Noise - 'Exposing to the Right' versus Lower ISO

[ed_hurst]

Hello All,

 

Having studied some of the excellent information on the web (mostly found via Photo.net), I believe that

I understand the merits of 'exposing to the right' - i.e. minimising noise by exposing to the right hand

side of the histogram (but avoiding clipping), thus using the full sensitivity of the sensor. I tend to get

the exposure effect I want by then reducing the apparent exposure during RAW conversion.

 

However, when using long shutter speeds or wide apertures is impossible (e.g. because I am shooting a

moving subject or if I do not have a tripod with me and want greater depth of field), then 'shooting to

the right' often involves increasing the ISO - something which of course tends to increase noise. So I

am increasing noise in order to do something that decreases noise!

 

My question is - is it usually better to do this, because 'exposing to the right' decreases noise by a

larger amount than the noise increase caused by the required increase in ISO? Or is it better to 'expose

to the right' only when doing so does not require a higher ISO (because the increase in ISO wipes out

the advantage of 'exposing to the right')? If anyone has any actual data on this, that would be much

appreciated.

 

Best wishes, and thanks in advance for your help.

[alexdi]

While I suspect it's theoretically better to expose right, even at the expense of ISO, it doesn't matter in practice. It's robbing Peter to pay Paul. More recent DSLRs have more bits to play with in the shadows anyway, so even where an ISO shift isn't required, it doesn't make much of a difference.

 

DI

[beauh44]

Hi Ed, I'm afraid I don't have any "actual data". And while I understand the rationale behind "ETTR", I also understand that one can't always do it for many reasons, one of which you cite. It's also hard to get a low-key photograph when I "ETTR". I think when one is shooting still landscapes it's a bit easier to pull off. Like most everything in photography there are usually trade-offs and compromises. When confronted by the situation you describe, I personally increase the ISO and try to (mostly) expose to the right because the software to combat noise has gotten so good. One surefire way to get a LOT of noise though is to <B>both</b> "expose to the left" (underexpose) <B>and</b> use a high ISO value.

[peterlyons]

I don't have the actual data you're requesting, so I'll just piont out that the latest issue of

Digital Photo Pro has a pretty extensive article on it, that could be worth reading. I haven't

finished it myself yet, so I don't know whether the issue of ISO and noise is addressed.

[ronald_moravec1]

Expose no more than necessary to get the detail required in the darks as long as you do not push the brights off scale to the right when making raw files. Same as with film. Use the converter to adjust exposure /brightness to get the highlights where you want them same as in developing film.

 

Overexposing and pulling back to darken is not required.

[mark u]

The answer depends on how your camera implements different ISO settings. There is clear evidence to suggest that some EOS DSLRs produce noisier images at "intermediate" ISO settings rather than the whole stop 100, 200, 400, 800, 1600 sequence - probably because at least some of the implementation of the intermediate settings is not based on hardware amplifier gain. Once the gain required by the ISO setting is above one data number increment per electron, there is nothing further to be gained by increasing ISO through hardware amplification or otherwise (hence why the highest ISO setting may come with warnings). You are only using the full sensitivity of the sensor at its "base ISO". In general, you will do better to use a higher ISO setting rather than pushing an underexposed shot from a lower ISO, providing the selected ISO is on the "main sequence" and is the lowest that will give a well exposed result.

[ed_hurst]

Good point. For the sake of argument (and only to look at one set of variables at once),

let's assume that this factor does not apply. I.e let's assume that the camera implements

all increments properly (which I think is the case with the 1 series cameras)...

[ed_hurst]

Ronald - for a description of why it might be best to over-expose (without clipping -

keeping the scene within the sensor's dynamic range) and then adjusting to darken during

RAW conversion - see this link:

 

http://luminous-landscape.com/tutorials/expose-right.shtml

 

I'm no expert, but it seems logical to me...

[jason_hall4]

http://www.digitalphotopro.com/tech/exposing-for-raw.html

 

Here is a link to the article Peter mentioned.

