Introduction – Sorry, But It’s True
I have taken thousands of pictures through dozens of different headsets, and I noticed that the Apple Vision Pro (AVP) image is a little blurry, so I decided to investigate. Following up on my Apple Vision Pro’s (AVP) Image Quality Issues – First Impressions article, this article will compare the AVP to the Meta Quest 3 by taking the same image at the same size in both headsets, and I got what many will find to be surprising results.
I know all “instant experts” are singing the praises of “the Vision Pro as having such high resolution that there is no screen door effect,” but they don’t seem to understand that the screen door effect is hiding in plain sight, or should I say “blurry sight.” As mentioned last time, the AVP covers its lower-than-human vision angular resolution by making everything bigger and bolder (defaults, even for the small window mode setting, are pretty large).
While I’m causing controversies by showing evidence, I might as well point out that the AVP’s contrast and color uniformity are also slightly lower than the Meta Quest 3 on anything but a nearly black image. This is because the issues with AVP’s pancake optics dominate over AVP’s OLED microdisplay. This should not be a surprise. Many people have reported “glow” coming from the AVP, particularly when watching movies. That “glow” is caused by unwanted reflections in the pancake optics.
If you click on any image in this article, you can access it in full resolution as cropped from a 45-megapixel original image. The source image is on this blog’s Test Pattern Page. As if the usual practice of this blog, I will show my work below. If you disagree, please show your evidence.
Hiding the Screen Door Effect in Plain Sight with Blur
The numbers don’t lie. As I reported last time in Apple Vision Pro’s (AVP) Image Quality Issues – First Impressions, the AVP’s peak center resolution is about 44.4 pixels per degree (PPD), below 80 PPD, what Apple calls “retinal resolution,” and the pixel jaggies and screen door should be visible — if the optics were sharp. So why are so many reporting that the AVP’s resolution must be high since they don’t see the screen door effect? Well, because they are ignoring the issue of the sharpness of the optics.
Two factors affect the effective resolution: the PPD of optics and the optics’ modulation transfer function sharpness and contrast of the optics, commonly measured by the Modulation Transfer Function (MTF — see Appendix on MTF).
People do not see the screen door effect with the AVP because the display is slightly out of focus/blurry. Low pass filtering/blurring is the classic way to reduce aliasing and screen door effects. I noticed that when playing with the AVP’s optics, the optics have to be almost touching the display to be in focus. The AVP’s panel appears to be recessed by about 1 millimeter (roughly judging by my eye) beyond the best focus distance. This is just enough so that the thinner gaps between pixels are out of focus while only making the pixels slightly blurry. There are potentially other explanations for the blur, including the microlenses over the OLED panel or possibly a softening film on top of the panel. Still, the focus seems to be the most likely cause of the blurring.
Full Image Pictures from the center 46 Degrees of the FOV
I’m going to start with high-resolution pictures through the optics. You won’t be able to see any detail without clicking on them to see them at full resolution, but you may discern that the MQ3 feels sharper by looking at the progressively smaller fonts. This is true even in the center of the optics (square “34” below), even before the AVP’s foveate rendering results in a very large blur at the outside of the image (11, 21, 31, 41, 51, and 61). Later, I will show a series of crops to show the central regions next to each other in more detail.
The pictures below were taken by a Canon R5 (45 Megapixel) camera with a 16mm lens at f8. With a combination of window sizing and moving the headset, I created the same size image on the Apple Vision Pro and Meta Quest Pro to give a fair comparison (yes, it took a lot of time). A MacBook Pro M3 Pro was casting the AVP image, and the Meta Quest 3 was running the Immersed application (to get a flat image) mirroring a PC laptop. For reference, I added a picture of a 28″ LCD monitor taken from about 30″ to give approximately the same FOV as the image from a conventional 4K monitor (this monitor could resolve single pixels of four of these 1080p images, although you would have to have very good vision see them distinctly).
Medium Close-Up Comparison
Below are crops from near the center of the AVP image (left), the 28″ monitor (center), and the MQ3 image (right). The red circle on the AVP image over the number 34 is from the eye-tracking pointer being on (also used to help align and focus the camera). The blur of the AVP is more evident in the larger view.
