[HN Gopher] TV backlight compensation (2020)
___________________________________________________________________
TV backlight compensation (2020)
Author : pcr910303
Score : 311 points
Date : 2022-10-02 06:44 UTC (4 days ago)
(HTM) web link (www.lofibucket.com)
(TXT) w3m dump (www.lofibucket.com)
| Rygian wrote:
| This is almost identical to a problem I'm trying to solve, which
| is to turn a potato-quality picture of a sheet of paper into a
| clean scan, turning whatever levels of gray conform the paper
| background become a uniform #ffffff white. The obvious solutions
| (equalizing, converting to bitmap, ...) don't work because what's
| white in the top left (say #ccc) is wildly different from what's
| white in the bottom right (say #888), and the shift is non-
| uniform due to potato-quality lighting.
|
| Glad I caught this post, I hope the solution can contribute to my
| problem (although I do not have a way to obtain a fixed ground
| truth -- lighting will change for each picture.)
| sorenjan wrote:
| Sounds like local contrast adjustment. There are several
| different ways of solving it, here's a couple that look like
| they work pretty well:
|
| https://stackoverflow.com/questions/63251089/how-to-do-a-loc...
|
| https://stackoverflow.com/questions/65666507/local-contrast-...
|
| One possible preprocessing step could be to do a high pass
| filter on it, if the shadows vary slowly over the image.
|
| There are also more specialized techniques specifically for
| removing shadows from documents, like these:
|
| http://civc.ucsb.edu/graphics/Papers/ACCV2016_DocShadow/
|
| https://faculty.iiit.ac.in/~vgandhi/papers/shadow_removal_ca...
|
| I also found this, an image editor based approach if you just
| want to do a few images manually:
|
| https://janithl.github.io/2021/12/remove-shadows-and-uneven-...
| daedbe wrote:
| A common alternative solution in this case would be to use an
| adaptive thresholding technique such as Otsu's method.
| komatsu wrote:
| Otsu's method finds a single threshold value in an adaptive
| way. This can't solve a scanned document thresholding
| problem.
|
| btw: The iOS Notes app has quite a capable document scanning
| tool. It's cleverly hidden though.
| Rygian wrote:
| I'm pretty happy with the scanning feature of Evernote, and
| I think there are some other nice apps in the Android app
| store, but my goal is to have a solution that is not
| captive (either to a specific vendor or to a SaaS
| solution).
| Rygian wrote:
| Thanks, I was not aware of Otsu's method.
|
| From the Wikipedia article, "Otsu's method performs badly in
| case of heavy noise, small objects size, _inhomogeneous
| lighting_ and larger intra-class than inter-class variance. "
| (Emphasis mine.)
|
| Right now my solution is at the stage of local thresholds
| with a configurable block size.
|
| Thanks to your pointer, I know now that my next steps will be
| to review the Niblack or the Bernsen algorithms. (Or just
| integrate ImageJ.)
| comboy wrote:
| Just so you know, there are many scanner apps which solve this
| problem already, not sure how many of them are open source
| though.
| crazygringo wrote:
| If your content is black and white, just use a local contrast
| filter and then threshold it. It's easy to do, but it does
| result in monochrome so you lose antialiasing. If you're at
| 300+ dpi though that doesn't usually matter. This is commonly
| done with PDF scans where monochrome output is desired for high
| compression. Easy to do with ImageMagick.
|
| If you want to preserve aliasing and also color generally, I'm
| sadly not aware of any open source solution for that. Various
| scanner apps seem to do it with varying degrees of success; I'd
| be curious if there's a standard algorithm for it. It feels
| related to the de-curving algorithms that take a book page and
| make it flat. So you'd be modeling both the page curvature and
| black/white values simultaneously. Seems possible for general
| lighting/shadow, but wouldn't work for reflectivity from camera
| flash.
| Tomte wrote:
| Would https://www.imagemagick.org/Usage/compose/#divide help?
| unglaublich wrote:
| I wouldn't call this over-engineering. It's a reasonable solution
| to an actual problem.
| axiolite wrote:
| I think the reasonable solution is: Buy a new TV. We're not
| talking about a jumbotron display here. A cheap new TV with
| proper color is likely very inexpensive.
| agent008t wrote:
| Where is the fun in that? We are alienated enough from the
| stuff we consume as it is.
| adrianN wrote:
| Why create waste when it's not necessary?
| tgsovlerkhgsel wrote:
| If you're not doing it as a hobby, the one-off effort put
| into repairing an item (or in this case, engineering the
| correction) is also "waste".
|
| If you want to dedicate that time to improving the planet,
| avoiding the waste of one TV is likely not a better use of
| your time than e.g. fixing some bug in some popular open
| source software that causes it to be less efficient.
