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Author Topic: Sony A7RII ISO Invariance  (Read 17286 times)

amolitor

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Sony A7RII ISO Invariance
« on: November 18, 2015, 10:24:18 am »

I have two very short responses:

ETTL?

and

Quantization Noise
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hubell

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Re: Sony A7RII ISO Invariance
« Reply #1 on: November 18, 2015, 02:14:27 pm »

Perhaps someone can explain the real world implications of this concept of ISO Invariance in setting exposures. Does it not permit us to be more careful in protecting highlights from blowing at the possible expense of underexposing by 1-3 stops, knowing that we can bring up the shadows pretty cleanly? To put it differently, why do ETTR and run ANY risk of blowing highlights?
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AlterEgo

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Re: Sony A7RII ISO Invariance
« Reply #2 on: November 18, 2015, 02:19:43 pm »

why do ETTR and run ANY risk of blowing highlights?

ETTR, ETTL - do not forget about rawconverter and camera profile... they may or may not wreck havoc on your left or right side  ;D ... because in some converters you push or pull exposure slider after a lot of things are done to the data
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Hans Kruse

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Re: Sony A7RII ISO Invariance
« Reply #3 on: November 18, 2015, 05:39:57 pm »

A bit of an old story :) The first camera with that property or at least very close to was the Nikon D3X back in 2008. Canon still hasn't done it. Btw. in these forums you cannot really admit shooting a Canon  ;)

AlterEgo

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Re: Sony A7RII ISO Invariance
« Reply #4 on: November 18, 2015, 05:41:14 pm »

The first camera with that property or at least very close to was the Nikon D3X back in 2008.
I 'd assume that MFDB with just one real ISO and the rest nominal ISO done by tag in raw were before 2008... no ? or may be even Sigma's FOVEON (the original) based cameras
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amolitor

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Re: Sony A7RII ISO Invariance
« Reply #5 on: November 18, 2015, 06:35:53 pm »

I've seen this idea espoused elsewhere and, fundamentally, it's not a very good idea.

By all means, preserve the highlights you're interested in preserving, but you're better off using the analog amplifiers to whatever extent you can than you are amplifying in the digital domain, because, quantization noise. This will manifest as posterization in some cases, which can be repaired with some judgement, and will result in loss of low-contrast fine detail.

Generally, you don't lose much, and whatever you do lose was likely to be lost somewhere in the pipeline unless you're fanatically careful, but you do lose stuff and you wind up making extra work for yourself.
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thompsonkirk

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Re: Sony A7RII ISO Invariance
« Reply #6 on: November 19, 2015, 01:18:45 am »

Was I supposed to think the 'pushed' version was acceptable?  It looked much more noisy than the 12800 version to me.

Using higher ISO with modest underexposure would be a better bet?

Kirk
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Hans Kruse

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Re: Sony A7RII ISO Invariance
« Reply #7 on: November 19, 2015, 05:13:29 am »

Was I supposed to think the 'pushed' version was acceptable?  It looked much more noisy than the 12800 version to me.

Using higher ISO with modest underexposure would be a better bet?

Kirk

If anything I saw the pushed version worse than 12800. The contrast is different which make it a bit difficult to compare. But to me the 12800 looks cleaner than the 6400 pushed one.

Slobodan Blagojevic

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Re: Sony A7RII ISO Invariance
« Reply #8 on: November 19, 2015, 08:41:11 am »

We had this discussion a year ago. I posted an example showing Canon files at 5000 ISO and the other one at 500, i.e., 3 and ⅓ stops pushed. The higher-ISO one looked better.

Stefan12345

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Re: Sony A7RII ISO Invariance
« Reply #9 on: November 19, 2015, 08:50:19 am »

In my book, ISO 640 pushed 5 stops equals ISO 20480 (640*2^5)
Am I missing something?
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michael

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Re: Sony A7RII ISO Invariance
« Reply #10 on: November 19, 2015, 08:55:56 am »

As mentioned in the article (but no harm is saying it again), the intent wasn't to espouse this approach (and yes, the low ISO / pushed image is worse), but simply to draw the concept to the attention of an audience that may not be as well informed and technical as some on this forum.

Michael


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Slobodan Blagojevic

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Re: Sony A7RII ISO Invariance
« Reply #11 on: November 19, 2015, 09:01:48 am »

.. to draw the concept to the attention of an audience that may not be as well informed and technical as some on this forum...

