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# If 100" x 56.25" = 16x9 Then Why...

I decided to make my screen 100" wide.

Therefore I multiplied 100 x 9 / 16 and got 56.25 for the height.

I then made the borders wider on my 120" retractable screen so that the image area is 100" x 56.25" exactly.

The problem is I can't seem to get images that I think are 16:9 to fit the screen area. I should mention that I have to do some keystone correction to square up the image since I do not have lens shift. I usually use the main menu of the Terminator II DVD to fit the image to the screen.

Questions:

Did I do the math right?

Does the keystone correction screw up the aspect ratio of the image?

On most DVDs, are the main menus 16:9 or are they that funny size that has narrow bars top and bottom.

Is it possible that there is something odd about the HD72?
It is actually 1280x768 resolution.

I would think the best course of action would be to make the screen 16:9 and live with the miss fit since I am likely to replace this projector with a 1080p unit when the bulb burns out. Sound reasonable?

Thanks in advance for any suggestions as to what may be wrong.

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How far off is the image from what you expected? The math seems correct so I would think you should be pretty close. As far as I know keystone correction doesn't alter the projected image size. Instead of using a DVD you should be able to output a blue screen; usually when there is no video input although some projectors have that as an option in the menu to display it. Maybe you could take a quick picture and post it?
A 1280 x 768 Resolution is 15:9 not 16:9

That being so, your well off the mark.

for a 100" "WIDE" image your figures should be 100" x 60"

Here's a simpler math equation.

100" divided by 15 = 6.6"
6.6" x 9 = 60"
According to this link the HD72 has a WXGA mode for 1:1 pixel mapping at 15:9, but also an HDTV mode where it converts the incoming to 16:9. You must have it set to WXGA?

That should straighten it out, but it should be noted that a number of HD presentations are of movies in 1.85:1 format also, so there are no absolutes.
Borders?... I don't need no stinkin borders.

Can you measure the projected image and adjust the borders to fit?

If you are projecting onto the screen at an angle, the height can be altered due to the geometry change. Is tilting the screen a few degrees an option? Which way are you off?
Quote:
Originally Posted by kbgl

Borders?... I don't need no stinkin borders.

Can you measure the projected image and adjust the borders to fit?

If you are projecting onto the screen at an angle, the height can be altered due to the geometry change. Is tilting the screen a few degrees an option? Which way are you off?

I could make the borders match this particular projector but repainting for each projector is not really an option. My preference would be to make a proper 16:9 image area and if this projector does not fit it properly when running in 16:9 mode then I will live with it.

I am well ware that the projector is native WXGA and I run it in 16:9 mode. For 720p content the image occupies 720 pixel in height and the projector allow you to shift it up and down within the 768 pixels. Thinking about this has made me realize that I should find something with true 1280x720 content and then shift the image to the max vertically. I may find that I do not need to tilt the projector as much.

The problem is that in 16:9 mode the image seems to be a bit too wide for the height of the screen. I have noticed as Laserfan pointed out, that some content is 1.85:1 which is close to 16:9 but a bit smaller in height. This leads to small bars top and bottom on a 16:9 screen.

I think what I need to do is find a DVD that I am sure is 16:9 and then fit the image properly to the screen. By using maximum digital vertical image shift I may be able to minimize the projector tilt and therefore reduce the keystone correction.

Kbgl mentioned tilting the screen. I have often wondered why people don't consider this option when they don't have vertical lens shift. This would be particularly easy when you make a floating screen that sits in front of a black wall or drapes.

Simply tilt the screen downwards until the image is squared on the screen. I suspect in most cases the screen would actually end up being perpendicular to the viewer's line of site.

As you can see from this photo I had considered tilting my screen in the beginning.

One advantage to a retractable screen is that you can retract the screen to fit the lower edge of the image. I know that means that the border only fits the sides and bottom but better that then the bars top and bottom.
Could you use some type of tape to adjust the borders that could be removed later?

Would there be any chance of damaging the screen when the tape is removed?
Quote:
Originally Posted by kbgl

Could you use some type of tape to adjust the borders that could be removed later?

Would there be any chance of damaging the screen when the tape is removed?

I think you could get away with adjusting the height of the image area by applying tap across the bottom of a retractable screen. Applying it to the edges would cause problems as the screen is rolled up. The difference in thickness across the screen roll would lead to worse waves etc.
Quote:
Originally Posted by tiddler

I think you could get away with adjusting the height of the image area by applying tap across the bottom of a retractable screen. Applying it to the edges would cause problems as the screen is rolled up. The difference in thickness across the screen roll would lead to worse waves etc.

Can you get it off a few months or years later without pulling off the screen material?
Quote:
Originally Posted by kbgl

Can you get it off a few months or years later without pulling off the screen material?

That's a good question! I don't know.
If you use "Gaffer's" tape, you should be able to remove it without residue.

JP
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