Video Calibration

The New Wave of Color Calibration Technology: Cube Calibration

ARTICLE INDEX

Cube Calibration In Use

Test Setups and Calibration

Testing was done with two totally different setups to fully evaluate how the different products perform. Chris Heinonen tested the SpectraCal ColorBox using both a Sony VPL-HW50ES Projector which has a built-in CMS, as well as a Sony KDL-32EX308 LCD TV that contains only a 2-point white balance control. All of his calibrations were done using CalMAN 5.0.4 or 5.1, with an i1Pro and C6 meters.

Mark Vignola used a Lumagen Radiance 3D XS video processor with a JVC RS25 projector and a Panasonic VT30 plasma display. Calibrations were performed using CalMan 5.1 software, along with an i1Pro2 meter. Cube calibration is available in CalMAN as well as the Chromapure calibration software packages.  Chromapure however, only supports the Lumagen Radiance and not the ColorBox.  In order to reduce the number of variables, we chose to both use CalMAN.  We will report back on Chromapure's interface in a later review.

Beginning with the Sony VPL-HW50ES, the SpectraCal ColorBox allows for up to 262,000 points of data, but that is certainly overkill for our use. Instead I tested it with 729 points and 4096 points, to see if there was a large difference. For both of these settings I first got them as accurate as possible inside of the Sony CMS without making large adjustments. Large adjustments lead to irregular display responses, as we discussed earlier. Some would actually suggest no adjustments beyond white point, but the Sony already had very good response at different saturations so I just left it calibrated.

As the ColorBox does nothing besides color correction, all you need to do to use it is place it in your HDMI chain before the display, and then select one of the six memories using the remote. Then in CalMAN you choose which memory you are going to use, and use their 3D LUT workflow. I chose a gamma of 2.2 and the standard Rec. 709 HDTV colorspace. I also chose a target dE of only 0.5, which is much lower than the default. This will cause it to take longer, but should provide more accurate results. Calibration of the grayscale for each took around 15-20 minutes using the C6 colorimeter. Calibration of the color was a much longer process.

The 729-point cube took around 3.5 hours to complete. The 4096-point calibration took almost 8 hours and over 10,000 readings to finish. Happily I started this before going to bed one night, so it was easy to let it complete in the dark without being disturbed. The C6 is a fairly fast meter with CalMAN, but for doing a huge number of readings like this I would really like an even faster one. I certainly wouldn't use a spectrometer as it would be very slow. Once both were completed, with different memory locations, I was free to switch between them to compare.

Calibrating the Sony HDTV is much more limited in setup before calibration. All I could do for it was pick the most accurate color temperature and then adjust the white balance. Everything else was left at the defaults, as there is no CMS to use to adjust it. I only used 125-points for the Sony, mostly wanting to see if the ColorBox can take a display that costs 20% of what it does, and turn it into something with far more accurate color. Thankfully running the calibration on the Sony only took an hour with that few points.

In Mark's set-up, the Lumagen sits as the last piece of equipment before the both the plasma and projector. Both the Panasonic VT30 and JVC RS-25 have fairly full complements of calibration features, including CMS and grayscale controls, but Lumagen suggests its users only select a color pre-set that gives oversaturated colors, and then do nothing more than set brightness, contrast and high grayscale. Once these were completed, Mark conducted the CalMAN 3D LUT calibration workflow exactly as Chris did. CalMAN also allows users to select which CMS we'd like to calibrate: the Lumagen possesses 4 memory positions, but can accommodate 8 different full CMS calibrations. These can be mapped, as the user sees fit, to any number of different situations. Unlike the ColorBox, the Lumagen is limited to only 125 points of color correction, plus 21-points on the gray-vector, so no selection is made by the user regarding how many points are corrected. While Mark conducted calibrations on both the RS-25 and VT30, we'll only be discussing the results from the plasma for simplicity purposes.

The i1Pro2 is not as fast of a meter as Chris's C6, so automated calibrations took a little longer in his set-up, with Calibration of the grayscale taking about a half an hour, and 125 point color calibrations taking approximately an hour to complete. Either way, the process is fairly streamlined and painless once things get started.

