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.

01 DLP Pixel Shifting
How 1-chip pixel-shifting works: This illustration shows how BenQ and other DLP projector manufacturers use pixel-shifting to offset two sub-frames generated by the 2716 x 1528 mirrors in a single Texas Instruments 0.66-inch DMD. These are flashed so quickly that the viewer only sees one full frame image with higher details than each separate sub-frame.

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.)

02 Epson Enhancement Tech Illustration
4K enhancement: The Epson illustration describes how it's (and JVC's) 1080p pixel-shifting models use a 45-degree offset (similar to DLP XPR pixel-shifting projectors), but first direct light through three RGB panels (either LCD or D-ILA) to create two sub-frames, instead of using a color wheel and a 1-chip DMD.

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:

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.

03 contrast comparison 2
Contrast and sharpness: Which of the targets above looks sharper to you? It should be the one on the right, which has higher contrast but is otherwise identical.

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.

04 JVC Multi element lens

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).

05   Mantis enhancement comparison
Presets and Enhancements: All projectors feature a variety of display modes, presets, and enhancement controls, some of which can increase perceived detail. In this comparison, both images are closeup screen photos from an Epson HC-5050UBe, set to its default Preset 2 on the left, and Preset 4 plus sharpening on the right. The right image may now appear sharper overall, but too much sharpening can cause unwanted artifacts like dark or colored edges (see arrow).

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.

06 screen materials
Screen material and resolution: The photo on the left shows a swatch of Da-Lite's HD Progressive 1.1 matte white screen material pressed against the white foamcore board we used as our projection surface (see below). It shows a close match that does not appreciably enhance contrast or detail. On the right is the HD Progressive 1.3 swatch with 1.3 gain. Note how the brightness and contrast improve on the vertical resolution scale, making the black text jump out from the background.

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.

07  4KUHD Resolution Target wBoxes

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.

08 Full Mantis With Box

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.

09 LEFT 10RIGHT   Test pattern closeups
11 MantisCloseUp
Camera Images: Two DSLR cameras were set up to record the pertinent vertical-resolution (left) and horizontal-resolution sections (right) of the test target and real world images. Details shown in the test results section in Part 2 are from closeups of the areas highlighted in the red boxes that clearly reveal the vertical and horizontal resolution as well as differences in image quality in the real world test image.

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.

Comments (5) Post a Comment
Cory Potts Posted Mar 19, 2020 5:40 AM PST
Very interesting and a large need for this comparison exists in the industry with huge price disparities due to “native 4K”. My only suggestion would’ve been to use a larger screen, as 90” is almost attainable now with LCD/OLED panels and most choose well over 100” to see an apparent different in 4K.

Thanks for putting all the thought, time and effort into this.
Tony Posted Mar 19, 2020 10:13 AM PST
Can't wait for the results! I like these types of scientific testing articles. Fun to read and useful. :)

Side question: I work in an industry where I have access to large Foamcore and Ultraboard products. I wondered years ago if a matte, white board would be a good screen surface. They are matte, completely smooth, fairly easy to hang and move, and by nature of being a material that is meant to be printed on, true white. We did a test in our office and it seemed to work well, but I never compared it in a room next to actual screen material. I posted the idea on an AV forum, but received a lot of push back from folks in the screen selling business, but I still wonder about it. I know you make your money from suggesting commercial home theater equipment, but honestly, if your room conditions do not require a special screen material (acoustically transparent, high gain, black level increasing), how did the foamcore board do?
Mike McNamara Posted Mar 19, 2020 5:32 PM PST
Tony: The side-by-side comparisons with screen material shown in this article clearly demonstrate how at least one screen material with a 1.3 gain helps to increase contrast (a very good thing with projectors in general, and better for HDR content). I found that the 1.1 matte white screen sample was very close to the foamcore board in terms of contrast, but just slightly dimmer (giving the foamcore the advantage.) However, there are major concerns with using foamcore as a screen material: 1) HOW in the world could you ship a theater-sized sheet of foamcore or get it through most doors? 2) If you opt for smaller sheets of foamcore and tile them together, how do you hide the boundaries between sheets, which would show up as thin lines or worse? 3) How do you stop individual sheets from buckling over time, or humidity from de-laminating the paper surface (which I've seen happen to my kids science-board projects)? If you can overcome these problems, then maybe foamcore would be a good screen choice.
Tony Posted Mar 20, 2020 8:13 AM PST
Thanks for the response. To answer you:

1) Foamcore is shipped all over the world and most of it is not damaged. I have the advantage of receiving boxes full of board. Ultraboard is even tougher in that is has a hard plaster facing on it. I guess theater owners would have to group buy (I know...unlikely). 2) The boards would only be 4' to 5' tall. My basement walks out to a garage - easy for me to get in. People get 8 ft long sofas into their homes all the time. 3) See Ultraboard - hard, matte, plaster surface. Also you could attach them directly to a flat wall or a simple wood frame.
Cory Posted Mar 20, 2020 9:39 AM PST
Hey Mike, Thanks for all of your tremendous work on this project. The comments about the 1.1 vs. 1.3 gain screen material are interesting as the dark areas of the picture are also 30% brighter (making the contrast ratio identical-passive screen material) this is even obvious in the pics above which I assume were taken in a lit room (and this raising of black level would be even more pronounced in an all black theater) but I do admit that ALR screen might cheat this a little. I understand that for HDR the biggest handicap front pjs have is that they aren't bright enough to get to the levels most HDR movies were mastered at, necessitating the use of tone-mapping for pjs. I have two thoughts here 1.) All content with low IRE values, not just non-HDR content, benefits from having a black floor as close to 0 as possible 2.) who would want to look at a 120" screen with 1000-4000 nits brightness (sunshades?) I think this is what fuels the LCD vs. OLED debate, do you prefer absolute blacks or cornea-searing whites because no technology boast the state of the art in both areas currently. I think the solution is brighter projectors that maintain their excellent contrast and black levels as more screen gain is just a band-aid but, I'm a black level fanatic so my comments might not be representative of the rest of the group.

Thanks again for your work.

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