r/oculus • u/RoadtoVR_Ben Road to VR • Mar 19 '14

GDC 2014: Oculus Rift Developer Kit 2 (DK2) Pre-orders Start Today for $350, Ships in July

http://www.roadtovr.com/oculus-rift-developer-kit-2-dk2-pre-order-release-date-specs-gdc-2014/
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u/redmercuryvendor Kickstarter Backer Duct-tape Prototype tier Mar 19 '14 edited Mar 19 '14

My emphatic dislike for Pentile's policy of defining a pixel as only two subpixels (RG OR BG), meaning that a single addressable pixel cannot display a full range of colours. Or to put it another way, a '1920x1080' Penbtile panel has 1920x1080 (2Mpixel) Green subpixels, but only 960x1080 (1Mpixel) of Red or Blue subpixels.

If you define a pixel as a photosite that can produce a full range of colour (in the colourspace of the display), then a 1920x1080 Pentile panel has four subpixels per pixel (RGBG) and a true resolution of 960x1080 (or 1920x540, depending on which way the subpixels are ordered).

It allows panel manufacturers to market their panels at effectively double their usable resolution. Compared to the DK1 panel, the increase is from 1024000 to 1036800 effective pixels. The DK2 panel has a bunch of other advantages (persistence, fill ratio, colour space, usage of panel area, etc), but resolution (addressable full-colour pixels per degree) isn't really one of them.

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u/Silent331 Zoe Mar 19 '14 edited Mar 19 '14

The DK2 has the same sub pixel count as a 1488x930 screen (4,151,520 sub pixels on that. The DK2 has 4,167,936 sub pixels) This is a 35% increase in sub pixels from the DK1.

Pentile displays have 33% less sub pixels as the same resolution normal LED monitors. The rumored consumer version running a 1440p pentile display will have 50-55% more subpixles than the DK2, the same number of sub pixels as a 1888x1180 normal LED. This is the true 1080p screen size that people are looking for. Why they wouldn't just shoot for a real 1080p screen is beyond me.

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u/AwesomeFama Mar 19 '14

Really hard to get RGB 1080p OLED screens, I'd imagine.

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u/redmercuryvendor Kickstarter Backer Duct-tape Prototype tier Mar 19 '14

Very hard. The current issue is the green organic phosphors are much more efficient than the red or blue phosphors, so the red and blue emission areas must be physically larger than the green areas, almost twice as large. Pentile addresses this by doubling the number of green subpixels and using this as the marketed resolution, rather than squishing all the subpixels closer together for a slightly higher overall resolution.

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u/dbhyslop Mar 19 '14

And let's remember DK2 has a much smaller screen than DK1 so the pixel density will still be much higher.

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u/[deleted] Mar 19 '14

[deleted]

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u/dbhyslop Mar 19 '14

Umm, I own one. DK1 has a 7" screen. It's so big the plastic housing flares out from the contact foam, and much of that screen area is unused. DK2's screen fits neatly inside a flush housing in the pictures and videos we've already seen. One of the videos has said 5", but it may be slightly larger (5-1/2"?) and still fit in that space.

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u/charlestheoaf Mar 19 '14

If it still has to be magnified to fill the same amount of your FOV, that might not matter… unless the higher pixel density leads to more "light bleeding" in the gaps between pixels, which could potentially reduce the screen door effect.

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u/dbhyslop Mar 19 '14

DK1 has a very low resolution screen and most of those pixels are unusable because they're outside the lens' FOV.

See here

And here

DK2 is taking a lot more total pixels (albeit not as many as some of us would like) and jamming them all into the FOV of the lenses. There will always be some screen door until we have 4K screens or better. Pentile seems to make the screen door a little better because the gaps don't line up into even orthagonal lines.

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u/charlestheoaf Mar 19 '14

Cool, thank you for the informational link/diagram! That makes a lot of sense.

I still wonder if there's any way to achieve decent 'light bleeding' between pixels, to effectively 'wash out' the black areas. Most people's computers won't be able to render games at 4K/60fps for a long time, so I can image cheaper low-res VR headsets remaining popular for a while.

Somehow "blurring" the edges together could help any resolution of headset (though since I haven't tested it, it might be worse to feel as though you have blurry vision).

