ISO 100, OMD-EM1II and firmware 3.0?

Started 3 months ago | Questions
katastrofa Senior Member • Posts: 1,010
Re: Basics of digital camera ISO

"The image you see is a perceptual illusion, tailored to human vision, not a direct funelling through of the light from the original scene. It doesn't exist until you've processed the latent image."

Nitpicking slightly, "the image you see" exists only in your brain. There is a helluva lot of data processing inside our vision system.

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bobn2
bobn2 Forum Pro • Posts: 62,008
Re: Basics of digital camera ISO

katastrofa wrote:

"The image you see is a perceptual illusion, tailored to human vision, not a direct funelling through of the light from the original scene. It doesn't exist until you've processed the latent image."

Nitpicking slightly, "the image you see" exists only in your brain. There is a helluva lot of data processing inside our vision system.

It's a good nitpick, and also helps the point along. The way an image is presented, including gamma encoding and tri-stimulus colour, is all designed to trick the brain's data processing into interpreting what it sees as a convincing representation of the original scene. It's not a physically straight forward presentation of the light from the scene.

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bobn2
bobn2 Forum Pro • Posts: 62,008
Re: Calling your bluff

katastrofa wrote:

Ok, so what if we applied multiplication to the digital signal instead of gain to the analog one? That wouldn't add any noise.

It depends on how well you do the multiplication. A big problem with digital processing is rounding errors, which whilst not strictly noise can look a lot like it. Image processing tools which work in extended floating point representation do produce better results than those that work in integers. Older digital cameras had 16-bit image processing pipelines, and really could add 'noise' due to rounding errors. Camera processors are often taken from mobile phone technology, and these chips often have GPUs in them which allow fast FP arithmetic, so it can be expected (if the programmers use them) that they'll produce essentially noise free processing.

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spike29 Senior Member • Posts: 1,782
Re: Basics of digital camera ISO

bobn2 wrote:

spike29 wrote:

bobn2 wrote:

spike29 wrote:

bobn2 wrote:

.....

That's a common problem in this discussion, although also an irrelevance. When you realise what the photographic process is, and what ISO actually does, you realise that whilst where the sensor starts and stops is of academic interest, it's irrelevant to the discussion. ISO says what lightness should result from a given exposure.

This is one of the clearest , most understandable short definitions i read about this subject .πŸ™‚

Simplified but accurate enough.

Thanks for the feedback. I'll remember it and use that text again

I will explain why i find this to the point, most of the time ISO value is connected to "gain" of voltage or current or digital gain in threads and webpages which brings your mind to a "amplifier". Which is a trap of misconceptions and assumptions. (I did) most internet searches don't help to untangle the confusion either, on the contrary it tighten the knots even more.

That's why this simple text don't distract you and don't sent you in a maze of half truth's. and keep you on track for the next information.

So as far is i remember all the basics:

While ISO isn't a Gain/Amplifier but more a (wanted) result of the several gains (to get the signal in range of correct processingvalues for readout and conversions) along the road of capturing photons towards a image represented in a rawfile. This in order to get the image correct(lightnes) represented on screen or paper. By getting a underexposed sensor/pixel , low amount of photons on a given shuttertime, and by setting a ISO value you define the lightnes you want to correct that (under)exposure in the camera to get a correct lightness in your jpeg/tiff.

A word of caution there, the term 'underexposed' is something of a trap, too. The pixels's job is to measure exposure, whatever it is. 'Underexposed' is a relative term, relative to the exposure you want, and what exposure you want depends on what you're trying to do and towards what end you're trying to manage exposure. It doesn't relate to any requirement in the pixel or any need for some absolute level of exposure. A low exposure doesn't 'need' boosting, it just needs the desired lightness value assigned to it.

Understood, i see how easy it is to drift off from the exact definitions.(and translation errors)

new question:

What if you alter a rawfile of a 1600iso image and change the stored value of 1600iso in the exif in lets say 200iso? (lets say this is "base iso") drops the lightnes of the image in a rawdeveloperapplication 3stops down? so it looks like a -3EV Exposurecorrection?

