Digital’s Analogue – Expose to the right and exposure
Digital’s Analogue – ETTR and exposure
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by Guest Writer: Robert Fisher
As part of our efforts to advance interest and techniques relevant to digital black and white photography, we’ve a guest article by Canadian photographer Robert Fisher. Robert examines some of the underlying similarities between the Zone System, HDR techniques and the digital exposure guide known as ETTR (expose to the right).
The views expressed here are those of the author and do not necessarily represent those of Northlight Images.
Article Copyright ©2011 Robert Fisher.
As photographers, we live in exciting times.
We have a terrific array of choices available to use that enable us to make outstanding photographs.
Many, a majority safe to say, have migrated from film photography to digital. Some have stayed with film for a variety of reasons.
Unfortunately, what unites us in our endeavours – photography – also divides us. The digital vs. film debates that pop up regularly on internet fora are but one example of this divide.
There are those who believe film concepts can’t be applied to digital and others who believe film concepts are outmoded because of digital.
Neither are really true.
The title of this article was chosen so as to leave open to interpretation what the intention was. Let me steer the interpretation in one direction with two statements:
- The Zone System is analogue HDR.
- ETTR is a digital Zone System.
Perhaps three of the more controversial techniques in photography have a connection. At least I believe they do and after reading the rest of the article, perhaps you will too.
About the Author
Robert Fisher is a Canadian-based freelance photographer and writer.
His blog, commercial services and image galleries can be found at:
He can be contacted at:
photog (at) rf-photography.ca
Whether you do or don’t, your feedback is most welcomed.
Before making the connections, let’s take a step back and make some definitions of these concepts. None of the explanations is an in depth dissertation of each concept but rather an overview to set the stage for the later comparisons.
The Zone System
The Zone System was a process created by Ansel Adams and Fred Archer (although Archer is often forgotten about) for exposing and developing of black and white sheet film.
Black and white because that’s really all there was at the time. That said, colour film doesn’t respond as well to altered exposure and development and doesn’t have the brightness range of B&W.
Sheet film because each sheet of film could be developed individually as needed; unlike roll film.
The Zone System can be used with roll film, you just need to switch rolls to switch exposure so that an entire roll can be given the same development later on. The Zone System divides brightness into 11 sections (Zones) of grey ranging from pure black (Zone 0) to pure white (Zone X).
|I||Near black, with slight tonality but no texture|
|II||Textured black; the darkest part of the image in which slight detail is recorded|
|III||Average dark materials and low values showing adequate texture|
|IV||Average dark foliage, dark stone, or landscape shadows|
|V||Middle gray: clear north sky; dark skin, average weathered wood|
|VI||Average Caucasian skin; light stone; shadows on snow in sunlit landscapes|
|VII||Very light skin; shadows in snow with acute side lighting|
|VIII||Lightest tone with texture: textured snow|
|IX||Slight tone without texture; glaring snow|
|X||Pure white: light sources and specular reflections|
Zone descriptions from Adams
Adams also created the ‘middle grey’ standard for light meters.
The mantra for the Zone System is ‘expose for shadows and develop for highlights’.
The Zone System also works on the basis of a ‘place and fall’ method of exposure.
Understanding how light meters are calibrated, Adams could ‘place’ an important shadow area on the Zone he wanted by adjusting his exposure (expose for shadows). All the other areas of brightness would then ‘fall’ into different Zones based on the placement of the shadow.
Depending on which Zones those other areas of brightness fell into Adams could adjust development of the film to effectively move some of those Zones around (develop for highlights).
If, for example, a shadow area that would otherwise be Zone II (very dark grey, with little detail) were placed on Zone III (dark grey with detail & texture), then an area that would have been in Zone VIII (light grey with detail & texture) would fall into Zone IX (nearly white with little to no detail).
Adams could then reduce development of the film and pull that highlight area back into Zone VIII. This increased exposure also resulted in reduced grain in the negative and print.
The reverse would be done if a shadow area were placed on a Zone darker than where it would otherwise be. This process of adjusted exposure and development has more impact on highlights than shadows which is why highlights can be pushed and pulled around but shadow areas remain mostly unaffected.
The ‘pushing’ of highlights into higher brightness zones (reduced exposure and extended development) comes at the cost of increased grain in the negative.
