1. A method for converting a digital image from color to gray-scale, the method comprising: using a processor to: (1) select an unconverted pixel of a color digital image having red, green, and blue color channels; (2) multiply the red color channel of the pixel by α; (3) multiply the green color channel of the pixel by β; (4) multiply the blue color channel of the pixel by γ; (5) add the results of (2), (3), and (4) together to arrive at a gray-scale value for the pixel; and (6) repeat (1)-(5) for each remaining unconverted pixel of the color digital image to arrive at a gray-scale digital image, where α, β, and γ are weights corresponding to the three color channels R, G, and B, respectively, wherein α+β+γ≈1 and α>β.