Think of the ISO development process as a table of lightness values against exposure values. (What a processor is doing is like 'painting by numbers'). By changing the ISO you shift all the lightness values up or down the table. If you set the ISO three stops lower. then all the lighness values end up against three stops larger exposures, so if you dindn't actually change the exposures, the image will be rendered three stops darker.

(highlights stayed clipped so those are gone and black is black so you scrunch the DR of the tonecurve. )

The sensor tone curve is pretty much a straight line, unlike film. It doesn't get 'scrunched'

I meant from rawfile, which has a defined white and black, shifting down the ladder gets more "blacks" but the clipped data of white don't re-enter when original white is -3ev corrected. That's what i ment with smaller DR , the top end of the lightnes scale is cut off  from the image. You can't adjust what isn't there.

But i get your point. Camera electronics is build to give a clean as possible readout under a wide range of photons capturing to give the best possible latent image.

Wile ISO is used to bring the latent image to the desired lightnes for cooked jpeg in camera, the same ISO value is used by the raw developer to preview the captured image as intended.

and this altered exif shows the "real image" what's captured by the sensor showing the real lightnes it would show on base ISO? (except the clipped data)

There isn't a 'real image' in the sense you mean. What the sensor captures is what in film days would be called a 'latent image'. The image you see is a perceptual illusion, tailored to human vision, not a direct funelling through of the light from the original scene. It doesn't exist until you've processed the latent image.

Or are some "gains" non reversible? (i think simplified that all gain before ADC is irreversible, after the ADC it's just "software calculation" and fully reversible. )

I think it's best to forget about 'gain'. It has to do with optimising the camera electronics, and nothing to do with photography. If you don't optimise the capture electronics for low exposures (which is what happens when you raise the ISO) you won't recover the shadow information lost in the resultant noise. If you optimise for low exposure, then use a high one, you won't recover the clipped highlights.

I am getting there πŸ˜‰

Your explainations are getting clearer for me.

To determine the lightness in the output file, all the camera needs to be able to do is measure the exposure in each pixel. 'Gain' doesn't change the exposure in the pixel, but it can change how accurately it is measured.

Is this the reason that dynamic range changes when ISO raises? less accurately means less steps between black and white (full exposure)

So far as DR is concerned, the problem is that if you apply voltage gain before the ADC you boost the higher signals up above the ADC maximum, the larger exposures can't be digitised. Thus each stop of gain means a loss of a stop at the high end. Once that loss stops lowering the noise floor, there is no point applying any more voltage gain. There's another question of just why manufacturers continue unnecessarily clipping the raw file, which we can have if you want.

People have difficulty with this concept because they tend to call both the input and output 'exposure', in which case they think of 'gain' as giving a bigger 'exposure' from a smaller one, but that is not what is happening. Exposure and lightness are different things, which is why two words are needed.

Extended ISO at the high end i can think of: Just add measurement's at the lowest part of the sensor output voltages until noise overgrows mesurable signal and higher iso values are redicules because you can't separate random noise from the actual latent image capturing enough to get a reasonable clear image at the end anymore.

The real problem is that the noise is in the signal, which is why photography is somewhat different from common electronic applications. The SNR goes as the square root of the number of photons captured. The problem with very small exposures is just not many photons.

But at the low end below base iso. Why don't use that as base iso?

See upthread. The thing,about th Lo settings is you can meter as normal, get higher exposures, thus more photons, thus less noise.

Got it. metering is for the determination of the shuttertime to get a proper exposure and shuttertime increases when lowering iso so more photons are able to reach the sensor/pixel with in the shuttertime.

Not shutter time, exposure. Remember, exposure is controlled by shutter, aperture and the light coming from the scene. The ISOI that you set provides your meter with a target exposure, that's the exposure that the meter measures when it's centred. You can get that target exposure by changing any of the shutter speed, aperture or light coming from the scene (if you have control over that). This is hard to conceptualise if you're thinking of 'exposure' as the output of the process, how light or dark the final image is. Many people do this, including supposed experts that write web sites (for instance, I've caught the Northrups doing this, left a comment, not responded to). Exposure is what you control at the input. Lightness is what you get at the output.