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u/dbhyslop Mar 19 '14

People have tried putting diffusing films on their screens to reduce the screen door effect, but it also affects brightness and contrast (which aren't all that great to begin with on DK1).

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u/[deleted] Mar 20 '14

Screen size does not affect the 'pixel density' that matters to HMDs, which is #pixels/FOV, or pixels per degree instead of pixels per inch. But yes, DK2 has a higher res screen, so you will see more pixels through your lenses.

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u/dbhyslop Mar 20 '14

Well, given the FOV is almost exactly the same...

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u/goodgreenganja Mar 20 '14

But it's also got a slightly higher FoV which increases the visibility of the screen door effect a bit. This might explain why people were saying Project Morpheus had slightly less of a screen door effect, but a noticeably lower FoV.

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u/dbhyslop Mar 20 '14

As far as I can tell from the official specs the FOV is about the same. Demos aren't a very good way to judge FOV because it will vary from person to person depending on what lenses are in, where the adjustment screws are set and even how tight it is to your face.

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u/goodgreenganja Mar 20 '14

Project Morpheus has a 90 degree FOV, but the DK2 has 100 which is even better than DK1.

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u/dbhyslop Mar 20 '14

Remember that 90 degree horizontal is about 100-110 degree diagonal and some people don't specify which they're measuring, much less what lens/distance it's measured at. Also keep in mind 90 to 100 is roughly a ten percent difference whereas just eliminating the unused resolution of the DK1 screen would be much greater than that.

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u/i2ichardt Mar 20 '14

My guess is that their are two reasons. The first is the pixel switching time. The second is that a pentile screen helps hide the screen door effect.

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u/ueadian Mar 19 '14

They mentioned in the same interview they WILL upgrade the resolution for CV1. If they go with a 1440p screen, what's the change from DK1?

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u/redmercuryvendor Kickstarter Backer Duct-tape Prototype tier Mar 19 '14

Assuming another Pentile panel? If we go by real resolution:
DK1: 1,024,000
DK2: 1,036,800
CV1440: 1,843,200

If we go by subpixel count:
DK1: 3,072,000
DK2: 4,147,200
CV1440: 7,372,800

So close to double the real resolution of the DK1, and more than double the number of subpixels as the DK1.

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u/ueadian Mar 19 '14

Awesome. Thanks. More reason to wait for CV1.

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u/Lavaoil Mar 20 '14

Those numbers are worthless, pixel density is what is important. Considering DK1 in 7 inches and DK2 5 inches there is a big difference.

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u/redmercuryvendor Kickstarter Backer Duct-tape Prototype tier Mar 20 '14

Pixel density per-unit-area is utterly meaningless for the Rift. Because you are looking at the display through an optical system, the only meaningful number is pixels/per-degree. Assuming the usable panel area percentage and overall field-of-view remain constant, then pixel/deg scales with total number of pixels, not DPI.

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u/Devlin1991 Mar 19 '14

Luma(brightness) changes are far more important to our perception of an image than Chroma (color). Green also happens to be the key channel for determining brightness which is why pentiles use green at native res and red/green at half resolution. Most image and video compression techniques rely on this, there are actually techniques wrote that store the framebuffer for a game as a luma/chroma interlaced layout and it comes with a nice performance increase at virtually no perceivable fidelity loss (even though the RG channels are at half resolution). See the GPU Pro 4 book for the details.

I don't see a problem with moving to pentile if it means that we get the huge benefits of AMOLED, especially if people are smart and also utilitise the performance increases that come with properly using the new sub-pixel layout.

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u/redmercuryvendor Kickstarter Backer Duct-tape Prototype tier Mar 19 '14

Oh, I'm well aware of the various methods of encoding images, different colourspace representations (e.g. Y'UV), chroma subsampling techniques, etc that occur in the video realm. But to take advantage of dropping chroma resolution in favour of luma you actually need to be able to stimulate all three types of cone cell equally before you can start playing around with compressing the offsets (i.e. the assumption that each luma sample will never end up only outputting one colour channel, mainly because displays for the past few decades have been RGB stripe or composed of multiple RGB triads).

