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Archive 2013 · Understanding 'Native' ISO and resulting non-native ISO's
  
 
Karl Witt
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p.1 #1 · p.1 #1 · Understanding 'Native' ISO and resulting non-native ISO's


Hi folks......a recent thread in N&W forum here: http://www.fredmiranda.com/forum/topic/1181162/0 shows a pretty impressive ISO 10,000 image from a Canon 1Dx

If I am correct the 'native' ISO for a given camera is determined by that particular sensors pixels 'analog' rating of light gathering ability

The rest of the ISO's are an Analog to Digital gain + or - in conversion?

We are not told that I know of our Camera's 'native' resolution?

Is there proven truth that 1/3 stop increases in ISO are not as good as full stop increases?

Any deviation up or down from native is then a digital alteration and introduces noise or alters dynamic quality of image. So is it possible that how the Digital conversions are done that a higher ISO can actually produce a cleaner/lower noise image than a lower ISO (below the native ISO) rating?

Does anyone know for sure the native ISO for a MKIII and a MKIV and the 1Dx??

This may a little over my head but I think I have a grasp on it and technically would like input to get even a better grasp on it.......please
And thanks......
Karl




Jan 11, 2013 at 08:08 PM
snapsy
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p.1 #2 · p.1 #2 · Understanding 'Native' ISO and resulting non-native ISO's


The native ISO of a sensor is that which has the highest light saturation capacity when metered at middle gray, which also yields the highest dynamic range offered by that sensor. The fake "low" ISO setting on cameras is produced by exposing 1 stop above metered gray and then digitally reducing the exposure by 1 stop to produce the same output brightness, albeit with less dynamic range. ISOs above native ISO are handled either via analog amplification, digital multiplication, or a combination of the two.

For traditional CMOS sensors which have high sensor electronic read-out noise (all Canon sensors and Nikon D3/D700/D3s sensors), analog amplification yields lower effective read noise at higher ISOs than it does at native ISOs because the amplification increases the relative signal to the constant read-out noise. This doesn't mean the resulting image at High ISO will be less noisy, since most of the noise in the image is the result of photon shot noise, which is a function of only exposure, and typically when you double the ISO you halve the exposure, which means 1/2 the amount of light reaching the sensor. On most entry level/prosumer cameras there is only a single amp which only handles full ISO increments (200, 400, 800, etc..), and so the intermediate levels are achieved by over/under exposing by the fractional stop difference and then adjusting digitally, thus the intermediate ISO levels will not be optimal. Pro-level cameras typically have two amps, one for the full ISO increments and another for the 1/3 stop increments.

For newer CMOS sensors which have low sensor electronic read-out noise (Sony EXMOR sensors), there is not much to be gained via analog amplification vs digital since the relative read-out noise is so low to begin with. Still, it has been measured that the D800 uses analog gain up to around ISO 1000 and digital gain thereafter.

Edited on Jan 11, 2013 at 08:39 PM · View previous versions



Jan 11, 2013 at 08:30 PM
David Kirsch
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p.1 #3 · p.1 #3 · Understanding 'Native' ISO and resulting non-native ISO's


Karl, I don't have a clue as to the answers to those questions, but they are good ones and I would like to see some knowledgeable responses.

David



Jan 11, 2013 at 08:34 PM
Karl Witt
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p.1 #4 · p.1 #4 · Understanding 'Native' ISO and resulting non-native ISO's


snapsy wrote:
The native ISO of a sensor is that which has the highest light saturation capacity when metered at middle gray, which also yields the highest dynamic range offered by that sensor. The fake "low" ISO setting on cameras is produced by exposing 1 stop above metered gray and then digitally reducing the exposure by 1 stop to produce the same output brightness, albeit with less dynamic range. ISOs above native ISO are handled either via analog amplification, digital multiplication, or a combination of the two.

For traditional CMOS sensors which have high sensor electronic read-out noise (all Canon sensors and Nikon
...Show more

I knew that!

I am digesting your info, it is a bit overwhelming but it is helping
My thanks
Karl



Jan 11, 2013 at 08:41 PM
Monito
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p.1 #5 · p.1 #5 · Understanding 'Native' ISO and resulting non-native ISO's


For the 5D Mark II, the lowest noise ISO of the trio 100, 125, and 160 is 160. Likewise 320 is the lowest of 200, 250, and 320. Further, 640 is the lowest of 400, 500, and 640. Similarly 1250 is the lowest of 800, 1000, and 1250. Beyond that, noise decreases in a relatively linear way.

So, for the 5D2, I shoot at 160, 320, 640, 1250 or any higher ISO as needed. If I had to go to an intermediate ISO for some reason, I would and not worry about it, but so far I haven't.