|
| Let's say you make a change to Firefox that makes it use
| 0.1 Watt less on average, and let's be conservative and
| assume the ~350 million Firefox users use it for one hour a
| day on average. That's 35 MWh per day saved. Assuming 0.1
| kg CO2e/kWh, that's a saving of 3.5 tons of CO2e saved
| _each day_.
| nmilo wrote:
| What a ridiculous premise. The value of your time does
| not come in some sort of interchangeable unit where 1
| hour of TV repair is comparable to 1 hour of Firefox bug-
| fixing. Realistically, if the author decided to get a new
| TV, he would not spend that new-saved time trying to make
| up for the environmental damage he caused by throwing his
| old TV out.
|
| (And who is even to say your bugfix would save power?
| It's not like Firefox has a power-usage detector in their
| CI pipeline.)
| batch12 wrote:
| Not to mention the time spent shopping, fuel spent
| delivering, time spent setting up and configuring...
| adrianN wrote:
| Fair point, but I bet that making Firefox take 0.1W less
| on average is vastly more work that fixing a TV image.
| And if you write blog post about it, maybe other people
| can fix their TV with less work.
| anon4584 wrote:
| There are other ways to improve the planet as well.
|
| If everyone spent 2 hours a year removing washed up waste
| from the beaches, it would have made a big difference.
| smileysteve wrote:
| Washed up waste is the tail end, the only "big"
| difference it makes is to the localized beach until the
| next tide/current comes from the source of the pollution.
|
| Saving the monitor, releasing the diy reduces a (minor)
| head end of the problem that is not only leading to long
| waste in a landfill, but also metals and plastics in
| water.
| [deleted]
| RajT88 wrote:
| I don't know if I am going to ever fix a TV this way.
|
| But the knowledge of how to create a custom shader is
| going to come in handy one day. More and more I am
| finding, most knowledge comes in handy some time. You
| just have to remember at the right time what is possible
| and go refresh your memory on it.
| Arrath wrote:
| I wonder if something similar could be used to keep my TV from
| ratcheting up the overall brightness/backlighting whenever a
| subtitle is on screen.
|
| The constant ramping of brightness is rather distracting.
| kasabali wrote:
| There should be an option to disable automatic brightness.
| Arrath wrote:
| I swear I've dug through the menus time and again! I guess
| I'll have a look again tonight.
| [deleted]
| ifqwz wrote:
| The quality of computer monitors is appalling - after buying and
| returning several monitors because of quality issues, I briefly
| considered doing this system-wide to fix colour uniformity
| problems. Eventually I chose to keep my old monitor instead. It
| has uniformity problems as well but it doesn't cost me $1000
| extra to keep.
|
| But it's a damn shame that you can't throw enough money at
| manufacturers to make them make monitors without glaring QA
| problems. No matter how much you spend they sell you shit.
| BoorishBears wrote:
| My XDR has been pretty flawless, and on the less exorbitantly
| priced end, I've had good experiences with a few business
| oriented IPS models (most recently the Samsung UR55).
|
| My main gripe is gaming monitors seem to be consistently the
| worst panels they can get their hands on.
|
| It seems like they realize gamers will put up with a lot of
| garbage in exchange for raw "power" and take full advantage of
| the fact. I'm 99% sure that's why we saw brands like Wasabi
| Mango (who used to take B grade panels and sell them on the
| cheap) disappeared... the manufacturers just started shipping
| them as gaming models.
| autoexec wrote:
| If you fill your entire screen with nothing but a single
| solid color (try #FF6400) does it show up correctly? That is,
| without any gradient or areas of the screen where the color
| appears darker or lighter (especially around the edges or in
| the corners?).
|
| I've yet to find a modern monitor that doesn't have a problem
| with that basic test, which is pretty disappointing
| considering accurately representing a single color should be
| easy and I've had several CRTs that could do it.
| adrian_b wrote:
| I use a pair of Dell monitors with IPS screens (U2720Q and
| UP2414Q).
|
| I always use as background a solid grey (#808080) and there
| is no noticeable non-uniformity.
|
| I have tried now your color (#FF6400) on the U2720Q.
| Because this color is much brighter, if you look carefully
| you can see that there are small areas at the corners,
| especially at the 2 lower corners, with lower brightness.
| Also the 2 lateral edges have a slightly lower brightness,
| but the difference from the center is less visible than for
| the 2 lower corners.
|
| However the areas affected are small (maybe a width of
| about 1/30 or 1/40 of the screen width) and you really have
| to look with the intention to find non-uniformities. When
| looking casually at the screen there is no obvious non-
| uniformity.
|
| For emissive displays like CRT or OLED it is easier to
| achieve uniform brightness over the screen.
| ifqwz wrote:
| Most people will tell you that their monitor is flawless,
| then you do simple tests like that one and the monitor
| shows that it has severe issues and they respond "uh I
| never noticed, well I don't care". Which is precisely why
| manufacturers can get away with the shit that they sell.
