1. A signal-processing system comprising: a processing component; and a memory storing a signal-processing routine, which when executed causes the processing component to enhance an input image to produce an enhanced output image and store the output image in the memory by computing, by constructing multi-scale intermediate-image pyramids, a photographic-mask intermediate image, without low-contrast details, in which smooth, homogeneous regions are separated by high-contrast edges, and a temporary-image intermediate image with enhanced mid-contrast detail, retained high-contrast detail, and reduced low-contrast detail, wherein constructing multi-scale intermediate-image pyramids further includes constructing a low-pass pyramid, a band-pass pyramid, a photographic-mask pyramid, and a temporary-image pyramid, wherein each pyramid has a number of intermediate images at different scales ranging from a highest-resolution intermediate image to a lowest-resolution intermediate image, and employing values of the photographic-mask intermediate image and the temporary-image intermediate image to produce the output image that is stored in the memory and that is globally and locally contrast-enhanced, sharpened, and denoised, with global contrast enhancements including one or more of brightening, darkening, histogram stretching or equalization, and gamma correction and local contrast enhancements including one or more of adaptive lighting, shadow lighting, highlight enhancement, and 3D boosting.