Kia ora tatou:
in all my workshops which deal with camera craft and postproduction, I’ve taught the technique of ETTR, or expose to the right. In the process I’ve made a number of assumptions which I assumed were correct, but now I’m beginning to rethink those and I want to share those thoughts with you. This, of course, assumes that you are shooting Raw rather than JPEG. Before I get there, I want to revisit the whole question of how you go about setting exposures for each of the two methods.
Shooting a JPEG file, as most of you know, is very similar to shooting slide film. Those of us have made the transition from film to digital will understand how important it is to be careful in your exposure of slide film. The same thing applies to a JPEG. When you expose a JPEG, you need to think of it as slide film, that is that the critical part of the exposure is correct exposure of the highlights. The aim here should be to place the highlights exactly where you want them to be. If you want them to be right but with fine texture, it’s important to ensure that you don’t overexpose or “cook” them. Remember that when you press the shutter, you are effectively creating the finished file, according to the camera settings you have chosen. This is important to remember: you make your choices (exposure, contrast, saturation, tone, white balance) and you live with the consequences. Postproduction on a JPEG usually does not have the flexibility of working on a raw file. Add in the fact that a JPEG can only deliver an eight bit file compared to the 16 bits of a raw file, and the only real reason for shooting a JPEG is convenience.
A raw file on the other hand, being pure data written to the card, offers us all sorts of extra flexibility. Our file isn’t contaminated by decisions regarding exposure, contrast, saturation, tone and white balance. Or is it? I’d venture to suggest that there is a way in which we are subtly doing that very thing, that our JPEG settings do have an effect on the raw file we produce.
Two questions have been nagging me for some time now, and I really haven’t had a decent answer to them. Time and again, at workshops, students new to shooting raw have asked me the question: do I set my camera to sRGB or Adobe 1998? The other question which I’ve been asked is whether the choice of white balance affects the finished raw file. Well it doesn’t. And it does. Let me explain.
The technique of exposing to the right means deliberately biasing your exposure so that your histogram is as far as possible to the right without clipping. In fact, with a degree of careful experimentation, you can allow your histogram to clip slightly and get away with it, by using the recovery slider or highlights control in your software to bring those very bright highlights back within range. The advantage of doing this is that you record more data in the shadow areas and therefore reduce the potential amount of noise in the shadows. You make these decisions based upon the histogram on the back of your camera, which has largely replaced the exposure meter of old. In the old days (some would say good) of film, you would make decisions based upon your meter and live with the consequences until such time as the film came back from the lab. Then you knew whether those decisions had been accurate ones or not. Digital cameras, with the advantage of instant feedback in the form of the histogram, allow us to make those decisions and then correct in the field. Or so it would seem.
The issue comes down to the histogram, to how accurate it is, and just what it is telling you. Is it giving you an accurate histogram off the raw file? Is it showing you what she will get when you open up the picture in the computer? If you have ever sat there at your desk, with a memory card in the camera and the same file open in your software (for example, Lightroom) you may suddenly realise that the two are quite different. So which one do you trust? And can you rely upon the histogram when you are out in the field? Yes and no. It depends upon the choices you have made. To do that, we need to revisit just how your camera produces a raw file.
When you make an exposure, the camera writes that data directly to the card, without applying any of the JPEG settings you have chosen to it. At the same time as it is doing this, it generates a small JPEG thumbnail so that you get a visual representation of the file as if it were a JPEG! These last six words are critical. In other words, the thumbnail on your back LCD panel is a small JPEG, generated not by the raw file, but from the JPEG settings you have chosen, were you to switch from shooting raw to JPEG. The implications of this are staggering. On my Sony Alpha 900, choosing the vivid setting gives me a rendition with increased saturation and contrast. Thus, the histogram which I see on the back of my camera shows me the picture as if I were shooting a JPEG. If I switched to JPEG, the finished file on my card would accurately match the one on my LCD panel.
A raw file does not.
In fact it will have none of the characteristics of a” vivid” file until I generate that in postproduction.
If you work in Lightroom or Photoshop, you will know that increasing the contrast in postproduction causes both ends of the histogram to move farther apart. Furthermore, changing colour space from sRGB to Adobe 1998 causes a subtle shift in the histogram, allowing it to work within a wider gamut. If you find, using sRGB, virtual files are consistently clipping when shooting raw, then the culprit may be there.
If you are going to consistently shoot raw, then you need to set up your camera so the JPEG rendition is as close as possible to the actual way in which the raw file is rendered. In other words, if you are shooting raw, you need to get over the look of the file on the back of your camera and concentrate only on the histogram. As I suggest at workshops, use the picture to assess your composition and the histogram to judge exposure. If your camera allows you to do so, make sure you turn on the RGB histogram. Using only luminance can lead to highly inaccurate exposures.
So here are some suggestions for getting a more accurate histogram:
1. Make sure your camera is set to the Adobe 1998 colour space. This will give you a longer-scale and more accurate histogram.
2. Dial your contrast back to 0 or as low as it can go. This will have a similar effect to suggestion one.
3. Similarly turn off any in-camera sharpening which can interfere with your perception of the scene. You can always sharpen later.
4. Be more careful with your white balance. Using the daylight setting, which I’ve tended to recommend as a way to improve previsualisation can lead to inaccurate histograms when working in light which does not contain an even range of wavelengths (rock concerts, sunsets and the like). If in doubt, you might switch to auto white balance (although by and large the accuracy of the selection in most cameras isn’t that flash). If you are really fussy, you may want to invest in one of those scrambler disks that allow you to custom-set your white balance.
Using all of these suggestions will probably give you a file that looks banal, strange or even boring. You probably won’t want to show it to other people. What it should do however is give you a more accurate representation of the raw file as it opens in your software. It will of course give you a greater opportunity to shoot a more accurate file.
I have a close friend from the film days who shares the same name as me, but whose philosophy on making pictures was quite different to mine. His exposures and film processing technique were rough, to put it mildly. He subscribed to be philosophy of ” bu#@*! the exposure, get the shot!” near enough was good enough. As a consequence he very very quickly became a master printer. He had to. He also put a lot of money into the pockets of the paper manufacturers. I on the other hand, who really didn’t want to spend days massaging a single print into some semblance of acceptability, put all my efforts into getting the best possible exposures.
After all, it worked for Ansel Adams didn’t it?
And digital photography is no different. There is always room to sharpen camera craft, always new understandings to be had.
Nga mihi ki a katoa