Acer AL1731, Service Manual

Page: 11 / 78

10
Note 8) Definition of Crosstalk (Refer to the VESA STD)
The calculation for shadowing is made from the 2 luminance measurements Gbkg and Lsh,
as follows:
Lmax -Lmin
C
T
=

x100 %
Lmin
Where Lmax is the larger value of Gbkg or Lsh , and Lmin is the smaller of the two.
♦
To determine background and foreground levels (colors),first set the background to any
gray scale or color level suitable for shadowing determination.(Note that it may take
several iterations of adjusting background level and box levels to determine the proper
value for the background .Next display the box levels to determine the proper value for the
background level. Look for shadowing in any direction from box E. Independently vary the
gray level (or color) of the background and box E until the worst case shadowing is
observed. This defines the background (Gbkg) and foreground (Gfg) levels to be
maintained for the remainder of the test.
♦
One point only (the target) will be measured. To determine that point proceed as follows
Using the background and foreground gray levels of step1 (Gbkg and Gfg). Turn on each
box at a time. Look for the case with the worst shadowing. The box causing the worst case
is the shadowing source, or Bsrc. Use Bsrc and the box opposite from it that lies directly in
the shadow path. That is the target box, or Btgt. Note that box Eight be either Bsrc or Btgt,
depending on the shadowing conditions, but typically Bsrc and Btgt will be a pair of
opposite boxes, A&C or B&D. Btgt will only be displayed for aligning the LMD. It will be
turned off for the actual measurement.
♦
The target box point (Btgt) will be measured with the source box (Bsrc) turned on then off.
(Btgt is for alignment purpose only) Display the background only at level Gbkg. Display
Btgt determined in step 2 above. Using the correct distance, angle, and measurement
aperture, align the LMD to the center of the Btgt. Turn off Btgt. With Gbkg set to its proper
level, measure the luminance (or color). Next,turn on the source box Bsrc. Again measure
at the center point of Btgt (without Btgt present.). In this case the LMD will be measuring
the shadowing level, Lsh.