The gamma is fixed in all Picture modes except Custom, where the Pro menu offers several fixed gamma options. Initially, the Custom mode's enticing adjustments and the potential for separate calibrations for 2D and 3D lured me in, but this proved to be a mixed blessing. I could regale you with the contents of 50-plus pages of calibration notes (I write large) accumulated over several days of multiple setup attempts. But I'll try to be a little more concise.
Gamma affects the brightness in the mid-brightness region. The most commonly recommended playback gamma hovers around 2.2. But, as measured, the gamma options available in the Custom mode's Pro menu were questionable if you want an accurate reproduction of the source. Even the highest available gamma setting (2.6) measured below 1.7 in 2D, and at some brightness levels in some settings, it clocked in at under 1.0. The Custom mode's 3D gammas were slightly better up to 70 IRE, but they still measured nowhere near the numbers indicated by their settings.
I abandoned further attempts to use the Custom mode for 2D. Fortunately, calibration in the Cinema and/or THX modes, as performed in the service menu, was good to excellent. The 2D color points were also virtually spot on, although in all cases, the intensity/brightness of the individual colors measured higher than optimum. Turning down the Color control helped, but since it affects all colors simultaneously, it couldn't precisely correct all of them.
The calibrated Cinema mode produced satisfactory gamma results in the GT30. The calibrated THX mode worked nearly as well as Cinema, but the Cinema mode's gammas were a bit closer to the ideal 2.2. 2D images looked more fully saturated and three-dimensional in Cinema than in THX, though these differences were subtle. I'm talking about the illusion of three dimensions in 2D playback here, not the use of the set's 2D-to-3D conversion feature. Properly set up, a good HDTV is inherently capable of producing a believable sensation of depth from 2D sources—something we seem to have forgotten in the race to 3D nirvana.
I also noted that after I made adjustments in the service menu, the measured results in normal operating mode were sometimes different. These differences were significant enough on the GT30 that I had to jump in and out of the menu to make my incremental adjustments until the out-of-service-menu results were satisfactory, a tedious process.
Apart from having to do calibrations in the service menu, there were no downsides to using the calibrated Cinema or calibrated THX Picture modes for 2D. But Cinema and THX don't offer the ability to do separate calibrations for 2D and 3D, even in the service menu, which defaults to 2D as soon as you open it. Custom mode, which does offer separate calibration controls for 3D in the user menu, suffered from the low gammas I mentioned earlier. However, while these were a bad bargain for 2D, I found that they produced a noticeably brighter, punchier 3D image than either Cinema or THX. A low gamma enhances 3D brightness, a benefit for plasma technology, which has less inherent brightness than LCD.
Oddly, while the 2.6 gamma setting in 3D measured closer to 2.2 across most of the brightness range, that setting (and 2.4 as well) looked dark and gloomy. For reasons that remain puzzling, the lower gamma settings—2.0 or 2.2, which actually measured far lower than that—looked much better. These gamma settings appear to have been cannily crafted to add significant brightness without washing out the picture or producing any other visible, distracting artifacts.
Other than the common failure to properly handle 2:2 pulldown, and a failure to cleanly upscale 480p material to 1080p (see the Scaling block on the Video Test Bench chart), the GT30's HD video processing was good. The SD processing (upscaling and deinterlacing from 480i to 1080p, not shown in the charts) was borderline on 3:2 SD (marginal on two different tests, but a pass on a third). The set also failed a 2:2 SD pulldown test.
2D Performance
The GT30 offers gorgeous color on most sources, even with its somewhat inaccurate color gamuts (the points were spot on, but the intensities of the colors diverged from the HD standard, even with the color control turned down). However, the set exhibited a slightly pink tint across most of its screen when it displayed a full-screen white field of even moderate brightness.
The calibrated GT30 also had a noticeable brownish shift in dark grays, plus a subtle tinge of green, which was most noticeable on black-and-white material. It was less visible in color, although once I began to look for it, I could see it in flesh tones. All of the GT30's color deviations were subtle and thus easier to spot in side-by-side comparisons than would be likely in a solo evaluation. None of these appeared to be related to the calibration, nor could I correct the issues with the Tint or Color controls.
