Electronic devices may have camera modules that include an image sensor and processing circuitry. The image sensor may capture an image from a scene. The processing circuitry may extract image statistics and exposure levels from the image. The processing circuitry may use the image statistics and the exposure levels to generate a first exposure time, a second exposure time, and gain settings for the image sensor. The image sensor may capture additional images from the scene having long-exposure image pixel values that are captured using the first exposure time and short-exposure image pixel values that are captured using the second exposure time. The processing circuitry may generate a long-exposure image and a short-exposure image from the second image. The processing circuitry may generate auto-exposed high-dynamic-range images of the scene using the long-exposure image and the short-exposure image.