Those "in-between" ISOs...

Hey All -


I've read a number of conflicting opinions / theories about using in-between ISOs, the 320, 500, etc. - and I'm hoping someone here is able to share "just the facts ma'am." (!)


I'm curious if those 1/3 increment ISOs are good to use, or should be avoided. In various photo mags I see ISO 500 or 320 etc. but more often I see 100, 200, 800, etc.


Is it true that camera CPUs arrive at those 1/3 ISOs by interpolation? That would mean they're not "native" to the capture system, but does that make them (by definition) inferior?


I've used my 40D at various ISOs and don't see anything unexpected at the 1/3 ISOs...


I'd like to learn the "best practice" ways to shoot - is avoiding in-between ISOs part of it?


Thank you for any thoughts you can share.

i dont tend to use many "in between" ISO's, I tend to either use 100, 200, 400, 800, but instead of jumping to 1600, I like to use 1000 for soem indoor shooting that doesnt quite need to be 1600, so i guess you coudl say I use 1/3 ISO's more so at higher ends.

I don't use the 1/3 ISO's myself, but that's more out of habit than anything. I'd say you've answered yourself: "I've used my 40D at various ISOs and don't see anything unexpected at the 1/3 ISOs...". If it looks good to you, I say run with it!

Ha! I think you're right CS, I should just leave well-enough alone. Like Mal, indoors I use ISO 1000 frequently. I wonder if 1600 would be better though, since it's a "native" ISO.


I stick by the "use the lowest possible ISO" rule and it seems to serve me well. But I wonder if I'm missing something by avoiding those in-between ISOs. The only one I ever use is 1000, when 800 won't give me a fast enough shutter, but I don't necessarily need to double the sensitivity and go to 1600.

I'm sure Daniel Browning will be along shortly to explain things.

It's not interpolation, it more like using levels. It is just like shooting something at 100 and the in RAW bumping up the Exposure by 1/3 takes it to 125 and 2/3 would take it to 160. I actually use ISO 160 on my camera when shooting portraits just to pay homage to Kodak VC 160 film. I know it isn't really making any difference but it is a mental thing. OCD if you will.

This issue came up on a thread I started about my first baseball captures.....this is from Chuck Lee, click on the link;


Bill and Peety,
<blockquote>
<div>[img]../Themes/hawaii/images/icon-quote.gif[/img] Bill W:</div>
<div>Your
statement "walking ISO down" is fully understandable and shooting at
"tweener" ISO's is interesting...I'll search for DB's entry on this
subject.</div>
</blockquote>


The tweener ISOs on a 40D at 160, 320, 640, 1250 are better than the
default 100,200,400,800,1600. ISO 160 is as good as it gets on a 40D. Read Thisit's for the 30D but pertains to the 40D as well. This is not true for the 5D where the standards are best.


Regards


Bill

Thanks for the link Bill. The bottom graph is easy enough to understand, but the top one is a complete mystery to me.


for what it's worth, I've never seen any combing in my RAW files.


I worked my way through the links and found his 40D page, with the same "dark noise tests he did for the 30D. But I still can't make sense of it.


He refers to the 'tween ISOs as "upscaled fake ISOs" and "downscaled fake ISOs." The only conclusion I can draw (so far, without some help) is that the sensor multiplies or divides the native ISOs to arrive at the 'tween ISOs.


But he never says if that's a bad thing (though the word "fake" doesn't exactly inspire confidence in using them!).

The short answer is: don't use tweeners.

Read on for the long answer.

Quote:

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Originally Posted by canoli

I'm curious if those 1/3 increment ISOs are good to use, or should be avoided.

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It depends on how picky you are. If you want maximum dynamic range, you'll avoid at least half of them.

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Originally Posted by canoli

In various photo mags I see ISO 500 or 320 etc. but more often I see 100, 200, 800, etc.

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Not surprising. Few people are aware of what the optimal settings are and the reason why they are optimal.

Quote:

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Originally Posted by canoli

Is it true that camera CPUs arrive at those 1/3 ISOs by interpolation?

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In some cameras, yes. This includes the 5D2, xxD (50D, 40D, 30D), xxxD (500D, 450D, 400D), and 1000D.

In other cameras, the tweener ISO settings are achieved through a separate analog amplifier. That includes the 5D1, xD (1D, 1D2, 1D3), and xDs (1Ds, 1Ds2, and 1Ds3).

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Originally Posted by canoli

That would mean they're not "native" to the capture system,

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Correct.

Quote:

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Originally Posted by canoli

but does that make them (by definition) inferior?

