Colorto grayscale image conversion using modulation domain quadratic programming

We propose a new polynomial-time grayscale conversion algorithm applicable to general color images. The output grayscale image is modeled as a linear combination of three color channels where the mixing coefficients are computed by a constrained quadratic programming scheme using modulation domain features of the input color image. The optimization is formulated such that local color space distances between pixels in the input image are approximately preserved in the output grayscale image. Our experimental results demonstrate that the proposed method performs favorably compared to state-of-the-art conversion algorithms, often producing a grayscale image with better visual distinctions between patches that are close in the color space of the original image.