This is for the photographers who post process their compositions in Photoshop (or possibly Lightroom).
When you are processing your photographs, you want to avoid clipping shadows and highlights. Clipped shadows (a completely black area) or a blown-out highlights (areas of solid white) means portions of your image have lost their detail. The usual precaution against this is to use the histogram tool. However histograms cannot show you where in the image the clipping has occurred. You’ll see indications at either end (left for shadows, right for highlights) but there are no indications of midtones issues. The middle of a histogram can take any shape depending on the content of an image and isn’t much help with actual evaluation. Fortunately, Photoshop has come up with better tools that address these shortcomings.
The one I want to discuss today is the easiest one to use, the Clipping Preview. It is, in effect, a histogram overlaid on your image and not just a graph.
To see the clipping preview, Alt/Option-drag the black (shadows) or white (highlights) slider at the bottom of a Curves or Levels adjustment layer or panel. In Camera Raw and Lightroom it is the same thing but with the tone sliders. Highlight is a solid white image while shadows is solid black. Where you see Indicator colors is where clipping is occurring. Not all clipping needs to be addressed, but you do need to evaluate the loss of detail and decide if it should be returned. The color keys are the same as in the histogram’s window, the colors shown are channels or mixes of channels. All black in the highlight or all white in the shadow is all channels clipped.
That’s it for today but remember, if processing for printer output, make sure your are in CMYK mode and your last processing step should be soft proof ( view > proof colors or Ctrl/Cmd Y). My personal workflow is to run Gamut Warning first, then Soft Proof to evaluate the actual clipping (not all out of gamut needs to be compensated for).