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June, 2015

With digital photography, the first view of our images is on the screen on the back of the camera. But just how reliable is that image preview, as well as the histogram that can also be displayed on the camera? And, more to the point, are there times when it is giving you less than accurate information about the photo you just shot? In this article we’ll take a look at that question, concentrating mainly on how it relates to exposure with Raw files.

The Camera Preview is Not the Raw File

The first thing to understand about a camera preview image is that in most cases it’s not a view of the actual raw file. It is a small JPEG preview that is created on the fly. Depending on how your camera is set up, it may also be applying additional adjustments to give a slight boost to contrast and sometimes saturation. This is similar to how a camera may apply some adjustments to files when you’re shooting in JPEG mode. In most cameras you can turn these in-camera adjustments off, or dial in your own settings for things such as brightness, contrast, saturation, and sharpening. And keep in mind that even if you have configured these settings and do have them turned on, they are not applied to Raw files.

Overexposure and Highlight Clipping

One of the more useful features of digital cameras is the ability to see a histogram of the shot, as well as an indication of where highlights in the image may be “clipped”, or recorded as a total white with no detail. This is usually presented as a flashing black overlay on the clipped highlight areas. But the important thing to keep in mind is that when it comes to highlight clipping (and, in some cases, shadow clipping as well), the histogram and the clipping display may not be accurate. On my camera, for example, I’ve learned that a shot that shows highlight clipping on the camera preview may not have any clipping when I work with the Raw file in Lightroom or Adobe Camera Raw.

Take a look at the image below. This is a photo of the camera display of a shot that includes some shadow tones, a lot of midtones, as well as very bright highlights in the breaking surf. The camera display shows the highlight clipping display of flashing black over the bright surf area. Additionally, the highlights also appear to be clipped in the camera histogram.




If you were taking the camera’s display (both the histogram and the clipping warning) at face value, you might be moved to adjust your camera settings to reduce the exposure. But I did not do this because, knowing my camera as I do, I know there is usually a discrepancy between highlight clipping on the camera display and what I actually see when I work with the Raw file in Lightroom. Some clipping in the camera display usually means no clipping, or very minor clipping, in the actual Raw file.

You can see this below. The unadjusted Raw file in Lightroom shows no highlight clipping at all (the highlight clipping triangle above the histogram is not turned on), and the histogram is noticeably different from the one on the camera, which does show highlight clipping. In the case of this image 1 and a 1/3 stop of overexposure still gives me an excellent file with no highlight clipping, even though the camera suggests there is significant clipping. Your “mileage” may vary, of course, depending on your camera, but the point is to find out how much variance there is so you can more accurately interpret what the camera histogram and image preview is telling you.

The takeaway here is that you should do some testing to see what the possible differences are in how your camera displays highlight clipping and how the actual Raw file looks in image editing software. This is incredibly important information that you can use in terms of judging the exposures by viewing the image and the histogram on the back of the camera. For instance, the shot of the coastal scene above was the brightest shot of a three-shot HDR sequence. But if I was shooting a single shot, and if I was not already familiar with the difference between how my camera displayed highlight clipping and the actual highlight clipping, I might be moved to change my exposure and make another shot. But based on what the actual raw file looks like, I know that the clipping is not as bad as the camera display indicates and that I have the ability to adjust the Raw file and that no highlight detail will be lost.


 

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