| BoorishBears wrote:
| I've owned pretty much every "notable" monitor in the
| formats I care about in the last few years, I'm sure I'm
| pickier than you.
|
| The fact is you can pay for a good enough monitor to
| truly be flawless, it just costs more than people are
| envisioning. For example, my late revision 5K Ultrafine
| nearly as flawless as the XDR. I didn't list it because
| people who don't know better latch onto the wifi teething
| issues the first revisions had, but the panel is
| approaching the limit of little backlight bleed as the
| technology allows (and the limits are not as poor as
| people are making out).
|
| -
|
| Honestly I've seen the opposite though, people who don't
| realize that any piece of screen large enough,
| photographed with exposure cranked way below normal will
| show _some_ sort of pattern and confuse _that_ with
| "terrible backlight bleed".
|
| But that's the panel equivalent of people who only watch
| Star Wars space sequences with brightness cranked to 11
| in a pitch black room to judge HDR bloom...
| Sohcahtoa82 wrote:
| On my main monitor, a test like that fails spectacularly.
|
| If I put a solid purple, then if my eyes are directly
| perpendicular to the very center of the screen, it works
| fine. As soon as I move up or down, either the top or
| bottom of the screen becomes very noticeably blue.
|
| But in daily use, I never notice it. If I lean way back in
| my chair, then yeah, I'll need to adjust my screen to be
| able to see it.
|
| But this is a 144 hz 1440p monitor I got for $400 brand new
| in 2015. Pixel response times are great. The monitor works
| exceptionally well on all the Blur busters tests. It is an
| amazing monitor for gaming...
|
| ...except in dark scenes. It's a TN panel, which by default
| kind of lacks in contrast and brightness, and so to make it
| look good, I had to tweak contrast, gamma, and brightness
| settings, and it results in some clipping. #020202 and
| #010101 look like they get rounded down to #000000, and
| #050505 and #040404 look like they're getting rounded down
| to #030303.
|
| If I draw a pure black-to-white gradient, then there's
| noticeable banding. Like colors are only being represented
| in 7 bits per channel, and the darkest colors lose even
| more.
|
| But again, in daily usage, especially in games (as long as
| it's not a dark scene) and videos, it's not even
| noticeable.
| BoorishBears wrote:
| Yes, I know what backlight bleed is...
|
| I've probably owned something like 15 monitors in the last
| 5 years, the XDR may not live up to the 25k reference
| monitor dreams, but no mere mortal would be able to drive
| one anyways.
| jiggawatts wrote:
| Monitor? No.
|
| But I just recently purchased a Sony A95K QD-OLED
| television, and _holy cow_ the uniformity is just
| breathtaking. You start noticing the deficiencies in your
| own vision.
|
| There's a similar panel available as a computer monitor,
| but unfortunately only curved and 1440p.
| jabroni_salad wrote:
| Gamers hit up blurbusters to see how the motion is and it
| either looks okay or you get a headache. The OEMs optimize
| for that (hence the focus on g2g and adaptive sync) and then
| just jack up the saturation slider to compensate for
| everything else.
|
| And hey, those wasabis and catleaps got you a 1440p IPS panel
| that did 90% of what you want for 50% of the price at a time
| when 1440p and IPS was still kind of rare to own. Most people
| who got one were upgrading from a typical TN so even a crappy
| IPS looks good in comparison. I was playing eve online at the
| time and caused at least 10 people in my corp to buy them
| when they saw how much screen estate you got at a higher res.
| BoorishBears wrote:
| You're misunderstanding the comment: the point is Wasabi
| Mango and co were good because they were charging
| significantly less for the lower grade panels.
|
| Now manufacturers are possibly prioritizing the highest
| grade panels for non-gaming use and using extremely
| expensive gaming monitors as a dumping ground for
| everything else.
|
| For example, the 28" UR55 has few complaints about
| backlight bleed and in my experience with having bought
| several is a reliable choice. Meanwhile the oddly similar
| 28" Odyssey G8 is known as a "buy and return until you get
| one that's ok" type of monitor, as are many other gaming
| monitors these days.
|
| Gamers seem conditioned to just accept inferior panel
| quality as long as the other specs work, while business and
| casual customers would probably just buy another monitor if
| they saw weird issues. They might not know the term
| backlight bleed, so they'll still see it just fine.
| nottorp wrote:
| You talking about mainstream "gaming" monitors? I'm just a
| programmer and gave up on those long ago. Getting entry level
| monitors targeted at graphic designers now. Namely Asus ProArt
| and I think Dell has similar stuff?
|
| They don't have 240 Hz and sub 0.01 ms response times though,
| so if you're buying your hardware based on bigger numbers in
| specs they won't do.
|
| They're probably not that great for actual designers either,
| but they're good enough for me.
