Image quality: 4k pixel shift vs Actual 4k - Page 7 - AVS Forum | Home Theater Discussions And Reviews
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post #181 of 207 Old 09-05-2018, 09:13 AM
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Originally Posted by sage11x View Post
That’s a good theory— I often have to change the shutter speed to avoid my camera picking up the RBE when taking still shots so I imagine this would effect the appearance of pixels as well.

Actually, I can recreate the effect. These were both taken on the BenQ TK800. Here is a shot where the pixels are visible.



Still, it doesn’t exactly explain the TVSPro video where you can clearly make out individual pixels in the UHD51a next to the HT2550. There is clearly something happening in the light path that allows the Optoma to have a more clearly defined pixel grid. Whether or not this was an engineering choice or not I cannot say. Jarno, I asked you this in another thread but you never responded, would you be willing to run some test patterns and take some close up shots so that we can compare? I can provide the patterns when I get home or I can link you to them.

Thank you for the fast retest

Ok, that sounds good, may be i need some time but i will do it. A Download link should be fine.

Displaying in PC Mode 4K Resolution?
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post #182 of 207 Old 09-05-2018, 09:38 AM
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@sage11x , hope you understand I'm not criticizing you for quoting a questionable number from a usually reliable source like Art who I often quote. Just trying to correct the technical record before an unfounded rumor spreads. If anyone knows of any currently available projector with an RGBRGB color wheel that has a verified 2X specification please let us know. Otherwise, RGBRGB+7200 rpm = 4X. Now, back to 4K.
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post #183 of 207 Old 09-05-2018, 11:39 AM
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Quote:
Originally Posted by Dave in Green View Post
@sage11x, hope you understand I'm not criticizing you for quoting a questionable number from a usually reliable source like Art who I often quote. Just trying to correct the technical record before an unfounded rumor spreads. If anyone knows of any currently available projector with an RGBRGB color wheel that has a verified 2X specification please let us know. Otherwise, RGBRGB+7200 rpm = 4X. Now, back to 4K.
No, I definitely didn't think that. I also don't want to be responsible for spreading FUD but I swear that's not the first time I read that. In fact, I remember seeing something similar about the UHD65 way back when which is why I didn't even flinch when Art mentioned that about the UHD51a. I don't know-- hopefully one of the more technologically inclined among our ranks will read this and clear it up. I went to the manufacturer sites and BenQ doesn't spec colorwheel speed any longer and, as far as I can tell, Optoma never did.


Oh man... all this stuff will make your head spin after awhile.

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post #184 of 207 Old 09-05-2018, 11:41 AM
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Quote:
Originally Posted by Jarno_Germany View Post
Thank you for the fast retest

Ok, that sounds good, may be i need some time but i will do it. A Download link should be fine.

Displaying in PC Mode 4K Resolution?
For the life of me I can't find the patterns Darinp and I were using...


But that's OK. I think there are some patterns in this suite we should be able to use:
https://www.avsforum.com/forum/139-d...terns-set.html


When I can get home I'll post some shots and list what patterns I used. Hopefully we can get some examples up for everyone to see.

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post #185 of 207 Old 09-06-2018, 04:11 PM
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Quote:
Originally Posted by sage11x View Post
For the life of me I can't find the patterns Darinp and I were using...


But that's OK. I think there are some patterns in this suite we should be able to use:
https://www.avsforum.com/forum/139-d...terns-set.html


When I can get home I'll post some shots and list what patterns I used. Hopefully we can get some examples up for everyone to see.
Ok, that looks like a lot of stuff, have to download it on weekend.

To stay the most on topic, it would be cool if someone with a real 4k and or some 4k eshift epson jvc owners could do the same ,-)
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post #186 of 207 Old 09-09-2018, 11:30 AM
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Quote:
Originally Posted by Jarno_Germany View Post
Hello 3DBob,
thank you for your efforts but your comparison pictures from the Optoma devices are a little bit questionable.
The gritty look you showed us is not what i see on my UHD300x.

