Watch the Histogram

Watch the Histogram!

The histogram display is one of Camera Raw's most useful but often most-overlooked features. Throughout this chapter, I've emphasized the usefulness of the histogram as a tool for analyzing the image, and especially for judging clipping. But the histogram in Camera Raw differs from the histograms you see on-camera in an important way.

Camera Raw's histogram is more trustworthy than the histograms that cameras displaythey show the histogram of the JPEG you'd get if you shot JPEG at the current camera settings rather than raw. As a result, they're useful as a rough guide to exposure, but not much more. The same applies to the overexposure warnings offered by most camerasthey're usually quite conservative. Camera vendors tend to apply a fairly strong default tone curve to the default, in-camera raw-to-JPEG conversion, perhaps in an effort to produce a default result that more closely resembles transparency film, so the histogram and exposure warning derived from the JPEG very often are not an accurate reflection of the raw capture.

Camera Raw's histogram is a great deal more reliable. It shows you, dynamically, the histogram of the converted image, displaying clipping in its various formsclipping highlights to white, clipping shadows to black, or clipping one or more channels to totally saturated color. It also lets you see the effect of the various controls on the converted image data. Watching what happens to both the histogram and the preview image as you operate the controls will give you a much better understanding of what's happening to the image than simply looking at the preview alone. In later chapters, we'll look in detail at the many ways you can use the Camera Raw controls to get the best out of your raw captures. But if you're new to digital imaging, or even if you're just new to digital capture, it's well worth spending some time mulling over the contents of this chapter, because digital capture really is significantly different from film. Understanding how numbers are used to represent images is key to grasping and, eventually, exploiting that difference.