Extreme Close-Up of AVP and MQ3
Cropping even closer to see the details (all the images above are at the same resolution) with the AVP on the top and the MQ3 on the bottom. Some things to note:
- Neither the AVP nor MQ3 can resolve the 1-pixel lines, even though a cheap 1080p monitor would show them distinctly.
- While the MQ3 has more jaggies and the screen door effect, it is noticeably sharper.
- Looking at the space between the circle and the 3-pixel wide lines pointed at by the red arrow, it should be noticed that the AVP has less contrast (is less black) than the MQ3.
- Neither the AVP nor MQ3 can resolve the 1-pixel-wide lines correctly, but the 2- and 3-pixel-wide lines, along with all the text, are significantly sharper and have higher contrast than on the AVP. Yes, the effective resolution of the MQ3 is objectively better than the AVP.
- Some color moiré can be seen in the MQ3 image, a color artifact due to the camera’s Bayer filter (not seen by the eye) and the relative sharpness of the MQ3 optics. The camera can “see” the MQ3’s LCD color filters through the optics.
Experiment with Slightly Blurring the Meta Quest 3
A natural question is whether the MQ3 should have made their optics slightly out of focus to hide the screen door effect. As a quick experiment, I tried a (Gaussian) blur of the MQ3’s image a little (middle image below) as an experiment. There is room to blur it while still having a higher effective resolution than the AVP. The AVP still has more pixels, and the person/elf’s image looks softer on the slightly blurred MQ3. The lines are testing for high contrast resolution (and optical reflections), and the photograph shows what happens to a lower contrast, more natural image with more pixel detail.
AVP’s Issues with High-Resolution Content
While Apple markets each display as having the same number of pixels as a 4K monitor (but differently shaped and not as wide), the resolution is reduced by multiple factors, including those listed below:
- The oval-shaped optics cut about 25-30% of the pixels.
- The outer part of the optics has poor resolution (about 1/3rd the pixels per degree of the center) and has poor color.
- A rectangular image must be inscribed inside the “good” part of the oval-shaped optics with a margin to support head movement. While the combined display might have a ~100-degree FOV, there is only about a 45- to 50-degree sweet spot.
- Any pixels in the source image must be scaled and mapped into the destination pixels. For any high-resolution content, this can cause more than a 2x (linear) loss in resolution and much worse if it aliases. For more on the scaling issues, see my articles on Apple Vision Pro (Part 5A, 5B, & 5C).
- As part of #4 above or in a separate process, the image must be corrected for optical distortion and color as a function of eye tracking, causing further image degradation
- Scintillation and wiggling of high-resolution content with any head movement.
- Blurring by the optics
The net of the above, and as demonstrated by the photographs through the optics shown earlier, the AVP can’t accurately display a detailed 1920×1080 (1080p) image.
AVP Lack “Information Density”
Making everything bigger, including short messages and videos, can work for low-information-density applications. If anything, the AVP demonstrates that very high resolution is less important for movies than people think (watching movies is a notoriously bad way to judge resolution).
As discussed last time, the AVP makes up the less-than-human angular resolution by making everything big to hide the issue. But making the individual elements bigger means less content can be seen simultaneously as the overall image is enlarged. But making things bigger means that the “information density” goes down, with the eyes and head having to move more to see the same amount of content and less overall content can be seen simultaneously. Consider a spreadsheet; fewer rows and columns will be in the sweet spot of a person’s vision, and less of the spreadsheet will be visible without needing to turn your head.
This blog’s article, FOV Obsession, discusses the issue of eye movement and fatigue using information from Thad Starner’s 2019 Photonic’s West AR/VR/MR presentation. The key point is that the eye does not normally want to move more than 10 degrees for an extended period. The graph below left is for a monocular display where the text does not move with the head-turning. Starner points out that a typical newspaper column is only about 6.6 degrees. It is also well known that when reading content more than ~30 degrees wide, even for a short period, people will turn their heads rather than move their eyes. Making text content bigger to make it legible will necessitate more eye and head movement to see/read the same amount of content, likely leading to fatigue (I would like to see a study of this issue).
