I let myself get pulled into responding to a thread at Creative Cow’s DaVinci forum on 3D LUT calibration, but felt that the subject might benefit from a bit more elaboration. I’ve been researching LUT calibration of prosumer display devices in greater detail for a small section of my upcoming book, which I hope will cast some more light on an admittedly arcane subject about which there’s a bit of confusion. However, LUTs are an example of high-end tools and methodologies that are increasingly within the reach of smaller facilities who aren’t afraid of a bit of research, and 3D LUT calibration, once the domain of high-end film facilities, is worth knowing more about if you require color critical monitoring.
To massively oversimplify, a 3D LUT is a three-dimensional look-up-table for taking incoming image data and converting it to another set of image data—in other words it’s a color and contrast transformation. 1D LUTs are suitable for calibrating a monitor’s gamma response, but a 3D LUT is required for changing the gamut, or range of color that a display shows.
LUTs can be used for many purposes, but in the case of monitor calibration, the process of using a 3D LUT is one of using software and a monitor probe to analyze your monitor, to figure out exactly what the difference is between your uncalibrated display and the ideal video standard that you want it to show. Once the software has figured out the difference, it generates a 3D LUT that can transform an incoming video signal in such a way so that it will appear, on the analyzed display, as if it has the perfect gamut (red, green, and blue primaries) and gamma response.
It’s a bit of a mathematical hat trick, but it works, is accurate, and is an accepted means of display calibration throughout the postproduction industry. Using 3D LUTs for outboard monitor calibration of any display requires three things:
- An outboard LUT calibration device (usually taking HD-SDI in from your workstation’s video-out and putting HDMI out to your display)
- Software for analyzing the monitor (using a probe) and generating a LUT that’s appropriate to your calibration device (there are many different formats)
- A probe for doing the analysis (good probes aren’t inexpensive)
Keep in mind that outboard 3D LUT calibration only works if the display you’re calibrating is capable of the color gamut that’s required by the standard you’re trying to calibrate to. In the case of Plasma displays, a 3D LUT will bring the typically oversaturated primaries back into line with, say the standard Rec. 709 RGB primaries that you want to be monitoring with, as well as setting proper gamma for the display.
There are several software and hardware solutions, some expensive, some more affordable. Here’s a list for your own research:
Hardware (All capable of 3D LUT processing)
- Filmlight’s Truelight SDI
- Cine-Tal’s Davio
- Blackmagic’s HDLink Pro
- Filmlight’s Truelight color management system (CMS)
- Cine-Tal’s Cinespace
- Light Illusion’s Lightspace CMS
Probes (different software supports different probes)
- Filmlight Truelight Probe (for Truelight CMS)
- X-Rite Hubble (works with Lightspace and Cinespace)
- Klein K-10 (works with Lightspace)
- Konica Minolta CS series (works with Cinespace)
- Photo Research PR series (works with Cinespace)
Cinespace and LIghtspace probe support has slowly expanded over time, these notes are true as of a quick look at the company websites today. Don’t take my list as gospel, you’ll want to re-check. Also, I’m not picking favorites, each of these systems is in use in different post houses.
If you’re interested in more information, check the company sites at http://www.filmlight.ltd.uk, http://www.lightillusion.com, and http://www.cine-tal.com. In particular, the Lightillusion site (run by colorist and developer Steve Shaw) has some great whitepapers that he’s written that should shed a lot more light on the subject than my brief overview here. Check it out.