Why bother changing base ISO?

Started Jul 18, 2007 | Discussions thread
Hans Giersberg Veteran Member • Posts: 3,938
Posterization

Even assuming that bumping up an ISO 100 image doesn't result in more noise than just shooting at a higher ISO to begin with (a dubious assumption), you are still left with the fact that the darker tones are represented by fewer tonal levels than the lighter tones. So when you brighten up the darker tones, you'll have more and more posterization, depending on how much you brighten the image. Remember, the brightest stop on a 12-bit camera is represented by 2048 tonal levels. The next brightest stop is represented by 1024 tonal levels. Then 512 levels, and 256 levels, etc. On a D200, by the time you are two stops below midtone, all of the information is contained in only 128 tonal levels. That's OK if it's in shadow. But when you brighten this, you'll start seeing the posterization.

You're basically saying you're too lazy to do it right. If so, expect subpar results.

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