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Monday, March 3, 2008

Color Choice: Luminance, Chrominance And Hue

Among the tools at your disposal, the LCH Editor gives you a powerful weapon for finessing the color relationships in your images

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The underwater photo examples originally were made using the Nikonos underwater system—a body and flash with two lenses (a 15mm wide-angle and 35mm with extension tubes for close-up work). The processed Kodak Ektachrome film was scanned to produce JPEG and TIFF files. Later, using Nikon Capture NX, the JPEG and TIFF files were converted into NEF files, which gave me the ability to use Capture NX tools to their fullest and enabled me to use nondestructive editing techniques. All image-editing and image- previewing/comparing was accomplished using the Microsoft VISTA operating system and Nikon Capture NX software's browser. I used TechSmith's SnagIt software to capture screen views that helped illustrate how the tools were used.

To achieve the “after” effects, I applied the LCH Color Lightness tool to affect two portions of the color spectrum. One LCH curve darkened colors in the area of red, which I then painted on the fish, leaving any red in other areas unaffected. The darkened reds reveal more detail on the fish's surface, along with the appearance of added contrast and sharpness.

The second LCH curve adjusted the bluish portions of the spectrum throughout the image, darkening the sky above the coral reef and the water areas below. As a result, the sky has a more dramatic appearance, and the waters below are darkened. The darkened waters help diminish the typical appearance of flash bounce-back off floating particles in the water.

Chrominance, or chroma, is the second image aspect that portrays the image's color information. Using various tools, it's possible not only to adjust a color's depth, but also its brightness and hue. What's the point? Well, this control offers opportunities for both correcting color fallacies and applying personal creative vision to an image. Color fallacies can occur as a result of a camera's color rendering and/or sensor being unable to accurately reproduce one of nature's colors.

For example, if you've ever tried to photograph a flower that has a blue-purple color, you may have noticed that the color's rendering isn't quite as you remember it. Similarly, other colors might not be as you recall. Being able to adjust color rendering through chrominance control is a convenient operation that lets you adjust for accuracy or change color according to your personal ideas for image design. I should point out that as the color science and engineering of color engines evolves (and has evolved to this point), color accuracy will continue to improve.

color choiceFigure 4: Sea Urchin on a Fan Coral provides a subtle illustration of the effects of the LCH Editor's Chrominance tool.

color choiceFigure 5: The Master Lightness control was used to enhance darker areas.

color choiceFigure 6: The red-yellow chroma was increased to brighten the urchin's inner spherical surface area.

color choiceFigure 7: The blue-violet chroma range was increased to enhance the violet-colored details on the fan coral's surface.

color choiceFigure 8: The aqua-blue tones were increased to bring out details on the fan coral and darken the background.


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