| kevingadd wrote:
| The first graphic design monitor I bought from Benq had a
| busted image processor so that you couldn't turn off the
| sharpening - only set it to -5% (blurry) or +5%. Eventually I
| complained enough that they sent me a different monitor that
| didn't have the problem.
|
| I've had bad experiences with some of Dell's pro-grade
| monitors too. It feels like modern displays are so complex
| firmware and hardware wise that it's just very hard to find
| one that isn't defective in some way. This replacement Benq
| works for basic uses but its freesync is broken and it's
| already developed burn-in around the edges after about 1.5
| years.
| nottorp wrote:
| Funny, when I bought my first designer-ish monitor I threw
| a (gaming) Benq into the trash.
| deergomoo wrote:
| > Asus ProArt
|
| I'm using one of these and I'm very happy with it. Reasonable
| price, 75Hz, supports USB-PD + has its own USB ports so I can
| one-cable it with my work laptop.
|
| Most importantly they come factory calibrated. I consider
| reasonable colour reproduction important even though I only
| use it for programming. I stare at this thing for 8 hours a
| day, it needs to look good.
|
| In fairness I also have a 165Hz LG UltraGear gaming monitor,
| and the image quality is almost as good. My only complaint is
| the black levels and grey uniformity suck, but for someone
| who wants performance _and_ quality it's a decent option.
| nottorp wrote:
| > I consider reasonable colour reproduction important
|
| When I got my first I wasted 2 hours rewatching a movie I
| had seen recently. Just because i didn't know it can look
| that good on a monitor :)
| londons_explore wrote:
| Gnome (Ubuntu, Linux) allows a custom shader to be applied to the
| whole desktop, including fullscreen apps.
|
| Here is an up to date fork with some example shaders:
| https://github.com/Hello1024/gse-shader
|
| I use it to make sure a 'sensitive' pixel on my screen never
| turns on (it's a row of pixels which, if the difference between
| it and the pixels to the side have more than a certain difference
| in brightness, the whole screen fails - presumably due to a power
| supply fault in the column driver circuitry).
| speedgoose wrote:
| How did you manage to find the issue?
| londons_explore wrote:
| I noticed the screen only died when playing videos and always
| died at the same point if I rewatched a video. Notably,
| greyscale videos _never_ caused the issue. Then I went
| through a video frame by frame to get to the frame it died
| on. Then I erased parts of the frame to find which part
| caused it. Eventually I found that if the red or blue pixel
| in the 481st column and the green pixel in the 482nd column
| have a difference of brightness of too much, and neither are
| 255 or 0, the screen dies.
|
| I'm pretty sure the problem is the column drivers (which put
| data onto the column lines). They take in serial data, and my
| 1920 screen has 4 column drivers, each responsible for 480
| columns, so the 481st pixel is the first column that the 2nd
| column driver deals with.
|
| It uses more power during the row sync pulse (because it has
| to drive all the column lines to the correct voltages for
| whatever is being displayed). It uses more power for grey
| values (because 255 or 0 are solid on or off, while mid
| values are typically dithered, wasting energy in the column
| capacitance). I would guess all these worst-case events for
| power consumption within the column driver, combined with
| probably 'barely passing qa' silicon, means that in edge
| cases the power sags, something gets reset, and the whole
| screen fails.
|
| So my fix is a shader to make sure the worst case conditions
| can never happen all at once. Visually, it isn't really
| noticeable. And with more work it could probably be turned
| into something that could be shipped to customers (within the
| GPU driver) without any customer complaining (for example if
| you are a laptop manufacturer who has purchased millions of
| screens with this fault).
| jcims wrote:
| What's the odds that such an obscure problem happens to
| someone with the patience and wherewithal to figure it out
| *and* fix it? Pretty impressive.
| fuckstick wrote:
| It's probably not all that obscure. There's an awful lot
| of ewaste.
| londons_explore wrote:
| I did consider replacing the screen, but the only source
| I could find was China with 60 day delivery by boat, and
| I decided to find a workaround till the screen arrived...
| The screens now arrived, but the workaround is so good I
| can't be bothered to fit it.
| moffkalast wrote:
| That is some top tier investigating and persistence, hats
| off. I would've used the excuse the upgrade the monitor
| lol.
| CamperBob2 wrote:
| Or replace the 30-cent capacitor that's likely causing
| it.
| londons_explore wrote:
| It's likely one of the power bond wires from the glass
| screen to the silicon IC. Without equipment stretching
| into the millions of dollars, you won't be fixing that.
| EZ-Cheeze wrote:
| I want to be able to edit anything on my screen in ways defined
| by me: "hide any faces" "put a red circle around any animal"
| "hide any word under three letters"
|
| http://zeroprecedent.com/lore/flipside.html
| londons_explore wrote:
| Well now you have all the building blocks to implement it...
