Question about real projectors

i personally use a nice home-made projector which is 640x480. to make a long story short, i did a few things to fix the screen door effect, and other problems with DIY projectors, and it looks good. everyone i know is very impressed by its picture quality, and i project on a 60" dalite projection screen...

as for commercial units, yes, they look great. 640x480 will be fine, maybe a LITTLE pixelated, but keep in mind, TV resolution is 352x288. 640x480 is not that low... and if its 800x600, most likely you will get a decent picture from it.

all in all, to save a few bucks over those really nice ones, that solution will work out great for you, you shouldnt be disappointed.
 
first, to respond to tahustvedt,

NTSC resolution (not HDTV, just standard) is 352x244. PAL is very close, but a little different, and a different Hz. its amazing to think we watched shows on that low of res...

resolution really depends on how big your screen will be. mine is 60"across, so that works well for 640x480... doing a calculation, my pixel size comes out to be 0.09". thats pretty small and will NOT look pixelated.

the bigger screen you get, the better res you should probably have. however, ive noticed that with higher res, less light can get trhough due to more densely packed "pixels". so, if you are using a 100" screen, with high res, you will need quite a bit more light than with a 60" 640x480 display.

like is said, mine is 640x480 and looks more than fine on 60" screen.

as to how i got rid of screen door effect? well, the closer you get your panel to the fresnel, the better... this produces a much crisper and better looking picture. i took my overhead panel apart, and gutted it. then, i took out what was needed, controller board and panel.

i took this and mounted the LCD panel DIRECTLY to the glass stage of my OHP. so now, instead of the panel being like 2" away from the fresnel, its now about 1" or less. it looks a world better. not to mention that the light is more concentrated, because i masked out a opening for the panel on the glass... so MUCH more light goes directly to the panel, and doesnt disperse out the sides.

EVENTUALLY, i will get my site back up and give some of you an idea of what im talking about, and i have many screenshots of the finished product (of it actually playing movies and such).

i have recently given up on furthering the project because right now, this works too well to spend anouther $500 to make it a little better. plus, i just got a job working at a high-end audio/video store, and i get to buy everything at cost.

i have my eye on a sharp progressive scan, 1080i, 1000 ANSI lumen projector... this baby will project a progressive scan image on a wall 100" in size, that will rival most HDTV bigscreens :)

but, its $3,999. i need to see what MY price is, should be around $2,500. im tired of the ghetto projector setup sitting in the room. time for real toys.
 
hehe. I wish I had the real toy.

I`m not going to be using the OHP design. but I do have a quetion you might know the answer to. Are PCX lens or fresnal magnifier sheets better for projecting the image. I`ve heard both are pretty good. Whats your opinion?

ps. I`ll be waiting for the return of your site..,
 
where did you get 352x244 from?

http://archive.ncsa.uiuc.edu/SCMS/training/general/details/ntsc.html

http://srd.yahoo.com/goo/broadcast+...dio-etc.net/articles/Lines Of Resolutioin.htm

From this website I see that the horisontal resolution of regular broadcast NTSC is 330, I did not know that. :) I was certain that NTSC is allways 480 (525) lines, but here they say that NTSC broadcast is limited by law in USA to 330 both horizontally and vertically. No wonder there's a lot of confusion. I live in Norway BTW, PAL-country.

EDIT:
To make it even more confusing, here's a website that claim broadcast NTSC is 460x480.


Anyway, DVD-resolution is always 720x480 for NTSC and 720x576 for PAL. To view all the lines of an anamorphic DVD you need a 1024x768 projector or an 800x600 projector with an anamorphic lens.


Tor Arne
 
Tahustvedt,

The picture resolution thing is confusing. Usually when they talk about screen resolution in "lines", they are talking about a confusing way of describing what the horizontal resolution would be if the 4:3 screen were square with the same number of vertical lines as it currently has. I think NTSC DVD is described as having about 540 lines screen resolution.