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Yes. Digital manipulation of the raw file is always inferior because it always increases quantization error and sometimes also clips highlights by 1/3 stop. It could have been implemented as metadata ISO and would have avoided posterization completely while still offering the same benefit to the user.

If the cameras were engineered with the correct bit depth (e.g. 12 bits for the 5D2 instead of 14), then the quantization error from tweener ISO settings might actually show up in the extreme shadows as posterization. In this case the two mistakes cancel each other out (14 bits is enough to hide posterization).

Quote:

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Originally Posted by canoli

I've used my 40D at various ISOs and don't see anything unexpected at the 1/3 ISOs...

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The difference is not visible to most people when they use typical tone curves and default raw conversion parameters. That's because most defaults are tuned for very little dynamic range: just 5-7 stops between highlights and shadows. If you shoot scenes that have a little more contrast, such as 9 to 11 stops, the difference is more noticable. That is because the difference is in read noise dominated tones.

Quote:

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Originally Posted by canoli

I'd like to learn the "best practice" ways to shoot - is avoiding in-between ISOs part of it?

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On some of cameras with analog tweeners (1D3, 1Ds3), some of the settings have slightly less read noise, but generally the loss in highlight headroom is not worth it. In all other situations the tweeners are either worse or the same.

I should mention that tweeners can sometimes help broken raw converters. Canon's DPP, for example, doesn't use the correct white point for many of their own cameras. They set it too low, ignoring plenty of good data in the highlights completely. In that case, the -1/3 ISO settings (160, 320, 640, etc.) will move the actual white point down to the same spot where DPP "thinks" the white point is, so you get back that 1/3 stop of highlights. Of course, other raw converters don't have this bug, so they see the highlights either way. I don't suggest forming your shooting strategy around bugs in raw converters. Better to just live with the 1/3 loss (which is very minor) or switch to a better converter.

The +1/3 digital tweeners (ISO 125, 250, 500, etc.) are the ones that have negative effects. Compared to ISO 100 with a fixed exposure, ISO 125 clips 1/3 stop of highlights with no improvement in read noise. Compared to ISO 200 with fixed exposure, ISO 125 has 1/3 stop *more* highlight headroom, but it also has nearly double the read noise. That means ISO 200 actually has more dynamic range and less shadow noise than ISO 125.

That's not to say they that tweeners should never be used. For JPEG shooters (not raw), it's important to get the image brightness just so, and sometimes ISO is easier to change than exposure. Video, too, benefits from tweeners for the same reason.

Quote:

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Originally Posted by Maleko

...instead of jumping to 1600, I like to use 1000 for soem indoor shooting that doesnt quite need to be 1600, so i guess you coudl say I use 1/3 ISO's more so at higher ends.

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I would suggest ISO 1250 instead, because it has noticably less noise than ISO 1000 for the same exposure.

Quote:

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Originally Posted by Keith B

in RAW bumping up the Exposure by 1/3 takes it to 125 and 2/3 would take it to 160.

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Yep. That's exactly how 125/250/500 work in the camera, too. The other tweeners (160, 320, 640) are slightly different: they start with the next-highest ISO and subtract 1/3.

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Originally Posted by Chuck Lee quoted by Bill W

The tweener ISOs on a 40D at 160, 320, 640, 1250 are better than the default 100,200,400,800,1600.

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I wouldn't put it that way. They yeild the same result as shooting ISO 200 +1/3 EC. You lose 1/3 stop highlights, but gain less noise. They're really the same, not better. (In a fixed exposure, ISO 160 has lower read noise in absolute ADU, but the SNR is the same, so it's not better that way.)

Quote:

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Originally Posted by Chuck Lee quoted by Bill W

ISO 160 is as good as it gets on a 40D.

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ISO 100 has 1/3 stop more dynamic range and 1/3 stop higher SNR in the shadows than ISO 160.

To attain maximum dynamic range, tweeners should be avoided until they are implemented the correct way, as metadata.

Ah. I didn't think interpolation was the correct term for this. I guess it makes sense. I was just thinking how it relates to resizing images.


So if I understand correctly, ISO 160 on my 5D mkII isn't necessarily a bad thing as 125 would be? But 200 would be better and then bump my lights down a third. Right?

Quote:

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Originally Posted by Daniel Browning

Quote:

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Originally Posted by Maleko

...instead of jumping to 1600, I like to use 1000 for soem indoor shooting that doesnt quite need to be 1600, so i guess you coudl say I use 1/3 ISO's more so at higher ends.

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I would suggest ISO 1250 instead, because it has noticably less noise than ISO 1000 for the same exposure.