| EZ-Cheeze wrote:
| I'll do it when I can just tell the computer to do it -
| maybe 2024
|
| It will be interesting to rewatch movies with all the faces
| blanked out - they're eye-magnets that prevent you from
| noticing other details, for example in body language
| franky47 wrote:
| Funny how recent developments in AI have warped our
| comprehension of what is easy to ask to a computer vs
| what is hard.
|
| Obligatory related XKCD: https://xkcd.com/1425
| xattt wrote:
| AI is turning out to be the singularity that science
| fiction writers talked about. You just have no freaking
| idea what's next at this point.
| somat wrote:
| I am halfway convinced that the singularity has already
| occurred and has been ongoing from the 1700's* however,
| being carried along with it, you can't see it directly,
| you can only dimly sense it's tidal pull.
|
| It is like a black hole. how long does it take to fall
| into a black hole? the answer is a surprising "just about
| forever" due to time itself dilating as you approach the
| center.
|
| * think about it, mankind had been trundling about with
| effectively the same economy for many thousands of years
| then at some point about three hundred years ago it went
| exponential and has not slowed down.
| lesuorac wrote:
| Besides the fact that GPS already exists, it seems like
| it would take longer (~20 years) than the 5 years claimed
| to detect birds.
|
| > The GPS project was started by the U.S. Department of
| Defense in 1973. The first prototype spacecraft was
| launched in 1978 and the full constellation of 24
| satellites became operational in 1993
|
| https://en.wikipedia.org/wiki/Global_Positioning_System
| squeaky-clean wrote:
| Never forget to read the alt-text joke on an XCKD comic.
| The punchline on this one is based in some truth.
|
| > In the 60s, Marvin Minsky assigned a couple of
| undergrads to spend the summer programming a computer to
| use a camera to identify objects in a scene. He figured
| they'd have the problem solved by the end of the summer.
| Half a century later, we're still working on it.
|
| https://dspace.mit.edu/bitstream/handle/1721.1/6125/AIM-1
| 00....
| GauntletWizard wrote:
| What's really incredible to me is how right the
| prediction was, but also that it was _real_. In 2014,
| classifying images as "containing a bird" was a nigh-on-
| impossible task. Not an impossible one, and image
| classification was already in production use in limited
| forms with mapping agencies and the like, but beyond
| anyone's capability at the time. In 2017, Not Hotdog was
| a novelty app - Image classification was real, but
| limited, and didn't have a great reputation yet. By 2019,
| papers[1] were being written on image classification as a
| service and where their pitfalls were, but the idea was
| solid and sound; Today in 2022, it's something you'd have
| to research and test before buying for your startup but
| not a hard product to find.
|
| [1]https://arxiv.org/abs/1906.07997
| 1-6 wrote:
| This technique is cool but it seems like it would cause poorly
| performing pixels to get worse over time.
|
| Would it be possible to create an inverted image that would
| correct the backlight by burning in the bright areas? It would
| seem like a more difficult task to accomplish because pixel burn-
| in time is a variable that's hard to measure.
| justusw wrote:
| This is such a cool idea and execution. I also like the DIY
| approach to patching MPC BE yourself, which shows how far OSS can
| take you.
|
| I wonder, when applying a linear transformation like in the
| shader described, will the total available color space decrease?
| Simply put, if a one-dimensional color value on the arbitrary
| scale between 1 and 100 needs to be decreased by 20 for
| correction, the resulting maximum will be 80. Does that mean the
| total available color values will be less?
| actionfromafar wrote:
| Mostly yes but it also depends. What happens is exactly that,
| there will be a clipping in the color band(s) you are
| correcting for.
|
| This can easily be verified with a simple thought experiment:
| imagine an area is almost completely red. This area will have
| to be complemented with full blast of green and blue to even
| achieve white, or partial blast of green and blue to achieve
| gray.
|
| It can not achieve any color without a red component, hence
| reducing the area of the color triangle for that part of the
| screen.
| klodolph wrote:
| No. Color perception is relative.
|
| Basically, what you are doing is adding a cast to the image.
| This cast cancels out with the cast that the backlights give.
| When you add two complementary color casts to each other, you
| end up with neutral gray.
|
| This results in an image which is darker, but still has the
| full color range that the TV is designed for.
| sorenjan wrote:
| This reminds me of the world cup in South Africa, where the
| spectators used vuvuzelas to make a unique sound that I found
| hard to endure. I figured it would be easy to use a notch filter
| to remove it, but I could never find a way to implement it it
| real or near real time, only as post processing.
| ermir wrote:
| I remember the broadcasters also implemented this solution
| straight into the stream, the TV spectators did not have to do
| anything.
| Retr0id wrote:
| Wow, I'm very glad to see this!
|
| This exact idea has been floating around in my head for ages, and
| I always wondered how well it actually worked - now I don't need
| to wonder. I started thinking about it as a potential solution to
| OLED burn-in. Thankfully, my OLED TV doesn't have any burn-in
| yet, so I never needed to investigate further.
