Background compensating bar code readers

A method for reading a luminescent bar code on a background surface whose reflectance may vary over the coded area, comprising

• providing a beam of light focused to a small area and containing at least one predominant frequency band,
• scanning the beam across the bar code,
• selectively collecting reflected nonluminescent light in a first frequency band,
• selectively collecting light in a second frequency band predominantly resulting from luminescence of the bar code,
• converting the collected light in the first frequency band into a first signal responsive to the reflectance of the background surface,
• converting the collected light in the second frequency band into a second signal responsive to the amount of luminescent light.
• modifying the first signal to provide a third signal that varies with background reflectance substantially as does the second signal.
• combining the second and third signals to provide a fourth signal of substantially constant amplitude and substantially independent of the local background reflectance under the luminescent material of the bar code, and
• decoding the information in the fourth signal.