Optoma GT720 Projector - Performance
7/14/11 - Art Feierman
In this section we consider the brightness, sharpness, and image noise of the Optoma GT720 home theater projector. Also considered are the physical attributes of light leakage and audible noise of the GT720.
Optoma GT720 Brightness
Let's look at the GT720's numbers:
Lumen Output and Color Temp at 100 IRE:
Cinema= 1143 @ 6721 (with default BC of 6)
Bright= 2121 @ 6807
Presentation= 1535 @ 7811
Classroom= 1315 @ 6771
Blackboard= 1969 @ 6692
Game= 1640 @ 7643
These numbers are "right out of the box".
Lumen Output, Low Lamp, Bright mode:
GT720 Projector measures: 1941 lumens
That represents a drop of only about 8.5%. Most projectors drop 20-30% in their eco-modes. It would seem the wise thing for most owners to run in eco-mode. That's a small drop in exchange for longer lamp life, and Optoma says the GT720 will get 3000 hours at full power, but 5000 in eco.
Brilliant Color plays a big role in the GT720. With Brilliant Color off, in fact, you have less than 1/3 the brightness of setting it to 10. As Optoma has even Cinema defaulting to 6, I figure they don't expect you to use settings lower than that.
Effect of Brilliant Color on lumen output (Bright mode):
BC on 10 (default): 2121
BC on 6 (as in Cinema): 1442
BC on 0: 631
|Color Temp over IRE Range:|
After Mike's full calibration, placed in User (has to be there), with Brilliant Color set to 10, the Optoma GT720 measures a rather dazzling 1810 lumens (and a color temp of 6321K at full white). Below are the calibrated color temp results, a significant improvement over the default Cinema or User 3 above:
Color Temp over IRE Range (Post calibration):
20 IRE - 6603
30 IRE - 6630
40 IRE - 6642
50 IRE - 6589
60 IRE - 6828
70 IRE - 6626
80 IRE - 6426
90 IRE - 6407
100 IRE – 6321
Note that after Mike's calibration, the brighter ranges got a bit warmer (lower color temps), the opposite of pre calibration. But, the amount of shift is a lot less. Still, the GT720 does end up with slightly pushed reds. For a gaming projector - no problem. For serious home theater, most others can do a little beter.
Average GT720 gamma = 2.09
The measured gamma is a little lower than the theoretical ideal 2.2. This means mid-brightness areas will be a touch brighter than 2.2. A difference of .11 is very slight.
Below, the effects of Brilliant Color on the brightness (and image in general):
Brilliant Color = 0
Brilliant Color = 3
Brilliant Color = 6
Brilliant Color 10 - not shown, is brighter and more contrasty still. It is the default setting for most of the preset modes.
As you can see, the more Brilliant Color applied, (these photos taken at the same exposure), not only is it brighter overall, but if you look in the dark areas, the added contrast + brightness makes details more visible. Of course, a Brilliant Color setting of 10 can be a bit over the top. You'll see some flattening of colors in skin tones (too few colors - so faces look a bit mottled). Cinema does not default to 10, but Mike did use BC at 10 for his calibration.
Optoma GT720 Sharpness
Hey, The Optoma GT720 is 720p resolution. We're so used to reviewing 1080p projectors (probably about 5 to 1 compared to 720p models), that we sometimes forget that while a 720p projector can have good optics, and a technically sharp image, having only 720p means that you have slightly more than 40% of the pixels of 1080p, and therefore the lack of resolution becomes the cause of the image appearing less sharp. If this were a 1080p projector with the same optics, you'd have 2.25 times the number of pixels, so your image would appear to have more detail, be sharper.
Top left: Optoma GT720, Top Center - Runco LS-5, Top right - Mitsubishi HC4000.
2nd row left: Panasonic PT-AE4000, center: Epson Home Cinema 8350, Right: BenQ W6000
Note that only the first two images are from 720p projectors. The first is the GT720 of course. The image next to it, however, is from the Runco LS-5. That 720p projector is a whole different class of projector, and sells for 10x the price of the GT720!
Optoma GT720: Bottom Line Sharpness
The GT720 looks fine for a low cost 720p projector. The image bows a little bit (not rectangular), a result of the short throw optics (though it can be done better).
Overall sharpness is good, but the image will look soft compared to any 1080p projector, at least when viewing 1080p content. Again, this is the weakness of working with, and outputting, a lower resolution signal (1080 reduced to 720), rather than optical shortcomings.
No overt light leakage, that would affect use in a typical family room, bedroom or other handy location. There is a small amount of light leaking through the lens, but you really have to go hunting for it. If this projector had better black level performance, the light leakage might even be noticeable at times, on dark scenes, but overall, forget about it!
I noted some minor motion artifacts - at least more than I'm used to, when using a Silicon Optix test disc. For a true entry level priced projector, I'd have to say, overall, no real problem. Even standard background mosquito type noise, which is more prevalent on DLP projectors, was typical for the breed, and that's good, considering price.
I'm almost surprised, except we've seen a number of other Optoma single chip DLP projectors in cases about the GT720's size. Audible noise, as expected, is greater than almost any LCD projector - but, hey, there aren't any home LCD projectors anywhere near the price. Comparing the GT720 to other low cost DLP home entertainment projectors, the GT720 seems to be a little quieter than most. Optoma claims 30 db at full power and 28 in eco. Those are good numbers for a low cost DLP.