Posted on December 4, 2017 By Ron Jones
ACER V7850 4K Capable Home Theater Projector Review – Special Features: 4K/UHD Resolution Support, HDR Support, Wide Color Gamut (WCG), Color Wheel, AcuMotion (CFI), Other Available Image Processing Features, Vertical Lens Shift
Originally the “FauxK” or “4K-lite” terms were applied to pixel shifting 1080p resolution projectors – JVC first, then Epson as they rolled out a whole line of them. Those projectors going back to 2011, could accept 4K content, processed it, and fed it to chips that could display the picture as two sequential images, shifting a half pixel diagonally for the 2nd set of pixels as compared to the 1st. This allows for more detail, but the pixel size (relative to true 4K) is huge – twice the height and width, four times the area. Think of 4K as a baseball, and 1080p pixel shifters as a softball, in terms of pixel size.
Now enters the new TI consumer chip, as used in the Acer V7850, which is also using pixel shifting. It splits the difference in resolution at 2716×1528, just about half way between 1920×1080 and 3840×2160. But, like the lower res pixel shifters, it still uses large pixels compared to true 4K, but in this case with an area only about 1/2 as large (area-wise) as 1080p pixels.
The bottom line is the Acer V7850 is capable of displaying a more detailed image than 1080p pixel shifting projectors, but still one notch below what is possible with a true native 4K projector. This difference in visible resolution between the V7850 and a native 4K projector can be rather subtle, but visible when using a high quality native 4K/UHD resolution video source. This assumes the native 4K projector has good alignment of the red, blue and green sub-images (good panel alignment) and also has a good quality lens with sharp focus.
There are three major components touted when it comes to UHD. Obviously, first, is the 4K resolution itself. But some people may find one or both of the other UHD enhancements equally important. To take advantage of all that UHD has to offer also requires support for High Dynamic Range (HDR), and Wide Color Gamut (WCG). I’ll address HDR here, and WCG below.
HDR – makes a difference. I like to think of it this way when using it. It essentially has a different gamma curve – the picture is displayed with a greater difference in relative brightness between the brightest content (e.g., sunlight glint off of shiny surface), and average brightness content. This gives the image more pop, less “compression” of the image’s dynamic range (in theory), and overall is a desirable feature. But for best results it does need lots of brightness, a good native contrast and low black levels, so there’s plenty of opportunity for compromise – both with all home theater projectors, and for that matter with all but the most expensive of the “4K” LCD TVs and OLED TVs.
The V7850 lacks automatic detection of HDR for the incoming 4K/UHD signal and the user must manually switch to HDR mode where there are 4 levels of HDR offered via the projector’s menu. This essentially applies one of 4 different gamma curves intended to display HDR content. The user will need to select the specific setting that best matches both the characteristics of their specific setup (overall image brightness with their specific screen size and gain along with projectors settings) as well as the setting that works best with the specific HDR program (some are mastered darker or brighter than others).
There are 2 real limitations to how effective the V7850 is in displaying HDR video. The first is true for virtually all consumer projectors and that is the peak brightness for the brightest image highlights will be much less than with the most capable HDR enabled flat panel displays. The peak brightness that can be achieved when using a projector depends not only on the light output of the projector, but also on the size and gain of the projection screen being used. With a HDR flat panel display the peak highlights can be displayed at up to 10 times the brightness of the reference white level while with a projector the peak highlights can usually be displayed with a brightness that is no more than 2 or 3 times the reference white level. As a result the visual impact of HDR will not be as great with a projector based solution. I would also note another complication is the HDR videos (using the HDR-10 standard) are being created assuming the display will support the brightness levels associated with HDR enabled flat panel displays and there are no existing standards for how to “tone map” these HDR videos for display on a less bright HDR projection system. I must also note that the V7850 has a rather limited native contrast ratio and moderately high black levels. This means the projector’s inherent dynamic range is rather limited and as a result I found that HDR content did not to have the dynamic impact that is found when using projectors (e.g., JVC or Sony) with significantly higher native contrast and much lower black levels.
Like the other DLP 4K/UHD lamp-based projectors, Acer’s literature may talk about wide color gamut and being compatible with BT2020, but in fact the V7850 and similar 4K DLP projectors are essentially limited to Rec. 709 color space. The wider DCI-P3 color space is reached by the best of the 4K capable projectors out there, both lamp-based and laser-based, while full Rec. BT2020 color space is not yet supported, nor yet needed, for consumer 4K/UHD projectors.
The wider that color gamut, the more intense the colors can be. For example, the brightest, most saturated color red you see on TV, say a red balloon, is no match in terms of color compared to that same balloon in real life. Support for DCI-P3 color space would get us a good step closer to real, and puts us on par with digital cinema projectors. The ability to project a much wider color gamut than Rec. 709 falls short on the Acer V7850. The bottom line is the V7850 can accept signals that support WCG but the colors are essentially displayed at the more limited Rec. 709 values, the same as with HDTV.
Acer spec’s the V7850 as using a RGBRGB 6-segment color wheel. This means for each rotation of the color wheel the red, green and blue sub-images are displayed twice. This color wheel is rated as having up to 6X speed, thus in the best case the RGB sub-images will each be displayed 6 times for each frame of the video. This is basically the best configuration currently offered for DLP projectors using a single display chip along with a color wheel. Some viewers tend to see a “rainbow effect” (i.e., color separation artifacts) with single chip DLP projectors and the slower the speed of the color wheel the more visible the rainbows. I was able to see some very occasional rainbows when viewing an assortment of programming with the V7850.
Creative Frame Interpolation – CFI – sometimes called smooth motion, is offered under Acer’s name of AcuMotion.
Some home theater owners like to use CFI for sports viewing but don’t like the effect it has for viewing movies. Acer offers 3 levels of CFI, with the lowest setting introducing the least noticeable effect. We often note that CFI processing can cause a soap opera effect (SOE), or looking like “live digital video”, with higher frame rates than the slower movie frame rate of 24fps. I did see some SOE even with the least aggressive setting for AcuMotion on the V7850 when watching movies played from Blu-ray discs. While CFI may not detract from viewing live sports events, for many home theater owners looking for the “cinematic look” when viewing movies, use of CFI can detract from the experience.
I would note that I personally find use of CFI acceptable when viewing 3D movies since I find it adds to the virtual reality experience that 3D is attempting to offer. However, the V7850 does not support displaying 3D from a Blu-ray player, so that doesn’t apply in this case.
I found the AcuMotion offered by the Acer V7850 to be of average quality for this class of home theater projector. The V7850’s AcuMotion, when used at the more aggressive settings could sometimes be tripped up with certain types of fast on-screen motion but with a setting of 1 (least aggressive) it did offer smoother motion with minimal artifacts, but with some SOE visible for 24fps movies.
Super Resolution – image processing to improve perceived sharpness and detail. I generally preferred to keep this feature turned off during my viewing for this review.
Dynamic Black – Dynamic Black is supposed to be a lamp dimming technique to lower black levels on dark scenes (same idea as a dynamic iris, but inferior, for several reasons). The problem with lamp based projectors is the lamps just can’t dim and brighten fast enough (i.e., fast enough to actually improve the image quality or dynamic range). In use I found that feature offered no real benefit to improve the contrast or to lower the black levels when watching a movie.
Having an optical lens shift adjustment is a lot more common on home theater projectors using 3LCD and LCoS technology than for DLP projectors. The V7850 offers vertical lens shift with a rather limited 15% range (of the image height), but even with this limitation it still makes placement of the projector relative to the screen’s location a lot more flexible than having no vertical lens shift at all.
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