Today’s Question: When in manual mode with the shutter button 1/2 way down, besides seeing a meter reading on the back screen of my Sony camera, I also see a histogram of the proposed raw shot. I once read that the histogram on the back of a camera is from a JPEG interpretation of the raw shot just taken. Is this also true for my proposed shot? Does it matter if DSLR or mirrorless?
Tim’s Quick Answer: It is true that the histogram you’re seeing is based on what can be thought of as an in-camera conversion from the original raw capture to a JPEG preview image. However, that histogram can still be considered quite accurate in terms of the potential for the final image.
More Detail: The fact of the matter is, a raw capture isn’t really an image the way a JPEG is. A raw capture is really just a data file that contains the information collected by the image sensor during the exposure, along with other metadata added by the camera. In effect, you can think of a raw capture as not having a real histogram at all. The raw data needs to be interpreted into full pixel information in order to calculate what the histogram should look like.
This is why you will see a slightly different histogram in the camera, in your raw processing software, and with other tools that interpret the raw capture to present a preview or histogram.
Because you are able to interpret the raw capture with quite a bit of flexibility in post-processing, the histogram you see in the camera or before processing can’t be considered the “final word” in terms of the overall exposure and color information for the image. The raw data can be “finessed” a bit, so that you can recover detail you thought might have been lost, or apply various other corrections to the photo.
While the in-camera histogram either before or after a photo is captured certainly can’t be considered absolutely final in terms of the final potential for the image, it does provide a very good sense of what is possible for the image, as long as you haven’t applied very strong adjustments in the camera. For example, if you apply an extreme increase in contrast in the camera, the histogram will reflect that contrast and may lead you to make inaccurate assumptions about the photo.
So, provided you are keeping the in-camera adjustments at relatively neutral values, I would say that the histogram you see either before or after the capture on the camera’s display is going to be quite accurate for evaluating the exposure for the photo.