Post processing is not required with either camera.
People who buy this caliber of camera usually want to present the best photo possible. They are more likely to do post processing to achieve the perfect photo.
But you can do ''point-and-shoot'' with either camera and get excellent results.
But remember:
Great pots and pans do not make a great chef.
Great cameras do not make a great photographer.
The willingness to learn is what is needed to improve our abilities as a chef or a photographer.
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A fairly common thing I've heard about the Canon 20D is that precisely b/c it's more professional than ,say, the DRebel XT, more post-processing is required to bump up the image quality. In other words, b/c the XT is more consumer oriented, less post processing is required.
Is this true?

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