A method for forming an enhanced image of tooth tissue for caries detection obtains fluorescence (50) and reflectance (52) image data from a tooth (20). Each pixel in the fluorescence image data is combined with its corresponding pixel in the reflectance image data by subtracting an offset to the reflectance image data value to generate an offset reflectance image data value, and then computing an enhanced image data value according to the difference between the fluorescence image data value and the offset reflectance image data value, whereby the enhanced image (64) is formed from the resulting pixel array of enhanced image data values.