Introduction

When I first saw a box from Optoma that was delivered by UPS and picked it up, I figured that it might be promotional materials, since it was lighter than I would expect for a projector. The box was shaped like one for a 15"or 17" LCD computer monitor, with a handle on top, but when I opened it I was surprised to find that there was a projector inside. It was the Optoma HD72.

The HD72 is a single panel DLP projector, using a 1280x768 DarkChip2™ DLP™ chip.

I should mention up front that I was somewhat skeptical about this projector because I knew that it used a seven-segment color wheel, which included one white segment (along with two sets of red, green, and blue for RGBRGBW).

White segments (which are actually clear, but are used for white light) are common in business DLPs to raise the lumens and help fight ambient light in business meetings for PowerPoint^® presentations. They are much less common for home theater DLPs because, while they can give more lumens to combat ambient light, it is by adding white and so is not as useful for images with pure colors (e.g., a portion of the picture that calls for only the red primary) and can create somewhat unbalanced images when used.

The Design

The HD72 includes a feature from TI called BrilliantColor and allows the user to choose from ten different levels. I chose to watch with it set to 3, as going much higher seemed to make some colors look incorrect to my eyes. After some viewing, I was surprised to see that the problems I had expected with blown out whites from the white segment on the color wheel did not manifest themselves.

Getting out the oscilloscope I had been loaned for determining when the mirrors on the DMD chip are on and when they are off relative to the color wheel, and using test patterns, I found the answer to this one. With the BrilliantColor at 3 and the Contrast at 4 (my preferences), the mirrors were staying off during the white segment on the color wheel. Turning the Contrast way up would make it come on for bright white segments of the image, but I hadn't been watching that way. So, for me, the white segment was not affecting the upper portion of the gamma curve.

I estimate that the area of the white segment was about 8-10% of the total area of the color wheel. When the white segment is used fully I estimate that it raises the total light output for white by about 20% over a wheel with just the primaries and no white segment (a GBRGBR wheel). However, since the white segment wasn't being used with my Cinema settings, the lumens for white would be about 10% lower with the GBRWGBR wheel vs a GBRGBR wheel, and the contrast ratio about 25% lower, if all except the wheel were equal.

I do know people who would prefer having the white segment on for a projector like this all the time, just because the extra brightness on the screen is important to them. And for things like SuperBowl parties with lots of room lights on or otehr light coming into the room, the white segment would allow the projector to fight the ambient light a little better than without it, to many consumer's eyes. For a situation with external ambient light (light other than that originating from the lens of the projector and also not counting the reflections of that light around the room and back) reaching the screen, I would be likely to put the projector in a mode which did use the white segment. I found that it was useful to configure the Cinema mode to my settings, which did not have the white segment being used, and the Dynamic mode to settings where it did get used (much higher Contrast setting and BrilliantColor at 3 or even higher). The default settings for Cinema and Dynamic were pretty close for this.

I found that the remote worked well and the menus were easy to use. The remote will light up the buttons when any button is pressed, which is easier than remotes with a dedicated button for the light, at least until a person is more familiar with a remote. Bouncing the signal off a screen worked some of the time, but not others. Pointing the remote in the general direction of the projector was more consistent for me.

The projector also includes some controls on the main unit itself as shown here:

Here are some menu examples.

The HD72 has a feature called ImageAI, which is lamp modulation based on image content. The idea is to dim the lamp in very dim images and raise the power to the lamp in bright images. With gamma modification, most levels except the very bottom ones (and the very top ones depending on the algorithms) can be maintained at their correct levels, but with a lower absolute black level (or more On/Off CR with the same white level).

Unfortunately, while I could see the ImageAI at work on some images over the component input, with test patterns I found that I could not get it to change any light output between high and low lamp over HDMI, and with the component input, the behavior was inconsistent with what is required to raise the actual On/Off CR.

I expect a system like this to have the absolute black level of low lamp mode with all video black images and the white level of high lamp mode with an all video white image, but this is not what I observed or measured. Sometimes I would get the absolute black level of the high lamp mode, and sometimes I would get the white level of the low lamp mode. Since it didn't look like it was going to help the On/Off CR, plus the fact that fan noise comes with ImageAI (or high lamp mode), and because I had seen flicker in some images with it turned on (what I did observe was somewhat like what I've seen with the AE900 at times and I would expect some people to detect it and some people not to), I just disabled the ImageAI feature and set the lamp to Low.

Click Here to Go to Part II.