Editor's Note: The debate about the effect of pixel-shifting techniques on image detail began when Epson and JVC initially opted for addressing 4K UHD content with enhanced pixel-shifted images from native 1080p projectors, and moved into full swing when Texas Instruments introduced its DLP XPR (Xpanded Pixel Resolution) micromirror display technology that relies on pixel-shifting with 1080p or larger micromirror chips to deliver the full pixel count in a UHD signal to the screen. We'd like to think that the dozens of product reviews by us and other experts—and the many pixel-shifting UHD-capable projectors sold successfully into the home theater market—have proven that, putting aside other factors like lens attributes, inherent contrast, and image processing, pixel-shifting works effectively for delivering sharp 4K images at normal viewing distances. Yet, we still get comments from readers complaining that pixel-shifting somehow represents a form of cheating by the manufacturers, even as the lower cost associated with using this technique remains the only thing that makes 4K projection attainable for many of us.
Against this backdrop, our contributor and imaging tech expert Mike McNamara, the principal at In-Depth Focus Labs in Hopewell Junction, NY, undertook a study that looked at six different UHD projectors representing a range of display technologies and price points. By examining (and photographing) the magnified result of test patterns and still pictures on the screen, he was able to see how differences in the imagers and other factors, in aggregate, affected each projector's ability to fully resolve UHD vertical and horizontal resolution. In Part 1, Mike explains the background behind the testing and how he conducted the tests. In Part 2, found here, we share the photographic results and some conclusions.—Rob Sabin
As the market for affordable 4K UHD Home Theater projectors has grown over the last few years, so has the debate about which projection technology delivers the most detail and sharpness on screen. On the one side of the debate stage (pardon me for the analogy) you have "native" 4K UHD projectors—whose imaging devices map the data on a one-to-one basis from each pixel of a 4K UHD video frame (containing 3840 x 2160 pixels) to a corresponding imager's pixel or mirror. After light from a bulb or laser passes through the imager or is reflected off its mirrors (depending on the technology) it travels through the lens to form a full frame on screen. If content is coming from a typical movie disc in a 4K UHD Blu-Ray player, a full frame is formed 24 times per second (24fps), while for streaming movies, original camera footage, and gaming the frame rates range from 30fps to 60fps or higher.
On the other side of the stage you have "pixel-shifting" projectors with lower resolution imagers, either 1920 x 1080 pixels or 2716 x 1528 pixels. Those that claim full UHD-resolution use Texas Instrument's XPR (Xpanded Pixel Resolution) DLP micromirror technology, and feature either a 0.66-inch (2716 x 1528 pixels) or 0.47-inch (1920 x 1080 pixels) micromirror chip. The system starts by splitting the incoming 4K UHD content signal into either two or four subframes, and then overlays these sub-frames on screen with a slight offset. This occurs at such high speeds (1/120th of a second or 1/240th of a second per sub-frame) that the human eye perceives only one higher-resolution full frame (lasting 1/60th to 1/24th of a second per frame) instead of two or four lower res images. The slight offset mentioned is critical, and shifts half of the sub-frames to the right or left at a 45 degree angle, with part of each offset sub-frame overlapping the stationary sub-frames. If this sounds confusing—it is! However, the end result is both a measurable and perceptual increase in detail in the projected full frame image compared to projectors using the same imagers but no pixel-shifting. It's also very similar to how the human eye works. You don't notice it, but your eyes vibrate back and forth at high speeds in a process that increases the details you are able to perceive, even in moving objects.
The biggest advantage to using a pixel-shifting method over a native 4K UHD imager is lower price. Currently, native 4K UHD imagers are far more expensive than their lower-res cousins found in pixel-shifting models. That's why you can now purchase a pixel-shifting projector claiming to deliver 4K UHD resolution for just over $1,000, while native 4K UHD projectors typically cost five to ten times as much. A disadvantage is a slight increase in noise or vibration from the projector from the components that shift the optical path, but this is usually hidden by the noise from the projector's cooling fan.
