Beware the well travelled LCD Panel

[Mike Brennan]

Used a Sony Broadcast 23 inch Luma panel recently that was well travelled and knocked about.

 

It had obvious registration errors in the form of vertical colour fringing, not across the whole screen, just on one side. Also had colour shading at the very (side) edges of the panel.

 

We flipped the camera upside down to prove it!

 

So much for the "always in perfect registration" of LCD panels?

 

 

Mike Brennan

[Phil Rhodes]

Hi,

 

That's interesting.

 

While I'm not challenging what you're saying you saw, it absolutely cannot be a "registration" problem in the traditional sense of the word. The colour filters are silk-screened onto the front of the matrix and there is no way they can move. There are several things you could have been seeing:

 

- After a while the backlights age (this is the most common failure mode for LCDs.) This can cause them to dim, hotspot, and change colour, possibly in a way that will upset the balance of the filters on the front.

 

- After a while, the backlight can start to bleach the colour out of the filters. Normally this just manifests itself as a lowering of saturation.

 

- Signals that have been in an analogue domain at some point can moire with the pitch of the LCD's pixels. Depending on the picture content this can cause what appears to be colour fringing. This is usually adjustable.

 

- Some LCDs can appear to colour shift when viewed from different angles, usually because the thickness of the silkscreened filters is not equal and you end up looking at only those that are "sticking up" above the "horizon". Some CRTs have the same issue with the way the shadowmask or other front-end grid is etched. Normally you have to view from very extreme angles to see this, though, and you would generally get luminance falloff too.

 

- Some of the colour filters are polarising, the angle of which may be random and change over the surface of the display. Viewing through a polarising filter (sunglasses) can cause all kinds of strange colour fade effects.

 

That's about all I can think of. If it looked exactly like a CRT registration error, I'd be checking the lenses and to see that the colour splitter block (if any) in the (video) camera had taken a whack. Normally this will craze the filters and cause all kinds of other problems, though.

 

Phil

[Mike Brennan]

Yes,

 

It had me thrown for an hour as it was so bad I couldn't believe it was the (new) lens and also assumed a LCD would always be in registration.

 

Turning the camera upside down didn't make a difference, it was still out of registration on left hand side. (unless the lens fault rotated with the camera!)

 

We get to revistit the beast with a new apple in the near future to get to the bottom of it.

 

Glad to hear that it is unlikely to be LCD as its constant registration is one of its advantages over a crt

 

Mike