Now i am ready to start on understanding noise types. πŸ˜€

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Cafe Racer Contributing Member • Posts: 535
Re: ISO 100, OMD-EM1II and firmware 3.0?

ozturert wrote:

You'll lose about about 1 stop of headroom in highlights but gain 1 stop of shadow headroom.

Do you mean you get an image that is 1 stop brighter than it should be when using ISO 100 (low)?

I use Low ISO only if there are no highlights that I want to preserve.

Couldn't you under-expose by 1 stop to preserve highlights when using low ISO (100), if the highlights are already 1 stop brighter than they should be?

I've never used an E-M1ii so I'm not familiar with how ISO 100 behaves.

Cafe Racer.

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ozturert Forum Member • Posts: 78
Re: ISO 100, OMD-EM1II and firmware 3.0?
1

No the image isn't 1 stop brighter. Highlight details are lost very fast at iso100. For example if there are bright sections in the sky, I try not to use ISO100.

Shadows are just the opposite: Shadows are cleaner and you can recover quite a bit more information from shadows at ISO100. I use ISO64/100 when shadows are more important than highlights.

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Cafe Racer Contributing Member • Posts: 535
Re: ISO 100, OMD-EM1II and firmware 3.0?

ozturert wrote:

No the image isn't 1 stop brighter. Highlight details are lost very fast at iso100. For example if there are bright sections in the sky, I try not to use ISO100.

Shadows are just the opposite: Shadows are cleaner and you can recover quite a bit more information from shadows at ISO100. I use ISO64/100 when shadows are more important than highlights.

1 stop loss in the highlights sounds a lot. Have you tested to see if an ISO 100 image on the E-M1ii has any additional brightness added, compared to the same image taken at ISO 200 that's been given the same amount of exposure to light? If not, it's worth testing.

My G80 artificially adds brightness to an image taken at ISO 100 compared to the same image taken at ISO 200. This is what makes the highlights clip sooner and gives more brightness to the shadows, making them look better. It's kind of like a subliminal ETTR, which as we know helps to reduce shadow noise.

I'd be interested to know how the E-M1ii behaves in this scenario.

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ozturert Forum Member • Posts: 78
Re: ISO 100, OMD-EM1II and firmware 3.0?

I'll try in more detail tonight

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Richard Turton Regular Member • Posts: 238
ISO 100 Compared to Overexposure

Can the same results as ISO 100 be obtained by over exposing ISO 200 by one stop?  The answer is no.  The Signal/Noise Ratio of ISO 100 is almost a full stop better than ISO 200 overexposed by one stop.  The available headroom is lower with ISO 100, but as long as clipping does not occur you will get less noise with ISO 100.

Cafe Racer Contributing Member • Posts: 535
Re: ISO 100 Compared to Overexposure

Richard Turton wrote:

Can the same results as ISO 100 be obtained by over exposing ISO 200 by one stop? The answer is no. The Signal/Noise Ratio of ISO 100 is almost a full stop better than ISO 200 overexposed by one stop. The available headroom is lower with ISO 100, but as long as clipping does not occur you will get less noise with ISO 100.

Have you tested the E-M1ii to see if an ISO 100 image has any additional brightness added?

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Richard Turton Regular Member • Posts: 238
Re: ISO 100 Compared to Overexposure

Cafe Racer wrote:

Richard Turton wrote:

Can the same results as ISO 100 be obtained by over exposing ISO 200 by one stop? The answer is no. The Signal/Noise Ratio of ISO 100 is almost a full stop better than ISO 200 overexposed by one stop. The available headroom is lower with ISO 100, but as long as clipping does not occur you will get less noise with ISO 100.

Have you tested the E-M1ii to see if an ISO 100 image has any additional brightness added?