The question remains as to whether any pixel-shifting projector can truly match the resolution and detail of a native 4K UHD projector, be they the DLP XPR models mentioned above (built by BenQ, Optoma, ViewSonic, Vivitek, LG, and too many others to mention) or native 1080p projectors that don't actually lay claim to putting all the pixels in a UHD signal up on the screen. The manufacturers in the latter group argue that the significant increase in detail provided by their advanced pixel-shifting technologies, in combination with other features that maximize detail, add up to a far better value for consumers—and can even produce images on screen that are nearly indistinguishable from native 4K UHD images when viewed at normal distances. Brands here include Epson and its 3LCD partners, which label their pixel-shifting projectors 4K-enhanced (or 4Ke), and JVC, which labels its 3-chip LCoS-based D-ILA models 4K e-shift. (Though the company is dropping this approach later this year in favor of a combination of true native 4K D-ILA projectors and DLP XPR projectors. The e-shift technology will still be used in some native 4K D-ILA models to effect the impression of 8K resolution.)
Which one of these camps is correct? Does a pixel-shifting projector have to produce a measurable 4K UHD resolution in order to deliver a compelling 4K UHD experience? Or can other features including contrast, lens quality, color accuracy, color saturation, and image-processing (i.e. sharpening) improve details and image quality enough to make up for a deficiency in measurable pixel resolution for the vast majority of viewers? To find out, we meticulously compared the on-screen resolution of five pixel-shifting projectors containing a cross section of imager technologies to each other and to a native 4K projector.
Here are projectors we included in our test:
- JVC DLA-NX7:/DLA-RS2000 ($8,999) A high-end native 4K, 3-chip LCoS-based projector with premium lens/optics. See the review.
- BenQ HT9060 ($8,999): A high-end 1-chip DLP XPR projector using the 0.66-inch digital micromirror device (DMD) and 2-phase pixel-shifting with a high-output LED engine and premium lens/optics. See the review.
- Optoma UHD60 ($1,799): A budget-priced 1-chip DLP XPR projector using the 0.66 inch DMD and 2-phase pixel-shifting with average lens/optics for its class. See the review.
- ViewSonic X10-4K ($1,499): A budget-priced 1-chip DLP XPR compact lifestyle projector using the 0.47 inch DMD with 4-phase pixel-shipping and small, short-throw lens commensurate with its portable design. See the review.
- Epson Home Cinema 5050UBe ($2,999): A mid-priced 3-chip, native 1080p LCD projector with two-phase pixel-shifting and premium lens/optics. See the review.
- JVC DLA-X790/DLA-RS540 ($3,999): A mid-priced 3-chip, native 1080p LCoS projector with 2-phase pixel-shifting and premium optics.
Factors Affecting Resolution
Before we get to the results of our tests, let's define a few terms and take a quick look at how other projector features and the variables mentioned may affect perceived resolution and details on-screen.
1080p vs. 4K UHD Resolution. For starters, 4K UHD projectors and displays are often erroneously described as providing four times the resolution of a Full HD 1080p projector or display. In reality, 4K UHD displays actually provide four times the number of pixels on screen—but that only equals two times the resolution. That's because the number of pixels reproduced in each dimension (horizontal and vertical) determine the measurable resolution in a digital display. One white pixel followed by one black pixel = two pixels of resolution (also called two lines of resolution). Therefore, the horizontal and vertical resolutions found in a 1080p display only have to be doubled in each direction to create the resolution of a 4K UHD display (1920H x 1080V pixels) x 2 = (3840 x 2160 pixels). If a pixel-shifting technology can increase a 1080p imager's resolution in both directions by even one new pixel for every two native pixels, the image on screen should look 50% sharper than a 1080p image. By comparison, 8K UHD displays have eight pixels in the same direction for every two in a 1080p display, and that's what is needed in terms of pixel count to actually get four times the resolution.
