Tuesday, May 27, 2008

Adventures in LCD Part I

Ok, recently I sent a +3 Speccy to a guy who lives in Finland. The guy goes by the name of Mr_Spiv (of Scoopex), who decided he'd try his hand at some Speccy coding. The Speccy got to him in one piece and appears to be working fine. Except for one minor problem, his LCD TV gives him a shite picture.

So intrigued by this, I thought I'd help out. We established the problem was not with the Speccy as it gave a good picture when plugged into a normal TV. So next to try some further tests...

First up, try a different device on the LCD TV that uses SCART. So Mr_Spiv attached a PC Engine to his TV. Same thing, bad picture. Ok, so it's the TV doing something odd.

At this point I remembered playing a Wii on a Toshiba 32" LCD TV. It would do some "odd" things with the picture. Difficult to explain what it looks like, but basically, where the picture was motionless, the picture was fine (maybe some scaling, but nothing bad). But where there was movement, an odd effect could be seen. Almost like some kinda "on-the-fly" jpeg compression going on. Very weird. "This is what Mr_Spiv must have been seeing" I thought.

So now this has become almost a challenge for me - find an LCD TV that gives a decent picture on its SCART input. So off I go and buy the cheapest, known brand LCD TV I can from Argos.

A short drive and £110 later and I'm the proud owner of a Samsung SM741MP 17" LCD TV. I bought it from Argos as they have a 30-day money-back guarantee, so if it didn't work right, I could always take it back and get my money back. Magic.

So on to testing this nice new LCD TV. I hooked the Speccy up via the SCART socket and instantly I was shocked at the picture. The first most noticeable thing was it appeared to be interlaced! What? Speccy? Interlaced? Ok, I've seen it in demos but an interlaced +3 menu? The next thing I noticed was some odd discolourations in funny places. Almost the same as you see when using a Speccy via the RF cable, only this was via an RGB cable. Most odd.

So an explanation? The interlaced effect I can explain. The odd colour issue I can not.

My theory for the interlaced look is this. Basically, this LCD TV is an LCD monitor. It can only handle vertical refresh rates in the region of 56-75Hz. So how does it display a 50Hz picture? Easy. It basically turns 3 50Hz frames into 2 75Hz frames. Very clever stuff, but with a static old skool 8-bit picture, it suxx big time, trust me.

Anyhow, this part of the story does have a happy ending. Jojo, the missus, kinda liked the look of the new LCD TV. So as the old Sony one in the bedroom is developing an odd "corrupt settings" issue, I decided to retire the Sony to the loft and the Samsung LCD TV is set up in the bedroom. Happy wife - bonus! ;)

The adventure had only just begun...