1. A method of generating a composite image of a scene from an achromatic image of the scene and at least two monochromatic images of the scene on a device having a processor, the method comprising: executing on the processor instructions configured to: for respective composite pixels of the composite image corresponding to an achromatic pixel of the achromatic image and at least one monochromatic pixel of respective monochromatic images, adjust the monochromatic pixels according to a gradient between the achromatic pixel and neighboring achromatic pixels to produce a set of adjusted monochromatic pixels; and compute the composite pixels of the composite image from the adjusted monochromatic pixels.