1. A method at least partially implemented by a computer, the method comprising: fusing multi-channel images into a single image based on importance-weighted gradients, each multi-channel image comprising multiple channels, the fusing comprising: for each channel in each image of the multi-channel images: adjusting the channel to have a same mean gradient as a maximum mean gradient channel; measuring local salience for respective pixels in the channel; assigning a normalized weight to each pixel of the pixels based on respective ones of the local salience measurements; generating an importance weighted contrast form based on normalized weights associated with respective ones of the pixels in the channels; constructing, using the importance weighted contrast form, a target gradient based on pixels in each of the channels; and creating the single image from the target gradient; wherein the importance weighted gradients are measured using respective salience maps for each channel in the multi-channel images.