Technical aspects of ISF Calibration

First, I want to begin by detailing what services are actually offered, and what constitutes an ISF calibration of a video display. This is best achieved by discussing the four aspects of a picture, and then detailing how those four aspects are actually affected by calibration.

  1. Dynamic Contrast – The difference between the darkest black the display can produce, and the brightest white that can be produced, without causing crushing in the blacks or clipping of the whites.
  2. Color Saturation – The manner in which the display decodes color signals from programming. When saturation is incorrect, it can result in flesh-tones that are either too red or yellow, for instance.
  3. Colorimetry – Also known as color accuracy, this is the manner in which the display mixes Red, Green and Blue signals to produce various shades of white (or black). From the factory, televisions tend to have the blue dialed up too high, and the green low, in order to produce a “brighter”, more appealing picture.
  4. Resolution – Displays all have a native resolution (usually 1080p these days), and when receiving a signal that is of a different resolution, the video processing built into the display has to make the best guess possible as to how the incoming signal should appear. Displays do not normally have very good processing built in, and this will cause a noisy, sometimes distorted picture surface.

The following steps are what occurs during a normal calibration:

  • Using colorimeter and software, I take pre-calibration readings to determine how well the display is currently adjusted. Software will record these measurements for use later.
  • Using Pattern Generator and software, beginning adjustments are made to Brightness and Contrast (sometimes known as Picture).
  • Display Gamma is measured for each adjustment possible by the display’s menu, and depending upon room conditions, closest to the correct curve is chosen for the environment. Gamma is defined as how smoothly or aggressively the display makes the transition from Black to Grey to White. The more light controlled the room is, the more smoothly you can make the transition and still have excellent picture quality, but in a room containing more ambient light, a more aggressive Gamma curve is needed to maintain the same picture quality.
  • Grey scale calibration is next, with meter and software used to track RGB mix, and then adjustments are made to Cut and Drive controls. If you put a 10 step gradient display on the screen, Cut is how the display produces the lower half (Black to Gray) and Drive is how the display produces the upper half (Grey to White) of the black to white spectrum. Grey scale calibration can be 2D or 3D, depending on the level of adjustment provided by the manufacturer. 3D will provide a 3rd control known as luminance.
  • Color Gamut is set, next. Gamut is the range of colors that the display will produce, and is represented by a triangle consisting of 6 points, the three vertices of the triangle being Red, Green and Blue (Primary Colors), and then 3 midpoints between the vertices being Yellow, Cyan, and Magenta (Secondary Colors). These points are measured and diagrammed according to the C.I.E. Chromaticity chart, and adjustments made to get the actual range to equal the Adobe 1998 standard for the color triangle. These adjustments are made using the Color Management System (CMS) controls provided by the television manufacturer. Sometimes they are as simple as two selections (Native, and Auto), or they can be much more complex, offering up to three controls to adjust each of the 6 colors.
  • Once this is all accomplished, Brightness and Contrast are checked again to ensure accuracy after the other adjustments, Color and Tint are set, and finally Sharpness is checked.
  • Post Calibration measurements are taken, recorded by the software, and a report is generated in .pdf form that will show pre-calibration measurements next to post-calibration measurements, along with a place to record pre and post display settings for quick reference

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