1. A computer-implemented method to retarget a sequence of images using a non-linear warp function generated by optimizing an energy equation based on automatic and interactive constraints, the computer-implemented method comprising: without requiring user intervention: identifying a plurality of aspects of a source sequence of images having a first format, the plurality of aspects including at least two aspects selected from gradient, saliency, motion, and scene-change; and generating a set of automatic constraints identifying at least a first feature region to be preserved in the source sequence of images, based on the identified plurality of aspects of the source sequence of images; generating a set of interactive constraints based on user input identifying at least a second feature region, different from the first feature region, to be preserved in the preview sequence of images, the set of interactive constraints specifying at least two feature-region aspects selected from location, orientation, shape, and saliency, whereafter the source sequence of images includes at least one non-feature region; generating a non-linear warp function by operation of one or more computer processors and to warp from the source sequence of images to an output sequence of images having a second format having a different aspect ratio and a different resolution than the first format, wherein the non-linear warp function is generated by optimizing an energy equation based on the sets of automatic constraints and interactive constraints; and applying the non-linear warp function to the source sequence of images in order to generate the output sequence of images, wherein the output sequence of images preserves the first and second feature regions and does not preserve the at least one non-feature region, wherein the output sequence of images is output.