I tried to take a photo too, and i think, there is a problem with the exposure time on your takes. I think you did freeze only a part of the 4 subframes, they need at least 1/60s, what exposure time did you use?

Here is a example of my UHD300x, i used a Camera with sensor shift stabi and a longer exposure time.approx 1/10. The result is not perfect but close to what i see in reality. (standing much closer than 1m in front of my 110" screen)

My experience was, that the benq w1700 was unbearable bad as an 4k pc monitor, text was so bad readable, no matter what i have done. Only magnify it 150-200% helped, but not every program was affected by this magnify setting. The Optoma is so much better in this regard, it is supprisingly close to real 4k
Sorry for not replying to this sooner. I just saw it. Your Pic of the UHD300x is very interesting as it does look like the Benq TK800 fine pixel arrangement. That said, I did look closely at the screen and the image I got of the UHD50, and it had a coarse pixel arrangement just as my pic shows. Maybe they cleaned that up in successive Optoma 4k projectors, I really don't know. It is interesting. I have to say, I did see a very early UHD50, so take that into consideration.
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post #187 of 207 Old 09-11-2018, 11:35 AM
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This is totally unscientifical, but after less than a week of use, my lowly JVC X590R with pixel-shift looks way sharper than my old Epson 8500UB. I haven't watched a lot of movies, but Jack Ryan looks about 10x better on Prime. The overhead footage of the car driving through the heavily treed snowy mountains in france was crazy sharp.
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post #188 of 207 Old 10-06-2018, 03:29 PM
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Quote:
Originally Posted by Dave in Green View Post
Optotune actually has some really excellent and honest wording in their description of their XPR-25 that I've quoted below. I've boldfaced and underscored one word that helps make this one of the most accurate descriptions of what DLP+XPR actually accomplishes:
Quote:
Optotune’s XPR-25 is an Extended Pixel Resolution 4-position Actuator. With a clear aperture of about 25mm it has been designed for Texas Instrument’s 0.47” DMD and enables the perceived image resolution to be increased from its native 1080p to 4K.
Perceived is the key word because it accurately describes the image resolution we see with these DLP XPR projectors. We don't get 3840x2160 discrete pixels on the screen at once as we get with true native 4K. But we do get four separate sets of 1920x1080 pixels sequentially flashed so rapidly on the screen that we perceive it as a 4K image. The reality of DLP+XPR is that for a fraction of the cost of the least expensive true native 4K projector we can get images we perceive to be so close in detail that it's hard to tell the difference.
Apparently the DLP folks are pretty sensitive about this issue because Optotune was convinced to revise their website description of the XPR-25 to exclude any reference to perceived resolution. Instead they now state:

Quote:
The result is a high-quality 4K display.
So this thread will remain as historical reference to Optotune's original XPR claim of perceived 4K.

optotune.com/index.php?option=com_content&view=article&id=312:e xtended-pixel-resolution-actuator-xpr-25&catid=35
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post #189 of 207 Old 10-07-2018, 09:44 AM
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Native 4K is truth=not affordable. 1080p XPR 4K is perception=affordable. Truth is in the eye of the beholder, if you can afford to behold it....

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post #190 of 207 Old 10-07-2018, 11:55 AM
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Honestly, I think 4k e-shift is plenty. It looks fantastic, the 5040UB is very sharp and detailed. I don't see the issue with it at all if the 5050UB offers 18GBPS.

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post #191 of 207 Old 11-20-2018, 01:11 AM
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Quote:
Originally Posted by BattleAxeVR View Post
....
What's slightly more interesting is how the 0.66 inch chips do it, since they do downscale, but they downscale twice, once per shift, using a bilinear filter (as opposed to point sampling) from the 3840 x 2160 source image to produce two distinct 2716 x 1528 images. This is not a 1:1 mapping but a ~1.4 : 1 mapping (since ~1.4 the number of pixels horizontally times ~1.4 vertically is 2x, i.e. the length of a standard hypotenuse of a 1x1 square).
.....
Greetings BattleAxe, thank you for your excellent posts.

