Discussion in 'Projectors, Screens & Video Processors' started by petrolhead, Jan 21, 2003.
See here - http://www.home-entertainment.co.uk/firstlook_read.asp?ID=2528
Don't think this reviewer quite knows his stuff though:
"Faroudja's DCDi (Directional Correlation
De-interlacing) circuit bodes well for smooth picture quality on progressively scanned material - the format's becoming a favourite in home projector circles. "
Fascinating. And there I was thinking that we would use DCDI to turn an interlaced source into a progressive one....
You got me there
What I was trying to say is that:
The signal can either be interlaced or progressive.
An interlaced signal can be de-interlaced and turned into a progressive signal by using something like DcDi (which is a de-interlacer - hence the term).
All projectors, computer monitors and plasma screens can only display a 'progressive' image and if they are fed an interlaced image will use an onboard de-interlacer, (typically a simple line doubler in the cheapest makes) to convert the interlaced video signal into a progressive signal that the display can actually show.
What all this means is that the reviewer's sentence makes no sense because the Faroudja circuitry is not used for progressive input to a projector, it is only used to convert the interlaced input into a progressive signal internally. A progressive input would bypass the faroudja circuitry completely.
Interesting, so what happens when you feed a progressive signal in then?
As far as i know, when feeding a progressive signal, the de-interlacer on the projector basically has nothing to do! Whether it is actually bypassed or not I don't know.
Perhaps someone else can identify if, when the projector senses a progressive signal, it completely bypasses its own descaler.
Ok, time to clear up some wrongs here:
1. The Faroudja circuitry is not used for progressive input to a projector.
2. When feeding a progressive signal, the de-interlacer on the projector basically has nothing to do!
Dead wrong. The Faroudja circuitry is very much used for progressive input to a projector. Among other stuff it is responsible for:
b. Resampling of the chroma and luma channels (this will reduce the chroma artefact seen on numerous dvd-players)
c. Color representation, such as gamma, rgb offset and rgb gain.
When the reviewer said "smooth picture quality" I assume he was referring to the excellent scaling, resampling and color representation of the Faroudja chip which is one of the best in this area. With a progressive source.
3. Perhaps someone else can identify if, when the projector senses a progressive signal, it completely bypasses its own descaler.
Descaler? I have no idea what you are talking about. The image always needs to be scaled, and you can see an enormous difference between the work done by different scalers. The Faroudja chip is one of the best.
I didn't realise that the faroudja DCdi performed the scaling as well as things like chroma and colour correction. I assumed that the faroudaj dcdi in the unit merely performed the deinterlacing and then additional circuitry in there performed the remaining scaling, gamma correction and so on.
I've looked at the faroudja web site at the data sheet for the FLI2200 video deinterlacer as an example and this does indeed contain scaler and we would reasonably assume that it would also perform gamma correction being internal to the projector.
I've no idea which particular chips the X1 contains by the way.
Therefore I retract my previous post - basically it means that some of the circuitry is always used for progressive, and some of it is only used when in interlaced input but since it all resides on the same chipset it becomes a bit of a non-issue really.
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