Exposing to minimize noise (when using high ISO)

[KmH]

Reading a few posts here I think it seems better to slightly overexpose the shot and bring it back in post. Is this correct, and if so what level is a ballpark recommended overexpose level? Thanks

There are limits, the following does not apply to specular highlights, and only applies to Raw image data files, not JPEGs.

If all 3 color channels are completely blown, there is no usable image data left and nothing can be recovered ("bring it back in post")

If 1 color channel has usable data (2 channals are totally blown out), some detail can be recovered, but not very much.

Having usable data in 2 channels is better still.

 

[analog.universe]

Reading a few posts here I think it seems better to slightly overexpose the shot and bring it back in post. Is this correct, and if so what level is a ballpark recommended overexpose level? Thanks

There are limits, the following does not apply to specular highlights, and only applies to Raw image data files, not JPEGs.

If all 3 color channels are completely blown, there is no usable image data left and nothing can be recovered ("bring it back in post")

If 1 color channel has usable data (2 channals are totally blown out), some detail can be recovered, but not very much.

Having usable data in 2 channels is better still.

I'd like to add (just for clarification), that this stuff is relevant for parts of the image you actually need exposed properly. If there's some background element, or light source, in the image, it may be completely acceptable to let that area blow all 3 channels, for the sake of getting better exposure on your subject. For the subject, and other important parts of the image though, KmH's advice is spot on.

 

[unpopular]

It is my philosophy that it is always best to avoid any blown hilights or plugged shadows, even if there is no detail there at all. The reason for this is because once you start drawing down the exposure in post, you'll end up with posterization in any region which is at 0 or 255. If that region is larger than a few pixels, then it will become noticeable.

I tend to think of specular hilights between 240-255, not pinned at 255.

 

[analog.universe]

It is my philosophy that it is always best to avoid any blown hilights or plugged shadows, even if there is no detail there at all. The reason for this is because once you start drawing down the exposure in post, you'll end up with posterization in any region which is at 0 or 255. If that region is larger than a few pixels, then it will become noticeable.

I tend to think of specular hilights between 240-255, not pinned at 255.

Whether or not you get posterization depends on how you draw your conversion curves. If you convert the highlights with a "soft-knee" non-linear style curve, you can avoid posterization (or quantization, or whatever you call it) errors. Also, when the ISO is at the levels we're talking about, there is often not enough dynamic range left to maintain proper highlights as well as proper shadows. The point being made is that exposing for the shadows gives you better noise control in post.

All the techniques we're talking about involve difficult shooting conditions. This isn't really about ideal circumstances or what you would do all the time. In a pinch, when you have to shoot at extreme ISO or not get the shot, these techniques help you get a better shot. It does involve much more work and attention to detail in post than if the shot was lit as you would prefer. None of the "slider" controls in any RAW converter I've used let you do this stuff effectively. You pretty much always need to draw something in by hand in one of the various curves tools.

 

[unpopular]

I hear what you are saying about posterization and curve, and that is absolutely accurate. Regardless, I think it's better to avoid clipping whenever possible and wherever suitable.

Obviously in a contrasty night situation where Zone V placement is going to be -8ev from the lightest region, you'll need to blow some hilights.

 

[WhiskeyTango]

It is my philosophy that it is always best to avoid any blown hilights or plugged shadows, even if there is no detail there at all. The reason for this is because once you start drawing down the exposure in post, you'll end up with posterization in any region which is at 0 or 255. If that region is larger than a few pixels, then it will become noticeable.

I tend to think of specular hilights between 240-255, not pinned at 255.

Whether or not you get posterization depends on how you draw your conversion curves. If you convert the highlights with a "soft-knee" non-linear style curve, you can avoid posterization (or quantization, or whatever you call it) errors. Also, when the ISO is at the levels we're talking about, there is often not enough dynamic range left to maintain proper highlights as well as proper shadows. The point being made is that exposing for the shadows gives you better noise control in post.

All the techniques we're talking about involve difficult shooting conditions. This isn't really about ideal circumstances or what you would do all the time. In a pinch, when you have to shoot at extreme ISO or not get the shot, these techniques help you get a better shot. It does involve much more work and attention to detail in post than if the shot was lit as you would prefer. None of the "slider" controls in any RAW converter I've used let you do this stuff effectively. You pretty much always need to draw something in by hand in one of the various curves tools.