1. It comes as a surprise to find out that down scaling is used by the 2716x1528 XPR chip to display 4k content. Was always under the impression that it worked under the same principle as in the .47 XPR, but using a 2-way shifter instead. Any reason given why point sampling is not used?

2. Is there a reason why there's no paring of Optotune’s XPR shifter with the larger native 2k .66 DMD?


Many thanks and best regards,

Last edited by qoopy; 11-20-2018 at 01:52 AM.
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post #192 of 207 Old 11-20-2018, 09:05 AM
 
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Quote:
Originally Posted by qoopy View Post
Greetings BattleAxe, thank you for your excellent posts.

1. It comes as a surprise to find out that down scaling is used by the 2716x1528 XPR chip to display 4k content. Was always under the impression that it worked under the same principle as in the .47 XPR, but using a 2-way shifter instead. Any reason given why point sampling is not used?

2. Is there a reason why there's no paring of Optotune’s XPR shifter with the larger native 2k .66 DMD?


Many thanks and best regards,
Thanks.

1. You can't use point sampling during a non-one-to-one input-to-output map, mathematically it just doesn't work.

Going from 3840 x 2160 to two shifted 2716 x 1528 frames, implies that each shifted image is sampled at (0,0) and (0.5, 0.5) pixels offset, respectively. Then there is the non-integer scale factor of 1 / ~1.4, both of which mean that if you point sampled the 4K image you wouldn't get the right colours at the right places, and it would introduce all kinds of artifacts. Of course, you can always do point sampling and take four samples instead of one, then manual bilinear filtering (4 input samples to 1 output sample) during the downscale, but that amounts to the same thing as bilinear sampling in hardware. Who knows how these chips work, but downscaling is done in hardware mostly these days.

2. There are native 4K DLP projectors using XPR now to do 4-way 8K. The one from Barco can accept 4K 240hz too, which is wicked for gaming. I don't see the point why they'd ever release a native 2K one when cinema DLPs use the 4K chips (without XPR since there is no 8K DCI content yet AFAIK). Shifting once diagonally from a 2K DLP instead of a 2.5K DLP would only get you halfway to 4K resolution, or 4M pixels instead of 8M. Shifting twice would require 240hz operation which the older chips cannot do, at least not in 1-chip mode. Although the DCI variants are all 3-chip designs so they can do 120hz no problem, maybe even 240hz since the 4K native DMDs do 240hz now.

The most interesting thing I discovered about all this, tech-wise, is how XPR differs from e-shift. e-shift is superior for 2-way shifting, actually cannot function in 4-way shifting, because of how it uses a single value, the circular polarization angle, to control the amount of shifting that a birefringent crystal does. That's why no 4-way e-shift, because stacking two would make alignment a pain. It's also true in the other way, e-shift is better in the sense that it has no mechanical moving parts to it, it's just an LCD and a crystal wedge, but LCD means the input light has to be pre-polarized otherwise you'd lose half your lumens. So that's the real reason why DLP uses XPR instead of e-shift, at least for the 2x shifter variants.
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post #193 of 207 Old 11-20-2018, 04:57 PM
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Originally Posted by BattleAxeVR View Post
Thanks.


The most interesting thing I discovered about all this, tech-wise, is how XPR differs from e-shift. e-shift is superior for 2-way shifting, actually cannot function in 4-way shifting,
2D shifting using double refraction is not only possible it was tried @

Non-mechanical sub-pixel image shifter for acquiring super-resolution digital images - OSA Publishing

Yet what places this stuff into the no free lunch category is temporal behavior, eg. you dont have ideally behaving displays nor sensors, but will behave x times worse.

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post #194 of 207 Old 11-20-2018, 05:48 PM
 
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Yeah, TN doesn't switch from one extreme polarization state to the other instantly, in fact white-to-black or black-to-white (which is what LCD-based shifters do, basically) response times can be as high as 10ms, it's only gtg response times which are 1ms or so now.

