Why is ISF calibration even
Most consumer televisions including HDTV's
are not calibrated out-of-the box (OOB) for proper home viewing. Why? There
are a few main reasons:
- More time to
manufacture (higher price!)
- Break in period
(typically 100 hours) causes original settings to shift anyway
- They are set up to
display a very bright picture for the showroom floor
This third reason is totally contrary to
proper home viewing, and typically effects the user settings (like brightness,
picture, color and hue).
While users can adjust brightness, picture,
color and hue, there remains an underlying issue that needs to be addressed -
grayscale. When television was first created, it produced black and white
images only. Color was a later addition to the standard. So, a proper black
and white image is first required before any colorization is added.
The underlying setup of this black and white image is called grayscale. In
terms of calibration, I adjust the red, blue and green "guns" so they work
together, producing a gray color image consistent with varying picture
brightness. These adjustments are performed in the display service menu, using
proper color instrumentation and a signal source. Performing this calibration
without these necessary tools (using one's eye) and achieving a calibrated
display is impossible. After grayscale is calibrated, the basic user settings
above may be adjusted and the display produces an image as per the program
Other calibrations I
address affecting television enjoyment are geometry, convergence, overscan/underscan,
Y/C error and color decoder.
An example of a geometry error would be a television image skewed or tilted. If
titles in credits of shows or movies get routinely cut off at the edges, your
television is probably suffering from geometry problems!
Convergence defines how well the electron gun images overlap each other.
Convergence is normally fixed in a direct view display, and adjustable in a rear
Y/C error is a timing error between chroma and luminance. This error might
produce a red edge on the left side of a face, and a blue edge on the right side
of a face. Y/C error is not always correctable through a service menu
The color decoder defines how the hue and saturation of the three primary colors
(r, g, b) are set up. In some cases there are adjustments to correct the red
and green colors to proper hue and saturation. The blue is normally corrected
in the user menu. Where possible the red and green color decoding is corrected.
Where possible Scan Velocity Modulation (SVM) is defeated. SVM is an artificial
picture enhancement technique that adds increased picture definition at the cost
of induced artifacts. In most cases a more pleasing picture is obtained without
SVM applied in the circuit.