I’ve got more to cover in Neil’s Messy Basement with an eye on home entertainment and immersion, and the next part of my journey jumps me back into the fray of virtual reality! I’m in the process of reviewing the HP Reverb G2 VR headset, and I decided to share this guide before the review so it’s understandable how I got to my results.
I’m very excited by this guide because I think it will make a world of difference for many VR headset owners. Even if tools aren’t yet available for all headsets to address the problem, I think what is shared here could help motivate more user-driven features that will improve the VR experience for all.
The HP Reverb G2 is a special animal. One group of users and reviewers regularly credit it as being crystal clear and one of the sharpest HMDs on the market. In contrast, another large group of users are frustrated with the headset because its sharpness is limited to a small focal area – a “sweet spot” – and things quickly blur depending on where the user is looking. It didn’t make sense to me that a VR headset would have such a divided response.
My experience was closer to that of the second group of users; I had a window of clarity, and then I had a blurry periphery that I thought was normal for today’s level of technology. Fortunately, I could do better. In fact, I think we can ALL do better.
- CHROMATIC ABERRATION EXPLAINED
- UNRAVELING THE CHROMATIC ABERRATION MYSTERY
- HOW TO EVEN THE PLAYING FIELD
- STEP ONE: CONFIRM YOU HAVE CHROMATIC ABERRATION
- STEP TWO: PREPARE YOUR TOOLS
- STEP 3: LET’S FIX IT!
- STEP 4: CLEAN IT UP!
Chromatic Aberration (CA) is a failure of a lens to focus all colors to the same point. Like light being divided into a rainbow of colors through a prism, we can see Chromatic Aberration (CA) when we view our VR experiences through the curved lenses of an HMD. While the dead-center of the HMD lens may be sharp and pristine, it will usually grow blurry as we look towards its edges. Good examples of Chromatic Aberration are bits of text that double as we look outward, instrumentation and details that are out of focus beyond a small focal area, and the colored blurring of object edges as we look in different directions.
Solving the mystery of why different groups of people respond to the HP Reverb G2 so differently began with Microsoft. My first hint was their announcement that they updated the Windows Mixed Reality (WMR) platform with Chromatic Aberration Correction, and this correction works for the HP Reverb G2 and other unnamed WMR headsets.
Published well over a year ago, I couldn’t figure out why I was experiencing these CA distortions on my HMD. The Microsoft story was old, the software had been updated a couple times since, and my HMD is brand new. Did my software really have the correction implemented, or was my experience the best that could be expected with current HMD technology?
I read through countless articles and posts about the HP Reverb G2 “Sweet Spot” with possible solutions that included finding the perfect positioning, adding special head-strap padding devices, and even wearing reading glasses in VR. It all seemed fruitless until I found this gem in the Flight Simulator 2020 discussion forums.
A poster (CptLucky8) discovered a series of hidden Windows registry keys that activate the WMR chromatic aberration correction for the red, green, and blue color paths. As Microsoft published their standardized correction a few months earlier for everyone, why was this even a thing? Furthermore, while CptLucky8’s settings made a big difference for me, I still had more adjusting to do. Why?
Shown below, I decided to create a chromatic aberration test: a page of shapes and colors that when viewed in virtual reality, would immediately show which colors are problematic, and make it possible to do live adjustments to find the clearest result. I will explain the process later in this article.
When I shared footage of my before and after findings with industry experts Dr. Jon Peddie (Jon Peddie Research) and Mark Poppin (Babel TechReviews), they were surprised. They remembered some distortion on the HP Reverb G2, but not to the level I was showing, experiencing, and fixing. Why was this the case?
Soon after I got the HMD, I bought add-on corrective lenses for the HMD so I didn’t have to wear glasses while playing in VR. To make sure my results were correct, I wore my glasses to confirm the special corrective lenses weren’t causing the distortion. As I was seeing Chromatic Aberration while wearing glasses, I was home free…or so I thought! I later realized that the footage I sent to Jon and Mark had the corrective lenses still installed. When I removed those lenses and just viewed the HMD without wearing glasses altogether…the Chromatic Aberration was GONE. My glasses and the corrective lenses were both equal culprits!
