The upgraded AV system is now installed in LR4- news item to follow.
We were faced with a number of challenges and I thought I’d talk about some lessons that came out of the exercise.
One of them is that EDID (Extended Display Identification Data) management is not as mysterious as one might think…
PC: Hello screen I want to display something. Can you tell me what resolutions and timings you support?
Screen: Sure, here’s a list.
PC: Thanks. I see that the highest resolution we can both handle is 1900 x 1200 @ 60Hz so I’ll send that.
Screen: Whatever. *displays video signal*
Easy right? Well not so easy if you are routing multiple sources of varying/unknown display capabilities through a 4×4 IO matrix onto 2 screens and 2 projectors each of which you want to display at a non-native 1280 x 1024. Get it wrong and you end up with stretched or squashed images, sluggish switching, 800 x 600 defaults or, in a worst case, no image at all.
Thankfully we can trick the system at various points into doing what we want it to do.
Firstly, the Extron matrix allows us to place a ‘phoney’ EDID file at the input to the matrix which means the information request never makes it to the projector/screens. We can lock down each input to act as a 1280 x 1024 display. This means that the matrix output and projector make just one EDID handshake to this resolution on boot and never move away from it, ensuring that the projectors aren’t wasting time re-scaling (flickery blue screen anyone?) each time an input is switched. We can then manually fix the lectern PC resolution to 1280 x 1024 to comply and enjoy quick and responsive input switching.
Secondly, in order to manage the various unknown resolutions of laptops that may be connected we place a small switcher/scaler between the laptop and the matrix. Again, we can place a phoney EDID file at the input that acts as the display’s data to force a first time laptop to use an output of 1280 x 1024. We also tell the unit to output at 1280 x 1024 so that any manually set resolutions scale correctly and never stretch or squash, instead fitting within 1280 x 1024 frame at their correct aspect ratio. Technically, we should place a higher quality scaler on each matrix output in the rack set to the projector native of 1900 x 1200 instead of relying on the projectors cheap built in scaler but the difference would be negligible.
It’s worth noting that you can still manually override the automatic EDID triggered resolution settings in Windows- most displays have a range of inputs they can handle and the Extron scaler can basically handle anything you throw at it. Interestingly, Windows registry remembers the display and the setting you used for it so if you manually set to another resolution then come back another time, the laptop will use the last resolution set on that particular display. I am yet to explore whether that can be changed- another time maybe.
The control system is another story…