| xvector wrote:
| OLED TVs already compensate for burn in. A lot of your pixels
| are probably already somewhat "burnt" but you can't perceive it
| due to the corrective measures your TV takes. You'll only
| really notice it when it's irredeemably bad.
| Candas1 wrote:
| OLED TV's try to prevent burn in, I am not sure it can
| compensate burn in
| empiricus wrote:
| I don't see how the TV can compensate for the burnin
| without having an external picture of the screen. I have a
| couple of years old OLED TV, and it has burn in... The
| Netflix logo, the netflix animation, and subtitles are
| quite visible all the time now. This is despite running
| periodically the TV pixel refresh or however it is
| called...
| astrange wrote:
| It has a memory of the history of what's displayed on
| screen and uses that to predict what's burned in. This
| can obviously be a privacy issue, so there's a trade off
| in making it too exact.
| orbital-decay wrote:
| _> I don 't see how the TV can compensate for the burnin
| without having an external picture of the screen._
|
| Build a comprehensive degradation profile of your LEDs.
| Keep the burn-in accumulation buffer that tracks
| intensity and usage amount of each subpixel. Use it in
| your EOTF to correct the picture.
|
| Some color-accurate monitors like Eizo are even profiled
| for temperature (and have a grid of temperature sensors)
| empiricus wrote:
| sounds good in theory, but what about gradual errors
| accumulating after thousands of hours/millions of frames?
| [deleted]
| serd wrote:
| Could you share a photo? I'd really like to see that.
| empiricus wrote:
| https://i.postimg.cc/1Xy6V5wb/oledburn.jpg
|
| not the greatest picture (some reflections). should have
| used a gray background, but I used red because this color
| is the most affected.
|
| The burnin is mostly harmless, but the middle blob is
| very annoying; yellow parts of the image become greenish
| when they get to the middle of the screen.
| ornornor wrote:
| Ah that sucks. How old is the tv? And what's the
| brightness in it?
|
| My 3 year old Panasonic gets used a lot but we keep the
| brightness down to the 45-55% range (it's plenty bright)
| to avoid burn in. We also don't display static content on
| it. And when we do, it's mostly from Kodi which dims
| itself after 10 min or so.
|
| All that to say for those who are fearful of OLED because
| of burn in: don't be. With some precautions, it's fine.
| And having true blacks is absolutely glorious. I enjoy it
| every time I use the screen.
| zepolen wrote:
| Which tv is this?
| sss111 wrote:
| second this!
| ahartmetz wrote:
| Burn-in is probably somewhat computable as a function of
| brightness, time, and temperature or so. So it can be
| compensated physically (burn out the other pixels... you
| don't want to be in the room, it's going to be annoyingly
| bright) or digitally by adjusting the signal.
| ludwigvan wrote:
| > I haven't yet watched a whole movie with the new color
|
| Love the hacker mindset. Once the problem is solved, the
| underlying issue loses its appeal :)
| dmos62 wrote:
| Pretty cool, but you could instead replace the LEDs.
| 1-6 wrote:
| Sourcing the LEDs, disassembling the panel, and re-soldering
| each LED is not scalable. The solution mentioned in this
| article can be open-sourced and distributed to the masses.
| kasabali wrote:
| Leds are sold as plug in bars. there's no soldering involved.
| taking out the panel safely is tricky, though.
| MrBuddyCasino wrote:
| I did this once, was pretty easy. The backlight color had
| turned completely blue. The strips can be bought as spare parts
| and swapped easily without any soldering. The hard part is
| finding out the parts number of the LED strip for the
| particular TV.
| dirtyid wrote:
| How much does backlight drift over time? I have a few calibrated
| monitors with "uniform compensation" that has gotten decidely
| less uniform over the years.
| dr-detroit wrote:
| causi wrote:
| I wish you could do this with phones. I know more than one person
| stuck with a crappy pOLED screen with that terrible green tint to
| the bottom third of the panel.
| jeroenhd wrote:
| Back in the day before operating systems copied the feature
| there were tons of Android apps that added a red shift on top
| of your screen by drawing over other applications (i.e. https:/
| /play.google.com/store/apps/details?id=com.csk.app.sh...,
| https://github.com/LibreShift/red-moon). This usually
| breaks/doesn't work with banking apps and other such secure
| contexts but for most apps that's probably fine.
|
| Sounds like you should be able to do this by just modifying Red
| Moon to draw a more complex overlay. If the entire screen is
| affected equally, the stock app may just be all you need!
| pferdone wrote:
| When I installed my DIY backlight solution (ala AmbiLight) to my
| TV I also had a red shift for some of my LEDs. But that was
| mainly due to the fact that not enough voltage reached the later
| LEDs on the strip to power green/blue because they need higher
| voltage than red.