<div style="CLEAR: both"]</div>

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Interesting! I will remember that! cheers

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Originally Posted by Keith B

So if I understand correctly, ISO 160 on my 5D mkII isn't necessarily a bad thing as 125 would be?

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Correct.

Quote:

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Originally Posted by Keith B

But 200 would be better and then bump my lights down a third. Right?

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I wouldn't call it "better". Think of ISO 160 as "ISO 200 with +1/3 EC". ISO 200 with +0 EC is better in that it has slightly less highlight clipping, but it's worse in that it has slightly more noise. If you use them with the same light (fixed exposure), and ignore the meter, then they both result in the same SNR and dynamic range.

That settles it. ISO 100 and increase the lights 2/3.

Quote:

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Originally Posted by Daniel Browning

They yeild the same result as shooting ISO 200 +1/3 EC. You lose 1/3 stop highlights, but gain less noise. They're really the same, not better. (In a fixed exposure, ISO 160 has lower read noise in absolute ADU, but the SNR is the same, so it's not better that way.)

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If they're the same then what's the problem. I actually shoot shoot ISO 160 +.3ev on my 40D so that would be the equivalent of ISO 200 +.7ev. I find the the +1/3 tweeners( 160,320,640...) better thanshooting to the right with the normal ISOs. I started this because of the dark noise histograms provide by Peter Ruevski. I discovered this plot because of a post on dpreview where the poster was concerned with the amount of noise in a ISO 250 photo he had taken. Thats' because ISO 250 is 200 -1/3ev. It's essentially under exposed ISO 200 which increases the appereance of noise in the image. In fact, it looked worse thanISO400. Ruevski's plot confirms thisfinding.As far as "dynamic range" I can still pull down 1-2ev of blown highlights with these +1/3ev "tweeners". For me it takes the guess work out of creating raws with less noise. For Daniel, it's about milking the camera for every last drop of dynamic range available. I do not purposely over expose my raws in the hopes of increasing their dynamic range. The overhead proided by the raw format simply provides a safety net in case the photo has some over exposed areas.


I understand what you are saying Daniel, but I sometimes have to wonder whether you have real world data to back up the claims you continue to make on this subject. I have not seen personally any more overhead "dynamically" with ISO 100 images than ISO 160 images in all the time I've been post proccessing 40D RAW files. Not that what you say isn't true. I just wish my 5D had as much with the normal ISOs. I am always approaching this sublect with a Missori mentalitity. "Show me" If it works better, I'll use it.


canoli, You will find that if you do some images of the sky, say in the evening, you will see a difference in noise when shooting at ISO 100vs. ISO 160. I suggest you try it for yourself. In fact, try all the ISOs and judge for yourself whether or not it is useful. As far as combing in files, who cares? Just do a level adjustment in photoshop and watch the histogram get combed.


If you want to put the camera on ISO 200 +.3ev, do it. Otherwise, you'll find ISO 160 0ev just as good and you won't have to think about it. In fact according to Ruevski you'll get 2/3ev faster shutter and a cleaner image than shooting ISO100. According to DB you'll be giving up something in terms of dynamic range. To some that is important, to othersit's not. The art of Photography, I believe, is theoffspring ofalimited dynamic range medium.And I'd rather have cleaner images than increased DR.


Great Discussion!!


Chuck

Quote:

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Originally Posted by Chuck Lee

I find the the +1/3 tweeners ( 160,320,640...) better than shooting to the right with the normal ISOs.

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The raw files have the exact same dynamic range and SNR, so if it's really any better it can only be due to issues with the raw converter, such as the problem mentioned above with DPP. Another example would be if the raw converter didn't have a good exposure compensation tool, like Adobe.

Quote:

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Originally Posted by Chuck Lee

I started this because of the dark noise histograms provide by Peter Ruevski.

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His read noise plots are fine, but they only account for Noise, not Signal. (By "signal", I'm referring to light, not the average level of the read noise.) ISO 160 only looks like less noise than ISO 200 because of a digital -0.33 EC. If Signal stayed the same, then ISO 160 would truly be better. But Signal doesn't stay the same: it goes down -0.33 with the noise, so the SNR stays the same.

Quote:

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Originally Posted by Chuck Lee

I discovered this plot because of a post on dpreview where the poster was concerned with the amount of noise in a ISO 250 photo he had taken. Thats' because ISO 250 is 200 -1/3ev. It's essentially under exposed ISO 200 which increases the appereance of noise in the image. In fact, it looked worse than ISO400. Ruevski's plot confirms this finding.

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Agreed.

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Originally Posted by Chuck Lee

I understand what you are saying Daniel, but I sometimes have to wonder whether you have real world data to back up the claims you continue to make on this subject.

