzing around ISO invariance, made 5 times as complex as it needs to be are irritating, and un-necessar. And there is as much misleading about them as their is of use.

Especially since every camera and sensor displays different characteristics, as an general theory it's total effect is negative in my estimationmation. Probably more confusion to be had the useful input to be gained.

Just look at McKloskie's lack of understanding of Invariance in his attempt to prove the K-1 Mk 2 cooked the images. He completely didn't understand the contrast value change and mistook contrast for resolution. He was motivated by not understanding an unusable theory. on by this theory. It has way to many un-knowable variables to be of use.

The whole of ISO invariance is covered by "use the lowest ISO possible, go higher than base ISO only to increase shutter speed to reduce or eliminate motion blur."

It doesn't take a 5 page dissertation to understand that.

And that is the elephant in the room, If you need a high shutter speed, and you have to increase you're ISO to get it, you're not going to get the same quality you'd get at a lower shutter speed. So, you're only using high ISO because you have to, and you take what you get. DR and IQ at that point are not part of the equation, the other variables , shutter speed's relationship to motion blur, has taken over. IQ and DR just are what they are, and based on whatever happens with ISO and shutter speed, they are as good as they can be.

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Last edited by normhead; 08-29-2018 at 01:13 PM.

[CarlJF]

Norm, nobody said that ISO invariance is something useful for photographers or even that they should care about it.

ISO invariance is only relevant to this thread to show that ISO, as it is implemented in modern cameras, isn't a physical property of the sensor itself but mostly the result of some electronic treatment and amplification of the signal. So, to answer the original question of this thread, manufacturers could launch cameras with much lower ISO than 100, if they wanted to, with the sensors they actually have on hand. To do this, they only have to modify the treatment of the data generated by the sensor. But to do so, they would also have to sacrify the highest available ISO, because sensor can't capture an infinite amount light. Thus, they don't do because people overwhelmingly prefer good performance at high ISO than being able to use extra long shutter speed in good light (which they can already achieve with a ND filter)... Or, said otherwise, not much people would buy a K-1 with an usable ISO range of 2 to 100, even if Pentax could tweak its sensor to do so.

[normhead]

ISO invariance is only relevant to this thread to show that ISO, as it is implemented in modern cameras, isn't a physical property of the sensor itself but mostly the result of some electronic treatment and amplification of the signal. So, to answer the original question of this thread, manufacturers could launch cameras with much lower ISO than 100, if they wanted to, with the sensors they actually have on hand.

The sensors do have a built in base ISO, that can't be changed. Manufacturers have found ways to approximate the effect of higher ISOs by setting the mid point of the curve of collected light and compensating electronically. But any change from using optimum ISO will involve some clipping. The image gathered by the sensor is constant., you can cut down on the amount of light captured and that will clip the bottom portion of the sensor's capability. So claiming 400 ISO all you've done is clipped the lower two stops and set your black point from 0 to two and moved the mid point of your displayed curve up one stop, so that the 400 ISO image will appear to have covered the whole range of the scene. These are essentially virtual ISOs, not base sensor ISOs.

Any attempt to go to a lower ISO beyond base values would increasing sense sensitivity, which would also increase dynamic range, but there is simply now way to create an ISO lower than base ISO if you're thinking making the sensor more sensitive is part of that. There are physical limits.

Cameras with lower ISOs simply have larger wells. You cannot make an image out of light levels the sensors are incapable of responding to. With film this would have been known as reciprocity failure. Instead of getting a long exposure, the light never crossed the threshold it needed to react with the silver compounds. So, it's not just a matter of artificially lowering the ISO through electronics. The sensor will have a level of light it is incapable of detecting, and once you hit that level it doesn't matter how long you expose, You won't have a change in your electionic state to produce an image from. Creating a lower ISO would have to be way more than just messing with the electronic gain systems for a colour system. You could go much lower ISO by restricting yourself to the levels used in night vision goggles, but that is done in part by restricting the light collected to the light that is most interactive with the sensor, they aren't full spectrum.

So you couldn't produce a K-1 with the same sensor that could produce useful 25 to 100 ISO, but you could use that original Phillps sensor that turned out to be a 25 ISO sensor, that essentially killed Pentax FF development for 12 years. Base ISO is based the lowest functional light gathering capability of the sensor, given that you want the mid point of the curve to be roughly equidistant from the lowest light detectable to the highest value before the highlights are blown out.

But changing base ISO requires a sensor change. At that point it's no longer a K-1, just to be clear. If you could just manipulate the electronics to alter the effects of base ISO, Pentax would have had an FF camera 12 years earlier.

[slartibartfast01]

The whole of ISO invariance is covered by "use the lowest ISO possible, go higher than base ISO only to increase shutter speed to reduce or eliminate motion blur."

Maybe I am missing something but ISO invariance implies that you don't need to increase the ISO to increase the shutter speed. Just shoot under exposed at 100 ISO then increase the exposure in processing.

