B&K Precision 1253 - Manual - Manual (Page 31)

A good initial procedure is to adjust the Bias controls for D65 using the 25 IRE Grayscale Window pattern and then
adjust the Gain controls for D65 using the 75 IRE Grayscale Window. The adjustments will interact and it will be
necessary to move back and forth between the calibration patterns several times before both patterns can be set to
D65. Use the PLUGE stripes at the left side of the Window patterns to ensure that the Black-level remains set
correctly, especially when adjusting the Bias controls. Readjust the Brightness control as necessary to maintain the
proper black-level.
After initially setting the color temperature to D65 at 25 IRE and 75 IRE measure the color temperature at 50 IRE
and 100 IRE using the appropriate Window patterns. The objective is to be as close to D65 as possible at all
grayscale levels. In direct-view CRT monitors the grayscale can usually be maintained within about +/- 200 degrees
Kelvin of D65 from 25 to 100 IRE. In CRT and fixed-pixel projectors the grayscale can usually be adjusted within +/-
500 degrees Kelvin and sometimes much better with careful adjustment. The flatter the grayscale temperature the
more accurate will be the picture color.
90 95 100
Use the 90/95 IRE boxes on the ANSI Gray pattern to ensure that the peak-white level is not clipped while adjusting
the Gain controls of DLP or LCD projectors. Use the Contrast control to maintain the desired brightness level of the
screen.
Staircase
0 50 100
The grayscale is often too blue (higher than 6500K) at 50 IRE and too red (below 6500K) at 100 IRE because the
blue CRT beam current is driven harder and may not track the output of the other CRTs. Some projectors have
additional gamma adjustments that can be used to adjust the tracking to flatten a blue hump in the grayscale color-
temperature curve at 50 IRE. The blue CRT beam current also limits first at high drive levels, which may cause the
color temperature to rapidly become too red at 100 IRE. To solve this problem, and reduce a blue hump at 50 IRE,
it is usually necessary to reduce the maximum brightness at 100 IRE, either by reducing the green Gain control
(and then the other Gain controls to achieve the correct color temperature) or to reduce the Contrast control, if no
green Gain control is provided.
Use the Bias, Gain, and Contrast controls to obtain the best 100 IRE brightness while achieving the flattest
grayscale color temperature. If the grayscale color temperature varies excessively, and particularly when it
becomes too red, skin-tones will become unrealistic and other colors will be inaccurate.