| infomax wrote:
| I have the same idea each time I read something about backlights;
|
| How easy would be to place a cheap LCD at the back of the main
| screen and mirror the same output (in horizontally inverted
| mode)?
|
| Technically it might require synchronizing the frame latency
| differences between the two devices, but would such a hack
| improve the perceived quality?
| rzzzt wrote:
| The cheap LCD will probably not be able to produce enough light
| to brighten up the main display, and if the two panels are not
| of equal size, you will need to add some depth to the unit and
| come up with a projection system to "blow up" the light map to
| cover the entire image.
| t4h4 wrote:
| Hisense Dual Cell might be what you're talking about.
| tim_hutton wrote:
| I need this for my Android phone to compensate for a burnt-in
| image.
| jeroenhd wrote:
| Like I said in another comment:
| https://github.com/LibreShift/red-moon with a more complicated
| pattern than just a single color may be all you need for many
| use cases.
|
| I don't think Android has an easy to use global shader system,
| so you'll be stuck with overlay windows and the incompatibility
| they have with banking apps/DRM crapware that locks you out of
| your own screen without root access.
| robomartin wrote:
| I have over a decade of experience in the design and
| manufacturing of advanced display systems and ran into precisely
| this problem around twenty years ago. At that time we
| experimented with and developed pretty much exactly this type of
| compensation; implemented on custom FPGA-based real time image
| processing boards.
|
| Just looking at the pictures, this does not look like a backlight
| problem but rather degradation of the liquid crystal layer. Yes,
| sure, there's interaction between the two. The purple shift,
| however, is very much something that was happening twenty years
| ago with some liquid crystal chemistries. Back then you could
| definitely tell which panels were not using high quality LC
| fluid.
|
| Apple had this issue with their second generation HD Cinema
| Display product (the first aluminum enclosure, 24 in, 1920 x 1200
| model). Some percentage of them would turn purple. I don't have
| Apple's stats on this. From my own experience the number
| fluctuated between 15% to as much of 50% of the panels in a batch
| going bad after moderate burn-in.
|
| Having said all that, this type of compensation or fix might be
| OK for a TV at home or the computer monitor on the desk of a
| doctor or even a coder. Not good --at all-- for someone doing
| critical color work, such as a graphic artist. The reason is that
| you introduce spatial nonlinearities and differential errors.
|
| The simplest way to put it is that you no-longer have the full
| 256 (or 1024) steps per R, G, B channel between 0 and 100%.
| Hypothetically, you might have 256 for green and, say, 200 for
| red and 175 for blue. This means that the path from black to
| white is no longer monotonic. You can have serious color
| rendering errors through the color space. For example, it might
| be impossible to make an accurate 50% gray because you just don't
| have the RGB values needed to accomplish that. Worse yet,
| everything between 47% and 53% gray might look exactly the same.
|
| You can also introduce serious gamma distortion. If, on top of
| that, you add a temporal element (video), well, it can be a real
| mess.
|
| The real solution (for critical workflows) is to replace the
| panel.
|
| BTW, this can apply to RGB OLED as well.
| drumdude wrote:
| I do this for a living. Sony digital cinema projectors use a type
| of LCD panel (SXRD) where the uniformity drifts over time. A
| special camera takes about 35 minutes to create a LUT to restore
| the projected image to a uniform white.
| aidenn0 wrote:
| Is SXRD just Sony's name for LCOS, or is it something distinct?
| jagged-chisel wrote:
| Is that 35 minutes spent collecting input, or calculating the
| LUT?
| washadjeffmad wrote:
| I imagine the process is Capture > Analyze > Generate > Apply
| > Repeat until all test images are within bounds and color
| matched, not stage 1: capture, stage 2: calculate, done.
| That's how it worked for our projection, at least.
| MayeulC wrote:
| Well, you could capture once over a range of inputs to get
| a much better initial first guess too!
| GauntletWizard wrote:
| I'd bet that they do some of that, too, but if you've got
| 100 images you want to get "perfect", it's probably
| faster to capture 10 of them uncalibrated, guess at the
| curve, capture those same 10 and 10 more calibrated with
| guess #1, and make a second guess, for a couple
| iterations than it is to capture all 100 images before
| any calibration and then all 100 again afterwards to
| confim, especially if there's any slop in the calibration
| curve.
| drumdude wrote:
| The camera handles everything automatically. It generates
| dynamic patterns on the screen and adjusts several times
| until it is satisfied with the result. It does this for red,
| green, blue, and white across 10IRE, 20IRE, ect up to 100IRE.
| The LUT is human readable and able to be uploaded and
| downloaded from the FPGA.
| Tade0 wrote:
| I damaged my laptop's screen by leaving it running at 100% CPU
| with the lid closed for too long(not my intent - that was "sleep
| mode"). The adhesive keeping the LCD layers came off, creating a
| diagonal striped clouding pattern.
|
| I was meaning to do something similar to the author[0], but
| couldn't make time and just used this opportunity to buy an
| external screen.
