An image processor merges images from a plurality of cameras including applying spatially-varying gains over images from individual cameras to obtain a consistent effective where the images are stitched together despite the cameras possibly having different camera exposures. The image processor can adjust the camera exposures to improve stitching results. In addition to gain modification, the image processor can also modify the images for other artifacts, such as veiling glare and make those less visible at the seams of images. The image processor also can take into account constraints on gain changes and optimize camera parameters to minimize stitching artifacts. Using a cost function, the image processor can optimize for constraints on camera exposure that would otherwise result in camera exposure differences that would themselves cause visible artifacts.