The way I've been reading this thread, I'm interpreting the recommendation as "shift the histogram as far to the right as you can WITHOUT clipping." I'm not seeing anyone suggest to blow the highlights, just to shift as far to the right as possible without blowing them out.

On the other hand, as someone else pointed out, if the only thing getting blown out is a lightbulb in an unimportant part of the frame, let it blow...

 

[Derrel]

Careful, methodical, somewhat extreme curves adjustments like analog.universe mentioned are one of the easier ways to correct for badly-bungled exposures.

"Some" cameras seem to be better than others when the photographer over-exposes and then "pulls back" the exposure in post processing.

As far as minimizing noise when shooting at High ISO values---one of the absolute best things you can do is to try and get a good white balance for the lighting conditions at hand, and actually shoot "to" a white balance. I think this is an overlooked technique, and a lot of people think that letting the WB run in AUTO mode is acceptable, but I find that many times, AUTO WB leads to more work than shooting "to" a specific WB. With a WB established, the color information can be calculated by the camera as it does its demosaic routine of the RGB data, and an "appropriate" WB will generally make life more pleasant when the files make it back to the computer. (Setting one,specific WB can be a bad idea inside some arenas where the lights color temps constantly cycle and WB shifts with the AC current...)

 

[analog.universe]

Careful, methodical, somewhat extreme curves adjustments like analog.universe mentioned are one of the easier ways to correct for badly-bungled exposures.

"Some" cameras seem to be better than others when the photographer over-exposes and then "pulls back" the exposure in post processing.

As far as minimizing noise when shooting at High ISO values---one of the absolute best things you can do is to try and get a good white balance for the lighting conditions at hand, and actually shoot "to" a white balance. I think this is an overlooked technique, and a lot of people think that letting the WB run in AUTO mode is acceptable, but I find that many times, AUTO WB leads to more work than shooting "to" a specific WB. With a WB established, the color information can be calculated by the camera as it does its demosaic routine of the RGB data, and an "appropriate" WB will generally make life more pleasant when the files make it back to the computer. (Setting one,specific WB can be a bad idea inside some arenas where the lights color temps constantly cycle and WB shifts with the AC current...)

Good point. I think one of the reasons for this is that often when in the low light conditions where this is relevant, the white balance of the scene is so extreme that the auto mode doesn't "believe" it or something. I feel like there are constraints on how far the auto will let white balance go. I find if I'm shooting a band in a bar or something, the white balance is way warmer than tungsten, in the ~2k's kelvin somewhere.

This is especially important when you're reading histograms to determine exposure. In the bar scene I mentioned, unless you've selected the proper white balance, the red channel looks like it's blowing when it's really not. Meaning you actually could've safely pushed farther to the right had the white balance been correct.

 

[unpopular]

It is my philosophy that it is always best to avoid any blown hilights or plugged shadows, even if there is no detail there at all. The reason for this is because once you start drawing down the exposure in post, you'll end up with posterization in any region which is at 0 or 255. If that region is larger than a few pixels, then it will become noticeable.

I tend to think of specular hilights between 240-255, not pinned at 255.

Whether or not you get posterization depends on how you draw your conversion curves. If you convert the highlights with a "soft-knee" non-linear style curve, you can avoid posterization (or quantization, or whatever you call it) errors. Also, when the ISO is at the levels we're talking about, there is often not enough dynamic range left to maintain proper highlights as well as proper shadows. The point being made is that exposing for the shadows gives you better noise control in post.

All the techniques we're talking about involve difficult shooting conditions. This isn't really about ideal circumstances or what you would do all the time. In a pinch, when you have to shoot at extreme ISO or not get the shot, these techniques help you get a better shot. It does involve much more work and attention to detail in post than if the shot was lit as you would prefer. None of the "slider" controls in any RAW converter I've used let you do this stuff effectively. You pretty much always need to draw something in by hand in one of the various curves tools.

The way I've been reading this thread, I'm interpreting the recommendation as "shift the histogram as far to the right as you can WITHOUT clipping." I'm not seeing anyone suggest to blow the highlights, just to shift as far to the right as possible without blowing them out.

This is why I meter the lightest region and push it as far as I can. If their are any plugged shadows then I know that compensating for them would blow the hilights.

