Ad
Ad
Ad
Pages: « 1 ... 4 5 [6] 7 8 9 »   Bottom of Page
Print
Author Topic: ETTR vs ISO  (Read 16995 times)
jrsforums
Sr. Member
****
Offline Offline

Posts: 722


« Reply #100 on: May 27, 2013, 11:11:50 AM »
ReplyReply

Hi John,


Not being a Canon guy I am not sure what the game is.  But it means the ISO setting that is 1/3 of a stop below what is labelled as ISO 3200 in-camera.

Jack

Thanks for the RD chart.

The game, as I understand it, is that for Canon 5D series (and other Canons...not some 1D's) they only really have true ISOs at full stops.

The 1/3 stops are "fake".  That is, if you set 160 ISO, it is really 200 ISO, but metering done as 160...therefore 1/3 stop overexposed...as in slight ETTR.  Therefore the shadows are slightly better.

For jpeg OOC, the RAW is pulled back 1/3 in the OOC post processing.  For 1/3 stop ISOs over the full stops, the image is pushed up in post.

I, personally, just set my camera to full stop ISO.  Since I shoot RAW only, I want to control whatever "ETTR" I am doing.

John
Logged

John
jrsforums
Sr. Member
****
Offline Offline

Posts: 722


« Reply #101 on: May 27, 2013, 11:21:03 AM »
ReplyReply

Jack, another interesting datapoint, which goes with your comment about diminishing returns at higher ISOs for the 5D3 is the DR chart from DxoMark

Logged

John
RFPhotography
Guest
« Reply #102 on: May 27, 2013, 11:29:49 AM »
ReplyReply

Bob, do you have UG ISO numbers/chart for the 5D3? 

I have not seen any.  Was thnking of doing it, but have not yet found the time (famous procrastinator).

No, John, I don't.  I don't shoot Canon and don't have the tools to do it.  

My question more more general in nature, though.  If the two figures are different, how does one choose which to follow or which is better?  I haven't compared figures for different cameras to see if or how the two may be different.  But if the two present differing or contravening information on choosing the best max. ISO setting it would be helpful to know how to reconcile the two.
Logged
Jack Hogan
Full Member
***
Offline Offline

Posts: 211


« Reply #103 on: May 27, 2013, 11:42:45 AM »
ReplyReply

Jack, I'm thinking about trying to model this camera and compare it to the D800. Can you tell me the full well capacity and the unity gain ISO? The standard deviation of the ADU random noise would be nice -- I'll assume shot noise if you have no information. I'll assume the standard deviation of the pre-amp noise is that of shot noise, and I can calculate the pre-amp mean noise from your graph once I have the unity gain ISO.

Jim

Hi Jim,

Reading off the chart in the earlier post, FWC appears to be around 67500 e- and UG around 400.  I get the curve in the graph assuming 8.4 ADU of random noise contributed by the amplifier at the output of the ADC.  It's not bad but it's not a perfect fit to the calculated read noise.  If I remember correctly the 5DIII has a couple of amplifying stages, which I treated as one in order to estimate this last figure.

Jack
Logged
jrsforums
Sr. Member
****
Offline Offline

Posts: 722


« Reply #104 on: May 27, 2013, 11:47:59 AM »
ReplyReply

No, John, I don't.  I don't shoot Canon and don't have the tools to do it.  

My question more more general in nature, though.  If the two figures are different, how does one choose which to follow or which is better?  I haven't compared figures for different cameras to see if or how the two may be different.  But if the two present differing or contravening information on choosing the best max. ISO setting it would be helpful to know how to reconcile the two.

Sorry...misinterpreted you question.

Probably Jim Kasson would best to answer this.  I could try, but would only be trying to interpret info he has provided me....and would probably do it poorly :-)
Logged

John
Jack Hogan
Full Member
***
Offline Offline

Posts: 211


« Reply #105 on: May 27, 2013, 11:50:05 AM »
ReplyReply

Q:  How does one reconcile the Unity Gain ISO figures with the Photographic Dynamic Range Shadow Improvement?

Bob, I am no expert on unity gain, but I believe that Jim proved a few threads ago that Unity Gain is in practice only meaningful in very specific applications such as when one does heavy duty stacking for astrophotography.  As far as I understand today PDR Shadow Improvement is as good as it gets in helping to make the proper SNR/DR compromise.