 

Jason

[matt_needham]

Different photogs using the same gear and seemingly the same techniques often get different results. Personal testing is the only way to find out what works best for you. Compare 2 photos of the same scene: one exposed normally at a lower ISO and one exposed to the right at an ISO one stop higher. Pixel peep if you like, but I'd compare prints. In my testing the only thing that significantly increased noise to the point where it was more visible in a print was underexposure and/or extreme tweaking in processing. I would much rather increase ISO than chance underexposure or camera shake. With both my 20D and 5D I find that ISO 1600 exposed a bit to the right is much cleaner looking than anything I ever got on ISO 400 film, so I'm happy with it. After reading the Jeff Ascough interview in the Weddings forum I've been even trying to overcome my fear of ISO 3200.

[santa1]

Ronald gives bad advise. Really bad advise. Do your homework on this and you'll see why for most images you DO want to expose to the right. Many images do not require the full breadth of the histogram in terms of dynamic range. For those images one could expose toward the left, right or even the middle. Following Ronalds advise you would expose to the left ("no more than necessary to get the detail required in the darks"). This would record a whole lot less information and anyone that would follow this advise would be poorly served. I'll leave it to him, and to others to do the actual research on exposing to the right and why it is normally quite important. There are even times when you want to expose BEYOND the right....a person in front of a bright window where you don't care if the window is blown out but you want the person to be properly exposed. There are very few times when exposing to the left makes any sense at all, and exposing "no more than necessary" so as to simply make sure your blacks are just within the histogram, as Ron explains, is quite possibly the most poorly informed advice I've seen here in a long time. A few minutes googling "expose to the right" should provide enough of a technical explanation. Hopefully Ron will study up on this a bit and gain some knowledge of the basics here.

[rhaytana__tim_adams_]

I'll chime in hastily here, as I have only a few minutes to post.

 

I read the Digital Photo Pro article with interest, as I respect and am a fan of Andrew Rodney's technical writings. I also read the Luminous Landscape article.

 

Trouble is, the shooting I do is all 'on the street' type stuff, with no time to fiddle with settings. I gauge the scene, take my best guess, adjust camera settings accordingly, fire away, and either get the shot or say goodbye to the shot forever. Few opportunities to bracket.

 

After reading the tutorials, I experimented with setting camera exposure to + 2/3 stop for a couple of days.

 

The result: too many blown highlights. The Luminous Landscape article indicated to ETTR until highlights are blown -- but that happened as soon as I jacked up camera exposure in the plus range.

 

A fair trial? Probably not. But I abandoned the experiment.

 

For wildlife/nature photographers, I definitely can see ETTR ... and that's what Luminous Landscape is mostly geared for. But not for 'decide in an instant' street photography, at least not for me.

 

FWIW, though, the two articles linked above convinced me to stop shooting -1/3 or -2/3. I used to do that occasionally. No more.

[kahkityoong]

I have no interest in graphs or technical explanations as outlined above. However I have

made more low-light exposures than I care to count. My experience with my Canon 5D is

that to minimize noise a low ISO (100 ideally) coupled with a rightward exposure. Low-light

exposures at high ISO are a recipe for noisy pictures. If you're going to use ISO 400 and

higher you better make doubly sure that expose to the right. Without clipping your highlights

of course.

[peterlyons]

Rhaytana, I think your case is valid. If it's not working for you, by all means, go back to

exposing as you used to.

 

In my case, I find that ETTR makes lots of sense. I've been doing it for several months

now, and am happy with the results.

 

My main subject is sailboats. So, often, I have a lot of bright tonal values in my scenes

anyway (white sails and hulls). If I want those to look white rather than gray, I can't trust

autoexposure. Well, actually, I do use autoexposure, but I adjust my exposure

compensation based on the scene. As a rule of thumb, I rarely ever shoot below +1/3

stop compensation, unless I'm shooting a dark subject, or a subject against a dominant

dark background. In those cases I often dial down to -1/3 stop. Overcast days are when I

most like to overexpose. The scenes are low contrast, and the bright gray sky fools the

meter, making the whole image unpleasantly dark. So in bright overcast, I go with +2/3,

and in heavy overcast, I'll do +1 or even +1 1/3, depending on my subject. I rarely ever

blow out a white that I need, and I have lots of good detail in the shadows.

