A Possible Problem with Expose to the Right!
Settings for an Accurate Histogram
By Ray Maxwell
We all agree that Expose to the Right is the best way to produce a digital image with a maximum of smooth tonality. I teach this in all of the seminars that I have led over the years. However, I always add one suggestion which I have never heard anyone else teach when they explain ETR. I always tell my students to go into the menu settings of their cameras and set the “Contrast” setting to minimum.
Before we go any further, lets set a few ground rules. You are going to be shooting RAW. Your camera can display a histogram on the LCD in the camera. You understand that the only controls on your camera that affect the RAW files are ISO, shutter, and aperture. (Yes, there are a few other controls in some cameras that can affect the RAW image. Please check your camera manual for these.)
You may ask…”What does setting the contrast have to do with ETR? When we teach ETR we ask you to look at the histogram on the LCD of your camera and expose so that the highlights are as far to the right as possible without clipping. What is the source of this histogram? Is it made directly from the RAW data? The answer is no, it is made from the image displayed on the back of your camera. This is an image that is processed from the RAW data according to the settings in your camera. The contrast setting affects the dynamic range displayed by the histogram and image on the back of your camera.
Try the following experiment with your camera. Place your camera on a tripod. Evenly light a test pattern like a step wedge. This will give you a subject with a known long tonality range. Now set your contrast to minimum. Shoot an image and note the histogram on the camera. Note how close the maximum step and the minimum step of the step wedge are apart on the histogram. Now set the contrast to maximum. Repeat the experiment. You will now find that the minimum and maximum steps in the wedge are off scale to the right and left. Now open the two images in your RAW image processor on your computer. You will now see that the two histograms displayed by your processing software are the same. The contrast setting had no affect on the RAW file.
What does all this mean? In order to display the full dynamic range of your camera in the histogram displayed on the back, you must set the contrast to minimum. You now can see the same dynamic range in the histogram on the camera as you will see it in your RAW processor on your computer.
When shooting RAW always set the contrast to minimum so that the histogram displays the full dynamic range the camera can capture. This makes for rather dull images on the back of your camera, but gives you better information about exposure and clipping.
I'll simply add to what Ray has written that it is also important that you set the colour mode to Adobe RGB, rather than sRGB – if your camera allows this, and for the same reasons. The same applies to White Balance (get it right), contrast, saturation and tint. In other words all of the JPG settings that your camera allows but which are irrelevant for raw. They simply make the camera produce an inaccurate histogram.
One more thing. The Leica M8, M8.2 and M9 are the only cameras that I am aware of that bases their raw histograms on an internal interpretation of the raw file rather than on a JPG. In fact JPG related settings aren't even available on the menus when shooting raw. Nice.