This article with tests is very convincing: http://photocascadia.wordpress.com/2011/05/13/canon-eos-5d-mark-ii-iso-noise-test/ Watch the little slide show and see the noise reduce dramatically from 250 to 320, for example.



Jan 11, 2013 at 08:47 PM
snapsy
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p.1 #6 · p.1 #6 · Understanding 'Native' ISO and resulting non-native ISO's


The key takeaway is that while there are measurable differences between the intermediate ISOs vs full-stop ISOs, those differences are rather small, esp. when compared to the noise differences produced by the exposure itself. Exposure is defined by the amount of light the sensor receives, which is a function of aperture and shutter speed only. Traditionally ISO has also been included in exposure because most equate exposure with output brightness, and also because up until recently most sensors produce better results by shooting at Higher ISO to achieve a given output brightness than by shooting at native ISO and digitally increasing the brightness in post, although that's almost not the case anymore with the Sony EXMOR sensors.

If you're looking to produce the best possible IQ it's more important to focus on getting the maximum exposure your scene will artistically allow (based on shutter speed/aperture/dynamic range demands), and then adjusting the output brightness down in post to the desired artistic level ("Expose To The Right"). This will yield much higher IQ gains than worrying about native or intermediate ISOs.



Jan 11, 2013 at 08:57 PM
skibum5
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p.1 #7 · p.1 #7 · Understanding 'Native' ISO and resulting non-native ISO's


snapsy wrote:
The native ISO of a sensor is that which has the highest light saturation capacity when metered at middle gray, which also yields the highest dynamic range offered by that sensor. The fake "low" ISO setting on cameras is produced by exposing 1 stop above metered gray and then digitally reducing the exposure by 1 stop to produce the same output brightness, albeit with less dynamic range. ISOs above native ISO are handled either via analog amplification, digital multiplication, or a combination of the two.

For traditional CMOS sensors which have high sensor electronic read-out noise (all Canon sensors and Nikon
...Show more

Yeah that pretty much covers it. Other than to give a few more details about the +1/3 and +2/3rds intermediates on the non-1 series cameras:

the +1/3's underexposing and then boosting digitally means that they give up DR and tend to have, at lower ISOs, less DR than both the primary ISO below AND above, digitally pulling up from the noisy near blacks brings up more shadow banding muck and noise. The +2/3rds simply take the primary ISO 1/3 higher and over-expose it by 1/3 and then shift 1/3 stop digitally and you get the same DR as from the primary ISO just above it and more than from the ISO 1/3 below it, shot as metered you get 1/3 stop better SNR since it exposes 1/3 stop longer, of course you could do the same thing by say shooting ISO 200 with +1/3 EC compared to ISO160 with 0 EC (likewise ISO160 EC -1/3 gives you ISO200 EC 0, the RAWs shift the numbers so it's not bit for bit the same file, but you basically get the exact same content either way) it is sort of like a 1/3 stop STP (shadow tone protection) in a sense if you just leave metering at EC 0.

The +1/3 ISOs aren't so hot, the +2/3 ISOs don't do anything for you per se but they don't hurt either. If you shoot them all with EC 0 and auto exposure the +2/3 ones give you images with a 1/3 stop better SNR and cleaner shadows but 1/3 less highlights than the shots you take at the primary ISO just above it. If you use M mode they are basically the exact same, if you use ISO200 and then flip to ISO160 you'd just then increase shutter speed 1/3 stop.

At some point all of the ISOs get treated digitally. For all the earlier Canon stuff the last time they used analog gain was ISO1600. SOmewhere around 7D or 5D2 era they started using analog gain up to ISO3200 I believe.
Once you get above ISO1600 and certainly ISO3200 the whole 1/3 thing mentioned above doesn't really apply any more for any of the cameras since it is mostly or all straight up digital raising it 1/3 step each time all the way up.



Jan 11, 2013 at 09:12 PM
abqnmusa
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p.1 #8 · p.1 #8 · Understanding 'Native' ISO and resulting non-native ISO's


Urban Legend




Jan 11, 2013 at 09:22 PM
Gunzorro
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p.1 #9 · p.1 #9 · Understanding 'Native' ISO and resulting non-native ISO's


Does anyone have a list of native ISO for various Canon models?


Jan 11, 2013 at 09:24 PM
jcolwell
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p.1 #10 · p.1 #10 · Understanding 'Native' ISO and resulting non-native ISO's


Hi Karl,

The topic has been discussed before,

http://www.fredmiranda.com/forum/topic/1058815

Hi Jim,

I don't know if the list is in the thread linked above, but I do recall seeing one.



