Most of us at one point or another have heard or read the maxim in digital photography commonly titled “expose to the right”. But do you really do this on a regular basis, and do you know how? More importantly do you know why? I’ll try to answer these questions as simply as I can and also provide some tips to put this practice into use every time you go out and shoot. Afterall, I don’t know of a single photographer that doesn’t want to come home with the highest quality images possible.
Many of the students I work with seem to be unclear about exposing to the right, and I think part of this can be attributed to 2 main reasons:
- Not having a full understanding of the reading and use of the histogram
- Depending on the LCD preview on the back of the camera as a way to aesthetically judge proper exposure, color, and contrast.
First, Let’s Talk About Camera Sensors
All digital camera sensors capture light in a linear fashion, starting from black to white (left to right on the histogram). This means they capture fewer levels of information in the shadows, and the maximum number of levels in the highlights, just before clipping. In other words, the sensor is much more sensitive to brighter levels of light that darker ones.
This is the main reason why we see digital noise in the shadows and not the highlights. The “signal to noise” ratio is much higher in the highlights, therefore noise can only rear its ugly head in the shadows where this ratio is much lower.
Because sensors capture more light levels in the highlights, or towards the right, there is more information that can be utilized by the post-processing software when we make our adjustments to the RAW file. This gives us more data to work with, preventing potential problems such as banding, loss of detail, lack of tonal separation in the shadows, and noisy images. We gain much better shadow depth, clarity, and improve our overall image quality, especially when printing, or making aggressive adjustments in post-processing.
How to Properly Read the Histogram
The histogram is your guide. If your camera supports the separate RGB channels of the histogram, use it, otherwise the simple white histogram is fine as well. Your goal is to make an exposure where the majority of the information is as close to the right edge of the histogram WITHOUT a spike on the extreme right hand side. A spike means the sensor has received more light than it can record, and rendered that part of the image pure white without any detail.
Be aware that in some cases this may be ok depending on the image and your creative goals – perhaps you want to purposely blow out part of the image, or a bright part of the scene has very little detail to begin with ie. an overcast sky.
The important thing to remember is that the size and /or shape of the histogram is irrelevant, all that matters is whether there are spikes on the extreme left or right edges of the display. Either means that detail has been lost. If you have spikes on both ends, that means detail has been lost in the highlights and shadows, and more importantly the scene’s dynamic range is greater than what your camera can capture. For the purposes of this article, I’m assuming that is not the case, and you can move the histogram to the right or left.
Exposing to the Right
So you’ve made an exposure, and the histogram shows there is a space between the levels you captured and maximum exposure or 100% (the extreme right). This means you’ve left potential image quality on the table. To expose to the right, you’d simply apply plus exposure compensation if you’re using one of the semi-automatic modes, or adjust your shutter speed or aperture accordingly if using manual mode. You want to let in more light in order to move the histogram further to the right just before it clips in the highlights. For example, in landscape photography, you typically set your aperture for maximum depth of field, so you would lengthen your shutter speed to let in more light.
However, here’s where lots of people get hung up. When you expose to the right properly, the preview on the back of your camera will look awful and very overexposed. You might be tempted to compensate by adjusting your exposure setting until it looks much better, but now you are basically throwing away image quality and not getting the most out of your expensive camera body. Use your LCD preview for composition and focus, not for exposure. Trust the histogram, and the quality of your images will increase noticeably.
The final part of this process is properly processing your RAW files. I use Lightroom 4, so I’ll focus on my workflow using this app, but the same concepts can be used in other raw processors. When you import your images, assuming you don’t apply any automatic settings, those that have been “exposed to the right” will again look overexposed. But by adjusting the exposure slider you can adjust them to your liking and get them looking great again. The difference is that now you are starting out with the cleanest data, and redistributing it back into the sweet spot of what we like to see visually. Shadow detail is much cleaner and easier to recover, and all subsequent adjustments to the image will deliver better quality and results.
*Real World Example*
Graphic 1: Image #1 on top is exposed to look good in the preview, image #2 on the bottom is exposed to the right. Notice the difference in the previews and histograms.
Graphic 2: Image #2 has been adjusted to look similar to image #1 using the exposure slider in Lightroom 4 which now sets overall image brightness. I’ve brought it down a little over a full stop.
Graphic 3: To open the shadows more and balance the exposures, I’ve added +70 to the Shadows slider to both images.They both look identical right?
Graphic 4: Above is image #1 at 2:1 zoom ratio in a dark part of the image with lots of detail. [Click on the image for a larger version.]
Graphic #5: Above is image #2 in the same spot, and you can clearly see how much cleaner and less noisy it is compared to image #1. In a 16 x 20 print, this difference would be easy to see. [Click on the image for a larger version.]
I hope this has been helpful, and clears up some confusion about this important and useful technique for maximizing your image quality. Please leave any comments, feedback, or questions in the comments below. Thanks for reading!