ANSI-Like Contrast
A standard way to measure contrast is using a black-and-white checkerboard pattern, often called ANSI Contrast. It turns out that with a large checkerboard pattern, the AVP and MQ3 have very similar contrast ratios. For the picture below, I make the checkerboard bigger to fill about 70 degrees horizontally for each device’s FOV. The optical reflections inside the AVP’s optics cancel out the inherent high contrast of the OLED displays inside the AVP.
The AVP Has Worse Color Uniformity than the MQ3
You may be able to tell that the AVP has a slightly pink color in the center white squares. As I move my head around, I see the pink region move with it. Part of the AVP’s processing is used to correct color based on eye tracking. Most of the time, the AVP does an OK job, but it can’t perfectly correct for color issues with the optics, which becomes apparent in large white areas. The issues are most apparent with head and eye movement. Sometimes, by Apple’s admission, the correction can go terribly wrong if it has problems with eye tracking.
Using the same images above and increasing the color saturation in both images by the same amount makes the color issues more apparent. The MQ3 color uniformity only slightly changes in the color of the whites, but the AVP turns pink in the center and cyan on the outside.
The AVP’s “aggressive” optical design has about 1.6x the magnification of the MQ3 and, as discussed last time, has a curved quarter waveplate (QWP). Waveplates modify polarized light and are wavelength (color) and angle of light-dependent. Having repeatedly switched between the AVP and MQ3, the MQ3 has better color uniformity, particularly when taking one off and quickly putting the other on.
Conclusion and Comments
As a complete product (more on this in future articles), the AVP is superior to the Meta Quest Pro, Quest 3, or any other passthrough mixed reality headset. Still, the AVP’s effective resolution is less than the pixel differences would suggest due to the softer/blurrier optics.
While the pixel resolution is better than the Quest Pro and Quest 3, its effective resolution after the optics is worse on high-contrast images. Due to having a somewhat higher PPD, the AVP looks better than the MQP and MQ3 on “natural” lower-contrast content. The AVP image is much worse than a cheap monitor displaying high-resolution, high-contrast content. Effectively, what the AVP supports is multiple low angular resolution monitors.
And before anyone makes me out to be a Meta fanboy, please read my series of articles on the Meta Quest Pro. I’m not saying the MQ3 is better than the AVP. I am saying that the MQ3 is objectively sharper and has better color uniformity. Apple and Meta don’t get different physics, and they make different trade-offs which I am pointing out.
The AVP and any VR/MR headset will fare much better with “movie” and video content with few high-contrast edges; most “natural” content is also low in detail and pixel-to-pixel contrast (and why compression works so well with pictures and movies). I must also caution that we are still in the “wild enthusiasm stage,” where the everyday problems with technology get overlooked.
In the best case, the AVP in the center of the display gives the user a ~20/30 vision view of its direct (non-passthrough) content and worse when using passthrough (20/35 to 20/50). Certainly, some people will find the AVP useful. But it is still a technogeek toy. It will impress people the way 3-D movies did over a decade ago. As a reminder, 3-D TV peaked at 41.45 million units in 2012 before disappearing a few years later.
Making a headset display is like n-dimensional chess; more than 20 major factors must be improved, and improving one typically worsens other factors. These factors include higher resolution, wider FOV, peripheral vision and safety issues, lower power, smaller, less weight, better optics, better cameras, more cameras and sensors, and so on. And people want all these improvements while drastically reducing the cost. I think too much is being made about the cost, as the AVP is about right regarding the cost for a new technology when adjusted for inflation; I’m worried about the other 20 problems that must be fixed to have a mass-market product.
Appendix – Modulation Transfer Function (MTF)
MTF is measured by putting in a series of lines of equal width and spacing and measuring the difference between the white and black as the size and spacing of the lines change. People typically use 50% contrast critical to specify the MTF by convention. But note that contrast is defined as (Imax-Imin)/(Imax+Imin), so to achieve 50% contrast, the black level must be 1/3rd of the white level. The figure (below) shows how the response changes with the line spacing.
The MTF of the optics is reduced by both the sharpness of the optics and any internal reflections that, in turn, reduce contrast.
