Every so often, earnest letters from my readers land in my inbox inquiring about the reasoning behind “expose to the right,” also referred to as ETTR. Do I practice it, and does it make any difference in the quality of my photographs?
Yes, I do. And, yes, it does.
First, let me explain that the following article is likely to be the most technical one you will ever see from me. Although I frequently write about the creative aspects of photography, it is important to understand technical fundamentals as well so that you can get on with creating better, more artistically compelling images.
Now, what is ETTR, you may ask?
The term refers to the diagram of the histogram you can view on your camera’s LCD screen and in digital photo raw processing software. The histogram is an approximate visual representation of the exposure of an image. It looks like this.
Tonal distribution of any given image is graphically represented by its histogram. The dark tones are on the left side of the graph, the mid-tones are in the middle, and the highlights are on the right side. To “expose to the right” means to expose your image so that the lightest tones are pushed to the right side of the histogram — the highlight side — just to the point before clipping or blowing out the highlights occurs. Clipping refers to loss of either highlights or shadows by either over- or under-exposing the image. A photo that is “clipped” will have data points touching the far left or far right of the edge of its histogram. That’s not what you want. The goal of ETTR is to expose the image so that the data points are pushed as far to the right as possible without actually touching the side of the binding box, and — for most images — away from the left edge. You can do this either by using the manual mode for exposing, or using exposure compensation.
With practice, you can learn to read the histogram properly and control exposure without overexposing or underexposing the image, regardless of your camera’s light meter readings.
So, why should you consider ETTR?
Tones in Highlights & Shadows
Tones are not recorded equally across the entire range of dark to light on digital sensors. When your digital camera records image data, the brightest part of the photograph (or highest stop) uses half of all the tonal values in the entire image. That is because a one-stop difference represents a doubling or halving of the exposure, and therefore a doubling or halving the tonal values recorded. The next highest stop uses half again of the remaining values, the next uses half of what is left and so on, such that the lowest (or darkest) stop uses only a small fraction of the tonal values available, as shown in the diagram below.
It’s all about the details.
Cameras still cannot record as much dynamic range in a scene as the human eye can detect. And, furthermore, there are situations where the scene’s contrast range is lower than your camera’s sensor dynamic range. So, in order to maximize detail from your images, you need to ensure that your camera’s sensor is collecting as much information as possible. That is the driving force behind ETTR. By using deliberate ETTR (exposing the image as light as possible without clipping the highlights), and then normalizing the exposure in post-processing, the maximum amount of information and detail is retained.
To be continued…Why you should “Expose To The Right” – Part 2