Tuesday, August 4, 2009
The Rembrandt Solution
What painting’s Grand Masters can teach today’s digital photographers
In high-contrast situations, our visual system separates the scene into various “zones” and analyzes the local contrast in each zone independently of other zones. For a scene to look natural, the local contrast must look right in each zone. By definition, the local contrast is correct in the correctly exposed regions of both the highlight and shadow exposures. By using what’s essentially a Cornsweet illusion-like pair of tonal gradients to merge the two correctly exposed regions of the images, natural-looking local contrast is maintained in both the shadows and highlights.
Put another way, you always get the best contrast and color in regions of your image exposed close to a midtone. By using a split ND, you can position the highlights and shadows close to a midtone and marry the two regions in a way that our visual system finds believable.
So why not just use Photomatix Pro or another HDR software package for all high-contrast scenes? Current-generation HDR software doesn’t always guess perfectly what the local contrast should be in each region of the image, sometimes producing an unnatural result. Today’s HDR software also tends to produce halos and oversaturated highlights if pushed too hard. Further processing in Photoshop is usually necessary. Any motion in the scene creates problems when you merge the images.
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