|
| I'm glad someone put in the work so that now I may be able to use
| my original screen again.
|
| [0] My most desperate idea was to run a RDP session locally and
| process the displayed image. Seemed simpler than trying to modify
| the content of the screen directly.
| dylan604 wrote:
| >The adhesive keeping the LCD layers came off, creating a
| diagonal striped clouding pattern.
|
| now this sounds like something my younger me would be
| interested in seeing. what kind of special effect look can you
| get from that by running different colors/patterns through that
| stripe? obviously, the only way to make it usable would be to
| record the screen externally, but it would not be the first
| time someone (ahem,me) pointed a camera at a screen for
| sfx/vfx. back in the old analog days, i would by crts
| specifically because of their "issues".
| jerf wrote:
| "The adhesive keeping the LCD layers came off, creating a
| diagonal striped clouding pattern."
|
| Oh, is THAT what that is. I have an ancient laptop where the
| screen is failing that way. Was trying to figure out what on
| Earth could produce perfectly diagonal streaks in an LCD!
| Though I'm still not quite sure how that connects; is the tape
| oriented diagonally?
| Tade0 wrote:
| > Oh, is THAT what that is.
|
| That is at least the explanation I got on some obscure forum
| where someone else had a similar problem and it was caused by
| heat.
|
| > is the tape oriented diagonally?
|
| Worse - it's a multi layer sandwich of filters etc. which
| need to be perfectly aligned for a clear image:
|
| https://www.azom.com/images/Article_Images/ImageForArticle_2.
| ..
|
| Funny thing is in my case the hottest part actually remained
| ok - it's the surroundings that got, for lack of a better
| word, ruffled.
|
| I've seen videos of Indian repair men disassembling a panel
| and putting it together to fix such issues, but IIRC only the
| back light ever came off.
| mordae wrote:
| If only my screen had issues with the picture. Instead, its
| internal clock lags behind the source, causing audio to be ever
| more delayed. It resets after a standby/wake-up cycle, though.
| It's annoying to restart TV after about 3 hours, though.
| TaylorAlexander wrote:
| I have a similar issue when using my raspberry pi as a Steam
| Link client for gaming. After a while the sound starts to get
| choppy, and this problem gets worse and worse until sound
| breaks entirely. But video still works. If I kill the game and
| re-start the steam link client the issue resets. Feels like
| some kind of clock drift, but in this case it seems to be
| affecting the ability to decode a digital stream. It's a very
| strange issue!
| nagonago wrote:
| Clever solution! It kind of reminds me of when I sometimes run
| sound through customized EQ and compression to compensate for
| crappy speakers. My approach is not quite as scientific as this
| though, just "tweak until it sounds good."
|
| I didn't know there was a version of MPC with a live shader
| editor, that is also very cool. This is actually a pretty good
| use case for such a feature.
| HPsquared wrote:
| I use Equalizer APO for this in Windows. Add some parametric EQ
| peaks (negative peaks) to cancel out resonant modes of my cheap
| speakers/headphones.
| atahanacar wrote:
| I use AutoEQ (https://github.com/jaakkopasanen/AutoEq) for my
| headphones. It works by "parsing frequency response
| measurements and producing equalization settings which correct
| the headphone to a neutral sound". They also have a huge
| database of already measured and equalized data, which is what
| I use.
| klodolph wrote:
| My home receiver came with a microphone. You plug it in and the
| receiver blasts noise through the speakers, and comes up with
| EQ to compensate automatically. This wasn't an expensive
| receiver, either.
|
| If you want a more scientific approach, you can use a tool like
| Room EQ Wizard, which is free--although it works best if you
| have some kind of flat response microphone, or calibrated
| microphone with a known response curve.
|
| (I'll also add that you're compensating for crappy acoustics in
| your room as much as you are compensating for crappy speakers.)
| rixrax wrote:
| I wonder if this is so 'generic' that e.g. AppleTV could add
| support for this? Take a photo of your TV with an iPhone when
| AppleTV is showing test image. And then the AppleTV output is
| calibrated appropriately to compensate for uneven backlight.
| bzzzt wrote:
| Calibrating color with an iPhone is already a feature in tvOS,
| so correcting for local errors looks like a nice improvement in
| that direction.
| dontlaugh wrote:
| Sadly it only works with iPhones that have FaceID.
| bzzzt wrote:
| Probably related to the quality of the camera.
| millimeterman wrote:
| There are already some companies that let you calibrate your
| TV's colors with your phone camera. Apple TVs do it and adjust
| the output signal while some new Samsung TVs can do it and
| actually apply hardware calibration. Adjusting for unevenness
| in the same way seems potentially harder but doable.
| jimnotgym wrote:
| Isn't this done with a ICC profile and a lookup table, in
| which case varying or across the screen does not sound
| feasible?
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