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I'll post a demonstration.

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Originally Posted by Chuck Lee

I have not seen personally any more overhead "dynamically" with ISO 100 images than ISO 160 images in all the time I've been post proccessing 40D RAW files.

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A 1/3 stop difference in read noise is pretty hard to detect. Most of my shots aren't even within 1/3 of my ideal exposure, there just isn't time to get it perfect.

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Originally Posted by Chuck Lee

As far as combing in files, who cares? Just do a level adjustment in photoshop and watch the histogram get combed.

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The combing is fine if you have a bunch of extra (wasted) bits. It would only be harmful if Canon was doing like Sony or Nikon and building them with just the perfect amount of precision.

Quote:

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Originally Posted by Chuck Lee

If you want to put the camera on ISO 200 +.3ev, do it. Otherwise, you'll find ISO 160 0ev just as good and you won't have to think about it. In fact according to Ruevski you'll get 2/3ev faster shutter and a cleaner image than shooting ISO100.

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Ruevski's chart correctly shows that the read noise in ADU is lower, but what really matters is SNR, and that is not improved over ISO 100 (in fact it's 1/3 stop worse).

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Originally Posted by Chuck Lee

And I'd rather have cleaner images than increased DR.

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In this case, ISO 100 provides both.

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Originally Posted by Daniel Browning

I'll post a demonstration.

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Until I get a round tuit, here's a chart that pretty much sums up everything about tweener ISO performance. (It's for the 5D2, and other cameras are slightly different, but it gives the idea.)


http://forums.dpreview.com/forums/read.asp?forum=1032&amp;message=31378147

Chuck Westfall does not answer your question but has some interesting discussion around ISO expansion on the 5D. His bottom line suggestion is to test for yourself. Its digital, test, test, test.....


http://www.digitaljournalist.org/issue0905/tech-tips.html


Mark

Thanks for your input folks, it is much appreciated.


Daniel, I was wondering if you could explain what "implement ISO as metadata" means. That's not your exact quote, but I think that was the gist of it.


Is it something you can explain to a more-or-less casual photographer? I love learning this stuff, but I'm not very well versed in all the terminology. If you can elaborate on that phrase a bit - without (if possible) getting too technical, I would really love to understand it. I assume not all of us know what that means, so maybe it'll be a worthwhile explanation for others too.


In any case, thanks again for your contributions.

Quote:

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Originally Posted by canoli

Daniel, I was wondering if you could explain what "implement ISO as metadata" means.

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White balance could be applied as a digital manipulation to the raw file before it's saved; instead, it is just "metadata", a recommendation for how to white balance the file in post. Currently, many ISO settings are applied as a digital manipulation to the raw file before it's saved. Metadata ISO would change that to be just a recommendation for how to push the file in post. It's very similar to how HTP works now.

Many camera manufacturers implement some ISO settings by digitally manipulating the raw file in the camera. This results in highlights that are blown needlessly (two full stops in the case of ISO 6400), larger file sizes (45 MB instead of 20 MB for the 5D2), and increases the precision needed to prevent quantization error.

There are no benefits to applying gain digitally in the camera, so those ISO settings should instead be implemented as metadata. Like white balance, the metadata ISO would only recommend a certain action during raw conversion.


Hope that helps.

Definitely helps Daniel, thanks very much.


I always thought of the ISO setting as a physical thing, sending more (or less) electrical current to the sensor, changing its sensitivity, its gain. That's what you mean when you say -

Quote:

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Originally Posted by Daniel Browning

Currently, many ISO settings are applied as a digital manipulation to the raw file before it's saved.

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So the capture is defined (partly) by the ISO setting - it is"hard-wired" into the result so to speak, right?


But you're saying manufacturers could forgo that practice completely and instead write the ISO setting into the metadata. Interesting.


I can't help thinking there must be some reason they went the way they did. It has to be more complicated and more expensive to build an auxilliary amp or dedicated electrical pathways to change ISO. Isn't there some benefit to having it "hard-wired" into the capture?

Quote:

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Originally Posted by canoli

So the capture is defined (partly) by the ISO setting - it is"hard-wired" into the result so to speak, right?

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Yes. Some of the ISO settings use analog gain (amplifiers), but many of them are just digital manipulations.

Quote:

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Originally Posted by canoli

I can't help thinking there must be some reason they went the way they did.

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I should point out that they used to have this feature on the Canon 10D. It disappeared from all later cameras.


I can think of several possible reasons:


* Because they can. Customers accept all sorts of compromises at high ISO, even ones that are completely unnecessary (like this). Many photographers never even use high ISO. Canon knows that few people use it and the ones who do just have to be willing to accept additional unnecessary compromises.

