Push vs. ISO

[thepancakeman]

So here's a question, to which I'm sure the answer varies by body, but I'd still be interested in the answers:

Are you going to get more noise in an image by using a higher iso or by underexposing at a lower iso and then pushing it in post? 

Personally I use Lightroom, but I'm not sure whether software choice affects the answer, so maybe that's part of the question as well.

[unfocused]

Great question. I've wondered the same thing as well.

On a related matter, I believe I have read that with digital, it is better to err on the side of overexposure than underexposure. This  has been hard for me to adjust to, because in the film world, an overexposed transparency was almost always worse than an underexposed one.

I tend to find that I prefer the look (on-screen) of a file that is maybe 1/3 to 1/2 under what the camera selects, but I wonder if I am making a mistake and should instead adjust the image in RAW.

[ejenner]

Well, it's a simple test to do yourself.  I have found that it is always better to up the ISO than to push with my T1i and 5D II processed from Raw with Bibble, DPP or ACR.   With the 5DII pushing 1 stop vs upping ISO is almost the same as far as I can tell.

I did wonder, especially with the difference in noise levels between ISO 400 and 800 with the T1i - but no, you are better off with the higher ISO.

This is what you should theoretically expect since the ISO is essentially just upping the gain, but right out of the sensor before introducing much of the electronic noise.  When you push the exposure you increase the signal and all the noise at the same time.

[gferdinandsen]

An interesting question.  I personally never really push more that about .66EV in ACR.  Since the advent of digital I do a lot more bracketing when I shoot so I find I don't have much need to add a lot to the exposure in ACR.

That being said, I find I can easily up the exposure by +2EV in ACR without a significan loss of quality.

All in all, I would rather shoot at ISO 100 if at all possible, I'd really like to have the option of ISO 25 or 64 too.

I guess there are several variables, on my 5D2, I can shoot at ISO 3200 indoors or at night so there is less of a need to push the exposure in ACR than other model of cameras.

I'm not quite sure I answered your question, but to sumarise, I would prefer to have the exposure as correct as possible on the CR2 file so I only have to make small ajustments in ACR

[awinphoto]

For the sake of arguement I popped out my 5d2 and snapped 2 photos of my small studio product photography setup which has blownout highlights all the way down to crushed shadows and all the light falloff creating all the midtones you could desire... ... an extreme situation mind you, but one taken at ISO 2500 and one at iso 400... shutter and aperture being the same... in photoshop I pushed the levels on the underexposed image and while the raw photos were a lot closer in tonality than my jpeg offerings of the same image, the ISO changed in camera (ISO 2500) came out the clear winner...  The raw 2500 has luminous (black and white noise) when zoomed in a hair more than 100% but the pushed image came out with more chroma noise (colored noise).  the luminous noise is easier to get rid of with noise filters than chroma... I've heard somewhere that with digital files it's pretty safe to underexpose 1 stop and compensate in photoshop, but anything more than that, as in my test, you're asking for trouble

[awinphoto]

It's also worth noting that the lower ISO image in my test came out warmer than the ISO 2500 image which came out cooler... both shot with AWB and my lights are constant output lights so nothing color wise changed... For what it's worth (the cooler color was more accurate to the actual sceen) albeit the warmer color was more pleasant to look at. 

[thepancakeman]

Well, it's a simple test to do yourself.

And yet another "why didn't I think of that??"   

I'll run some tests tonight and get back to you with results.

[dr croubie]

OK, here's my first test, as it were. This doesn't compare low- to high-iso, but it's some bracketed shots I had floating around.
7D, Samyang 35/1.4, canon-brand ND8, iso100, f/6 or so.
3 bracketed shots, -4/3 EV was 1/400s, 0EV was 1/160s, +4/3EV was 1/60s.
All processed the same in DPP, WB to daylight, standard style, sharpness 3, NR was 0/0, ALO PIC etc off.
100% crops from the centre of the frame.
The 1/400s shot was bumped up +1.33EV, the 1/60s shots was cut down -1.33EV in DPP. Certainly the 1/60s cut down looks better. As far as noise goes, it's best to just have everything set as high as possible to on the point of 1 pixel hitting its saturation point, no blowouts and least noise (but it's not always practical).

It's raining and grey here, so I can't go shoot a nice-looking bracket with variable ISO to answer the OP, maybe i can find one floating around in my collection later.

[neuroanatomist]

I expect you'll find results consistent with awinphoto's test.  The general rule is ETTR = expose to the right, meaning with digital, your best bet is to set your exposure such that your histogram is as far to the right (i.e. 'bright') as possible without clipping the highlights.  Often, you can keep the ISO low and get there with aperture and/or shutter speed.  But, if you've got the aperture and shutter speed you want for the shot, you're better off bumping up the ISO in the camera rather than in post.  Couple of nuances there, though - you should be using the RGB histogram, not just the luminance histogram or the 'blinkies' (highlight warning that's tied to the luminance histogram).  Clipping can occur in just one or two color channels, and be masked in the luminance average.  Even so, note that you can't entirely depend on the RGB histogram - that's based on the JPG preview created within the RAW file, and that preview is subject to the camera settings.  So, to judge exposure in-camera, as best you can at any rate, turn off the modifiers like ALO and HTP, and select Neutral or Faithful as your Picture Style (Standard boosts certain colors, and can result in apparent clipping when there's actually more headroom).

