Calibration

One of, if not, the most important operation that has to be performed within any Digital Intermediate Lab is the correct set up of the primary grading monitor. It is essential in 'closing the loop' so that the facility can completely trust and believe that what you are looking at is exactly what you are going to get when finally on print. The actual calibration is independent of choice of LUT provider or monitor, it is a necessary evil that must be undertaken on a regular basis to maintain quality.

Many facilities will insist that they calibrate every day, I would personally say that it is not needed every day but a carefully controlled environment is essential. The reason is that as a CRT display ages it will gradually degrade as the phosphors degrade with age. Alternatively as a projector ages, the Xenon lamp intensity will drop as the hours rack up during usage. I would suggest that a production facility should always do a final calibration before the client sits down to sign off the 'virtual film out.' If everything is calibrated and checked properly, the final viewing in the lab should be the last time it is viewed before final print marriage with the sound.

Display Choice

The choice of monitor is equally important. Although many of us are now using a flat LCD monitor as a computer screen and they are ultimately improving in quality and dynamic range, they still cannot compete with broadcast CRT monitors because they are a known quantity in how they react and how they are calibrated. However the argument against their usage is that they are backlit which can indeed appear over saturated because of their smaller size. Where as a 2K projector can now project a full 2K scan pixel for pixel - there are even 4K projectors starting to make an appearance, making the full cinema experience the choice of many - however it purely depends on the facility's available space. It is fine either way as long as you trust the monitor you are looking at.

Over the last few years, I would never have recommended grading using an LCD however problems that have plagued LCD's such as black level, viewing angle, and colourimetry have improved a lot in the past few years and are now coming of age. Personally I have a lot of faith in a Sony HD Broadcast monitor, I guess it is a known entity and has been very faithful to me over the years!

However everything is moving on and CRT manufacturing is gradually being phased out, so finding a new grade one broadcast monitor is getting harder and more expensive. Therefore, for accurate colour calibration, stability and contrast tracking the best monitors to use are those that have a great track record - grade one broadcast monitors.

 

The Point Of Calibration

Device calibration - CRT, LCD or projector has to be carefully done because the 'Cube' or 'LUT' applied will only be as good as the initial calibration of the chosen device. Each individual device will have a manufacturers set up which will calibrate correctly to a probe that is attached.

For instance Sony sell a probe to perform the calibration automatically, adjusting the guns to correct the levels across the screen. The probe attaches to the screen via a suction cup, shutting out all surrounding light and measures the intensity of patches displayed during the calibration procedure. The monitor will display a patch somewhere on the screen and the technician has to move the probe to cover the patch. The setup then automatically adjusts the luminance and levels to correctly display the white or grey patch. The calibration can be checked independently using a Minolta or Philips colour temperature and illumination probe.

Alternatively, if you are using a projector, because the image/patches are being projected you need a meter that measures from the screen, such as the Minolta. When profiling an individual projector, this kind of probe would be used, set up on a tripod and capturing the data from each individual patch needed to check the calibration of the projector.

Final Note: Just as a monitor/projector will adjust during its lifetime due to degradation, phosphors gradually dying and the lamp of a projector gradually fading, a probe will also need to go back to its manufacturer to also have itself calibrated. It seems a bit ironic that something built to calibrate would also need the same kind of procedure throughout its life. Its not critical but something to bare in mind if things are not quite looking as they should!

 

The Grading Environment

Careful consideration must also be given to the condition within any room to be used for film grading. Telecine suites tend to use lighting conditions more appropriate for projects to be seen under general living condition in normal homes, maybe without the log fire. Film projection however occurs in more controlled environments within a theatre and the ambient illumination is many times darker than home viewing of TV. For this reason the film grading environment must be similar, if not darker, than any cinema theatre. Any light contamination will reduce the contrast range of the grading monitor resulting in inaccurate grades being performed. If in doubt shut out all light except for the usual green 'Emergency Exit' that is always within any cinema screen - Health & Safety!