Monitor Calibration Blues
Mar 29, 2006 5:02 PM, S.D. Katz
Having worked for an entire summer on the D.I. for an animated film, I have new found respect for the importance of accurate monitoring of digital files. This may seem obvious, but having to make both an HD version for a digital cinema and 35mm theatrical release is a real eye opener. While we have been promised utter consistency in mass distribution of digital cinema versions of a movie, that fulfillment of that promise is still a few years away. Digital cinema theaters are a mix or old and new projectors most of which are not 2K or more importantly, not equipped with 10-bit Texas Instrument black chip imaging engines.
This means that as you take your color corrected film or digital cassette to a theater for digital projection, the picture varies from theater to theater. My experience is that at the moment, film projection is more consistent then digital projection. We can’t control that, but we can control the consistency between the screened image and the image on the grading or D.I. monitor. This is the responsibility of the grading facility, but today with floating point capability in After Effects and Indie productions (including film) being brought to boutique facilities to do interpretive color manipulation beyond scene to scene color correction, monitor calibration may not be getting the attention it deserves.
Even if you are not doing film work, monitors need to be calibrated frequently for broadcast bound images. However, many desktop production companies never calibrate their monitors other then matching color bars to scopes and waveforms. I’m talking about using a probe to evaluate the CRT and the entire data path.
Systems such as Discreet Lustre, Digital Vision Nucoda, Cine-tal Cinemage or FilmLight's Truelight demand using proprietary calibration systems. Yes, these are costly system, but they provide LUTs (look up table) for specific monitors for a selection of outputs including film stocks and broadcast TV monitors. Any monitor must be calibrated frequently because their color profile changes very quickly. While color shifts may be small, the colorist I know calibrate weekly or for each new project.
You have probably come across calibration and hardware probes for the print industry. Eye-On and Colorvision Spyder2 Pro are two popular hardware probe and software systems for photography and print media that I mention here only because there is no low cost, easy to use system for video. However calibration is not particularly difficult. Truelight from FilmLight has a probe and software solution for film and video that is superb and makes sense if you have invested in a good monitor—however, this is an expensive system.
What the probe does and why: A probe is essentially a light meter that measures each color of the monitor (RGB) individually and builds a LUT to correct for errors in the data chain (cables, graphic cards, etc.). Matching to film means that you have to be working with a lab, or at least have an idea about what film stocks are being used—Filmlight's system, for example, provides color cubes (their version of a profile) for the major film print stocks. In any case, the probe is used “to get the transition from dark to light linear and to compensate for white and black levels” as my friend Leonard Coster puts it. Leonard is color scientist and inventor who scans and records film through his own company Speedwedge in Australia. Leonard builds all his own gear and shared these thoughts on calibration with me:
“Film is log, TV is linear," says Coster. "I have built LUTs that "pleasingly" translate linear TV images to log for film purposes but again, the supplier of this data must keep their TV gear calibrated to TV standards for this to work out well. When I say "pleasingly" I am lucky that a direct mathematical conversion of the linear TV data range into density values (film) actually looks really good ! So I am happy that the results I am getting are as aesthetic as they are technically justifiable. Some broadcast monitors (e.g Sony) have built-in probes to correctly display video signals. If you are preparing Log data to be recorded you have to make sure that your monitor and system are displaying the Log data as it will look on film. This can be done easily enough with a LUT, but if you do not do this then the images will be WAY off."
What are the downsides of not calibrating your monitor? While it’s fine to say that you should always trust the scopes and waveform, there is a huge temptation to judge color on the monitor. The big issue is really where the black and white points fall. It is entirely possible to lose detail in the whites or the shadows by making artistic decisions and not paying close attention to the scopes. However, the scopes just keep you out of technical trouble. You still need good monitoring to be able to make artistic decisions accurately when you are well within the gamma of the data.
So what’s the solution? First, buy the best monitor you can afford. LCDs are good, but not good enough for serious color decisions for film. I have viewed data in a single afternoon on an LCD and a very serious calibrated Sony HD monitor and then viewed film recorded from that data in two film theaters and one digital cinema with a “Cinema” black chip Barco projector and found the LCDs to be extremely misleading. Frankly, they were useless in dark scenes where the difference between preserving mood and going too dark is a very narrow divide.
As we move farther along the digitization of media and improved viewing systems in the theaters and at home, all of us have to raise the bar on color management. Every step in the data path is critical, but all artistic decisions are based on the monitor. It’s worth taking out a loan to get the best gear you can.
Continue the discussion on Crosstalk the Millimeter Forum.