* Because of Customer Service. Some customers will have a rude awakening when they realize that Canon has been deleting 1, 2, or more stops of their highlight headroom for no reason. Even if Canon buries the metadata feature in some custom function, and provides copious documentation, many customers will get thoroughly confused about what it is or does. Misconceptions will travel rapidly on the web about it, no doubt. Even some raw processing programs might get confused by the metadata. Adobe, for example, doesn't implement HTP correctly, it just does a linear push without preserving highlights. Other converters might not apply the push at all, so customers will wonder why it's too dark.

* Because of Management. Canon had ISO metadata in the 10D, but removed it in all later cameras. It may have been removed on purpose, by edict from Management. Software engineers wouldn't remove a feature that was doing the obviously correct thing and replace it with the obviously incorrect thing for no good reason. A good reason would be if the manager said "cripple the camera or I break-a-you-face."

* Because of Marketing. Perhaps the feature was removed because Canon wanted to save that trick for a rainy day, so they could come out with a new camera with "2 stops more dynamic range at ISO 6400!" without any development cost. If they were nefarious enough, they could sell a firmware update to all cameras going back to the 20D offering ISO 25600 as metadata, with 4 stops more dynamic range across all cameras. Sony sells $1,000 firmware upgrades on some of its high end video cameras, so there's precedent.

* Because of Engineering. It's possible that the software engineers responsible for the firmware are unaware of the issue, but given the high level of competence they've demonstrated I think that's highly unlikely. I don't think Hanlon's razor applies.

* Because of Bureaucracy. This is the most likely reason, IMHO. Many suboptimal things happen in big corporations. Maybe the 10D metadata ISO feature did not have the correct "addition of feature form" filled out, and the engineer who added it was fired because he didn't follow the correct procedure for requesting authority to add a new feature. Maybe the paperwork for removing the feature was easier than the paperwork required for leaving it in.


Who knows.

hmm, a number of scenarios, all sounding plausible - and thank your for your reply by the way - but they don't seem to account for what I assume is true: that it's not only easier for Canon to implement metadata ISOs, it's more profitable as well.


In your first scenario, they chose the route they did "because they can." But isn't this costing them money and angering their more knowledgeable user base? Or have I made an incorrect assumption? I'm working from the premise that "hardware ISO" (for lack of a better term) is 1) complicated to configure, requiring different strategies for different bodies, 2) demands continual R&amp;D money, and 3) is susceptible to malfunction. Maybe #3 is no longer a concern, but it is one more electrical system that could conceivably break down.


If it'smore profitable to use metadata ISOs, then I wonder
if the reason isn't the one you listed later, the one requiring a "nefarious"
motive.. to roll out a brand new camera body featuring "FOUR EXTRA STOPS of
Dynamic Range!" That would be irresistible when the financial outlay is zero (or close to it). On the other hand, perhaps the cost, when you consider the deals and arrangements that Canon must have with RAW converter manufacturers, not to mention their own DPP...they may have to recode their products...or would they?


Getting back to the real-world implications
- if I may. Those "extra stops," the ones we lose when we use higher ISOs -
they're gone forever, right? No RAW converter can get them back because,
to the converter, they don't exist. Those HLs have been pushed off the scale and were simply not captured
during exposure. The trade off is that we get (the same amount?) footroom - we get the low range frequencies. Do I understand that all correctly?



Thanks again D.

Quote:

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Originally Posted by canoli

Or have I made an incorrect assumption? I'm working from the premise that "hardware ISO" (for lack of a better term) is 1) complicated to configure, requiring different strategies for different bodies, 2) demands continual R&amp;D money, and 3) is susceptible to malfunction. Maybe #3 is no longer a concern, but it is one more electrical system that could conceivably break down.

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I think we have a misunderstanding. I have no problem with the hardware ISO (analog gain): ISO 200, 400, 800, and 1600. They're great and I want to keep them as an option. The only problem I have is with the software ISO (digital gain applied in camera): including the high ISO (3200, 6400), low ISO (50), and tweeners (50, 160, 250, 320, 500, etc.).


Instead of doing the digital manipulations in the camera like they are now, Canon should allow the user to do them in post.

Quote:

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Originally Posted by canoli

On the other hand, perhaps the cost, when you consider the deals and arrangements that Canon must have with RAW converter manufacturers, not to mention their own DPP...they may have to recode their products...or would they?

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It's so simple that it takes less than a dozen lines of Matlab code to load the entire raw file and apply the EC. In any case, Canon has no qualms about breaking compatibility and other raw converters. They even added "metadata ISO" in the form of HTP, which some raw converters ignore and others support incompletely (Adobe).

