Exposure by Channel


Today’s Question: Is there a way to prevent exposure clipping of a specific color channel? I noticed that I was getting clipping of the blue channel on the left side of its histogram (no other color channels were clipped) and the combined RGB histogram and luminosity histograms showed no clipping on the back of the camera.

Tim’s Quick Answer: Preventing the clipping of a single channel requires that the overall exposure is adjusted, which in turn can require a review of the individual histogram channels for the image you’ve captured. And, of course, in some cases a single channel can be enough to require multiple exposures to create a high dynamic range (HDR) image.

More Detail: When a single channel is clipped, it means you have lost detail for that channel. In other words, you’ve captured an exposure that is less than optimal. In many cases you can compensate for this type of issue when processing your RAW capture on the computer, but I always recommend getting an optimal exposure in the camera.

It is important to review all three color channels (red, green, and blue) rather than just the overall luminosity histogram for a capture. Even when the luminosity histogram indicates there is no clipping of highlight or shadow detail for a photo, there may still be a loss of detail on an individual channel.

To be fair, in some cases it is not critical to retain detail for all three color channels in a photo. However, it is always better to have detail you don’t need than to lose detail you later wish you had.

When it comes to the original capture, the best approach to evaluating your exposure settings is to configure your camera to display individual histogram displays for each color channel. Most cameras include this option, or the option to overlay the histogram for all three color channels into a composite display. If a single color channel indicates it is clipped on the histogram, it is probably worthwhile to adjust your exposure settings and capture another image.

It is worth noting that the color space setting on your camera has an impact on the histogram being displayed. As a general rule I recommend using the Adobe RGB color space option in your camera in order to provide a more accurate histogram display. The sRGB color space option will generally provide a more pleasing image preview on your LCD, but a histogram that isn’t quite as accurate compared to the final result you can expect.