Contrast. The eye is easily fooled into thinking a higher contrast image has more detail and is sharper than one with lower contrast. That's one of the reasons why the U.S. Government has very stringent regulations defining contrast ratios for any image-capture device it purchases (such as cameras, camcorders, and spy-satellites). These ratios and the way they are determined must be listed whenever a product being sold to the government claims a measurable pixel or line-pair resolution. Unfortunately, the consumer display industry is not as stringent, and there are several different contrast ratio definitions in use, with ANSI contrast, Full On/Full Off, and Dynamic contrast most prevalent. When comparing projectors, ANSI contrast makes the most sense since it gives a better indication of what a viewer will see on screen when continuous-tone photos and video frames are displayed.
Conceivably, a projector with a higher contrast ratio but slightly lower resolution could project an image that appears sharper and more detailed than an image with lower contrast but slightly higher resolution.
Screen distance and size. Because our eyes can only discern a fixed amount of resolution across our field of view, with more in the center, a typical viewer's ability to see the difference between a 1080p and 4K UHD display varies with distance from the screen and the screen size. For example, most viewers sitting 8-10 feet from an 80-inch monitor or projected image can barely see the difference in detail between a 1080p and 4K UHD display or projected image. With smaller displays, the viewer has to be even closer to see the detail difference. On the other hand, viewers can see the difference between lower and higher contrast images, as well as between lower and higher color saturation in displays, from much greater distances. This explains why 4K UHD High Dynamic Range (HDR) displays at Best Buy or elsewhere look better from across the room than their 4K UHD SDR counterparts.
Lens quality and focus. It almost goes without saying that lens quality and focus accuracy will have an effect on a projected image's perceived resolution. Nearly all projector lenses should at least produce a tack sharp image in the center of the screen when focused properly. If they don't, they're defective. What is less understood before purchase is how well the lens performs across the entire image area, and how it improves or reduces overall contrast. You get what you pay for, and a high quality, multi-element glass lens (like the JVC lens in the above photo) will deliver higher contrast and detail by reducing lens flare, minimizing color aberrations, and maintaining even brightness towards the edge of the image. (In addition, a projector lens with motorized zoom and focus, lens memory settings, and wide-ranging horizontal and vertical lens shift gets higher points from us in reviews, though these may not have a direct correlation with resolution and detail.) Over time, a cheaper lens may also show optical distortions due to the use of plastic lens elements, which don't fare as well long-term next to a hot bulb.
Projection modes, presets, and enhancements. Almost every projector has a range of picture modes and image enhancements that can be set by the end user, and can affect the measured and perceived resolution to varying degrees. As mentioned above, contrast plays a part in resolution, and therefore changing modes from a high lumens mode (Bright) to a lower lumens mode (say, Cinema or sRGB), can affect on-screen resolution. Harder to quantify are the effects that a multitude of image presets and enhancements have on measurable and perceived resolution. For most projector owners, it takes trial and error to determine which of these settings deliver the most pleasing effects on screen, and these may vary depending on content or projection mode. For example, slight amounts of sharpening enhancements may improve both perceived contrast and details, especially with fine lines and text. But too much sharpening causes unwanted artifacts (see photo).
For our tests, we selected each projector's Cinema or Natural mode that would normally be used for viewing movies, as well as the projector's highest power setting. The exception was the ViewSonic X10-4K, which was set to its Brightest mode in order to achieve its highest tested 750 ANSI lumens output, which was still well below the luminance of the other projectors in this comparison. Default settings were used across the board for all other image presets and enhancement settings.
Screen materials and gain. When it comes to resolution, most potential projector buyers don't consider the effects that their screen might have on perceived detail and resolution. In general, higher screen gains may increase contrast from central viewing positions, but can create hotspots or lower contrast at wider viewing angles. Also, some older screens aren't optimized for higher 4K UHD resolutions, mainly because they have textures that can reduce or interfere with the perception of fine lines and details, or have lower contrast and colorations.
