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Why is ISF calibration even necessary?

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:

  1. More time to manufacture (higher price!)
  2. Break in period (typically 100 hours) causes original settings to shift anyway
  3. 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 content.

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 projection display.

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 adjustment.

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.