Friday, June 1, 2007
Turning On The Brights With DxO Optics Pro
DxO Optics Pro's Highlight Recovery brings overexposures back to life
Areas of an image lost to overexposure or excessive brightness can seldom be recovered, and digital sensors tend to be particularly sensitive to excessive burning in whites and brights. This “highlight clipping” occurs when the photosites of the sensor fill with the maximum amount of information they're capable of containing. In other words, the image becomes blown out.
Most sensors record light in a three-channel RGB mode, using a mixture of red, green and blue light levels to represent the image. Just as in the real world, combining the recorded levels of the three primary colors also forms the other colors of the spectrum. At the same time, luminosity is being recorded in a tonal scale from true black, at 0, to true white, at 255.
Clipped highlights, much like clipped shadows, are the points at which the sensor can no longer record detail. In an overexposed histogram, you'll notice that the spike of whites to the right of the screen doesn't smooth out before reaching the maximum tonality of true white.
If this occurs in all three channels, there's little that can be done. With Adobe Photoshop, you can try to bury smaller areas with the Clone Stamp or Patch tool. Obviously, this becomes problematic when the area you're trying to cover doesn't match the sampled area naturally, or it's just too massive to dampen effectively.
Photoshop's Levels adjustment is an option in less-extreme cases of overexposure, but “stretching” highlighted areas to compensate for exposure is anything but lossless. Gaps are created in the continuity of the tones; and contrast, brightness and detail in the shadows and midranges are often reduced.