Jan 11, 2013 at 09:42 PM
 

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skibum5
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p.1 #11 · p.1 #11 · Understanding 'Native' ISO and resulting non-native ISO's


Monito wrote:
For the 5D Mark II, the lowest noise ISO of the trio 100, 125, and 160 is 160. Likewise 320 is the lowest of 200, 250, and 320. Further, 640 is the lowest of 400, 500, and 640. Similarly 1250 is the lowest of 800, 1000, and 1250. Beyond that, noise decreases in a relatively linear way.

So, for the 5D2, I shoot at 160, 320, 640, 1250 or any higher ISO as needed. If I had to go to an intermediate ISO for some reason, I would and not worry about it, but so far I haven't.

This article with tests
...Show more

160 and 200 are essentially the same though for RAW

set ISO200 EC +1/3 or set ISO160 EC 0 and shoot with auto-exposure and get the same end result
they have the same DR

but yeah ISO250 though has less DR than not just ISO200 but than even ISO400 too! there is no way to adjust EC and get the same result from ISO250 as from ISO200 or 320 or 400. ISO250 being exposed 1/3 longer than ISO400 would have a bit lower photon noise though but is likely less important than DR loss and enhanced shadow junk



Jan 11, 2013 at 09:45 PM
skibum5
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p.1 #12 · p.1 #12 · Understanding 'Native' ISO and resulting non-native ISO's


Gunzorro wrote:
Does anyone have a list of native ISO for various Canon models?


I believe they are all in the ISO100-200 range, almost all around 100. (What 100 means has shifted a bit generation to generation, sometimes they were ultra conservative and sometimes less so, nikon had generally been less so and then Canon adjusted more to follow but more recently went more conservative again (one reason why comparing 5D2 to 5D3 ISO vs ISO is not quite fair to the 5D3, that cheats the 5D3 by almost 1/3 stop). I believe that there have been more Nikons where it has been more like ISO200 native.

(i thought i read that the C100 might have native at ISO400 or 800 though)



Jan 11, 2013 at 09:48 PM
Gunzorro
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p.1 #13 · p.1 #13 · Understanding 'Native' ISO and resulting non-native ISO's


Thanks Jim. I read something here recently, or rather a link, perhaps it was from snapsy, that showed some graphs with various bodies best ISO, range by range. Some were at 100 - 200 - 400, etc, others started at 125 or 160, and the progression remained the same. I was particular interested in base or native ISO, as well as what would be least noise at around 1600. I use base ISO most often, so it would be nice to know if I get the same or better IQ form 125 or 160 instead of 100! And when I do go to higher ISO, if 1/3 stop makes an impressive reduction in noise, I'd like to know, camera by camera.

It's one of those topics we all seem to be aware of, but no technical person has compiled a list. (Or have they?)



Jan 11, 2013 at 09:56 PM
jcolwell
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p.1 #14 · p.1 #14 · Understanding 'Native' ISO and resulting non-native ISO's


I probably remember the same link/thread. I recall that the 1DX base ISO is 160.

I often use ISO 12800 (160 x80) in really low light, with great results, some of which I have previously posted. I haven't tried the really high ISO settings yet, because I'm afraid they might fry my retina, or turn me into Goldmember!



Jan 11, 2013 at 10:16 PM
gdanmitchell
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p.1 #15 · p.1 #15 · Understanding 'Native' ISO and resulting non-native ISO's


snapsy wrote:
The key takeaway is that while there are measurable differences between the intermediate ISOs vs full-stop ISOs, those differences are rather small, esp. when compared to the noise differences produced by the exposure itself. Exposure is defined by the amount of light the sensor receives, which is a function of aperture and shutter speed only. Traditionally ISO has also been included in exposure because most equate exposure with output brightness, and also because up until recently most sensors produce better results by shooting at Higher ISO to achieve a given output brightness than by shooting at native ISO and digitally
...Show more

+1



Jan 11, 2013 at 10:58 PM
Access
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p.1 #16 · p.1 #16 · Understanding 'Native' ISO and resulting non-native ISO's


How do you guys know it's not just an artifact of the firmware and the level of noise reduction applied to the shot? B'cos we know even when shooting raw, with noise reduction turned all the way down, firmware is still applying some noise reduction... probably the noise reduction is applied at different levels (relating to ISO) and these levels are increased in steps every third ISO.