Setting Up The Test
As noted in the prior section, there are many variables that can affect the resolution of a displayed image. To make the tests as fair and accurate as we could, we eliminated as many variables as possible.
Resolution Target Tests. First and foremost, we selected a test target that contained the right elements needed to establish the maximum horizontal and vertical resolutions as they appear on screen. This was the industry-standard 4K UHD test target designed by Joel Silver at the Imaging Science Foundation. The red boxes on the target are added by us for this photo only to indicate where we concentrated our analysis and close up photos.Target Generator. The 4K UHD ISF target file was loaded into a Murideo Six-G pattern generator, which we connected to each projector using an HDMI cable that was certified (by a Murideo Six-A Analyzer) to handle up to 18Gbps 4K HDR signals. The pattern generator was then set to display the target at 4K UHD res (3840 x 2160 pixels) at 60fps, in SDR mode at 10-bits per color. This produced a signal with a bandwidth around 12Gbps, well below the capacity of the HDMI cable.
Real-World Test Image. In addition to the resolution test targets generated by the Murideo Six-G, we compared closeup sections (as indicated by the red box) of a super-sharp test photo of a praying mantis taken with a Nikon D600 DSLR. It was resized to 3840 x 2160 pixels and displayed on screen using the integrated USB media player of a Sony UBP-X800 UHD Blu-ray player.
Projector Setup. Each projector was positioned at a height matching the screen's center, and the lens was set to its widest position in order to produce the most lumens and highest contrast ratio. The projector was then moved back from the screen to a distance where it produced a 16:9 ratio image that filled a pre-measured 90-inch diagonal screen area.
Screen Material. To reduce light reflecting from the screen (which might reduce target contrast) and eliminate other screen variables mentioned previously, we didn't use a conventional screen. Instead, we secured two bright white foamcore boards with smooth surfaces to a wall that was already covered by black velvet cloth. One white board was positioned so that the center of the screen and vertical resolution scales leading to it were clearly visible, and the other was positioned to the right side of the target showing the last third of the image and horizontal resolution scales.
Focus. The manual-focus projectors from BenQ and Optoma were critically focused using two people, one positioned at the screen, and the other at the projector. Motorized focus for the Epson, JVC and ViewSonic models was performed by one person at the screen using the remote controls.
Screen Capture. To record the close up details of the resolution target and real-world content shown in the next section, two DSLR cameras were set up on tripods, each with its own fixed field of view. One was positioned behind the test projector to photograph a portion of the test pattern's vertical resolution scale (resulting in the image on the left shown below) and the other was positioned a few feet away from the left side of the screen to record a close-up of the horizontal resolution scale, but not where the camera would create a shadow (image on the right). Camera focus was performed manually to insure precise focus (both cameras had a focus-magnification function that helped this process). White balance was left on AUTO for both cameras.
Camera shutter speeds were then set to 1/30th sec to insure that at least two consecutive full frame images (each projected at 1/60 sec as noted above) were used to create the exposure. Aperture was varied slightly to insure the same exposure was used in all the comparison photos. Note: If you take pictures of a projected screen at shutter speeds faster than 1/60th sec, you risk capturing a half-frame (on pixel-shifting models) or color bands (with 1-chip DLP projectors containing a spinning color wheel.)
In interpreting the following results, our goal was to determine which if any of the projectors actually achieves true 4K UHD resolution on the screen as measured with an industry-standard test target, and how other projector features such as contrast and lens quality might affect perceived sharpness and detail. The results from the different technology approaches and projectors were revealing.
It's critical to note that the differences we saw among the projectors in magnified photography were far less evident or even indistinguishable from a 10 to 12 foot viewing distance. That's ultimately a subjective interpretation. But the close-up images we'll show you demonstrate what was really happening on the screen, and the pictures don't lie.
Check back for Part 2 and all of the results.