It’s something of a surprise, should you own a CRT TV to go with your retrocomputers, when you use it to view a film or a TV show. The resolution may be old-fashioned, but the colors jump out at you, in a way you’d forgotten CRTs could do. You’re seeing black levels that LCD screens can’t match, and which you’ll only find comparable on a modern OLED TVs. Can an LCD screen achieve decent black levels? [DIY Perks] is here with a modified screen that does just that.
LCD screens work by placing a set of electronic polarizing filters in front of a bright light. Bright pixels let through the light, while black pixels, well, they do their best, but a bit of light gets through. As a result, they have washed-out blacks, and their images aren’t as crisp and high contrast as they should be. More modern LCDs use an array of LEDs as the backlight which they illuminate as a low resolution version of the image, an approach which improves matters but leaves a “halo” round bright spots.
The TV in the video below the break is an older LCD set, from which he removes the backlight and places the electronics in a stand. He can show an image on it by placing a lamp behind it, but he does something much cleverer. An old DLP projector with its color wheel removed projects a high-res luminance map onto the back of the screen, resulting in the coveted high contrast image. The final result uses a somewhat unwieldy mirror arrangement to shorten the distance for the projector, but we love this hack. It’s not the first backlight hack we’ve seen, but perhaps it give the best result.
Thanks [Keith Olson] for the tip!
Oh that’s really clever.
HD and even 4K TVs with dead blacklights are easy enough to come by. This could be worth replicating.
Could you stack the LCD bits in the same way that people stack transparencies – to get higher contrast.
The polarizes may interfere with each other, plus the display will be generally less bright. But yes
Yes, and DIY Perks has done that too in another project :D
https://www.youtube.com/watch?v=ibEN9FTLdkI
Hisense did that a couple years ago, then abandoned the line shortly thereafter. Turns out that dual LCDs perform okay, but the backlight needed to be much brighter and this meant more power consumption and heat production. They switched to local backlight dimming.
Review of the one model, from 2021:
https://www.pcmag.com/reviews/hisense-75u9dg
Discussion on Reddit:
https://www.reddit.com/r/hardware/comments/w0u2rf/did_dual_layer_lcds_die/
DIY Perks actually has another video where he builds a “dual layer LCD”:
https://www.youtube.com/watch?v=ibEN9FTLdkI
Cool build but microLED displays are in the works and they have the equivalent ability for contrast.
There’s always an “yes but will solve this”, the reason this hack is interesting is because we have access to existing cheap equipment laying around.
Microleds have the problem of local fading and eventually burning the image in, while the MEMS projector won’t have this problem.
Mems dlp chips routinely get dead pixels after awhile due to mechanical failures of the microscopic hinge mechanism that supports each mirror or the electrostatic drive just not working anymore for those pixels for some reason.
I have 3 dlp projectors that have at least a few visible defects in the image (one in particular is just about unusable because a non-insignificant amount of pixels are dead now).
Unfortunately replacement dlp chips are usually more expensive than just buying a whole new projector. Nothing is immune to entropy, just different technologies have different strengths and weaknesses and thus are suited for different applications.
But at least it won’t burn in the channel logo or the closed captions, or the taskbar area when using it as a computer monitor. That was the major issue with CRTs, plasma displays, and recently LED based screens. A random dead pixel is less noticeable than a huge area of the display fading out and changing color because of static graphics.
Even a partly dead mems chill will be significantly higher detail than any “local dimming” display, so this is still reasonable if you have it. The real issue is the short throw arrangement and total brightness will depend on your specific hardware combination.
QD OLED has it already as well. This is just a lot cheaper at the moment, and also . . . Hacky, which is why it is here.
Does the final sentence miss a ‘s’?
who cares?
Keap im mined thiz iz hackaday, nod grammar.com (pleaze sjeck yor lynk)
Reel hackerz dont gif aboud speling, thay kan reed bettween te linez.
This reads like a transcript of a Dutch guy taking his “rielly” good English out for a spin :’)
Surely you mean orthography.com. Spelling is not grammar.
Yes, and this is hackaday, where we complain about and correct every little mistake with a smile. :)
I watched this video the other day but this is silly and seems unfinished. Aer we just supposed to ignore the entire room being lit up from the projector?
Yes, we absolutely are. Welcome to hackaday, where we talk about over engineered, imperfect, and impractical solutions, to problems probably solved elsewhere and in much better way. Yet exploration of novel and inventive methods add to ones learning and interest.
