CurtPalme.com Home Theater Forum

**AnalogRocks** · Posted: Sun Jun 21, 2020 5:02 am Post subject: DIY 4K Projector

https://www.youtube.com/watch?v=YfvTjQ9MCwY

gjaky · Joined: 05 Jun 2010 Posts: 2790 Location: Budapest, Hungary

Pure sh!t

**AnalogRocks** · Posted: Sun Jun 21, 2020 2:26 pm Post subject:

gjaky · Joined: 05 Jun 2010 Posts: 2790 Location: Budapest, Hungary

The problem is not with the DIY attitude, but with the claims he mades.
He entertains the idea that if you put some random stuff together you'll get a useful projector out of it. I don't want to discredit his efforts but the thing is not as simple as he shows, and is even harder to reproduce.
Start with the obvious:
- How would you manage color balance with a "random" white LED? Does that phone let's you calibrate colours accurately?
- What about contrast ratio? I don't think this projector would have any better contrast than any LCD projector from 20 years ago...
- I understand that the phone could stream any movie over Wi-Fi (in order to avoid the pain to copy the movie on the phone), but will you use a 3.5mm jack and a Dolby Pro Logic receiver to get surround sound?

So yeah, it's great to have a super duper DIY 4K projector with low light output, bad contrast ratio and colour space that surely won't even meet Rec.709. While all hot (4K) movies are processed in HDR and at least DCI-P3.

And apart from watching movies what else exactly can you do on this projector? -Is there any port on Android for space invaders? Wink

garyfritz · Joined: 08 Apr 2006 Posts: 12025 Location: Fort Collins, CO

https://play.google.com/store/apps/details?id=jp.co.taito.am.spaceinvaders
Mr. Green

km987654 · Posted: Mon Jun 22, 2020 9:01 am Post subject:

Looks great. I am sure its not perfect but I don't believe he thinks that either. If he didn't use the mirror and turned the PJ on its side it would be brighter as mirrors are not 100% efficient although he would need another lens wouldn't he?

**kal** · Posted: Mon Jun 22, 2020 1:41 pm Post subject:

I'd like to see someone who actually knows something about projectors, calibration, and how to measure the results do something like this.

Would be useful if some actual numbers on the performance of the DIY unit were provided instead of hyping that it's 4K (as if that matters if the rest is crap). All he says is useless things like "the contrast is great" and that "video playback is fantastic" and then shows screenshots of the two saying "see how much better it looks?" which makes absolutely no sense. You can't gauge anything through a video taken off some camera displayed on your own display.

Nothing wrong with DIY, juts call it for what it is. It would actually be a fun build.

Kal

**kal** · Posted: Mon Jun 22, 2020 1:52 pm Post subject:

**AnalogRocks** · Posted: Mon Jun 22, 2020 2:35 pm Post subject:

**AnalogRocks** · Posted: Tue Jun 23, 2020 2:14 am Post subject:

garyfritz · Joined: 08 Apr 2006 Posts: 12025 Location: Fort Collins, CO

First-surface mirrors are 94-99% efficient. No worries there.

Zebra · Joined: 02 Jul 2020 Posts: 87 Location: NJ USA

The guy in the video has an overly simplistic view of what makes a more detailed image on a projector (or TV). His assumption that more pixels automatically = more detail is wrong.

A higher pixel density only means you can sit closer or go larger before being able to see pixels.

There are a whole bunch of other factors that go into our perception of detail. The most important one is the quality of the content. I.e the quality of the footage captured and the bitrate of the final media. Dci movie files at the theater have a bitrate around 250mbps regardless if they are 2k or 4k. UHD Blu Ray has a 100mbps bitrate. 1080p Blu Ray is 40mbps. 4K Netflix is 15-25mbps - i.e. lower than 1080p Blu Ray. Quality and res are two different things.

The frame rate also makes huge difference. Try turning off frame interpolation on a 4k TV or projector and the image becomes indistinguishable from 1080p (with the same content). Or try and spot a difference between 1080i 120hz and 1080p 60hz. They look the same because you're seeing the same amount of info each second.

Contrast is also key. I'm talking about real contrast. Not that full on / full off nonsense. More real world contrast means more detail which is why LG's first 1080p Oled TVs looked way better than Sony's first 4k TVs. Try comparing a 1080p Pioneer Elite Kuro to a cheap 4k Walmart LCD. There's a reason why some hang on to 10+ year old tech...

With projectors, the lens quality is huge. Using a cheap plastic fresnel lens will cause a massive drop in quality. Quality glass is expensive and it goes up exponentially as they get larger. Commercial projectors use chips that are between 0.5" and 1.5". Using a 6" phone panel would require a way larger lens. Quality larger projector lenses sell for $5,000 - $20,000 on their own. With the cheap lens that guy used, more detail is the last thing you'd get.

Motion resolution is an issue with all LCD based displays. Without quality processing and frame interpolation, that 1080p or 4k image can look no better than old standard def with moving imagery. It's one of the many advantages CRT had over modern displays.

I think there are better ways of making a diy 4k projectors. Using 4 cheap used 1080p projectors off ebay with a video wall processor and an edge blending box, for example. Or using a gpu with 4 HDMI outputs.

If I was to use old phone screens for a diy projector, I'd probably forget about 4k and use 3 amoled phone screens with parts from an old 9" CRT projector. They're already somewhat set-up with quality lenses for larger screens at least.

**kal** · Posted: Fri Jul 03, 2020 5:01 pm Post subject:

Welcome to the forum Zebra and exactly right!

Unfortunately ignorant consumers like simple numbers. So when they see 4K they assume it's better than all 1080p. More is better right? and manufacturers cater to this simplistic view.

Don't get me started on the temporal resolution issue... We're not watching static windows desktops on our TVs projectors. Bitrate is incredibly important. Anyone remember superbit DVDs? https://en.wikipedia.org/wiki/Superbit

Kal

Zebra · Joined: 02 Jul 2020 Posts: 87 Location: NJ USA

**kal** · Posted: Fri Jul 03, 2020 7:32 pm Post subject:

**AnalogRocks** · Posted: Sat Jul 04, 2020 3:35 am Post subject:

Zebra · Joined: 02 Jul 2020 Posts: 87 Location: NJ USA

**kal** · Posted: Sat Jul 04, 2020 7:13 pm Post subject:

**AnalogRocks** · Posted: Sat Jul 04, 2020 11:46 pm Post subject:

**kal** · Posted: Sun Jul 05, 2020 2:02 pm Post subject:

The first HT projector I saw in person that got me thinking "ok, they're on to something good finally" was the JVC DLA-RS1 around 2007 timeframe. 15,000:1 contrast ratio. Green was horribly out of spec (oversaturated) and with no CMS many were using Radiance video processors to tame it to Rec.709 standards. I saw it at a local HT guy's house who also had a Marquee CRT projector.

Kal