[KenPapai]

Peter -- I appreciate your answer a lot. It's simple, to-the-point, and easily emulated by anyone reading this (I would hope). Others advice was good (or too entirely theoretical to map to practical space) and some advice was a bit... I won't say it. ;)

[gerrymorgan]

If anyone is still in doubt that exposing to the right (ETTR) is a good idea (assuming, of course, that it is practical for your shooting situation), try the following experiment. First take a shot without exposing to the right. Then take another, exposing to the right. On your computer, compare the file sizes. Notice that the file containing the ETTR photo is larger. This is because you get more information when you expose to the right. More information to work with in your photo is a good thing.

[JeffOwen]

In an attempt to avoid blown highlights I use the histogram on my 20D and watch for the flashing areas to see whether I have achieved a 'good' exposure. I was meticulous to achieve this on some shots taken this Autumn however I found that the RAW processor had to tweaked up to two stops for underexposure! I'm as confused as Ed over the 'expose to the right' recommendation.

[obi-wan-yj]

Just last weekend, I spent the night in the Strategic Air & Space Museum near Ashland, Nebraska. I didn't have the good sense to bring my tripod (was packing for the Cub Scout event earlier that day), but the lighting in the museum after dark was so cool that I couldn't help taking a few hundred handheld photos with my Canon 400D and Sigma 17-70 f/2.8-4.5 lens.

 

Most of these shots were at ISO 800 with exposure times in the 1/4 to 2-second range. Of course, I had to brace my body (and sometimes the camera) pretty significantly. I took a few shots at ISO 400 or 1600 as the natural lighting allowed or required. Since most of my subjects were static airplanes, I was able to take multiple versions of each shot while varying settings. In general, I found that ETTR by one stop helped with shadow definition, even when it meant using ISO 800 instead of 400. Moving from 800 to 1600 causes a dramatic increase in noise, so the benefit of ETTR wasn't as noticeable, but it still seemed to be there. I don't think I'd choose 1600 over 400, though. ETTR doesn't help *THAT* much.

 

Although I haven't taken the time to re-adjust the brighter ones, you can see a few of the shots from the following morning at

 

http://tatooine.jedi.com/digicam/2007/20071021/

 

I don't have the bulk of the photos from the previous night online yet. When I do (hopefully soon), they'll be at

 

http://tatooine.jedi.com/digicam/2007/20071020/

[zigzag]

And as a supplementary: how does 'Highlight Tone Priority' (HTP = 40D), preservation of highlights affect this, not having a 40D I cannot investigate but would this lead to 'Expose Further To The Right' (EFTTR)?

[zigzag]

One other point of note: when shooting with the intention of using digital blending or HDR, the whole AEB sequence can be shifted to the right, with the most EV +ve frame being carefully placed to avoid blowing highlights, i.e. a +/- 1.3 AEB, may be offset by a bias of +1/3 (e.g.), taking care with the (+1.6 = 1.3 + .3) frame does not blow highlights. I would expect this to be optimal but in rapidly changing light it is fiddly at best - it is something I am investigating currently with landscapes.

[david.seaton]

Jeff just a note on your comment:

 

"In an attempt to avoid blown highlights I use the histogram on my 20D and watch for the flashing areas to see whether I have achieved a 'good' exposure...."

 

The flashing highlight blown indicator on the LCD is based upon the JPG not the RAW, if you take a second exposure and over expose by 1.5 or 2 stops and STILL get the flashing areas on your LCD, then you've truly blown those areas in the original shot. If not, the raw will should still have detail

[john_g10]

I read this before somewhere and tried to push it almost to the rightmost but no clipping but my pictures were all overexposed. No dice.

[andy_jones2]

John G wrote "I read this before somewhere and tried to push it almost to the rightmost but

no clipping but my pictures were all overexposed. No dice."

 

You did compensate for it when you developed the images, right? If you expose to the right

it means you are deliberately overexposing the image compared to the ideal, so you have to

darken it when you develop it during processing. Sometimes, this concept is missed in the

recommendations for ETTR.

[john_g10]

No. The book that I read (John and Barbara Gerlach's) didn't mention that. I'm also not into post processing picture except cropping.