On the other hand, as someone else pointed out, if the only thing getting blown out is a lightbulb in an unimportant part of the frame, let it blow...

[...]So then I have to make a decision - are the hilights worth blowing? In the case of a light source, absolutely - and such I'd very meter off the lightbulb anyway.

---

But as I said earlier ETTR does not make a lot of sense in typical artifically-lit low-light situations which tend to have huge contrast ratios.

 

[MReid]

Turn off ADL, exposure compensation at 0.

Manual, set lens wide open and lowest shutter speed you can use to get acceptably sharp photos,
Take a shot at iso 400 800 1600 2000 etc etc go up the ladder.
Eventually you will reach the iso which gives you an as far as possible (as evidenced by checking your histogram and blinkies) exposed to the right exposure without blowing it out. Lock everything in and shoot that is the best you can do with your camera and lens combination.

If your histogram shows something is blown out...that is why you also need your blinkies on to tell you if the item being blown out is something you care about.

 

[MLeeK]

When you under expose you introduce more noise by boosting in post. When you overexpose you hide noise when you reduce exposure in post.

Yes if you favor under exposing then trying to fix it in post, you are again being counter productive and will gain noise. Increasing signal gain to gain more light is my least favorite way of doing so. I can accept an ETTR at base or close to ISO, but not at very high ISO

I get what you're saying...and I don't disagree. But the message behind ETTR, that often gets missed, is that underexposing and fixing is post, is the worst thing you can do. So rather than under expose, raise your ISO (thus moving the exposure to the right) and you will end up with less noise than if you had tried to raise the brightness in post.

But yes, if you can reach proper exposure at an ISO that you're comfortable with...then feel free not to raise it.
But some people have found that even lower noise levels can be accomplished (in the final image) by raising the ISO (thus exposing more to the right) and then normalizing the image is post. I'm sure there is a limit, for each camera/sensor/processor where raising the ISO is a worse option...and that's for everyone to experiment with and find what works for them.

You said that far better than I could!

In the gymnasiums and conditions I am working in there is no choice but to use a high ISO, period. You know, those candle lit school gyms? That's where I am at.
I HAVE to have my shutter speed up there to keep the motion blur at bay. I CAN use f/2.8, but the sharpest point of my lens is NOT at 2.8. With high ISO's I want to make sure my lens is SHARP. I TRY to shoot at f/4, but even f/3.2 is a sharpness improvement. Once I am there I am hitting a wall. If I get good exposure at ISO 3200 I have noise and less detail in my brightest shadows, let alone any darker shadows. If I boost up to ISO 6400 or even 12800 I have no noise issue in my highlights and less problem in my shadows. When I reduce that in post processing and add my black point level it improves even more. Combine that with the power of noise removal in ACR/Lightroom at even low numbers and I am golden-even at 12800 on my 7D or 50D.

My highlight warnings are on. I am pushing exposure to the point JUST before I'd have an unacceptable blow out. if I am shooting white jerseys (most sports have one white, one color...) and the white is blowing in SOME spots I am pretty safe. Highlight warnings tell you that you are completely blowing at least ONE color channel. If I am blinking on the highlights of the jersey, but retaining the wrinkles and textures I am good. NEVER do you want to wantonly (I like that word today) over expose. It has to be done properly.

 

[analog.universe]

Relevant to this discussion is that ISO settings like "HI" and "HI2" etc are digital cheats for the most part. All this theory is less applicable because these settings are not simply voltage gain on an analog amplifier like the rest of the ISO scale. You _could_ technically achieve the same results in post that these settings get you in camera.

 

[KmH]

It is my philosophy that it is always best to avoid any blown hilights or plugged shadows,

An impossibility most of the time because of dynamic range limits and the linear response an analog image sensor has.

Specular highlights, by technical definition, are 100% blown.

 

[unpopular]

An impossibility most of the time because of dynamic range limits and the linear response an analog image sensor has.

This has never been my experience except in the MOST contrasty of situations.

And so what? Even if specular were at 95% and not 100%, how much shadow detail am I really going to squeeze into the lower 5%, especially considering noise performance?

 

[analog.universe]

If we're just talking about specular highlights, you can get a lot more than 5%. Once it's blown, it's blown. Whether it's 1/3 stop over or 4 stops over. If that's the only thing in your image that's going, then you can sometimes push several stops without blowing anything else, which is a considerable amount of shadow detail.