Quote:

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Originally Posted by canoli

Getting back to the real-world implications
- if I may. Those "extra stops," the ones we lose when we use higher ISOs -
they're gone forever, right?

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Right.

Quote:

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Originally Posted by canoli

No RAW converter can get them back because,
to the converter, they don't exist. Those HLs have been pushed off the scale and were simply not captured
during exposure.

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Right. Of course if it is only one or two channels that were lost, some converters will try to "guess" what the correct values would have been, but that's a separate thing.

Quote:

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Originally Posted by canoli

The trade off is that we get (the same amount?) footroom - we get the low range frequencies. Do I understand that all correctly?

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There is no trade off between metadata ISO and in-camera digtal ISO.
It's all negatives. You get clipped highlights, bigger files, and
reduced precision.


There is a trade-off between low analog ISO and high analog ISO: high ISO reduces headroom but increases footroom.

doh. Actually I didn't misunderstand, I just forgot the original subject of my thread (!) - we were justtalking about the tweener ISOs weren't we?...thanks for clarifying.


couple things:


Would you avoid using HTP if you're going to convert with ACR? I don't use HTP because I don't trust it ("understand it" is probably more accurate). The 40D manual says it "improves the HL detail," and the "dynamic range is expanded from the standard 18% gray to the brightest highlights." So that means if you meter a white dress it will actually record as white; you don't need to apply EC for white (non-specular) highlights? Anyway, since I may eventually want to start using it (bridal shots), will you share your thoughts on using HTP and then converting in ACR? Is DxO a better all-around converter? (the only other one I know besides DPP, which I don't like at all)


Something else: Does the "separate analog amplifier" used in the 5D (and the other bodies you mentioned) mitigate, or eliminate the negative effects of the 'tweener ISOs? I don't think you commented on that. (I do know there's a reason why that 5D churns out such buttery smooth, satisfyingly sharp pix - maybe it's the pixel pitch, those big ol' 8.2&micro;m receptor sites...?)


and finally, from earlier in the thread -

Quote:

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Originally Posted by Daniel Browning

I should mention that tweeners can sometimes help broken raw
converters. Canon's DPP, for example, doesn't use the correct white
point for many of their own cameras. They set it too low, ignoring
plenty of good data in the highlights completely.

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Does this explain why everything in DPP looks so washed out compared to ACR? The contrast, the colors, really everything looks so much worse in DPP. This is why I said I don't like it at all. I've opened both apps side by side and have been astounded how differently they present the same image. I can tweak away and get them to match, but the ACR image begins from a superior state to my eye.


As always, thank you Daniel - as much as you're willing to write...!

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Originally Posted by canoli

Would you avoid using HTP if you're going to convert with ACR?

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It's not ideal, but it's usable. Ideally we'd be able to reverse the +1 EC that Adobe applies behind the scenes, but I don't know how to do that. (The Exposure Compensation slider works, but it also actives the clipped highlights guessing algorithm, which is not always desirable.) It would be better to use a +1 EC with the brightness slider instead of the +1 linear (simple) EC that Adobe does behind the scenes.

Quote:

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Originally Posted by canoli

The 40D manual says it "improves the HL detail," and the "dynamic range is expanded from the standard 18% gray to the brightest highlights." So that means if you meter a white dress it will actually record as white; you don't need to apply EC for white (non-specular) highlights?

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Not quite. If you normally have ~3 stops between the tone that you want rendered 18% gray and "clipping", then HTP will increase it to four stops. So if the bride's skin is where you want 18% to be, and 3 stops causes a lot of the dress to blow out, then you can enable HTP and it will give you 4 stops: enough to retain that detail in the dress.

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Originally Posted by canoli

Is DxO a better all-around converter?

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I think it has higher image quality (especially underexposed high ISO shots) and more control over the image, but I don't use it because Lightroom is so much faster and easier. I like Bibble a lot, I had that before Lightroom. I hear good things about Silky Pix. You might also consider some of the free raw converters. I like Raw Therapee and RPP.

Quote:

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Originally Posted by canoli

Something else: Does the "separate analog amplifier" used in the 5D (and the other bodies you mentioned) mitigate, or eliminate the negative effects of the 'tweener ISOs?

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Half of them do. The other half are inferior to digital gain in post because they add their own small amount of read noise to the signal. The ideal solution would be 1/3 stop gain from the primary gain amplifier, but that's not really important to me since tweeners have performance that is close enough when implemented in post with digital gain.