The 480 vertical lines of an NTSC DVD frame correspond roughly to the number of visible scan lines (488) out of the 525. The actual numbers 720x480x30 were simply a compromise based on average bitrates of the MPEG 2 signal, but are very close to the standard value broadcasters use INTERNALLY when mastering broadcast material. Its bandwidth is significantly reduced for actual transmission to comply with FCC bandwidth limitations. (A higher resolution implies more transitions per second, and hence a higher signal bandwidth.)

Interlacing makes things more complicated, based on how the interlacing is used. You have two options: You can go for a 488 line frame at 30 Hz, or a 244 line frame at 60Hz. Either way, there are significant compromises and limitations to the resulting picture. This is where progressive scanning DVD players become interesting - the freaky thing is that for NTSC, most DVDs (containing Film material) are actually encoded at 720x480 x 24 frames per second non-interlaced. The DVD player itself interlaces the signal and adds in extra half frames to make the signal compatible with NTSC TVs.

Just to make things more complicated, the 720x480 signal is encoded to play at 4:3, meaning that if you are going to play the DVD through a device that has square pixels, it should have a screen with resolution in multiples of 640x480.

This is actually why the 640x480 panels work exceedingly well with DVD sources - especially if a computer is being used to play the DVD in its native 24fps non-interlaced form.

Also, if you are going to use ananamorphic lens, it is not necessary to use higher resolution - that is only required if you are viewing the image on a 4:3 screen, and you want to show the whole expanded horizontal picture without scaling down the vertical axis (letterboxed). A normal anamorphic 16:9 encoded DVD for NTSC outputs at 853x480 on a 4:3 screen. If you have a 16:9 anamorphic lens, you should have absolutely no problems displaying the DVD at 640x480 and either expanding the picture horizontally, or compressing it vertically, or both... (Most 2.35:1 Anamorphic DVDs are letterboxed down to 16:9 and then anamorphically stored...)

Experimenting with "re-packaging" DVDs to make them more friendly to projectors is an artform in itself, and is probably more complicated to get right than building a projector from scratch.

Check out www.doom9.org for LOTS of really cool info on such stuff.

Bill.
 
bah, you dont need above DVD res to play a DVD. i output my dvd's at 640x480. they are just scaled down. in much the same way a 3D renderer for a game scales the graphics to the setting of your choice. on a computer (assuming you use hardware acceleration), directshow filters reinterpolate the pixels according to your resolution settings.

all in all, 640x480 is perfectly fine for entry level LCD theatre projection... for the cost/benefit ratio, increasing to 1024x768 or above is out of the question.
 
I just have a hard time accepting that you don't lose detail if you run an anamorphic DVD on a 640x480 panel which gives just 640x360 pixels.

No matter how good the scaling is I would think you lose some detail. I understand that it's not cost-effective in a DIY application to buy high-resolution panels though.


Hey! How it actually looks is what matters anyway. :)


Tor Arne
 
Tahustvedt,

The idea is that for a 16:19 dvd you DON'T run it at 640x360: you run it at 640x480 with everybody looking very tall :D .

This is how it is stored on the DVD (actually at 720x480). Anamorphic when applied to DVDs means that the vertical axis is expanded to use all available pixels on the disk to carry detail. The dvd PLAYER, when it encounters such a disk, does one of three things:

1) if it is outputting to a 4:3 tv, it compresses the signal vertically and letterboxes it;
2) If outputting to a widescreen tv (16:9) it outputs the signal directly - and the screen expands the signal horizontally;
3) If outputting to a high-rez computer screen, it expands both horizontal and vertical axes independently to letterbox the image without losing any detail.

The anamorphic lenses generally act to convert a 4:3 projector screen into a 16:9 Widescreen - allowing number 2 to take effect, and get the most out of the pixels on the dvd disk.

Of course, a 2.35:1 signal will be letterboxed anyway.

Try telling your dvd player that you have a 16:9 widescreen tv...

Bill.
 
Hi Cowanrg,

I actually have a couple of good DVD players. What I am talking about is being able to avoid the letterboxing effects that DVD players impose as standard when feeding a 16:9 signal into a 4:3 monitor/tv.

When letterboxed, the black pixels top and bottom are not carrying any detail. Only the ones in the middle of the screen are used. This reduces detail and picture quality.