What do you mean by "brightness added"?  These measurements apply to the raw files without post processing.  ISO 64 & 100 are 1.7 stops "brighter" than ISO 200, but the total noise is only about 1 stop higher so the low ISO files look cleaner.

OP Architeuthis Regular Member • Posts: 166
Re: ISO 100 Compared to Overexposure
1

Cafe Racer wrote:

Richard Turton wrote:

Can the same results as ISO 100 be obtained by over exposing ISO 200 by one stop? The answer is no. The Signal/Noise Ratio of ISO 100 is almost a full stop better than ISO 200 overexposed by one stop. The available headroom is lower with ISO 100, but as long as clipping does not occur you will get less noise with ISO 100.

Have you tested the E-M1ii to see if an ISO 100 image has any additional brightness added?

I had some time at the weekend and made test shots. Noise filter off, noise reduction off, Auto WB, raw files.

First I exposed to the right (ETTR; center spot) at ISO200 and then made test shots at ISO100 and ISO64 at identical aperture/shutter settings. Clearly the raws were darker at lower ISO (according to DxO the rwas should all be all at the same ISO83) and the histograms at lower ISO show that there is plenty of room for brighter pixels left. Unfortunately, I do not have the means here to look at the histgram spacing as bobn2 suggests. I corrected exposure in LR (+1 eV for ISO100, +1.6eV for ISO64), exported JPEGs. They are now of very similar brightness and I cannot detect any differences in S/N ratio in the shadows. In case there are differences, they must be very subtile:

ISO200

Extended ISO100

Extended ISO64

I conclude that (by a strange mechanism that I do not understand) the low extended ISO settings provide similar S/N ratio as base ISO200, but allow to collect more light (just as the differences in ISO values suggest). I will not hesitate in the future to use the low extensed ISOs, when light permits (unless someone convinces me about the opposite)...

Wolfgang

P.S.: I also made a test series to find out where the "ISOless" range of the EM1II starts. I will, however, open a new thread, since this is a different aspect...

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Cafe Racer Contributing Member • Posts: 535
Re: ISO 100 Compared to Overexposure

Richard Turton wrote:

Cafe Racer wrote:

Richard Turton wrote:

Can the same results as ISO 100 be obtained by over exposing ISO 200 by one stop? The answer is no. The Signal/Noise Ratio of ISO 100 is almost a full stop better than ISO 200 overexposed by one stop. The available headroom is lower with ISO 100, but as long as clipping does not occur you will get less noise with ISO 100.

Have you tested the E-M1ii to see if an ISO 100 image has any additional brightness added?

What do you mean by "brightness added"? These measurements apply to the raw files without post processing. ISO 64 & 100 are 1.7 stops "brighter" than ISO 200, but the total noise is only about 1 stop higher so the low ISO files look cleaner.

Sorry, I'm not referring to your chart, I'm asking if you've if you've actually carried out tests with the E-M1ii comparing ISO 100 and ISO 200?

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Cafe Racer Contributing Member • Posts: 535
Re: ISO 100 Compared to Overexposure

Architeuthis wrote:

Cafe Racer wrote:

Richard Turton wrote:

Can the same results as ISO 100 be obtained by over exposing ISO 200 by one stop? The answer is no. The Signal/Noise Ratio of ISO 100 is almost a full stop better than ISO 200 overexposed by one stop. The available headroom is lower with ISO 100, but as long as clipping does not occur you will get less noise with ISO 100.

Have you tested the E-M1ii to see if an ISO 100 image has any additional brightness added?

I had some time at the weekend and made test shots. Noise filter off, noise reduction off, Auto WB, raw files.