Quote:

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Originally Posted by canoli

(I do know there's a reason why that 5D churns out such buttery smooth, satisfyingly sharp pix

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The large sensor size allows lenses to be used as they were intended, which results in much higher MTF (contrast) than using the same lens on a crop camera. It also allows much thinner DOF.

Quote:

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Originally Posted by canoli

- maybe it's the pixel pitch, those big ol' 8.2&micro;m receptor sites...?)

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Nope. Myth busted: smaller pixels have more noise, less dynamic range, worse diffraction, etc.

Quote:

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Originally Posted by canoli

Does this explain why everything in DPP looks so washed out compared to ACR?

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No, the white point bugs in DPP manifest as very slight differences in the amount of clipped data. I don't think anyone would notice it casually. The washed-out look just comes from a different default style of raw conversion. As you said, both can be tweaked to get different results, but the defaults differ by a bit.

Thanks Daniel, for your suggestions on a RAW converter. It sounds like they're all going to have certain strengths and weaknesses; one will perform better for a particular image and not so well on another (user knowledge being equal).


As far as my DPP vs ACR issue, if the explanation is simply "different converters use different algorithms, have different defaults," then apparently I'm in for some surprises when I check out the rest of them...

canoli,


You can check out SilkyPix free for 30 days. http://www.shortcutinc.com/cms/index.php


It is a fantastic converter. I use 99% of the time. It does an excellent job recovering the +1-3 ev worth of data. (even when using tweeners! LOL)


I will humbly admit though that75% of the photos from my last shootwere processed with ACR 4.6 in CS3. I used SilkyPix for the initial viewing, culling, etc. I processed the keepers but could not get my 5D outdoor flash shots to look right in print. So, I opened Bridge and went to work. The default "auto" results from ACR resulted in much better print output. Go figure. Usually for me, ACR butchers flash shots. The 40D + 50mm 1.4 @ f2.0 candid/journalist shots were fine right from SP.


It's also interesting to see ACR use brightness rather than exposure compensation to push up a dark image. I had three shots that were overexposed and it did do a -.9ev compensation automatically to bring those in line. I have to say, I was somewhat amazed at it's performance with this set of images. I usually do not like the output ACR gives.

Quote:

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Originally Posted by Daniel Browning

Ruevski's chart correctly shows that the read noise in ADU is lower, but what really matters is SNR, and that is not improved over ISO 100 (in fact it's 1/3 stop worse).

Quote:

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Originally Posted by Chuck Lee

And I'd rather have cleaner images than increased DR.

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In this case, ISO 100 provides both.

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Not at the same shutter speed and aperture as ISO 160. You would have to shoot ISO 100 at -.7ev to get the same speed/aperture combination. I'm willing to sacrifice a whole 1/3 stop or DR for that. The real world result is that I canhandhold at1/125th rather than 1/80th shutter speedand geta cleaner and possibly sharperimage.

Quote:

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Originally Posted by Chuck Lee

Not at the same shutter speed and aperture as ISO 160.

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Hmm, so - without getting in between you and Daniel's discussion (as it's obvious you both can talk at a higher level about this than me), I think you guys did agree that some 'tweens are better than others. 1250 over 1000, 500 over 320...(okay, that 2nd one I just made up). But there is consensus on using 1250 instead of 1000 right? And somebody mentioned that 160 on the 40D was "as good as it gets [with 'tween ISOs]."


Which 'tweener ISOs are less bad and which ones should be avoided? I realize it depends upon the camera. Personally I am particularly curious about the 40D as it's my main body for now.


One more question - is any of this relevant to amateur photography? We all want to maximize our body/lens' potential, get the best images we can, but are the differences so minute that it takes 100% views on 24" displays to notice them? Or will a photo shot at one of the especially bad 'tweeners, printed 8x10, look obviously worse than the same photo shot at a native ISO?


Thanks guys!

Quote:

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Originally Posted by Chuck Lee

Not at the same shutter speed and aperture
as ISO 160.

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Agreed. I should have clarified that I meant a different exposure.

Quote:

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Originally Posted by Chuck Lee

You would have to shoot ISO 100 at -.7ev to get the same
speed/aperture combination. I'm willing to sacrifice a whole 1/3 stop
or DR for that. The real world result is that I canhandhold at1/125th
rather than 1/80th shutter speedand geta cleaner and possibly
sharperimage.

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Me too. I only use ISO 100 when I have plenty of exposure to spare. (1/3 stop is such a small difference anyway.)

Quote:

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Originally Posted by canoli

Which 'tweener ISOs are less bad and which ones should be avoided?

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The "minus 1/3" ISO (160 320 640 1250) are fine, the "plus 1/3" ISO are suboptimal (125 250 500 1000). Everything above ISO 1600 is suboptimal.