I often see comments like yours here, and see the perspective of a product designer, and not of a hacker/inventor.
What you see here is a prototype, a proof of concept of an idea, I’d go so far as to say that for large channels like DIY Perks the ‘product’ is not the projector backlit TV, but the video itself and the story/journey of the steps taken to get there.
Also he said it’s far from finished and invites us all to improve the design, no reason you can’t invent a shroud outta blackout cloth or MDF for your use case bro. the hard part is already done for you.
It’s also clearly a bright day judging by the sunglight coming in through the window and onto his face in a lot of the shots!
Funny enough, I think the sunlight are actually lights which desined to imitate sunlight. DIY Perks has a video from years ago where he built fake windows out of fresnel lenses and a light source with similar spectrum to the sun.
I guess folks really do need an intro to hacker mindset sometimes. It’s not a product, it’s a hack in the truest sense.
It’s a cool project but reminds me of CRT enthusiasts opinion of perfect blacks, versus the regular consumer CRT experience of vague gray all over the screen
yeah i choked on the first paragraph. seems like OP isn’t remembering the same CRT i am??
i’ve been around long enough that i had an OLED phone with perfect blacks and now i have an OLED phone where the blacks are defective somehow…i think the substrate is just straight up gray. so the ‘black’ pixels don’t luminesce but do reflect ambient light and even light from their neighbors?? i’ve had this phone for a couple years and i’m still having a hard time putting my finger on it but it’s illustrative that there’s huge quality differences even in OLED
Couldn’t imaging building a shroud over the entire thing?
Maybe use your large scale 3D printer to do it?
I think it’s conceptually on point, if somewhat non-viable in the real world but so what?!
The interesting part is if you can do this, then you can do a number of other things that are better than the status-quo but not quite as crazy as this. Just use your imagination.
I’m lazy, I’d probably just find a DLP TV with a broken color wheel and put an LCD on the front of it (:
A curtain will fix that.
Some people go to a lot of extra trouble and expense for “ambilight” and this comes with for free! /s
However it comes in one color. “We’ve got white and…… White. Which’ll it be?”
Really all he would have to do is create a custom enclosure based around how the old big screen projection TVs had, in the era before LCDs and Plasma were a thing. He’s doing the same sort of principle with that arrangement at the end.
cough ambilight crap cough
I really hoped that DLP would have been a contender for the in home TV market. I know it can be purchased but it’s a niche thing.
What impressed me about DLP was that blacks weren’t “cover up the light” but “ABSENCE OF LIGHT”.
Those sets could really give you a nice image. The units I had in my home for a few years were salvaged from a company disposal run (we had them in place and went with LED/LCD monitors, and they wanted to trash the DLP sets) With some work I had them both running for about 3 years when they gave up the ghost. The particular model was using LED drivers, so no color wheel and no lamp to replace. Unfortunately that meant that parts were difficult to source. When they died, they died. Not worth attempting to fix since they abandoned the design shortly thereafter.
Rear projection DLP TVs used to be a thing. Get one of those, replace the screen with LCD, and you’re most of the way there in a nice package.
That was one of my first thoughts while watching this video.
You’d have image alignment issues if the LCD screen wasn’t the exact same width as the DLP TV screen. Also, I think those were produced before 16:9 was the standard aspect ratio so much of the screen wouldn’t be in use.
Nope, DLP TVs and broadcast 1080i overlapped quite a lot (the old three CRT rear projection TVs were 4:3 aspect).
I don’t think I ever saw a DLP TV that wasn’t 16:9 (projectors is a different story, those came in 4:3 and 5:4 all the time for conference room use)
It is indeed clever, but the light falloff should be addressed. In every sceme where he shows off the capability of the display, there is a considerable amount of light being reflected back from probably the diffusion plane.
About DLP projectors, Barco has a new HDR projector which steers the light away from dark parts of the scene to other parts of the screen where more light is desired, increasing the contrast even more. Looks great, amazing technology!
Reminds me of a guy I knew who had a black jacket he always wore when working on his computer: he didn’t like the scattered light from light clothing degrading his display contrast.
The kicker was that he was a draftsman.
If there was an unused closet behind the wall on which the TV is mounted, the projector could be placed in there and projected onto the back of the LCD through a rectangular opening in the wall behind the LCD. It would solve both the depth issue and the excess light spill issues. The heat of the projector enclosed in the closet would need to be managed.
This is one of the best hacks I saw in a while. Worth the “best hack of the year” price. BTW: why we does not have a “best hack of the year” – community voted price in HaD yet???