Results and Analysis

Before the cube calibration, the Sony VPL-HW50ES was a fantastic performer. You'd have to be incredibly picky to want better performance that it could do out of the box with a simple calibration. If you are that picky and demanding, you can get even better with a 3D LUT added on. The gamma, grayscale, and CCT numbers all improved after the cube calibration, but not by gigantic amounts. That little bump of an error at 5% on the gamma is now totally fixed, though. When we move to the more challenging saturations and color checker tests, the average dE on the 50ES drops from very low, around 1.4, to obscenely low at below 0.75 dE 2000.

Practically speaking, if you look at the Sony VPL-50ES with a cube calibration, you are going to see a perfect, reference image without any real flaws. Colors, grayscale, gamma, and everything else is so close to perfect, you visually can't see the difference. The idea of seeing an image that is practically as good as the director of your favorite film is a bit crazy, but that is the crazy world we might be living in now.

Watching all of my favorite content, it was amazing how clear and detailed everything was. Skin tones were totally neutral, oceans and lakes looked more natural, and shadow details were much better with the improved gamma and grayscale. It was clearly the best picture that I've seen in my home, and possibly the best-projected image I've seen outside of a movie theater. I looked for all the flaws that calibrations can introduce, like banding and posterization and other bit-depth issues, and saw none of them. All I saw was exactly what was on every single Blu-ray I watched and nothing more.

I also switched between 9 and 17-point calibrations on the 50ES and saw no difference. I could move between them instantly using the ColorBox, but not once did I see anything that made a difference in my eyes. Because of this, I'm only reporting on the 9-point calibration, as the 17-point numbers were all almost identical, and really within the margin of error of the instruments. They were certainly within the <1 dE2000 level where you could see a difference side-by-side, and if I had both images up next to each other, I'm certain I would see the same thing on each. Perhaps if you work in a mastering studio you would need this, but in the real world, the extra 5 hours spent on the calibration made no visible change to my eyes.

With the cheap-o Sony TV, we did see a bit of a shift for the worse in the overall CCT, which is unfortunate. Aside from that, everything else improved across the board. Gamma went from way too dark to spot-on perfect, our grayscale dE2000 went from visible errors to absolutely nothing, and the color checker dE2000 error was cut in half. There was a bit of a rise in some of the saturations dE2000 numbers, but overall most numbers really improved, even on a display this cheap with no CMS controls. It didn't make it reference quality like the projector, but it made it much nicer than it was before.

In Mark's case, instead of testing how close we could get the VT30 before using its internal controls, we thought it would be interesting to test THX mode, which, according to THX: "offers the closest thing to a pre-calibrated setting out of the box. This reproduces the Rec.709 color gamut, luminance levels and other settings used by filmmakers in the mastering studio—with the push of a button." As you can see from the data we've presented, THX mode was decent, but not terrific. While some things aren't bad, nothing is perfect.

After the full calibration with the Lumagen, we can see a marketed improvement in all aspects of the displays performance. Grayscale now tracks very well, with an average dE2000 of 1.98, a significant improvement over what the THX mode was giving us (dE2000 5.6). While the gamma is substantially improved, these results could easily be improved by a few minutes of tweaking. Results on the saturations and color checker test are now an average of dE2000 of 1.6 vs. 4.9 in THX mode; a substantial improvement. Viewing results were equally as impressive as what Chris experienced. Blu-ray content looked superb: this summer's Avengers, a reference quality disc, looked stunning. The best way to say it is: everything just looked right.

We did note that the state of the display before calibration did seem to have an effect on the quality of results that we achieved. Mark started his calibration of the VT30 with absolutely nothing done inside the display except contrast, brightness and 2-point grayscale. All other controls were left at factory default – and while we did not show the data collected prior to calibration with the Lumagen, this starting point was actually worse than what THX mode provided. Alternatively, Chris's calibration of the VPL-VW50 started with an already calibrated display that measured very well even before external calibration was implemented. His results from the cube calibration were better than we saw in the VT30. What Mark achieved with the VT30 post calibration were more similar to the Sony LCD, which, as a result of simply having less calibration controls available, also started as a basically native, highly incorrect display.

While the point that you start at seems to affect post calibration results, this is likely a result of the cube calibration implementation in CalMAN software at this point versus the magnitude of corrections achievable by either of the external solutions we evaluated as all of the errors that we observed are well within the capabilities of being corrected by both the Lumagen and Colorbox. As the automated cube calibration matures, we anticipate that the starting point will become less important.