First I exposed to the right (ETTR; center spot) at ISO200 and then made test shots at ISO100 and ISO64 at identical aperture/shutter settings. Clearly the raws were darker at lower ISO (according to DxO the rwas should all be all at the same ISO83) and the histograms at lower ISO show that there is plenty of room for brighter pixels left. Unfortunately, I do not have the means here to look at the histgram spacing as bobn2 suggests. I corrected exposure in LR (+1 eV for ISO100, +1.6eV for ISO64), exported JPEGs. They are now of very similar brightness and I cannot detect any differences in S/N ratio in the shadows. In case there are differences, they must be very subtile:

ISO200

Extended ISO100

Extended ISO64

I conclude that (by a strange mechanism that I do not understand) the low extended ISO settings provide similar S/N ratio as base ISO200, but allow to collect more light (just as the differences in ISO values suggest). I will not hesitate in the future to use the low extensed ISOs, when light permits (unless someone convinces me about the opposite)...

Wolfgang

P.S.: I also made a test series to find out where the "ISOless" range of the EM1II starts. I will, however, open a new thread, since this is a different aspect...

Hi,

Thanks for that. Perhaps I should also open a new thread as what I'm trying to ascertain is not S/N ratio as base 200.

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OP Architeuthis Regular Member • Posts: 166
Re: ISO 100 Compared to Overexposure

Cafe Racer wrote:

Hi,

Thanks for that. Perhaps I should also open a new thread as what I'm trying to ascertain is not S/N ratio as base 200.

Hi Cafe Racer,

I am not sure whether I understand your question. But as I wrote above, no additional btightness is added to the histograms of the raw files - they look more or less as would be expected (-1eV (ISO100) and -1.6eV (ISO64)). Here are screenshots of the histograms of the unprocessed exposures that are shown above:

Wolfgang

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bobn2
bobn2 Forum Pro • Posts: 62,008
Re: ISO 100 Compared to Overexposure
1

Architeuthis wrote:

Cafe Racer wrote:

Hi,

Thanks for that. Perhaps I should also open a new thread as what I'm trying to ascertain is not S/N ratio as base 200.

Hi Cafe Racer,

I am not sure whether I understand your question. But as I wrote above, no additional btightness is added to the histograms of the raw files - they look more or less as would be expected (-1eV (ISO100) and -1.6eV (ISO64)).

You're looking at the wrong quantity, both of you. What the histogram is measuring is exposure, though in camera and setting dependent units. The exposure will be the same, since the exposure settings (aperture, shutter) are the same and, presumably, the third exposure parameter, scene luminance (the light coming from the scene) is also the same. Therefore there is no way that it can be different. The setting-dependent units get scaled down by a factor of two each stop lower ISO that is set.

Here are screenshots of the histograms of the unprocessed exposures

'Unprocessed exposure' doesn't mean anything. 'Exposure' is sufficient, and is what is being shown. Processing a exposure delivers a lightness, not a different exposure.

that are shown above:

Wolfgang

I'm not trying to be critical or pedantic here. Using the correct terms makes it much easier to conceptualise all this. Especially, confusing what 'exposure' is makes it really, really hard to work out what's going on.

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Cafe Racer Contributing Member • Posts: 535
Re: ISO 100 Compared to Overexposure

Architeuthis wrote:

Cafe Racer wrote:

Hi,

Thanks for that. Perhaps I should also open a new thread as what I'm trying to ascertain is not S/N ratio as base 200.

Hi Cafe Racer,

I am not sure whether I understand your question.

That's OK, I wasn't actually referring histograms or S/N ratio. Like I said it's probably best I start a new thread where I can describe it with photos.

But as I wrote above, no additional btightness is added to the histograms of the raw files - they look more or less as would be expected (-1eV (ISO100) and -1.6eV (ISO64)). Here are screenshots of the histograms of the unprocessed exposures that are shown above:

Wolfgang

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OP Architeuthis Regular Member • Posts: 166
Re: ISO 100 Compared to Overexposure

bobn2 wrote:

Architeuthis wrote:

Cafe Racer wrote:

Hi,

Thanks for that. Perhaps I should also open a new thread as what I'm trying to ascertain is not S/N ratio as base 200.

