aphelps Loc: Central Ohio

What is the procedure for "normalizing" exposure in pp after exposing to the right? What do we accomplish by ettr and then coorecting in post?

Ysarex Loc: St. Louis

What we accomplish is the least amount of noise and the maximum amount of DR possible. Use all of the sensor's capacity rather than just a portion of the sensor's capacity.

Here's an example. The scene is very high contrast to begin with -- the scene is backlit. The first image below is the JPEG my camera created. CAVEAT: My camera could make a better JPEG from this scene if I wanted that. I would have to reduce exposure and I could use my cameras functions to apply a lower contrast tone curve and come up with a better SOOC JPEG. Bottom line to that however is I would have to reduce exposure.

I inset a histogram for the JPEG in the lower left corner and you can see that the camera software nuked the image highlights to hell. That should be a nice sunny day blue sky there. Now if I did try to use the camera software to get a better image the reduced exposure I'll have to use is going to make those shadows on the right side even darker and noisier. Detail that's in those shadows will swamp into noise with less exposure.

Although the highlights in the camera JPEG are nuked those same highlights are placed right at the sensor's maximum capacity limit -- they're recorded in the raw capture. And that means they're mine to process. The second image below is my processed version of the raw file. I did record the sky and I was able to process it to my requirements. Because I exposed as much as the sensor could handle I was also able to get the right side shadows the way I want them with as little noise as possible and as much reach into the shadows as possible. That's where less exposure would have cost me dearly.

There is no single "normalizing" process you can apply in post. Different images are different and your editing software will start by showing you an image closer to the camera JPEG. You're going to do some work then to get the result you intended.

It's a risky game to play. If you try this and you're wrong and you blow those highlights in the raw capture it's checkmate. That's why your camera engineers designed the processing software in your camera to hedge back some and get a good JPEG from less than a full capacity sensor exposure.

Joe

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Hip Coyote

what joe said....Ive found this to be true and very helpful. It saved me in a lot of situations.

williejoha

By exposing to the right, the shadows will Be less grainy. As long as there is no clipping in the highlights you will be able to pull them back in PP. This will give you much better control over your overall shot. Hope this helps.
WJH

CHG_CANON Loc: the Windy City

Without the same software tools and a video tape of the process, it's hard to go into more detail than Joe's overall description, above. The 'in practice II' link below gives some screen prints at various comparative steps in the process for one example image:

ETTR in Practice

ETTR in Practice II

aphelps Loc: Central Ohio

Thank you Joe. Very comprehensive response.

bleirer

I'm walking around with the belief that it is only useful at base ISO. If you have to raise ISO to get the histogram to move right, you might as well not, because raising ISO is not the same as increasing actual exposure and you end up with no improvement. On the other hand if you can get more exposure using a tripod or being more careful about depth of field it is worth the effort.

TriX Loc: Raleigh, NC

👍👍 Excellent and concise Joe.

CHG_CANON Loc: the Windy City

There are numerous issues at play, including the camera brand and sensor type, particularly the idea of ISO invariance. If your camera is not "ISO invariant", like the largest population in the world - Canon EOS, then the ETTR approach remains very much relevant.

To slightly rephrase your point, the primary issue in digital exposure is to maximize the light reaching the sensor, via the size of the aperture and the duration of the shutter opening. After these two parameters are maximized for the composition, only then raise the ISO in the camera rather than attempting to brighten in post processing, particularly for Canon EOS bodies. For ISO invariant models, brightening the base ISO image in post may be a valid option, for static subjects. The individual photographer has to test and understand both their camera's RAW files and their software capabilities. Is the brightened base ISO image equivalent / better to the in-camera higher ISO image?

bleirer

I'm not against raising the ISO when necessary, I'm just reinforcing the known fact that there is no ettr benefit to using ISO to move the histogram even father to the right just to move it back left in post. At base iso there is certainly a benefit to using shutter speed or f stop to move right in camera and back left in post. Raising the ISO doesn't cause the extra noise, but failing to increase exposure via shutter speed or f stop does.

Ysarex Loc: St. Louis

Not only is raising ISO not the same as increasing exposure it is if anything the opposite. What does a camera exposure meter do when we raise ISO? It calculates a reduced exposure. What's the most common reason people raise ISO? They need to reduce exposure because they either need a faster shutter speed or smaller lens aperture. It's fair to say that raising ISO is equivalent to reducing exposure.

In most of our camera's ISO increases are most commonly implemented by either amplifying the analog sensor signal prior to processing through the ADC or scaling the digital values in the ADC before the raw file is written. Both methods effectively reduce the possible DR that you can capture. Here's an example: https://www.photonstophotos.net/Charts/PDR.htm#Nikon%20D7200 We call the process ISO clipping. Those two ISO implementation methods take the DR right off the top in a sense as they push up the digital values stored in the raw file. So in that sense your belief makes sense; if one of the goals of ETTR is to maximize DR then what's the point of shaving off a couple stops of DR with ISO before you start thinking ETTR.

The goal of ETTR is to expose as much as possible. If you can increase exposure then you can lower ISO. The only reason you're raising ISO is because you can't increase exposure.

But when you do increase ISO make sure you're not leaving any possible sensor capacity unused. Most of our cameras are engineered to make a good JPEG from an exposure that hedges back from the sensor's max capacity. In other words you've got the camera set to ISO 1600 and you're exposing to create a good JPEG then odds are you can expose more and still have an unclipped raw file. The problem with that is the whole reason you've set the ISO to 1600 is because you can't expose more. But can you raise the ISO more? If you can raise ISO more you should just be sure you're not going to ISO clip highlights.

I go through this with my students every bleepin' semester. Most of my students shoot Canon crop sensor cameras. They complain to me about noisy high ISO photos and show me examples. I tell them "well you should raise the ISO to get less noise." At first they react very confused by that remark. They're all triangle victims. They learned from watching exposure triangle videos that shutter speed relates to motion, aperture relates to DOF and ISO relates to noise. They believe if they raise ISO the noise will get worse. But that's wrong; noise relates to exposure not ISO. With their Canon cameras raising ISO reduces noise. Paul's comment is getting at this. We can't call it ETTR because as you noted ISO is not an exposure determinant but in the same sense that we want to squeeze the most out of the camera we first try to maximize exposure of the sensor. If we can't physically do that because the runners are just moving too fast or whatever reason then given the exposure we are capable of attaining we should maximize ISO.

The same caution applies that it's a risky game to play because if you clip those highlights in the raw file either by exposure or by ISO clipping then it's checkmate.

Joe

edit: I see you got in a comment while I was typing this one. It appears you understand.

bleirer

Thanks for the clarification. They say one sees their own worse faults in others, so I'm fighting against my own tendency to crank the ISO further right when I should be figuring out a way to increase exposure.

CHG_CANON Loc: the Windy City

It takes fortitude to trust the IS and / or tripod, always trying for the slowest shutter possible for the desired composition.

bleirer

I think exposure can be subjective, depending on your artistic intent and what looks good to your eyes, so there is a range of normal. If you want full control you'd have to shoot a card that had a standard greyscale, then you could slide the sliders in lightroom until the eyedropper over the 50% grey box read 50, the one over the black box read 4 and so on.

One strategy in lightroom is to to turn on the blinkies then to slide exposure until the middle values looked right, then stretch whites to the right and highlights to the left, then stretch blacks to the left and shadows to the right, until the blinkies are just 'off.'

anotherview Loc: California

Well put: "What we accomplish is the least amount of noise and the maximum amount of DR possible. Use all of the sensor's capacity rather than just a portion of the sensor's capacity."