Small monitor with "black blacks" needed for Pepper's Ghost

Escuta

Member
Hello, I require a number of 9.7" (or similar size) displays for Pepper's ghost illusions in an installation involving a number of compact viewing cabinets with internal dioramas. My signal for the video is HDMI. I initially tested a standard compact monitor with HDMI input but discovered that the black regions of the screen were not sufficiently black enough because of the backlight - and the square form of the display became apparent on the transparent film stretch across the diorama. I tried a 9.7" Android tablet with an Amoled display and this worked very well with excellent contrast and black blacks. These tablets require a HDMI to USB converter and software such as USB Camera Pro to display the video. The problem, is that such connections are fragile and if the cable gets bumped or pulls out during playback, it is possible to damage the device (I've damaged two such devices in development). There's also the issue that many tablets cannot use "on the go" (OTG) USB and charge simultaneously - not without a special circuit at least.

Can anyone please suggest an alternative to using tablets or perhaps an alternative to Amoled/Oled displays? I have found it hard to find any Amoled displays around the 10" size which aren't tablets.

Thanks a lot.
 
Last edited:

FMEng

Well-Known Member
Fight Leukemia
That's a tough one. Maybe viewfinder screens built for TV studio cameras and digital cinema cameras would offer something.
 

DrewE

Well-Known Member
If the video is pre-recorded, maybe you could transfer the video file to local storage on tablets and have them play it back, doing away with the HDMI connection altogether.
 

Escuta

Member
Thanks, yes, I did come across this very model after I wrote, and it is a possibility. The device playing the video is in fact a Pi 4, it's running some show control software called OSSIA-Score which plays videos on demand and controls LED lighting. Because of import duties the device you suggest may work out to be more expensive than tablets, which I can get, potentially, used. OSSIA Score has NDI streaming capability, so another option I'm exploring is having the Android device play a video stream sent over WiFi. This will avoid the dangers of USB. Unfortunately I have not yet found a NDI monitor app for Android. A potential work around may be to install Linux on the tablet - there should be some NDI program for that. Have never tried this but I may do some tests on an old Samsung phone I have lying around.
Quite a headache, this project! :)
 

Jay Ashworth

Well-Known Member
One thing worth noting here (says the TV guy):

NTSC analog video used to include a black-offset called "pedestal", where the black level was not 0IRE, but 7.5.

Digital video, HDTV, the sort delivered over HDMI to a current generation monitor, *is not supposed to have pedestal* -- black is supposed to be at *zero*. While LCDs will leak some backlight, and you might have to adjust for that if the video is right... make sure the video is right -- that it's being rendered out as 0, with no pedestal.

I can't actually tell you how to test for that, alas. Waveform monitors with HDMI in are scarcer than hen's teeth.

[ Citation: https://www.google.com/books/edition/_/dSCEGFt47NkC?hl=en&gbpv=1&pg=PA382&dq=hdtv+no+pedestal+ire ]
 
Last edited:

tladuke

Member
One potential alternative approach is to rear project the image on a dark black RP vinyl screen material. You may not have the room in your display enclosure for the folded optics but you will get much higher contrast ratio. A small form factor PICO class projector is about 5" square and can deliver 500 to 1000 lumens using LED source technology. In this application, depending on the ambient light, you probably only need 300 to 500 lumens. There are some really nice Black and dark grey RP materials that you can buy by the foot. It's very flexible and this material can be cold pressure laminated on to clear acrylic or glass by any graphics house that does digital print graphics for signage. You might consider an even smaller projector like the Axxa P7. It is a native 1080P DLP chip. They claim 600 lumens but realistically, it is more like 300 lumens at a contrast level you could use. You will need a first surface fold mirror to accomodate the short throw and possibly a +1 or +2 camera diopter lens for the projection lens.

I have used many different PICO class projectors for PG and it works exceptionally well. Nevertheless, if you can find a flat panel OLED display that you can afford, that is without question your best option.

Good luck!
 

ruinexplorer

Sherpa
CB Mods
Premium Member
Fight Leukemia

gafftaper

Senior Team
Senior Team
Fight Leukemia
What about shopping Alibaba to find some small bulk OLED screens for laptops or something like that and then building them yourself?
 
Last edited:

Escuta

Member
I had to leave this project and have just returned to it today.

Buy a roll/sheets of ND and keep adding till the video black goes away.

Post results if you can.

Unfortunately the ND gels didn't work. Once the backlight glow starts to disappear, the image is already too dark. I've tested this on the original monitor, which admittedly is pretty bad, but also on my Samsung LCD computer monitor - same issue in a darkened environment.

What about shopping Alibaba to find some small bulk OLED screens for laptops or something like that and then building them yourself?

Yes, I should look into this. I'll search the web to see if there are any guides but if you have any tips on how to power the units and how to get HDMI input, please let me know!


Any other suggestions are still most welcome! :)
 

Jay Ashworth

Well-Known Member
OLED TVs are now available up to *stupid* sizes; see if a) you can find an AV shop that will rent you one or 2) you have an angel who's thinking about buying a new TV, and will get what you need and loan it to you. :)
 

Escuta

Member
OLED TVs are now available up to *stupid* sizes; see if a) you can find an AV shop that will rent you one or 2) you have an angel who's thinking about buying a new TV, and will get what you need and loan it to you. :)

Thanks. It's actually smaller sizes that I'm looking for. I found this one that's a perfect size and format, and very affordable, but I'm not yet sure what kind of interface/controller I'd need:


And this one that has a MIPI interface for which I believe there are low cost controller boards available. I've written to ask about price and and to see if they sell small numbers (i need only 5).

 

Escuta

Member
I mean... what's the budget look like? These are broadcast level, but color accurate and you can inject black to them as reference...


Thanks this would be wonderful but the display is a bit too thick and our budget minuscule when converted to US$. R$5000 for 5 units = US$933.69. And also we pay about 100% on import duties (when caught!), so that can be halved. :)

I've tested with an AMOLED Samsung tablet. It could be brighter but it's adequate and the illusion works well.
 
Last edited:

Escuta

Member
To close up, finally, I managed to find a solution that allows me to use used or hired Amoled tablets with no risk to the equipment. It's through a javascript library called P5.js and offers wireless control of the video over a network. The networked communication is facilitated through a protocol known as websockets. On the controlling computer you run a simple webserver, I'm using one called http-server on Linux. The tablet accesses the server on its local IP address through a browser to load a page with the video to be be played embedded. Control is via OSC (open sound control) messages sent to the localhost on the server machine. The controls I'm using are play, stop and a seek command called 'time'. Unfortunately, this last command doesn't work on Chrome browsers on Android, so that rules out all or most of Kiosk browsers for Android which are restricted to Chrome variants. It does work however on Firefox for Android. There's a setting to hide the address bar and other software (can't remember the exact one I'm using) to put apps in full screen mode. For anyone interested, the relevant code from P5.js is their "video canvas" (see: https://p5js.org/examples/dom-video-canvas.html ) and the OSC control stuff I adapted from https://github.com/genekogan/p5js-osc. For script-based OSC commands I use the "oscsend" utility from the OSC implementation 'liblo'. See: http://liblo.sourceforge.net

Cheers,
 
Last edited:

J Katz

Member
Late to the game here.. but something that has always worked for me is covering displays/lightboxes with a soft stretched cover. Rose Brand Black Voile, Fine Gauze , Sharkstooth scrim or Black RP all work but you have to check compatibility because of Moire and it all is dependent on pixel size. The tooth of the fabric absorbs ambient light and gives a very matte appearance.
 

Users who are viewing this thread