Jan 11, 2013 at 11:06 PM
snapsy
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p.1 #17 · p.1 #17 · Understanding 'Native' ISO and resulting non-native ISO's


Access wrote:
How do you guys know it's not just an artifact of the firmware and the level of noise reduction applied to the shot? B'cos we know even when shooting raw, with noise reduction turned all the way down, firmware is still applying some noise reduction... probably the noise reduction is applied at different levels (relating to ISO) and these levels are increased in steps every third ISO.


The only raw-based noise reduction that's ever been analytically confirmed on Canikon cameras is impulse noise reduction on the Nikon D3s starting at ISO 25,600, which I presume also occurs on Canons starting with the 5DM3/1DX/6D. Bill Claff also detected a different type of NR on the 5DM3 at similarly high ISOs.



Jan 11, 2013 at 11:14 PM
Access
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p.1 #18 · p.1 #18 · Understanding 'Native' ISO and resulting non-native ISO's


Noise reduction has always been there, raw or not, it is an inherent part of any modern CMOS design. You always measure the reference voltage after resetting the sensor (but before opening the shutter). Then you subtract this from the final value obtained after closing the shutter.

The effectiveness of this type of noise reduction depends on the gain of the pre-amp. You can increase this gain, but if you adjust it too high, you also limit dynamic range (you can also the limit the dynamic range if you adjust this gain too low, but for a different reason).

The ADC that it hits after the pre-amp is fixed, with Canon either 14-bit or 12-bit in some of the older models. Different ISOs are typically created by adjusting the pre-amp gain, or at the very high end, re-scaling the final value (far from optimal since it will increase noise linearly, and farther limit the dynamic range).

I apologize in advance if my post is too technical or reliant on electronics knowledge, but this is the best I can express it.



Jan 11, 2013 at 11:51 PM
snapsy
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p.1 #19 · p.1 #19 · Understanding 'Native' ISO and resulting non-native ISO's


Access wrote:
Noise reduction has always been there, raw or not, it is an inherent part of any modern CMOS design. You always measure the reference voltage after resetting the sensor (but before opening the shutter). Then you subtract this from the final value obtained after closing the shutter.

The effectiveness of this type of noise reduction depends on the gain of the pre-amp. You can increase this gain, but if you adjust it too high, you also limit dynamic range (you can also the limit the dynamic range if you adjust this gain too low, but for a different reason).

The
...Show more

Yes but that noise reduction only serves to reduce the noise that the electronics itself added to the image. It's akin to an arsonist being called a hero for putting out a fire he started. Also, this reset-noise reduction strategy doesn't affect the signal side negatively and doesn't produce pixel-correlated smoothing effects.



Jan 11, 2013 at 11:59 PM
skibum5
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p.1 #20 · p.1 #20 · Understanding 'Native' ISO and resulting non-native ISO's


Gunzorro wrote:
Thanks Jim. I read something here recently, or rather a link, perhaps it was from snapsy, that showed some graphs with various bodies best ISO, range by range. Some were at 100 - 200 - 400, etc, others started at 125 or 160, and the progression remained the same. I was particular interested in base or native ISO, as well as what would be least noise at around 1600. I use base ISO most often, so it would be nice to know if I get the same or better IQ form 125 or 160 instead of 100! And when I
...Show more

The longer you expose, the more light you collect and the better SNR for most tones in the image. On all Canon DSLR ISO100 would give you the highest SNR for anything from your brightest darker tones and up. That said, on many Canon DSLR ISO 100 has barely, if any better DR than ISO 200 so you don't really lose any DR by using ISO200. In one or two cases ISO200 might have a trace more DR, but it's nothing ever meaningful in any way so you do end up with close to the full stop less exposure anyway. Perhaps since pattern banding sticks out more to the eye the equivalent measured DR between ISO100 and ISO200 might actually be a tiny bit higher at ISO200 though. But you are still using a faster shutter speed and collecting less light so the image would have more noise, maybe in a few cases where shadow pulls matter a lot it might come out a touch ahead, especially since it is hard to perfectly 100% exactly expose to the right (ISO160 might look a touch better on average in that regard since it might bias you to ETTR a bit more without your realizing it too).

For any tones close to mid-tone or higher ISO100 will still show less noise though since it collected light for one stop longer. On most bodies the general noise is so low at ISO100 or ISO200 that it doesn't make too much difference. If you want to sharpen as much as possible and utilize full MP count on a high density body ISO100 might let you do that a bit more cleanly than ISO200 though.

Anyway on 1 series they have a dual amp on non-1 series they do not and the ISO125, ISO250, etc. are not so hot as you give up DR and pull up junk from deep blacks while having 1/3 stop worse mid-tone SNR than ISO100 or ISO200 and only a minor 1/3 stop better for that than ISO160/200 ISO320/400.




Jan 12, 2013 at 12:11 AM
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