A portable electronic device may include an image signal processor that includes a clipping circuit, a pyramid generator circuit, and an image fusion processor. The clipping circuit clips pixel values that are under-exposed or over-exposed. The pyramid generator circuit applies a filter to the pixels of the image to generate a filtered image. Some of the filtered pixels may be generated from one or more clipped pixel values. The pyramid generator circuit identifies those filtered pixels that are generated from one or more clipped pixel values and marks the identified filtered pixels with a tag. The pyramid generator circuit decimates the filtered image to generate a downscaled image, which may include one or more filtered pixels that are marked with the tags. The image fusion processor fuses the downscaled image with another image. The pixels that are marked with the tags may be disregarded in the fusion process.