All of this also works on the basis that the total brightness range of the scene being photographed is within the range of the film to capture. If the brightness range (dynamic range) is wider than what the film can capture then the photographer needs to understand that there will be either blocked up shadows or overexposed highlights depending on the ‘place and fall’ decision.
Now we’ll move on to Expose to the Right, or ETTR.
ETTR is a method of exposing for digital photography. ETTR works on the basis that the highest image quality results from the lowest level of noise.
Reducing noise is achieved by capturing the most light in a pixel (i.e., not underexposing). The ETTR philosophy says that exposure should be adjusted so that the maximum light is captured at all pixels without overexposing highlights.
Adobe Camera Raw (ACR) histogram for a RAW file that was ‘Exposed to the right’
The histogram in an ETTR exposure should be bumping up against the right side of the graph but without overexposing the highlights.
When the image is brought into the computer and opened up in a RAW converter the brightness is then adjusted to ‘pull’ the various areas of brightness back to where they should be.
Starting to see some connection?
Using ETTR assumes that the overall brightness range of the scene being photographed fits within the dynamic range of the sensor (more connection?).
ETTR also works on the understanding that underexposure and ‘pushing’ brightness up to compensate in the digital darkroom will result in increased noise (the digital equivalent of grain).
ETTR only applies when shooting RAW (the digital equivalent of an unprocessed negative).
If the brightness range of the scene is wider than the sensor can capture, a decision needs to be made on whether to have blocked shadows or overexposed highlights. Or a different method of exposure needs to be used.
That brings us to HDR.
High Dynamic Range (HDR) imagery is a method where 2 or more exposures are made of a scene at different exposure settings.
Commonly referred to as bracketing. The number of exposures will differ depending on the exposure step between shots (i.e., 1/2 stop, 1 stop) and the overall brightness range (dynamic range) of the scene.
These multiple exposures are then loaded into specialised software where they are merged and blended. We can’t directly make use of these HDR images; however.
Current monitor technology can’t reproduce the wide dynamic range nor can printers. We have to process these HDR images back into something useful.
A black and white HDR image from Keith Cooper’s recent Nik HDR Efex Pro review
The way that’s done is through a process called tonemapping. Tonemapping compresses the wide dynamic range of the scene back into something we can see on screen and print.
Current monitors and printers can certainly see and reproduce the shadows and dark end of the brightness range. It’s the highlights or top end of the range that are most problematic.
Tonemapping then is, essentially, a process of ‘pulling’ highlight detail back into a useable range.
HDR is effectively an extreme version of ETTR. The upside is that by using this extreme version of ETTR and ‘pull’ processing the HDR image we get reduced noise in the final product.
Just as we do with ETTR and the Zone System. We can also ‘push’ shadow areas higher in HDR tonemapping but the result will be increased noise, just as we get increased grain by ‘push’ processing film in the Zone System.
Back to the two statements near the top of the article.
The Zone System is analogue HDR. The process Adams created for exposure and development allowed him to move highlights from one zone to another, to effectively map a tone from one zone into another. This is what HDR tonemapping does.
ETTR is a digital Zone System. ETTR is a form of increased exposure and reduced development that allows us to remap tones from higher to lower brightness. This is what the Zone System does.
The biggest difference between digital and analogue is that with digital we have the ability to remap tones all along the brightness scale whereas the film Zone System allowed a remapping of just the highlight areas through altered development.
Some may look at this and say the Zone System only applies to black and white film.
Well, in an absolute technical sense that’s true. But I’m not looking at this in an absolutely literal way. I’m drawing analogies and trying to illustrate how digital and analogue photography really aren’t as different as some make them out to be.
The same concepts of ETTR and HDR apply whether we’re talking about colour or black and white photography. Using ETTR and/or HDR doesn’t preclude converting to B&W later on and the tools for remapping tones work the same in either case.
Digital, film. Film, digital. The technology may have changed. The methodology and implementation may have changed. The lexicon may have changed. The goal and end result isn’t really that much different.
The thing that divides us – photography – is the thing that should unite us.
Robert has subsequently written a book covering the contents of this article and his expanded Digital Zone System editing techniques: – Book review: The Digital Zone System
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