Hi Cafe Racer,

I am not sure whether I understand your question. But as I wrote above, no additional btightness is added to the histograms of the raw files - they look more or less as would be expected (-1eV (ISO100) and -1.6eV (ISO64)).

You're looking at the wrong quantity, both of you. What the histogram is measuring is exposure, though in camera and setting dependent units. The exposure will be the same, since the exposure settings (aperture, shutter) are the same and, presumably, the third exposure parameter, scene luminance (the light coming from the scene) is also the same. Therefore there is no way that it can be different. The setting-dependent units get scaled down by a factor of two each stop lower ISO that is set.

Here are screenshots of the histograms of the unprocessed exposures

'Unprocessed exposure' doesn't mean anything. 'Exposure' is sufficient, and is what is being shown. Processing a exposure delivers a lightness, not a different exposure.

I'm not trying to be critical or pedantic here. Using the correct terms makes it much easier to conceptualise all this. Especially, confusing what 'exposure' is makes it really, really hard to work out what's going on.

Hi Bobn2,

Sorry for using wording that can be mistaken. With "same exposure" I meant the photos were taken at the same shutter speed/aperture detting and just the ISO was different...

Wolfgang

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Cafe Racer Contributing Member • Posts: 535
Re: ISO 100 Compared to Overexposure

Architeuthis wrote:

Cafe Racer wrote:

Hi,

Thanks for that. Perhaps I should also open a new thread as what I'm trying to ascertain is not S/N ratio as base 200.

Hi Cafe Racer,

I am not sure whether I understand your question.

Hi Architeuthis,

You've put in a lot of work here so I'll try to explain what I was trying to find out.

I put my Panasonic G80 on a tripod, I select Raw, switch to manual exposure mode and take two photos. Both photos are of exactly the same scene (nothing in the scene changes).

Ist photo taken at ISO 400 - 1/500 sec - f4

2nd photo taken at ISO 200 - 1/250 sec - f4

Would you expect those two photos to look the same?

This is not a trick question by the way.

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bobn2
bobn2 Forum Pro • Posts: 62,008
Re: ISO 100 Compared to Overexposure

Architeuthis wrote:

bobn2 wrote:

Architeuthis wrote:

Cafe Racer wrote:

Hi,

Thanks for that. Perhaps I should also open a new thread as what I'm trying to ascertain is not S/N ratio as base 200.

Hi Cafe Racer,

I am not sure whether I understand your question. But as I wrote above, no additional btightness is added to the histograms of the raw files - they look more or less as would be expected (-1eV (ISO100) and -1.6eV (ISO64)).

You're looking at the wrong quantity, both of you. What the histogram is measuring is exposure, though in camera and setting dependent units. The exposure will be the same, since the exposure settings (aperture, shutter) are the same and, presumably, the third exposure parameter, scene luminance (the light coming from the scene) is also the same. Therefore there is no way that it can be different. The setting-dependent units get scaled down by a factor of two each stop lower ISO that is set.

Here are screenshots of the histograms of the unprocessed exposures

'Unprocessed exposure' doesn't mean anything. 'Exposure' is sufficient, and is what is being shown. Processing a exposure delivers a lightness, not a different exposure.

I'm not trying to be critical or pedantic here. Using the correct terms makes it much easier to conceptualise all this. Especially, confusing what 'exposure' is makes it really, really hard to work out what's going on.

Hi Bobn2,

Sorry for using wording that can be mistaken.

Don't apologise, that wasn't the point. The point of using the terms correctly is to help conceptualisation. Each different word in a technical context has a distinct meaning, representing a distinct concept. Muddle the words and you muddle the concepts, or else, you're muddling the words because you're muddling the concepts. Clear terminology and clarity go together. I wasn't criticising, just trying to lend a hand for both of you to get the ideas straight.

With "same exposure" I meant the photos were taken at the same shutter speed/aperture detting and just the ISO was different...

Same exposure would be with the same EV (that is combination of aperture and shutter speed) and same scene luminance. You're correct in thinking that changing the ISO doesn't change the exposure if the EV stays the same.

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