Runco D-73d 3D DLP Projector, Part 2

In Part 1 of this report on my visit to Runco to see the D-73d 3D projector up close and personal, I described its LED illumination and use of linear polarization to isolate the left and right images. Now, I'd like to discuss the alignment of its dual projection engines, its color features, and its outboard video processing.

With two projection engines, aligning their images on the screen is critical. The D-73d provides manual zoom, focus, and horizontal and vertical lens shift because manual adjustment of these parameters is more precise than motorized. This can get you pretty close to perfect alignment, but often not quite close enough, so one of the engines also provides an electronic warping function that finishes the job to within less than one pixel. That engine also exhibits a bit of electronic overscan in order to allow a range of possible warping, which causes some minor moire artifacts that are visible on certain test patterns but not on most real-world content.

Another problem with a two-engine system is that the precise colors of red, green, and blue are not identical between them due to slight but inevitable variations in LEDs of the same color. As a result, the focus is not exactly the same for all colors. There is a bit of color divergence on white lines, and the image is softer than a single-projector image when viewed very close up. But this was not evident on real-world material at a reasonable viewing distance.

For 2D material, you can use only one engine, in which case the projector is essentially a Q-750i (see Home Theater's review here). Of course, the light level will be cut in half, but this is the videophile approach in a fully light-controlled room. If you're going to host a football party, you can view 2D with both engines running for more light.

The D-73d has several interesting features with regard to color. First, it provides a selectable color gamut, including Rec.709, SMPTE-C, EBU, DCI (this is the first Runco projector to offer the digital-cinema gamut), and Native (the natural colors of the LEDs, which are very close to DCI).

Normally, I'd select Rec.709 and be done with it. But during my time with the projector, we switched between Rec.709 and Native with Runco Smart Color, which automatically adjusts the skin tones to look more natural—i.e., not sunburned—with the otherwise expanded gamut, and I have to say it looked really good, especially reds and greens. Yes, it's not what the content producers saw on their monitors, but it looked more realistic, especially since the colors are not shown at maximum brightness so they don't appear to glow.

Other color features include a Personal Color Equalizer, which is Runco's name for a complete color-management system that offers hue, saturation, and level controls for all three primaries and three secondaries as well as the white point. This is the correct way to design a CMS, though it is relatively rare. Runco's implementation of Texas Instruments' BrilliantColor overlaps the primary colors to create the secondaries, much like a RGBYCM color wheel, which brightens the secondaries and white.

Like most modern displays, the D-73d includes a dynamic-contrast feature called, oddly enough, Constant Contrast. (According to Bob Williams, Runco's chief product architect, this is short for Constantly Optimized Contrast, which seems a more accurate name.) This feature varies the current applied to the LEDs, dropping it in dark scenes. It did lower the black level, but as usual, I preferred watching real-world material with this feature disabled.

Along with the projector itself, the D-73d package includes three outboard units that combine to form what Runco calls its 3Dimension processor. HDMI from the source device is connected to a custom 3D processor, which separates the left and right signals. Each of those signals is then sent to its own DHD4 video processor—the one with a front-panel display is the Primary, while the other is the Secondary. Finally, HDMI from each DHD4 is sent to the corresponding projection engine.

The DHD4s perform all video processing, such as deinterlacing and scaling, as well as grayscale calibration, color management, and all other processing functions for each projection engine. They can be set so that adjusting one affects both equally (useful for initial setup and calibration), or they can be adjusted independently to tweak the settings for variations between engines and to warp only one of them. There are a lot of settings, which can be copied and pasted into the memories for different inputs without having to enter everything each time.

The processor can even accommodate an optional, motorized anamorphic-lens system called CineWide with AutoScope. Watching a stack of two Panamorph lenses slide in front of the primary lenses is pretty cool, and it worked quite well, as I'll elucidate next time, so stay tuned!

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uavBruce in CO's picture

Why is a vertical stack used instead of side-by-side? It seems that since the signals are split left and right, that side-by-side lenses make more sense. It would simplify the alignment, especially with a re-design of the lenses so that they would end up close to each other so that the boxes were mirror images. Of course it's easy for me to say "re-design those boxes."

Bob Williams's picture


There is no difference in ease of alignment between top/bottom or side/side construction. It makes no difference to your eyes or the projectors where the images come from. The important thing is to keep the lenses as close to each other as possible. In terms of lens cost, top/bottom wins due to the 16:9 aspect ratio of the DLP chip. Imagine stacking two 16:9 rectangles vertically and then horizontally, and you will find that the smallest circle (lowest cost lens) can be made around the vertically stacked ones.

It's also usually a good idea in terms of design efficiency and reliability to use as much pre-existing architecture and knowledge whenever you design something new. All of our current projectors have horizontally oriented optical engines that cool from side to side. If we placed them next to each other, cooling both engines effectively becomes a challenge. Also, the lenses would end up pretty far apart. So, it ends up that the most reliable, cost effective design is a vertical stack.

uavBruce in CO's picture

Thanks for the response. That makes sense, especially the 16:9 ratio where the vertical height is much less than the horizontal to keep the lenses closer together, and the cost savings with re-using an existing architecture. It leads to another question....what's the possibility of projecting both signals through a single lense? Such as using a 4K chip with every other pixel used for the left and right signal, and then projecting out through the same lense? Or use half the chip for each side? As you can tell, I'm a non-engineer asking questions out of interest...thanks for your patience.

Scott Wilkinson's picture
This is already being done with the Sony 4K projector in commercial cinemas. As I recall, the imaging chip is divided into two parts, one for the left and the other for the right, stacked on top of each other, I assume because separating them vertically keeps them closer together. A split polarizing filter is placed in front of the lens, and viewers wear polarized glasses to see 3D. Like the Runco, there is no alternating of the left and right images, so each eye sees a continuous image.
uavBruce in CO's picture

Thanks Scott. Now it's just a matter of time before this really cool stuff hits the home theater at a reasonable cost. It might be a few years, but I'm pretty excited about the possibilities.

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