Jack
« Last Edit: May 27, 2013, 11:52:10 AM by Jack Hogan » Logged
Jack Hogan
Full Member
***
Offline Offline

Posts: 211


« Reply #106 on: May 27, 2013, 11:57:29 AM »
ReplyReply

I, personally, just set my camera to full stop ISO.  Since I shoot RAW only, I want to control whatever "ETTR" I am doing.

John

Ok, assuming that Bill's data for the 5DIII is correct and that you are shooting in full manual mode using the exposure/ISO strategy discussed in this thread, for maximum IQ and control you would want to keep doing what you are doing but always choosing ISO values 1/3 of a stop less than the standard ones (i.e. 159, 318, 636 etc. instead of 200, 400, 800...)

Jack
« Last Edit: May 27, 2013, 12:04:56 PM by Jack Hogan » Logged
Jim Kasson
Sr. Member
****
Offline Offline

Posts: 744


WWW
« Reply #107 on: May 27, 2013, 12:06:50 PM »
ReplyReply

Reading off the chart in the earlier post, FWC appears to be around 67500 e- and UG around 400.  I get the curve in the graph assuming 8.4 ADU of random noise contributed by the amplifier at the output of the ADC.  It's not bad but it's not a perfect fit to the calculated read noise.  If I remember correctly the 5DIII has a couple of amplifying stages, which I treated as one in order to estimate this last figure.

Jack

Thanks, Jack. I'm going to use Clark's numbers: FWC = 68900, UG ISO = 500.

From his read noise numbers, I fitted a curve, and came up with a pre-gain read noise mean of 2.5 electrons, and a post-gain read noise mean of 7.5 ADC counts. This gave me a pretty good fit to his read noise data. I'm going to assume the variance of the two components of the read noise is the same as the mean (a la shot noise).

Then I'll do some modeling and see if the camera differences that people are talking about can be explained by the model parameters, or if there's something going on in the Canon that I'm not modeling.

However, the results may take me a day or two to generate. Some actual photography is intervening.

Jim
Logged

jrsforums
Sr. Member
****
Offline Offline

Posts: 722


« Reply #108 on: May 27, 2013, 12:10:47 PM »
ReplyReply

Ok, assuming that Bill's data for the 5DIII is correct and that you are shooting in full manual mode using the exposure/ISO strategy discussed in this thread, for maximum IQ and control you would want to keep doing what you are doing but always choosing ISO values 1/3 of a stop less than the standard ones (i.e. 159, 318, 636 etc. instead of 200, 400, 800...)

Jack

...or be in a mettered mode, with +1/3 EC...if i wanted to mimic the exposure of -1/3 ISO  :-)
Logged

John
Jim Kasson
Sr. Member
****
Offline Offline

Posts: 744


WWW
« Reply #109 on: May 27, 2013, 12:13:00 PM »
ReplyReply

If I remember correctly the 5DIII has a couple of amplifying stages, which I treated as one in order to estimate this last figure.

Jack, that looks like a good assumption. Here's the result of my curve fitting:



Jim
Logged

Jim Kasson
Sr. Member
****
Offline Offline

Posts: 744


WWW
« Reply #110 on: May 27, 2013, 12:15:34 PM »
ReplyReply

Sorry...misinterpreted you question.

Probably Jim Kasson would best to answer this.  I could try, but would only be trying to interpret info he has provided me....and would probably do it poorly :-)

Not having an actual Canon, I am somewhat at a disadvantage here. Maybe my simulated 5DIII will shed some light on the subject when I get it implemented.

Jim
Logged

Vladimirovich
Sr. Member
****
Offline Offline

Posts: 1260


« Reply #111 on: May 27, 2013, 12:20:21 PM »
ReplyReply



Vladimirovich, that would be a smart way to handle the digital component of ISO brightening.  Do you know any current DSLR that does that?



Panasonic GH3 (Sony sensor, as it turned out) does for ISOs after ISO6400 (so they combine both amplification, be it analog and/or digital, _and_ tag)...

1) you can see that if you convert .rw2 to .dng using Adobe DNG converter and compare baseline exposure tags there, for example ISO6400 = 0, ISO12800 = 1, ISO25600 = 2

2) I did PDR test using Claff's utilities - here is GH3 PDR graph



« Last Edit: May 27, 2013, 12:23:08 PM by Vladimirovich » Logged
Jack Hogan
Full Member
***
Offline Offline

Posts: 211


« Reply #112 on: May 27, 2013, 12:23:26 PM »
ReplyReply

Thanks, Jack. I'm going to use Clark's numbers: FWC = 68900, UG ISO = 500.