[Scintilla]

Maybe I am missing something but ISO invariance implies that you don't need to increase the ISO to increase the shutter speed. Just shoot under exposed at 100 ISO then increase the exposure in processing.

That's what I was getting at. Assuming that bracketing is not an option for whatever reason, if you know your camera is ISO-invariant, you can get away with that in a single shot. If the camera isn't, then you have to pick either protecting the highlights (low ISO and push) or less noise (high ISO). That's all there is to it.

[normhead]

Maybe I am missing something but ISO invariance implies that you don't need to increase the ISO to increase the shutter speed. Just shoot under exposed at 100 ISO then increase the exposure in processing.

If the image was in any way superior to increasing the ISO that would make sense. But with out increasing the ISO most of the image will be blacked out even if you can reuse it. So you own't actually know if you have the image you want until you get into post processing. Given that it take bracketing to get the exposure you want. how will you even know if you're n the ball park with your exposure?
That would be possible if there was some way of displaying the 100 ISO image as if it was shot at 400 ISO. Wait, setting your camera to 400 ISO does that for you. What you've essentially done setting at 100 ISO and underexposing, is eliminated the value of chipping... and for what?

Sure you can do it, but why?

Is this whole theory designed to make your life more complicated?
You're still going to lose the dynamic range, using 100 ISO or 400 ISO, one stop ISO makes very little difference.
Or by was it designed by film aficionados who hate chimping, and like waiting until post to see what the image looks like? There are drawbacks to always shooting base ISO and under exposing that are being conveniently ignored. You can. but why?

I can also bang my head against wall whenever i want, but i don't do that either.

The only possible way I'd give up the functionality of using higher ISO would be if it produced a superior result. That has yet to be demonstrated to my satisfaction. If you're going to give up accurate previews, I want something in exchange for that.

[Scintilla]

But changing base ISO requires a sensor change. At that point it's no longer a K-1, just to be clear. If you could just manipulate the electronics to alter the effects of base ISO, Pentax would have had an FF camera 12 years earlier.

Thanks for the explanation -- goes a long way to pulling this thread back towards answering the OP's question, and this one paragraph is a nice effective summary.

[leekil]

The sensors do have a built in base ISO, that can't be changed. Manufacturers have found ways to approximate the effect of higher ISOs by setting the mid point of the curve of collected light and compensating electronically. But any change from using optimum ISO will involve some clipping. The image gathered by the sensor is constant., you can cut down on the amount of light captured and that will clip the bottom portion of the sensor's capability. So claiming 400 ISO all you've done is clipped the lower two stops and set your black point from 0 to two and moved the mid point of your displayed curve up one stop, so that the 400 ISO image will appear to have covered the whole range of the scene. These are essentially virtual ISOs, not base sensor ISOs.

There are two things compared, when "ISO invariance" is talked about. 1) The first case is using "regular ISOs" in older digital cameras (or as you call them "virtual ISOs") when the camera's electronics does amplification, which is generally analog, to achieve the light-gathering effect of a higher ISO. In the past, this also required various other necessary adjustments to improve the quality of the image at these "higher ISOs" to an acceptable level. 2) The other case is, where the image can be shot at base ISO, underexposed, even if the correct exposure would require a higher ISO, and then the levels can be digitally raised by a simple exposure slider adjustment in post-processing, and you end up with an excellent quality image.

Case 1 is most Pentax cameras before the K-5, a lot of processing was needed to get good higher ISOs, Case 2 applies to most Pentax cameras afterward. The term ISO invariance is really mostly shorthand for cameras having clean-enough sensors and A-D conversion on the low end such that the shadows don't turn to noisy crap (visible or otherwise), which becomes very noticeable if you try to raise the levels in the shadows.

[normhead]

There are two things compared, when "ISO invariance" is talked about. 1) The first case is using "regular ISOs" in older digital cameras (or as you call them "virtual ISOs") when the camera's electronics does amplification, which is generally analog, to achieve the light-gathering effect of a higher ISO. In the past, this also required various other necessary adjustments to improve the quality of the image at these "higher ISOs" to an acceptable level. 2) The other case is, where the image can be shot at base ISO, underexposed, even if the correct exposure would require a higher ISO, and then the levels can be digitally raised by a simple exposure slider adjustment in post-processing, and you end up with an excellent quality image.

Case 1 is most Pentax cameras before the K-5, a lot of processing was needed to get good higher ISOs, Case 2 applies to most Pentax cameras afterward. The term ISO invariance is really mostly shorthand for cameras having clean-enough sensors and A-D conversion on the low end such that the shadows don't turn to noisy crap (visible or otherwise), which becomes very noticeable if you try to raise the levels in the shadows.

Ya, people should really just say that. There's really nothing terribly complicated about it. K20D to K-5 12 EV to 14 EV, two more stops of shadow detail.