Understanding Contrast Masking

About three years ago I wrote a tutorial on contrast masking. It was published before I had started to use digital cameras, and was intended for use with files from scanned film. Below is an updated tutorial designed for users of digital cameras.
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Too Hot is Not Cool
A digital file is much like a film positive (transparency) in that the worst sin is to blow out the highlights. In fact it's even worse with digital than with film. Highlights on film tend to trail off gradually on the shoulder of the curve, while with digital it's more like hitting a brick wall. Overexpose — expose too far to the right of the histogram — and you end up with nothing, nada — empty white pixels with no data whatsoever.
So the strategy for digital photographers is to expose as far to the right side of the histogram as possible. (Please see my article Expose to the Right for additional reasons why this is the correct approach to digital exposure,andIf...