Monitor calibration is as important for TV and film post production as it is is for pre-press or photography. However, with pre-press the workflow is based around matching what comes off the press and with photography it may be a focused around getting a good print from a defined device but with post production the final output device is often a TV or even cinema projector of unknown colour capabilities. This doesn’t make calibration for post production less worthwhile, quite the contrary it makes it even more important that you know that what you are seeing on screen conforms to some standard or middle ground of possible output variables.
The first step before you begin calibration is to know what standard your are trying to match. For broadcast HDTV the most common standard is ITU-R Recommendation BT.709 , commonly abbreviated to Rec. 709. Rec. 709 has the same primaries and white point as sRGB but has a gamma (tone curve) of 2.4.
For movie work DCI is the standard to aim for. The DCI-P3 colour space has a gamut similar in size to Adobe RGB but with different primaries (R 0.680, 0.320 G 0.265, 0.690, B 0.150, 0.060) and a gamma of 2.6. The white point of DCI is slightly variable because even though there is a calibration white point as part of the spec (0.314, 0.351) productions are free to use other white points as long as all colours remain within the DCI gamut.
Lots of advertising video work is now favouring sRGB, given that ads are frequently viewed online. Whatever industry you are in a little research or questioning of clients should tell you what standard you should be aiming for.
Is your software ICC aware?
The second step before you calibrate is to consider the software in your workflow as that can influence the way that you calibrate the monitor. Some post production software, such as Adobe After Effects is fully ICC aware. This means that it can access a monitor profile and can convert the images displayed on screen from an ICC profile associated with a project to the monitor profile. This means that if you have a calibrated and profiled monitor you could have projects in various standards, such as Rec 709 or DCI and each would display accurately. However, most production software is not ICC aware and relies purely on the calibration of the monitor. So the monitor has to be adjusted to match the standard exactly. The software assumes that the monitor is displaying as per the standard and makes no adjustments.
With many good monitors it is possible to adjust them to a luminance, gamma and whitepoint values with calibration products such as X-Rite’s i1 Display Pro. However, adjusting their colour gamuts so that they match the standard is harder and requires a more advanced monitor that is capable of emulating colour gamuts other than its own native one. Monitors such as EIZOs ColorEdge CG series have 3D 16-bit look up tables that means they can emulate other colour spaces. The ColorEdge CG246, CG247 and CG277 have the ability to emulate the Rec 709 and DCI-P3 gamuts. Other monitors may have sRGB or other modes you can put them into that will do a more basic gamut emulation.
Once you’ve decided on your standard that should inform your choice of white point, gamma and also gamut if you have that option. What the targets aren’t so explicit on though is luminance. For broadcast 100 cd/m2 is normal. For DCI cinema work then some prefer values as low as 50 cd/m2, others up to 100 cd/m2. A lot will depend on your lighting environment. The darker the room lighting then the dimmer the monitor can be. Colour grading monitors may need to be calibrated to a specific LUT (look up table) to emulate a traditional film look.
Obviously, if you work with others then all the monitors need to be calibrated to the same targets, software such as ColorNavigator NX makes calibrating many screens to the same values much easier and allows for centralised administration in large workgroups. Solutions such as, ColorNavigator, Datacolor Spyder4Elite and X-Rite i1 Display Pro have some built-in presets for Rec 709 or other standards but always check them against the standard and your own company’s preferences. Most screens should be able to get quite close to the luminance, gamma and white point you’ve specified but only monitors with high bit look up tables and the ability to emulate colour spaces will be able to match the colour gamuts of the standards.
This article should guide you in the right direction for calibrating a monitor for post production work, but we’d really like your input as well. So if you work in post production and have your own opinions on how to calibrate monitors then please post a comment and share your knowledge.