So you will likely get some smearing due to it transitioning part-way through each frame, so that would mean perhaps the tops of e-shifted frames might be blurrier than the center or bottom. It's worth looking at to see if that's true. Still better than nothing though. I'm sure they must use some extreme overdrive for those shifters though, and single-pixel LCDs (like 3D glasses) could maybe be faster than LCD pixel grid displays. Or slower, not sure.

@gain3 , since you have so many insights, I think it's better if from now on you share them in these threads instead of my PMs. Share with the class!
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post #195 of 207 Old 11-20-2018, 05:51 PM
 
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Quote:
Originally Posted by sage11x View Post
That’s a good theory— I often have to change the shutter speed to avoid my camera picking up the RBE when taking still shots so I imagine this would effect the appearance of pixels as well.

Actually, I can recreate the effect. These were both taken on the BenQ TK800. Here is a shot where the pixels are visible.

And here is one which is closer to what my eyes actually see.



Still, it doesn’t exactly explain the TVSPro video where you can clearly make out individual pixels in the UHD51a next to the HT2550. There is clearly something happening in the light path that allows the Optoma to have a more clearly defined pixel grid. Whether or not this was an engineering choice or not I cannot say. Jarno, I asked you this in another thread but you never responded, would you be willing to run some test patterns and take some close up shots so that we can compare? I can provide the patterns when I get home or I can link you to them.
If they can make out individual pixels then either the shifting isn't working or they're filming at a much higher frequency than 240hz in order to capture individual sub-frames.

Seeing individual pixels is a bug, not a feature. I think those pics must have been taken with the shifter off or just happened to capture it fast enough so that it's capturing a distinct frame. Logically, there is no other possibility. If the shifting's working properly, the pixels should smear together. This is a GOOD THING PEOPLE!! That second picture looks way better than the first. Pixel grids are ugly.
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post #196 of 207 Old 11-25-2018, 07:30 PM
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Quote:
Originally Posted by BattleAxeVR View Post
....
1. You can't use point sampling during a non-one-to-one input-to-output map, mathematically it just doesn't work.
....
You're right of course. The brain wasn't working.

I've recently acquired a XGIMI Lune that claims to use the 4xXPR shifter , but it doesn't seem to resolve single pixel test pattern. Appreciate if you could kindly take a look at the attached screen shots, and see if there's a problem with the projector, or whether it is indeed 4K. Apologies for the low quality, as the screen wasn't set up yet.


By the way, why does the XPR shifter produce a dark grayish border around the projected image?


Many thank and best regards,
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post #197 of 207 Old 11-26-2018, 06:20 AM
 
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The light border issue is fixed now and has been discussed to death on AVS and elsewhere.

No shifting projectors will resolve 1-pixel test patterns because the pixels overlap, but they shouldn't. You don't want to see individual pixels! Their blending together is a feature, not a bug.
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post #198 of 207 Old 11-26-2018, 11:47 AM
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Optoma UHD40 projector can resolve 1-pixel test patterns. Each individual pixel from a 4k image can be seen and counted.
In the 1-pixel test image for 4k Full Chroma 4.4.4., everything is distinct. In fact, the details on the screen look better than in pictures, because some errors and optical distortions are induced by the photographing process.
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post #199 of 207 Old 11-26-2018, 05:23 PM
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Originally Posted by Voyager3D View Post
Optoma UHD40 projector can resolve 1-pixel test patterns. Each individual pixel from a 4k image can be seen and counted.
In the 1-pixel test image for 4k Full Chroma 4.4.4., everything is distinct. In fact, the details on the screen look better than in pictures, because some errors and optical distortions are induced by the photographing process.

Thanks for sharing, Voyager.

Does the UHD40 use a 2x or 4x XBR shifter, or is it a true 4K DLP?
Would you be kind enough to post screen shot of the same test pattern I used for comparison?

