1:1 Pixel Mapping and Digital Keystone Correction

Discussion in 'Projectors, Screens & Video Processors' started by Nic Rhodes, Dec 3, 2001.

  1. Nic Rhodes

    Nic Rhodes
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    I am very interest in one to one pixel mapping with a HCPC and a panel projector, however I need keystone correction. Every time I engage digital Keystone correction the de-interlacing / scaling circuits I am trying to by pass are getting engaged. Is there any way around this other than having no digital keystone correction?
     
  2. Roland @ B4

    Roland @ B4
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    I presume your projector doesn't have lens shift to enable the projecor to be tilted.

    You could tie the screen back which would give you some extra tollernce.

    It may bugger your warrenty but in the past with BIG lcd projector we used to loosen the bolts holding the lense barrel and tilt the actual lens and mount.

    As soon as you start to do it digitally it will lok horid as the scalling starts to cut in.
     
  3. Nic Rhodes

    Nic Rhodes
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    Thanks for the tips Roland. Currently I do not have a panel projector (I have a NEC 9PG) but due to circumstance currently beyond my control, I am not able to use it (to be resolved as soon as possible I hope). I have therefore been ‘experimenting’ with panel projectors as a quick fix, and a fun to learn thing. I have learned loads and really found the limitation of these systems.

    For the broader picture to stop people thinking I am completely barking mad:

    I don’t think panel based projectors used for presentations work well as home cinema products when connected to say a standard or progressive scan DVD player. I favour the tweaked panel projectors like the Sim2 range, wide screen Sony’s, Sanyo PLV’s and certain Toshiba’s (substitute you favourite like Hitachi). For me they give a far better film picture. I am not really convinced that XGA is a benefit over SVGA. I think SVGA is just fine for this. I have only seen one example where the addition resolution was pointed out to me as a benefit (at the Event). It is a minor point.

    However the projector that has some of the best potential I have seen is the Dual Mode Sim2 HT200DM. I couldn’t easily work out why is occasionally produced a stunningly better picture. So I investigated this further. The DM DLP chip has a resolution of 848 x 600. SVGA 800 x 600 EASILY fits within this but it also allows 16:9 NTSC discs to be viewed as 848 x 480. This allows the exact DVD 480 resolution figure to directly address the chip for optimum quality. The result is that the discs look great, bypassing the internal electronics (not the forte of the Sim2 200 range)?. However when a PAL wide screen image is presented, the chip doesn’t have enough resolution, the internal electronic seem to squash the image and the picture isn’t as interesting or as good quality IMHO. If you just R1 then this is not an issue but if you have like me R1 and R2 then it is. The Infocus ls110 / Toshiba MT5 and the Plus Piano all fit into this category.

    I therefore searched for a PAL compatible Dual Mode chip. It is not being released until much later (2003?). If you do the resolution calculations for 16:9 PAL then I come up with 1024 x 576. This could easily be accomplished by an XGA chip (1024 x 768) but you need to be able to do 1:1 pixel mapping to take advantage of this. This means that you need to drive the XGA panel either with a HCPC or something like a DVD player that can output an XGA signal (Cinematrix).

    I am currently considering a Cinematrix but have been experimenting with the HCPC and XGA resolution. It shows great promise, by-passing the yukky internal electronics, and gives a very clear picture. However as soon as Digital Keystone correction is applied, all falls apart! We are back to the equivalent of a standard DVD player feeding an ordinary panel projector. Motion artefacts, loss of sharpness and definition…..You loose all the advantages!

    Hence my problems. Jeff seems to have sus’ed this all out way ahead of everyone else as normal. His projector is now very cheap, as is the Cinematrix BUT I might need Keystone correction and hence I have hit a problem! If I could easily solve this I might treat myself to a new toy! I am currently looking at whether I can easily solve this…with your suggestions before I buy something.

    If you have a Cinematrix / HCPC feeding an XGA DLP panel then there is a potential for a seriously good picture in panel projector terms. Add an ISCO 11 and things potentially get better again (resolution / brightness etc). This is a long way from a DVD player feeding a SVGA projector, which is where I started.
     

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