This is a very significant finding because it raises the possibility (probability?) that everyone using corrective lenses with their HMD (glasses, add-ons, and possibly contact lenses) could require some personal software customization to reach the maximum clarity possible with their VR solution. When I think of all the different types of prescription lenses people use and how different combinations of lenses could affect the way light travels to our eyes, it makes sense that there are large groups of people having very different experiences with the same piece of VR hardware.
Based on my research, most if not all the HMD makers have some kind of chromatic aberration fix implemented with their solution. Unfortunately, this tends to be a one size fits all approach. Without some 1:1 customization for each user, I’m uncertain that the problem could be solved for everyone equally well.
Fortunately for me, Windows Mixed Reality users do have a solution, and I’m hoping these findings motivate other HMD makers and supporters to add this flexibility to their products too.
Download this image and get it displayed in a viewer while you are in virtual reality. For me, I found the best method was to open a desktop window in VR and open this full screen within the desktop. You want it to fill your visual space as much as possible.
Looking at the circles and shapes, be extreme, and move your head around. Do your best to view the circles through very different points of your HMD lenses. If you see any kind of ring “doubling” (like cheese sliding off a cracker), you’ve got yourself some chromatic aberration!
If you have chromatic aberration, the doubled circle will either be red, green, or blue. These are the color paths that need to be calibrated to get things back in focus.
In Windows 10 / 11, these are the registry keys that activate and correct for chromatic aberration:
You could do everything in regedit, but there is an easier and safer method:
- Download and install “WMR TrayTool“
- Run the tool. If necessary, choose “Show App Window” from its toolbar to bring up its main window.
- Choose the “Advanced” option in the menu
- Tick the “Use Color Distortion Correction” option
- Follow the adjustment instructions below
- Bring up the chromatic aberration test image again in virtual reality.
- Have this tool’s “Advanced” window in standby so you can make adjustments.
- To adjust each color channel, you will be changing the Red, Green, and Blue setting in the WMR TrayTool. These changes directly edit your Windows registry.
- Changing just one channel at a time (red, green, or blue), make small adjustments in either direction to minimize the doubling or chromatic aberration of the colored circles. If you see extra blue rings, you adjust blue. If you see extra red rings, you adjust red, and so on. Every time you make a change in the program, remove your HMD and put it back on for the setting to take immediate effect. You do not need to reboot or turn programs on and off while testing. The default value is “1” for all three color channels.
I have found that chromatic aberration is most visible with the following patterns:
- Blue CA is most visible with white, blue, and purple circles on black backgrounds.
- Red CA can be found on white circles on black backgrounds.
- Green CA is best seen on green circles with white backgrounds.
Remember to solve one color channel at a time because the circles can overlap otherwise.
When complete, you should be able to move your head around in VR and see minimal circle doubling for all three color paths. It is normal to get some doubling or blur at the very outer edges of your lenses because the curvature is so great.
While the chromatic aberration test image will find most of it, you may have a little more adjusting to do. Images may still be a pixel or two off which you can easily fix. Here are things to look for:
- An extra layer of colored pixels or a colored fringe on text. For example, letters may have a solid color border on one side that shouldn’t be there (red, green, or blue). Just make tiny adjustments so that border is gone.
- If you are using WMR, look at the white circles on your controllers when viewing them in VR and move them around. They should stay uniform unless they are positioned at the outer rim of your lenses where the curvature is too great.
- Look at object edges like tables and walls from different lens angles. It’s OK if they blur, but if you see dramatic colored borders, do your best to adjust for them.
If your results are like mine, the severity or importance of the “sweet spot” on the HP Reverb G2 and HMDs like it will be a lot less relevant. There is no reason to enter a tug of war with your HMD to get the best visible result!
While I found that IPD (interpupillary distance) adjustments had little to no affect on chromatic aberration, the focused area at the center of the lens seemed to grow in size when the lenses were closer to my eyes (version two of the HP Reverb G2 has a special insert for this purpose).
While this guide provided dramatic results for me, please have realistic expectations. Similar to how we see in real life, it is normal to have a focused center and a blurrier periphery. That said, I do believe that as more people adopt this solution, there will be a lot more consistency in how people describe their experiences with the HP Reverb G2 and similar HMDs.
In summary, I think the core lesson is we all see the world a little differently depending on our eyes and our eye-ware. It would be good if there were more widespread, user-friendly calibration techniques that could replicate my experience and what I learned for everyone. I know for me, the benefits are very clear.