Histogram Mismatch


Today’s Question: When I bring an image into Adobe Camera Raw, the RAW file’s histogram shows overall clipping on the left side. If the camera is not showing clipping, how can one prevent clipping in the RAW file?

Tim’s Quick Answer: The histogram you see in Adobe Camera Raw (or any software for processing RAW captures) is based on the adjustment settings for the RAW capture. In other words, if there was no clipping shown on the camera there shouldn’t be any clipping in the RAW capture data, and so you’ll be able to recover the detail that appears to be clipped by refining the adjustment settings.

More Detail: When working with a RAW capture it is a little to see an accurate histogram, because the actual histogram really depends on how the source data is processed. Keep in mind that a RAW capture represents the actual information gathered by the image sensor during an exposure. That information then needs to be processed in various ways.

For example, I think many photographers are aware that most digital cameras only capture a single color channel for each individual pixel on the image sensor. Software then needs to calculate the “other” values for each pixel to produce full color information.

The bottom line is that there is a degree of interpretation involved when processing a RAW capture. As such, the histogram may vary based on how the information is interpreted, and what adjustments are applied along with that interpretation.

The image you see on your camera’s LCD display for a RAW capture is essentially representing an in-camera RAW conversion. That means the histogram you see on the camera is based on the in-camera RAW conversion, while the histogram you see in Adobe Camera Raw (or other RAW-processing software) is based on the interpretation of that specific software.

To add to this confusion, changing the color space option on your digital camera will generally cause the histogram to change based on that color space. So even your camera might be capable of presenting different interpretations of a histogram for a given RAW capture.

Certainly it can be a little unnerving to see different histograms for RAW captures depending on how you’re viewing the image. But rest assured that if the camera shows there is no clipping you can feel confident that the information within the RAW capture represents no clipping of data for the photo. Thus, if you see clipping in software such as Adobe Camera Raw, it simply means you need to refine the adjustment settings to refine the interpretation of the RAW data.
So, for example, simply reducing the value for Whites and increasing the value for Blacks in Adobe Camera Raw will “recover” the information that appeared to be lost on the histogram display, based on the default interpretation of the RAW capture.