The Accu-Chart 11-Step Grey Scale Chart is an extended range test chart intended for use with high-performance video cameras including both CCD and tube types. The chart consists of two arrays of 11 neutral grey patches or "chips" ranging in reflectance from 2% of approximately 90% (about 5.5 f-stops). The arrays are arranged so that one increases in reflectance from right to left and the other increases left to right. The strips are mounted on a uniform grey background with a reflectance of 16%. A black-white-black test object in the center of the chart provides a black (<0.5% reflectance) reference for adjusting dead black level in amplifier set-up as well as a "super-white" (90% reflectance) patch for setting peak video in many applications. The black regions can also be used for flare compensation.
The grey scale values are chosen according to a power law producing a "Gamma" value of 2.2, the characteristic value for television receivers and monitors. To provide an overall system gamma of unity, the video camera is usually adjusted to a Gamma of 1/2.2=0.45. With the Gamma Compensated Chart, the video Signal from a camera adjusted to that value will appear as a linear "staircase" (equal steps) when viewed on a waveform monitor.
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