Quote:

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Originally Posted by canoli

One more question - is any of this relevant to amateur photography?

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It's a pretty minor effect by itself. Just like HTP is a pretty small effect, and ALO is a pretty small effect. But when you start combining all these small factors, it results in a big factor. For example, ISO 250 by itself may not increase shadow noise enough to notice. And ISO 200+HTP by itself may not either. But combine 250+HTP and the result will be much more noticeable: the shadow noise is as bad as ISO 640. Add ALO into the mix and you can get people wondering why their ISO 250 shot looks like ISO 1600.

Quote:

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Originally Posted by Daniel Browning

Add ALO into the mix and you can get people wondering why their ISO 250 shot looks like ISO 1600.
<div style="CLEAR: both"]</div>

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What are your thoughts on ALO (Auto Lighting Optimizer)?


How about the "Tone Curve Assistant" in DPP?

Quote:

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Originally Posted by Mark Elberson

What are your thoughts on ALO (Auto Lighting Optimizer)?

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ALO and the tone curve assistance are nice. ALO doesn't affect the raw file (it's just metadata), and I use it when I'm shooting video to get a little more highlight headroom. But for stills I don't use it because I prefer to have more direct control of the tonal values and contrast myself.

Quote:

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Originally Posted by canoli

Which 'tweener ISOs are less bad and which ones should be avoided?

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160,320,640, &amp; 1250 are the good ones (DB would say "more acceptable") You can emulate these as follows:


160 = 200 + .3ev; 320 = 400 +.3ev; 640 = 800 +.3ev; &amp; 1250 = 1600 + .3ev (I call these the +.3ev tweeners)


125,250,500, &amp; 1000 are the bad ones (DB would erase you from his friends list.. LOL [:D])You can emulate these as follows:


125 = 100 - .3ev; 250 = 200 -.3ev; 500 = 400 -.3ev; &amp; 1000 = 800-.3ev (I call these the -.3ev tweeners)

Quote:

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Originally Posted by canoli

is any of this relevant to amateur photography?

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I would say yes. It is why I stated that "ISO160 is as good as it gets on the 40D." I made this statement, unfortunately, without listing any qualifiers which started the whole tangent over 100 vs 160.


If the camera is on a tripod and I have setup my 40D or 50D to shoot +1 to +2ev ECand I am trying with all of my intelligible talent and top end RAW conversion softwareto soak every last drop of noiseless dynamic range out of my exposure thenDaniel is correct that ISO 100 is better than ISO 160.


If I am handholding the camera, letting it meter the lightand am maximizing the shutter speed and/or the aperture then I believe ISO 160 is the best you can get in terms of a low noise image on the 40D. I could have done the exact same thing by shooting at ISO 200 +.3ev EC. The difference for me, the Missouri amateur, (even though I'm from VA)is that I don't have to think about. That's the amateur part. If the settings are available, why not make use of them?


So, ask yourself, would you rather shoot at ISO100, f4, 1/80th or ISO160, f4, 1/125th using the camera's metering? And the ISO 160 photo at these settings will be cleaner. I find it a simple "no brainer"


In pondering the discussion this morning it dawned on me that until the 5D MkII these +.3ev tweeners only offered an enhanced lower noise effect on the XXD "crop" sensor bodies. You can see on the Ruevski Sitethere is no advantagefor the 5D. If you take into consideration the increased zoom effect that 1.6X sensors create it parallels the increase in shutter speed that the +.3ev tweeners offer. For all practical purposes for the amateur it compensates for the extra reach of the lens. Following the focal length reciprocal rule you get:


200mm @ 1/200th on 5D FF@ ISO100


200mm(320mm equiv.)@ 1/320 on 40D @ ISO160


I find this very "practical" and very simple for the amateur photographer to follow.


Hope this helps.............[:D]

But why did Canon say that larger pixels have better noise? Acording to Canon larger pixels colect more light, requires less amplification, there for less noise.The wayI seeit isliketwo shallow dishes of the same depth but one is say 40% larger,and put it out side when raining.Which will have morewater, the lager one. In retrospect it's the same thing in sensors,the more light the pixel well collects in a certain amounttime,the less it needs to be amplifed.Canon confirms thishere http://media.the-digital-picture.com/Information/Canon-Full-Frame-CMOS-White-Paper.pdf.


I am missing something here?

Quote:

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Originally Posted by Fast Glass

But why did Canon say that larger pixels have better noise?

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Since this thread is about tweener ISO settings, I thought it would be a good idea to respond to your question in a different thread:


http://community.the-digital-picture.com/forums/p/1055/14445.aspx#14445