DLP/LCD - can they show an interlaced image?

[joffonon]

I know that DLP & LCD projectors show a progressive image, but can any of them show a good old-fashioned interlaced image so that (for example) interlaced video retains the same look?

Jonathan

[LV426]

The only reason for interlacing a video signal is to give it the semblance of a refresh rate that is twice what it actually is ie to reduce visible flicker. Anyone who has seen a 50hz non-interlaced image on a CRT will know what I mean (when compared to a 50hz interlaced image on a CRT TV.

Given that LCDs by their nature do not exhibit refresh rate flicker at all, irrespective of the frequency at which they are driven, I don't see any reason why you'd want to do this.

In any case, I think the answer is, no. To display an image on an LCD, the whole (ie the two interlaced fields) picture has to be merged together and converted to a pixel array which is then supplied to the LCD panel.

[JonMace]

Originally posted by nigel
The only reason for interlacing a video signal is to give it the semblance of a refresh rate that is twice what it actually is ie to reduce visible flicker. Anyone who has seen a 50hz non-interlaced image on a CRT will know what I mean (when compared to a 50hz interlaced image on a CRT TV.

Given that LCDs by their nature do not exhibit refresh rate flicker at all, irrespective of the frequency at which they are driven, I don't see any reason why you'd want to do this.

In any case, I think the answer is, no. To display an image on an LCD, the whole (ie the two interlaced fields) picture has to be merged together and converted to a pixel array which is then supplied to the LCD panel.

I could be very wrong but I think you are incorrect a LCD PJ will display both interlaced and progressive scan signals, to get a prog scan signal you will need an out put from either a PC or a DVD play that has this facility (most DVD player don't) or else you will need to buy a line doubler for instance the Pro V or the Iscan Pro. If you wan't a prog scan input from Sky or video you will have no choice but a line doubler

[stevelup]

Hi

LCD and DLP projectors are inherently progressive and physically incapable of displaying an interlaced image.

Therefore all LCD/DLP projectors have a line doubler built in. Without this they would not be able to display an interlaced signal!

The only reason to get an external line doubler is that they are often better quality than the one built into the projector.

Regards,

Steve

[JonMace]

Thanks for correcting me Steve, all I know for sur is that the Iscan Pro has made a lot off differnce for me, and it also makes me think that the Pro V is therefore not worth it unless you want the built in TV scanner as the line doubler will probably not be much better than the one in the PJ

[LV426]

As stevelup confirms, LCDs have to be driven progressively. However, LCD devices intended for video use always contain a deinterlacer - they have to.

So, you can drive the device with either. But by the time it gets to the LCD panel, it's progressive.

The reason why external scaler/deinterlacers etc., make a difference is due to the standard of the inbuilt deinterlacer. If the LCD device has a relatively poor one, doing this work externally will improve the result onscreen.

However, if the inbuilt scaler/deinterlacer is good (as I understand is the case with, say, the Sony VW12 projector) then you might get a better result feeding it an interlaced signal and letting it do the work itself.

If this is the case, why are people getting so worked up about Progressive scan DVD players if and input to a projector will be PS anyway (forgetting for the moment the differences in quality between different deinterlacers, the so-called chroma bug which afflicts many, etc.).

[Gordon @ Convergent AV]

Rusty:

They are getting worked up for good reasons. The word prog scan is bandied about on these forums like turbocharged might have been in the car world in the 80's. A saab turbo a 911 turbo and Lotus Esprit turbo all work on same principles but are all not of same performance. It's the same with de-interlacers. They can increase performance but all are not equal. (excepted that you don't actually need a turbo charger to get an engine to work but you do need a de-interlacer to get a fixed pixel devcice to work...perhaps it's not such a great analogy after all!)

You generally get two types of material to deal with in our HC world. Material that was originally recorded on film and material that was aoriginally recorded with a video camera. They are distinctly different. Video camera's record in interlaced mode while film cameras take 1 progressive (frame) every second. Clever de-interlacers work out which is which and use approriate methods to try to re-constitute the orignal material to be shown progressively. The bulk of de-interlacers in LCD/DLP's of old didn't have this ability and used a common method which would result in quite a lot of artifacts.

Now, many folk look at specs for products to work out performance but there is more to it than that even. The presence of a particular chipset doesn't tell you everything. The application of that chipset is important as well so as with all this stuff the best thing to do is view to see what makes improvements.

Gordon

Originally posted by Rusty
If this is the case, why are people getting so worked up about Progressive scan DVD players if and input to a projector will be PS anyway (forgetting for the moment the differences in quality between different deinterlacers, the so-called chroma bug which afflicts many, etc.).

Good question. Because if the input is from a progressive dvd player, the PS/plasma should bypass its own progressive scan circuitry, providing a better picture.

There are two very big caveats in this statement :

The PS/plasma has to recognise the progressive signal and not deinterlace it again! For example, not all older devices recognise PAL progressive, because until a few months ago it did not officially exist.

For better deinterlacing, the circuits in the dvd player must be better than those in the PS/plasma. This itself is not always true, since some the latest PS/plasmas have dedicated hi-quality circuit built-in.

EDIT : Thanks for the extra info gordon

[Jim v2.0]

In the Sanyo Z1 manual, in the supported resolutions section for the VGA port, it goes up to a maximum of 1280 but this resolution has the word 'interlaced' in brackets next to it. Given the VGA feed is inherently progressive, what does this mean? It seems to imply that a progresive signal at the 1280 resolution will be displayed as interlace. As mentioned, this section is for the VGA port which always takes a progressive signal.

Any ideas what Sanyo are on about anyone?

This most likely means if you feed the Z1 a signal up to 1280x1024 interlaced , it will display the signal. In other words the bandwidth of the projector cannot cope with a 1280x1024 progressive signal, and will show a blue screen. However if you give it a 1024x768 progressive XGA signal within the refresh rate, it will display a down res'd version.

It does not mean it will display the signal as interlaced, which the manual wording would seem to suggest.

[Jim v2.0]

I can see the logic of what you say, but the VGA port in question does not accept an interlaced signal from the computer