For each pixel in the luminance image, compute the luminance, L:


Next, transform the image from RGB color space to HSL color space. The (R, G, B) triad you have just computed becomes (H, S, L) coordinates in HSL color space, where you can perform manipulations that are difficult or impossible in RGB color space.

First, you can replace the luminance computed from the {R, G, B) triad with the unfiltered high-quality luminance image. Note that if you wish to make the image brighter or darker, you can adjust the overall brightness of the image by gamma-scaling the luminance:

Increasing y increases the brightness of the image.

Next, you can control the saturation of the colors in the image. If the colors are too strong, you can reduce the saturation; if you want them more strongly saturated, you can increase the saturation. Since the saturation always lies between 0 and 1, gamma-scaling with a saturation scaling parameter, a, works well:

Increasing o increases the color saturation of the image.

After completing these image adjustments, the modified image is transformed back to RGB color space. Since the input value of luminance was scaled between 0 and 1, the transformed values of R, G, and B will lie between 0 and 1. If necessary, adjust these for the gamma of the monitor and scale them into the standard 0-to-255 RGB display color space:

Dfi = 2555

LRGB color imaging is capable of excellent color accuracy, and provides very flexible controls over the final appearance of the color picture.

•Tip: AIP4Win's Join Colors Tool uses the LRGB method for creating color images. If you did not make a luminance image, the software automatically generates one. The Join Colors Tool gives you independent control over the color balance and the brightness of the image.

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