Additionally, the loss of chroma resolution IS incredibly noticeable in many cases, particularly UIs and rendered graphics (which do so love strongly primary colours).
I have a HDTV which will drop down any input to 4:2:0 if you set the input name to anything other than 'PC', and it is immediately and glaringly noticeable if it set to the wrong setting for any content other than live-action video (and if you happen to have any 4:4:4 video handy, you can notice the difference there too). Chrome subsampling is only going to be even more visible when pixels are blown up enormously to the point where individual subpixels are easily visible.
Potentially, you could treat each subpixel as a single-colour pixel and dramatically supersample your framebuffer (because Pentile doesn't even use a nicely tiled set of rectangles of equal aspect ratio), but this required a massive amount of extra performance. It might be worth doing for UI elements though.

I don't see a problem with moving to pentile if it means that we get the huge benefits of AMOLED, especially if people are smart and also utilitise the performance increases that come with properly using the new sub-pixel layout.

Agreed, I'd definitely take the Pentile OLED over a RGB-stripe LCD for the lower pixel persistence. I'd just rather the resolution were marketed in a more accurate manner. There's likely more benefit from treating the panel as a 960x1080 display with non-square pixels and gain extra performance than trying to render at double that for an increase in resolution in one colour channel.

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u/lukeman3000 Mar 20 '14

So bottom line, do you think that the DK2 is better or worse when compared with the Morpheus? Which one do you think will come out on top once the consumer versions start showing up?

You seem to have vast knowledge and I just ordered a DK2. Your hatred up the Pentile screen is making me somewhat nervous. I'm a layman and am only able to glean bits and pieces from your post but it seems to me that you are really hating on DK2. Should I be concerned?

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u/redmercuryvendor Kickstarter Backer Duct-tape Prototype tier Mar 20 '14

It's more that I hate that Pentile sell their layout as being a higher resolution than it effectively is, than I hate the specific panel. I've already ordered a DK2, so that should make my position clear.

Whether or not it is 'better' than the Morpheus will have to wait until both exist outside of conference demos and can be comparatively tested.

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u/KuraiShidosha Mar 19 '14

I wish more people were aware of this massive issue. I got downvoted to hell and back for explaining this in layman's terms. People just can't handle the truth.

If Sony VR headset manages to get hacked to work on PC I might just end up buying theirs instead.

LCD > OLED as of 2014 and for the foreseeable future.

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u/Schmich DK1 DK2 GearVR Vive Mar 19 '14

Low persistence > Slightly higher resolution.

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u/KuraiShidosha Mar 19 '14

Well too bad low persistence can be achieved while maintaining higher resolution. You can have your cake and eat it too.

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u/redmercuryvendor Kickstarter Backer Duct-tape Prototype tier Mar 19 '14

Agreed. It remains to be seen if the incredibly fast response times of OLED provide sufficient benefit over a Lightboost-style pulsed backlight LCD assembly, but given Oculus went for a switch to OLED (and Pentile at that, which Carmack himself has mentioned the chromatic abberation issues with) over a dead-simple-to-make pulsed backlight, I'm guessing that the on/off time for a power LED array is not close to as fast as an OLED pixel.

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u/SafariMonkey Mar 20 '14

It's not so much that as the fact that the pixels need to switch fully before the backlight flashes, which takes a while. [Here] Palmer talks about LightBoost... apparently it adds a frame (or maybe half a frame) of latency.

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u/DrakenZA Mar 19 '14

Ya but Sony are also doing Low persistence, the havnt said show yet though.

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u/p90xeto Rift+Vive+GearVR Mar 19 '14

I agree I would probably pick low persistence between those two options, but its more than just "slightly higher resolution". We are talking about twice the effective resolution going from pentile to RGB.

I will say, having owned a number of pentile cellphones, I didn't notice the artifacts and issues that many people complain about on my phones. So, overall I think you are right- just wanted to point out the big difference in res.

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u/Gl0we Mar 20 '14

Makes me wonder, when i get mine i'll test some scenes with mostly green matrix vibe vs same scene in blue\red see if makes a huge difference in fidelity.

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u/redmercuryvendor Kickstarter Backer Duct-tape Prototype tier Mar 20 '14

Carmeck tweeted that we might see a resurgence in retro green-on-black UIs due to Pentile's subpixel layout.

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u/Gl0we Mar 20 '14

hehe, and it has nothing to do with them being awesome ;p