Many thanks and best regards,
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post #200 of 207 Old 11-27-2018, 12:38 AM
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Optoma UHD40 is a cheap 4x pixel shifter. Afternoon I will check your test pattern. I think that will be a difficult technical challenge. Best regards!
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post #201 of 207 Old 11-27-2018, 11:20 AM
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So, the projected test image looks a little better than in this pictures.

To see all details in a single picture, a very high resolution camera and a very good lens are needed (is not an easy task).
On the screen, all pixels are visible, including in corners, despite of a little softness caused of the projector's lens (which is a very goon one). In the edge of screen, the softness is accentuated because of camera lens.
In full dark-Magenta color, the pixels are not as visible as in other colors.

The small lines on the screen are actually gray-black, but because of some little chromatic aberration (magenta-green) and other factors, the camera interpreted them toward brown-red-mauve (in the detailed pictures).

To take the pictures in areas with small details, I moved the test-image in an editing software (at 100% scale), instead of moving the camera (which was on a tripod).
.................................................. .............................
In the last picture can be seen the maximum which projector can do regarding 1-pixel lines.
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post #202 of 207 Old 11-28-2018, 06:15 PM
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Quote:
Originally Posted by Voyager3D View Post
So, the projected test image looks a little better than in this pictures.

To see all details in a single picture, a very high resolution camera and a very good lens are needed (is not an easy task).
On the screen, all pixels are visible, including in corners, despite of a little softness caused of the projector's lens (which is a very goon one). In the edge of screen, the softness is accentuated because of camera lens.
In full dark-Magenta color, the pixels are not as visible as in other colors.

The small lines on the screen are actually gray-black, but because of some little chromatic aberration (magenta-green) and other factors, the camera interpreted them toward brown-red-mauve (in the detailed pictures).

To take the pictures in areas with small details, I moved the test-image in an editing software (at 100% scale), instead of moving the camera (which was on a tripod).
.................................................. .............................
In the last picture can be seen the maximum which projector can do regarding 1-pixel lines.

Greetings Voyager.

This is a most impressive piece of work, and what an excellent set up you have.
Looking at the last picture, it seems the single pixel lines have much lower intensity and width. It is also positioned off centred.

Any explanation why this might be the case?
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post #203 of 207 Old 11-29-2018, 07:37 AM
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Thank you!
The problem regarding 1-pixel line seems to be present only in black and white grids. As you can see in other pictures, black and colored 1-pixel lines can be represented much better, as in 1-pixel width text test chart.
Also, in your test chart, can be seen a yellow and a green 1-pixel lines between 1-pixel black lines, clearly visible.

This problem can be related to the size of each individual pixel on the DMD chip, and the space between them. A macro picture of the DMD chip can give more explanations.

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Last edited by Voyager3D; 11-29-2018 at 07:42 AM.
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post #204 of 207 Old 11-29-2018, 06:29 PM
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Thanks Voyager.
It seems to me the single pixel line should be evenly spaced as in the first picture below, rather than what your last picture showed. This may explain why single pixel image is difficult to visualize, but does it also suggest perhaps the pixels are not uniformly spaced?
Not sure if this makes any sense. Perhaps Mr. BattleAxe would like to clarify.
Thanks and best regards,
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post #205 of 207 Old 11-29-2018, 09:08 PM
 
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Those are interesting pics and especially videos! I like seeing the micromirrors move, awesome.
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post #206 of 207 Old 11-30-2018, 11:32 AM
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qoopy - in practice, all this details doesn't matter, because the image is very crisp, sharp, impressive.
"US Consumer Technology Association (CTA) has deemed the results (for Optoma UHD40/50) ‘real’ 4K." (trustedreviews)
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post #207 of 207 Old 11-30-2018, 02:18 PM
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Quote:
Originally Posted by Voyager3D View Post
… "US Consumer Technology Association (CTA) has deemed the results (for Optoma UHD40/50) ‘real’ 4K." ...
CTA is primarily a marketing organization. Their 4K standard is extremely brief and loose with virtually no specific engineering parameters cited. It's not a detailed engineering standard as you would get from a true engineering organization like SAE.
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