What I was talking about was making the most of a widescreen projector by feeding it with an input from ALL the pixels, and using the projectors optics to compress the aspect ratio without losing the detail that letterboxing imposes.

That is the aim of the anamorphic widescreen thread - using prisms to compress the aspect ratio along the vertical axis while leaving the horizontal axis untouched. i.e. it converts a normal 4:3 projector into a widescreen one.

It increases picture quality for widescreen sources by using the output from all pixels, and avoids the need to mask off areas of the LCD above and below the image area.

Bill.
 
cowanrg.

You should check out the DIY anamorphic lens thread in this forum. You'll see what I'm talking about. I've made many lenses and experimented with lots of prisms. It's not dificult to do.


I know what anamorphic is. And I know how DVD-players work. I know CRTs don't have to have square pixels. Just so you guys know I'm not a noob. :D

ALL DVD-players that I have tried can output letterboxed, 16:9 or P&S.


Tor Arne
 
Hi cowanrg,

Using prisms to do the widescreen is how the cinemas do it for Panavision and Cinemascope. I bought one on ebay last week and am currently playing with it. :)

It is a big sucker, and very heavy. I am also playing with some front-surface mirrored fresnel prisms that have an equivalent effect.

As for the DVD thing, yup, with some of the $1K players you can possibly switch off some of the effects mentioned above, but I have been doing lots of work with DVD and digital video, and the sad truth is that most expensive progressive scan DVD players use little more than the cheap scan-doublers everybody has been buying from ebay.

i.e. They totally corrupt the 24fps progressive original by interlacing it and adding half-frames to build the frame rate up to 30fps. Then they pass that through a scan doubler chip which attempts to de-interlace the resulting mess. Not good!!!

They do this because it is impossible to guarantee that the player will be receiving a pure 24fps input - anything originated on tv will be 30fps interlaced. Anything from Europe will be modified from 25fps. Only original film footage is 24fps (usually...)

Thus, to get the best results, use a software DVD player on a PC that can adapt to its input format, or do what I do - rip the DVD and re-encode it at a more appropriate resolution and frame rate.

Believe it or not, a decent PC will blow away the best hardware players.

Bill.
 
well, i believe you about the PC being able to blow them away. ive said that before, in this thread i think.

BUT, you are a little off-base about the DVD players' ability to deinterlace and such. its a LOT more complex than that. its not 24fps, its 23.976 exactly. and, its not 30, its 29.97. why? do i want to get into the whole inverse telecline alogarithm that goes on? no. its more complex than that. and i dunno why anyone would spend $1K on a player that has one of the crappy line doublers you are talking about. im talking about some really reference quality players. trust me, they do it well. sometimes equally well as a computer. you just gotta fork over the cash. (the one im personally referring to, and know works, is a Denon 3800. very nice player.

woneill said:
Hi cowanrg,

Using prisms to do the widescreen is how the cinemas do it for Panavision and Cinemascope. I bought one on ebay last week and am currently playing with it. :)

It is a big sucker, and very heavy. I am also playing with some front-surface mirrored fresnel prisms that have an equivalent effect.

As for the DVD thing, yup, with some of the $1K players you can possibly switch off some of the effects mentioned above, but I have been doing lots of work with DVD and digital video, and the sad truth is that most expensive progressive scan DVD players use little more than the cheap scan-doublers everybody has been buying from ebay.

i.e. They totally corrupt the 24fps progressive original by interlacing it and adding half-frames to build the frame rate up to 30fps. Then they pass that through a scan doubler chip which attempts to de-interlace the resulting mess. Not good!!!

They do this because it is impossible to guarantee that the player will be receiving a pure 24fps input - anything originated on tv will be 30fps interlaced. Anything from Europe will be modified from 25fps. Only original film footage is 24fps (usually...)

Thus, to get the best results, use a software DVD player on a PC that can adapt to its input format, or do what I do - rip the DVD and re-encode it at a more appropriate resolution and frame rate.

Believe it or not, a decent PC will blow away the best hardware players.

Bill.