Photogene's tools are along the left side of the phone when editing. Advanced tool options are displayed at the bottom when a tool is selected. This screenshot was taken before any editing was done to the photo.
This screenshot was taken after the photo levels were edited manually. The histogram and automatic-levels button is at the bottom of the screen. Photogene's developer intends to add individual histograms for red, green, and blue in version 2.0.