Why Exposing to the Right (ETTR) is BAD!

Started Mar 30, 2013 | Discussions thread
apaflo Veteran Member • Posts: 3,854
Re: (ETTR) is BAD! But saying so is going to get you a lot of flack

AnthonyL wrote:

apaflo wrote:

The whole point of ETTR is to know exactly where the highlights are exposed at.  If you are prone to losing them, you're doing it wrong.

Please feel free to correct me but I thought the whole point of ETTR was to ensure that the photo-sensors were as near filled as possible so that any noise in the shadows was drowned.

Filling sensor wells only happens if ISO sensitivity is set to a minimum.  The histogram for a shot at ISO 1600 will begin to climb up the right side when the sensor wells are less than 1/8th full.

The point is actually to bring the desired highlights as close to clipping in the Analog-Digital-Converter.  Granted though that that is also best done at the lowest possible ISO, if noise reduction is indeed the primary intent.

The photo-sensors that need being filled as much as possible may be those of the subject which may or may not be whole scene.

Whether it is filling sensor wells or peaking the digital value without clipping, the "subject" as such is not significant.  The brightest area where there is detail that is desired in the final image is what counts.  Lets compare this to the Zone System that Ansel Adams came up with, and a couple of interesting oddities show up.

Zone 0 is black, and Zone 10 is pure white.  Neither of them show any detail at all.  In otherwords, Zone 10 is off scale on the histogram.  (Catch the fact that the Zone System has 9 zones that preserve detail, and the JPEG format can record about 9 fstops of dynamic range.  It is not an accident that they are the same!)  Anything in Zone 9, where there is detail that is desireable, should be on scale at the right edge of the histogram. Likewise Zone 0 is anything at or below the noise level, which is anything causing a spike at the left edge of the histogram.  Any dark area with desired detail is hopefully kept to the right of the left edge.

However, there is another catch to this.  A JPEG derived histogram shows data from 0 to 255.  Anything brighter than 255 is clipped to 255 and all detail is lost.  But it is also true that while there is detail in the data between 245 and 255, it will NOT be seen on a monitor or a print.  It's washed out.  The same is true for data below about 30.  The data may have detail, but neither a monitor nor a print will show it.  With either a print or a monitor you just are not going to see any more than may 8 fstops at the most, and probably no more than 7 though it may be as low as 5.  (The Zone System and the JPEG format were both designed to have just a little bit of latitude beyond the best display systems!)

One effect of the above is that when editing an image it is best to keep highlights where we want to see texture (for example the highlight from the mainlight on the cheek, nose or forehead in a portrait) below about 246.  And areas like black hair should be kept above about 30.

But that is before any form of sharpening is applied!  Sharpen will cause edges to be boosted on the bright side and lowered on the dark side.  So an image with a lot of edge detail that shows a pre-sharpened range from 30 to 245 will usually end up with a little spike at the right edge of the histogram and a left side that probably goes all the way to 0 and maybe even will show a spike there too.

And that is what you'll see in virtually any image that has a lot of "Pop".

What we should take home from the above is that histograms are useful tools starting with the exposure in the camera and continuing right through processing to the point where the image is viewed.  Call it ETTR, or just call it attention to detail and being a perfectionist.

If the shadows don't matter then there is not much point.  If the highlights don't matter then they can be blown eg black dog in white snow.  In the latter case it is ideal if the shadows in the black dog are not underexposed, inducing noise, so it is the dog that needs have ETTR applied and thus the histogram (if using that) needs to be that of the dog and not that of the scene (metering).

It isn't "inducing noise" that would be the problem, but losing the desired detail.  But when the exposure is increased to retain that detail there is going to be a loss of detail in the highlights.  ETTR just means that you can see and measure exactly where detail in the highlights is lost.  It can be complex though, because it can require analysis of the blinking highlight display (which is just a different kind of histogram display) and/or looking at the histogram of an magnified portion of the preview image.

Also if not wishing to PP for whatever reason then surely just correct exposure is required.

I don't hear anyone suggesting that ETTR is a useful tool for those who shoot JPEG and use the image straight from the camera.  It is only very useful when post processing.

I don't like blanket statements and the OP's article is not well argued with repeated poor argument and he might have been better to start the article with

"So those are my reasons why ETTR sucks in my opinion. It makes most forms of photography more complicated and some downright risky (such as portraiture photography using off camera/on camera lighting a long with event photography where you’re constantly adjusting your exposure) and any other type of photography where there are external lights involved in the exposure of your photograph."

Thus far in my own experience I ETTR when I have the opportunity but usually I'm struggling with max apertures, high ISO and an already slow shutter speed (twitchy subjects in UK light) so it often becomes academic and I'm more interested in avoiding motion blur than having a bit of noise that I can just as easily PP so I don't really let ETTR  become some sort of mantra.

We can save ourselves a lot of extra work later by watching the histogram as we shoot.

Lots of folks rant about "get it right in the camera", and that is valid as a means of allowing things to be made the best they can be in post processing.

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