FWC: my figure comes out of the DxO full SNR curves - and they average the three channels (I am not sure whether they weigh them).  Are Clark's derived just from the green channel?  And I agree about the UG ISO: I had forgotten that Canon's Raw data is offset by a couple of thousand ADUs.  510 it is.

Quote
From his read noise numbers, I fitted a curve, and came up with a pre-gain read noise mean of 2.5 electrons

I used 2.4 e- so that looks good.  Look forward to the results.

Jack
« Last Edit: May 27, 2013, 12:33:37 PM by Jack Hogan » Logged
Vladimirovich
Sr. Member
****
Offline Offline

Posts: 1260


« Reply #113 on: May 27, 2013, 12:27:46 PM »
ReplyReply

I can see that working if the OEM conversion utility were used. But it may not work with third party converters that don't pick all the tags.

majority of commercial 3rd party raw converter either are communicated by manufacturer or will know that from simple test or reverse engineering... some like RPP will not honor the tag intentionally, by design... so it is not an issue... and I guess at some point raw files from MFDB (PhaseOne) were like that ? just ISO by tag ?
Logged
RFPhotography
Guest
« Reply #114 on: May 27, 2013, 12:56:07 PM »
ReplyReply

Sorry, refresh my memory, what's RPP?

So Adobe does pick up that tag then it appears?
Logged
RFPhotography
Guest
« Reply #115 on: May 27, 2013, 12:57:10 PM »
ReplyReply

Bob, I am no expert on unity gain, but I believe that Jim proved a few threads ago that Unity Gain is in practice only meaningful in very specific applications such as when one does heavy duty stacking for astrophotography.  As far as I understand today PDR Shadow Improvement is as good as it gets in helping to make the proper SNR/DR compromise.

Jack

Jim, do you concur about the use of UG and PDR Shadow Improvement?
Logged
Vladimirovich
Sr. Member
****
Offline Offline

Posts: 1260


« Reply #116 on: May 27, 2013, 01:00:05 PM »
ReplyReply

Sorry, refresh my memory, what's RPP?

a raw converter valued by an alternative lifestyle of raw conversion crowd


So Adobe does pick up that tag then it appears?

certainly = otherwise why do you think Adobe's own DNG converter writes the proper values ?

as it turned out the hidden expocorrection that Adobe's raw converters (ACR/LR) do is the sum of 2 values : one hardcoded in their code (that is what Adobe DNG converter shall reveal when you convert a native raw into Adobe's DNG) and another in their .dcp profiles
« Last Edit: May 27, 2013, 01:03:26 PM by Vladimirovich » Logged
Jim Kasson
Sr. Member
****
Offline Offline

Posts: 744


WWW
« Reply #117 on: May 27, 2013, 01:39:38 PM »
ReplyReply

Jim, do you concur about the use of UG and PDR Shadow Improvement?

The metric that I've been using is photon-noise-corrected signal-to-noise ratio at a particular average value that corresponds to the shadow tone that you're most concerned about. I would think that this would be strongly correlated with PDR Shadow Improvement. However, I don't have enough information of the specifics of Claff's measurement of PDR Shadow Improvement to do a rigorous comparison. Any pointer would be appreciated.

Thanks,

Jim
Logged

RFPhotography
Guest
« Reply #118 on: May 27, 2013, 01:52:24 PM »
ReplyReply

a raw converter valued by an alternative lifestyle of raw conversion crowd

Your ass isn't as smart as you think it is.   Roll Eyes  What's the name of the program?


Quote
certainly = otherwise why do you think Adobe's own DNG converter writes the proper values ?


And that's fine.  Just confirming.
Logged
bjanes
Sr. Member
****
Offline Offline

Posts: 2756



« Reply #119 on: May 27, 2013, 01:55:28 PM »
ReplyReply

Your ass isn't as smart as you think it is.   Roll Eyes  What's the name of the program?
And that's fine.  Just confirming.

A google search turns up this link.

Bill
Logged
Pages: « 1 ... 4 5 [6] 7 8 9 »   Top of Page
Print
Jump to:  

Ad
Ad
Ad