Behind Gamma's Disguise
A simple power law is often used to describe the light output of cathode ray tubes (CRTs). Its exponent gamma (γ) has been measured many times in many ways, with varying results. The failure of this simple formula to accurately characterize high-resolution CRTs used in film recording applications has led to a model that explains the observed light output from very low beam currents to high drive levels. It comprises a cathode model and an anode current “trim” function; the relationship between anode and cathode currents establishes the key parameters. The cathode current is represented by a blend of two power laws. The anode current is a fraction of the cathode current, determined by the intersection of a gaussian beam with a circular aperture. The resulting model successfully predicts the behavior of high-resolution CRTs, even at low output levels. It also explains the many varying results when attempting to measure a single value for gamma.
- Print ISSN
- 0036-1682
- Published
- 1995-07
- Content type
- Original Research
- DOI
- 10.5594/J17709