Ha! That sounds like the Adobe's explanation for the Import redesign  ;)

EDIT: Just to make shure this isn't interpreted as criticism; articles like this (back-to-basics), definitely make more sense than what Adobe did (dumbing down)
« Last Edit: November 19, 2015, 10:03:18 am by Slobodan Blagojevic »
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AlterEgo

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Re: Sony A7RII ISO Invariance
« Reply #12 on: November 19, 2015, 09:09:53 am »

In my book, ISO 640 pushed 5 stops equals ISO 20480 (640*2^5)
Am I missing something?
yes, raw files.
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Diego Pigozzo

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Re: Sony A7RII ISO Invariance
« Reply #13 on: November 19, 2015, 09:36:03 am »

As mentioned in the article (but no harm is saying it again), the intent wasn't to espouse this approach (and yes, the low ISO / pushed image is worse), but simply to draw the concept to the attention of an audience that may not be as well informed and technical as some on this forum.

Michael

I think it could be interesting to compare the result of denoising algorithms on pushed and unpushed images.
I don't know anything at all on those algorithms but* I think there could be advantages for them to have an unpushed image because more "noise details" would be available and, therefore, a more precise determination of the noise characteristics.
This could lead to a better handling of the noise.

But, again, I'm just babbling of something I know nothing about.
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amolitor

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Re: Sony A7RII ISO Invariance
« Reply #14 on: November 19, 2015, 09:47:10 am »

I have had a conversation with a chap who felt that he got better results with pushing and de noising. I disagreed, but they're not my pictures and it's not my call.

The "shape" of the noise is going to be different. You may or may not like the results more.

But you absolutely will unrecoverably lose certain low contrast detail. Which may or may not matter to you.

I was mainly surprised to see it on LuLa since it is essentially the opposite of ETTR.

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AlterEgo

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Re: Sony A7RII ISO Invariance
« Reply #15 on: November 19, 2015, 09:52:01 am »

I was mainly surprised to see it on LuLa since it is essentially the opposite of ETTR.
what is opposite of ETTR if we do not have enough /for whatever reason - even for the sake of experiment/ exposure (aperture and exposure time) to saturate the sensor @ lower gain /known as "ISO"/ settings ? in such situation it might be beneficial in many case based of course on a specific camera/sensor technology to use a higher gain... even when we saturate the sensor we still might do this /use higher gain still/ if clipping (or situation near clipping) does not ruin anything important vs pluses from higher gain possible positive effects on readout related noise
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AlterEgo

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Re: Sony A7RII ISO Invariance
« Reply #16 on: November 19, 2015, 09:55:41 am »

I think it could be interesting to compare the result of denoising algorithms on pushed and unpushed images.
I think it is interesting to use a raw converter with a proper raw conversion chain (that is exposure correction before WB/curves/color transform)

PS: and before demosaick too (that's obvious).
« Last Edit: November 19, 2015, 10:14:10 am by AlterEgo »
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Telecaster

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Re: Sony A7RII ISO Invariance
« Reply #17 on: November 19, 2015, 10:20:28 am »

I was mainly surprised to see it on LuLa since it is essentially the opposite of ETTR.

Well, Michael has long been an advocate of ETTR…but this is merely an informative piece.

With my current EVF cameras I just expose for a nice JPEG, which I'm comfortable using in most cases where electronic display is the intended viewing medium. For printing or when I want to more forcefully adjust tonality I use the RAWs.

If cameras offered smart ETTR metering, and smart JPEG processing to match, I'd use that.

High-bit JPEG has been around for awhile now. Why does no camera (that I know of) offer it as an option?

-Dave-
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dickgillberg

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Re: Sony A7RII ISO Invariance
« Reply #18 on: November 19, 2015, 11:33:46 am »

I've read the article and my self I'm always trying to expose well enough, close to rock 'n roll. Why do we want to do this tests at all? In my world, just expose properly for every shoot and do a good picture. That sade, I just got my A7R II and the quality works for me. I don't push the exposure 5 stops usually.  ;)
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AlterEgo

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Re: Sony A7RII ISO Invariance
« Reply #19 on: November 19, 2015, 11:46:42 am »

In my world, just expose properly
the question is not about the exposure, but rather about the gain (aka ISO) - which is not a part of exposure, but a part of your decision about exposure that you make before exposure starts and effects are applied after exposure ends...

note however that some people might also argue that for some sensors while gain is not part of exposure (aperture and exposure time = how much light you let in) it might affect how much of the said light during the exposure can ultimately be converted to photon-electrons (for example changing the gain can change sensel' well capacity and while again the gain is not part of exposure /in terms of how much light you let hit the sensor assembly surface/, it affects the the things rather during exposure process itself - but then again this mostly can be considered as a pre/post exposure effect for practical purposes)...

so to expose properly we need to know how gain works on our camera and not only that - but also if you have a particular raw converter in mind then how it handles the data, potential to screw things is enormous !
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