[Meh]

Great advice as usual neuro.  Noise will always be minimized by getting the brightest image you can get without blowing any highlights.  One line of your response is what actually answers the OP...

But, if you've got the aperture and shutter speed you want for the shot, you're better off bumping up the ISO in the camera rather than in post.

But why is that the case?  In other words, why does the camera do a better job of increasing the exposure (by ISO setting that is applied after the exposure) than adjusting the exposure in post (DPP, DxO, LR, etc.)?

[neuroanatomist]

Great advice as usual neuro.  Noise will always be minimized by getting the brightest image you can get without blowing any highlights.  One line of your response is what actually answers the OP...

But, if you've got the aperture and shutter speed you want for the shot, you're better off bumping up the ISO in the camera rather than in post.

But why is that the case?  In other words, why does the camera do a better job of increasing the exposure (by ISO setting that is applied after the exposure) than adjusting the exposure in post (DPP, DxO, LR, etc.)?

It's not that the camera does a better job at adjusting ISO, per se.  What ETTR does is maximize the amount of usable data in the RAW file - capturing the most shadow detail possible without throwing away any highlight detail, given the constraint of the sensor's dynamic range.  If you underexpose (which may be more pleasing in appearance), you may be throwing away shadow detail.  Granted - maybe it's not detail you wanted.  But if you don't capture it, you'll never have the option - data can be thrown away in post, but not created if they weren't captured in the first place.

[awinphoto]

Great advice as usual neuro.  Noise will always be minimized by getting the brightest image you can get without blowing any highlights.  One line of your response is what actually answers the OP...

But, if you've got the aperture and shutter speed you want for the shot, you're better off bumping up the ISO in the camera rather than in post.

But why is that the case?  In other words, why does the camera do a better job of increasing the exposure (by ISO setting that is applied after the exposure) than adjusting the exposure in post (DPP, DxO, LR, etc.)?

I'm not going to pretend i'm an expert at sensors, neuro may provide a better explanation, but I would have to say it's because the camera/sensor is the first to see and process the file and can do what it needs to do with those beautiful digic processors and sensor to provide the best image possible... where as when you do it in post, the computer is pretty much blind in the essence that all it "see's" is code and information of the digital file that your camera CREATED... Then when you do heavy post to it, it's amplifying the information of the digital file but basically it's creating information where information wasn't there to begin with, so your left with the noise as a result...  It didn't/doesn't know exactly what was there so it does it's best to guess for you.  It was kinda the same in film... you could underexpose and push the film in development or overexpose and pull the film, but it never was quite the same as nailing your exposure the first time... and even at that, like digital, you didn't want to push/pull your film more than 1 stop max unless you wanted some funky effects. 

[branden]

Simply put -- ETTR works because the "grain" in a digital photo is in the darker areas of the image and not in the lighter areas. When there's more light reaching the sensor, there's more separation between the "information" and the electronic noise.

That said, nothing is as good at reducing noise as reducing the size of the photo.

[Meh]

Great advice as usual neuro.  Noise will always be minimized by getting the brightest image you can get without blowing any highlights.  One line of your response is what actually answers the OP...

But, if you've got the aperture and shutter speed you want for the shot, you're better off bumping up the ISO in the camera rather than in post.

But why is that the case?  In other words, why does the camera do a better job of increasing the exposure (by ISO setting that is applied after the exposure) than adjusting the exposure in post (DPP, DxO, LR, etc.)?

It's not that the camera does a better job at adjusting ISO, per se.  What ETTR does is maximize the amount of usable data in the RAW file - capturing the most shadow detail possible without throwing away any highlight detail, given the constraint of the sensor's dynamic range.  If you underexpose (which may be more pleasing in appearance), you may be throwing away shadow detail.  Granted - maybe it's not detail you wanted.  But if you don't capture it, you'll never have the option - data can be thrown away in post, but not created if they weren't captured in the first place.

Thanks but you're missing my point I think.  Keying on your statement "you've got the aperture and shutter speed you want" I'm thinking of a situation where you just don't want or can't increase your exposure any further but the camera meter is telling you you're 2 stops underexposed.  You've got two choices... take the shot and adjust the exposure in post or increase your ISO by two stops.  This is, I think, what the OP is asking.  You're advice was to go with the ISO increase.  I'm asking why that's better than adjusting in post.

[dr croubie]

OK, I got bored and did another test, even though it's a bit cloudy, but the light stayed constand which is what counts.
7D, Samyang 35/1.4, f/8, on a tripod pointed at my muppet-skin rug.
I set the mid-point for metering at iso400 using liveview, 1/160s, then took shots at iso 100/200/400/800/1600/3200.
DPP processed all the same, WB Cloudy, Standard style, sharpness 3, 0:0 NR on all shots. Saved as 100% quality jpg, then cropped in GIMP and saved as 100% quality jpg.
The iso3200 shot I could only drag down 2 steps in DPP, so I dragged it down by another "75" (75 somethings?) using GIMP's "brightness/contrast" toolbox. Either way, iso3200 is rubbish, blowouts didn't come back and contrast is shocking. I'll put the DPP-processed shot in too, which will be +1EV than all the others...

<edit, just my luck, the page split. I'm moving images to the next page to make it clearer.>