Intel OPEN (660) 120/140/150 II - Manual (Page 133)

User Manual version 2.1
OPEN (660) 120/140/150
9-123
Why Calibration is Necessary
Calibration is a necessary step for the touchscreen prior
for its operation. Unlike mouse or keyboard applications
where the cursor is part of the image, a touchscreen is a
physical overlay with an independent coordinate system.
Only by knowing the position of the image can the PC
software convert touchscreen coordinates into image
coordinates. Besides, the differences among
touchscreens and controllers, calibration also
compensates for the variation in video image among
displays. The image is affected by horizontal and vertical
adjustments on the monitor and by the physical
mounting of the touchscreen.
Additional calibration complications include image
blooming, where bright-colored images expand, and the
"pin cushion" effect, which causes the corners of the
display to be stretched. Poor display linearity can cause
similar-size boxes to be larger at the edges of the screen
than they are in the middle, or vice-versa. The displayed
image can also be tilted. Even changing video modes can
affect the screen size.
Perfect calibration cannot be achieved in all
circumstances. For example, the user can encounter
parallax problems with a change in position, or because
the present user is not the same stature as the person
who calibrated the screen.
Even the most sophisticated calibration techniques can
only partially overcome such variations. Therefore, most
touchscreen software uses only a two or three-point
calibration sequence and relies instead on well-placed
touch zones and appropriate user feedback.
The three-point calibration sequence used by Elo
automatically corrects inverted touchscreen installations
and backward cable connections. X or Y-axis inversion is
normal for most touchscreens.