Re: Calibrating and HD LCD monitor with AJA color bars?

Michael,


The most accurate method to calibrate any professional CRT or LCD monitor is to use a monitor probe to set up the gain,bias contrast using established SMPTE monitor alignment specifications (assuming your are doing work in a country which comforms to SMPTE specs).

The SMPTE monitor specs are available as a white paper. Look up SMPTE RP-166, RP-167 etc. A monitor probe looks like a suction cup which attaches to the monitor screen to read the monitor display values. The probe actually has an meter "eye" in it to "sense and see" the display values.


Professional monitors allow adjustments for gain and bias etc whereas consumers monitor will not henceforth why they are not suitable for high end color grading applications.
Gain and bias are the equivalents of white and black balance and allow balancing out the RGB guns so they are all equal. Green is generally used the reference channel and the user will calibrate the Red and Blue channels to Green.

The number one reason why the whites or blacks on one monitor have a blue,red or green color cast when compared to another monitor is that the gain or bias is misadjusted. This will not be solved by setting up color bars to blue check. In fact have you ever noticed why color bars seen to be plus blue or red etc and regardless of what you do to the chroma or hue adjustment you never could quite get bars to look right? Well once again that is a good demonstration of the impact of gain and bias adjustments.


Aligning color bars via blue check is but one small part of properly calibrating a monitor for accurate and consistent color correction grading and/or judging exposure in the field.
Most of the information on the web regarding calibrating a monitor will center on using blue check without regard to the most important calibrations adjustments which are gain,bias,contrast. The reason being blue check is a "common man's" method to quickly set up the monitor and most user's are not using the monitor as a highly accurate grading monitor such as one found in a telecine color correction bay.

In the world we live in today using an inaccurately aligned monitor in the field or even for use with Apple's Color program or other grading system could lead to horrible and painful results if one does not use pre-established monitor reference alignment standards such as the SMPTE RP specs which professional facilities abide by. This is the only real method to allow for a unity reference which several facilities or users can share as a common point of reference and minimize client's concerns about monitors on set or in the edit bay looking different.

A monitor which has not been calibrated with a monitor probe is one which should not be used for serious color grading or as an exposure reference in the field. Such consumer grade monitor are suitable for viewing content NOT GRADING COLOR OR EXPOSURE!! So always advise the viewer or client of this condition or instruct them to use the properly alignment monitor as the reference for critical decisions having to do with exposure,color etc.

I use a CRT monitor probe to calibrate the CRT monitors I use in the field or in the edit suite if I intend to use it as reference monitor. A monitor probe allows matching multiple monitors which makes life a lot easier when a DP desires to have an accurate monitor to look at which also matches the DIT or video controller's engineering monitor.

Contrast adjustments are quite critical given that some LCD monitor such as an Apple cinema display can output such a high foot lambert 100 (FL) level well beyond the SMPTE 30-35 FL specs that you can be fooled into exposing inproperly. The process of judging contrast by eye and memory is not recommend for inexperienced users as their sense of where the contrast level looks right could be quite off compared to the SMPTE spec of 30-35 FL. A monitor probe will measure the FL values and verify once you have reached the proper FL values.

Nailing the proper exposure in the field cannot be done correctly if you have not calibrated contrast and brightness properly henceforth why a monitor probe is a necessary item to truly allow using a monitor as a critical reference guide in addition to a waveform monitor.


Note that for long term repeatability using a monitor probe to calibrate a monitor will always allow consistent results instead of using your memory to wing it by guessing how good the monitor looks from time to time. No one's memory is quite as accurate as an instrument which accurately reads the monitor display values without regard to external distractions. The monitor probe I use has a numerical readout which easily allows hitting specific alignment marks time and time again.

The are a number of different vendors which make monitor probes so I advise doing a google search and get some feedback on which monitor probe suits your application,budget, and requirements.


Tony Salgado