Projection formats

[Johnno]

In our forthcoming school play the Drama Queen wants to project the backdrops using a projector with native XGA resolution (1024x768 pixels) and slides designed in MS Paint and assembled in PowerPoint.

 

In order to fill the screen (the cyc wall of the stage) the projector is best operated in its 16:9 mode. What correction should I apply to the Paint pictures to ensure that a circle comes out as a circle?

 

In a technical nutshell how does a projector (Hitachi CP-X380) project 16:9 format? Would I be right in thinking they simply reduce the number of pixel rows illuminated, in this case from 768 to 576? (1024:576 = 16:9)

 

If so the Paint picture will be crushed vertically by the projector and the correction would be to draw the circle as an ellipse 4 units high by 3 units wide. Is that right?

 

The school's closed for the week otherwise I'd experiment. I spent this afternoon drawing "a summer garden" and then simulated its projection. The result was pretty ghastly. :D

[Pete McCrea]

The easiest way might be to simply make the slides with black bars top and bottom, running the projector in 4:3 and letting the spill go over the set/drapes. If your lucky the black won't be too light and so won't get noticed.

 

With the Christie units the projector blanks the top and bottom of the image, then takes the 4:3 image and compresses it to the new 16:9 area. Getting the correct scaling and images can then be fun. The easiest way to get the image right in this scenario can be to work in 4:3, then use Photoshop or A.N. Other software to compress the image to 16:9

[Fletch]

Hi There,

 

Not to spoilt the fun, and on a slightly different note, just be sure you are happy about how bright the images will be before you spend all your valuable time on this... as I looked at this before for an amateur group and we decided the stage lights at full would simply over power the projector. I don't know anything about the one you have chosen so this maybe OK.

 

I think Little DJ's suggestion sounds a good bet, as you are right it's not clear how a projector would do the 16:9. I would imagine you are correct that it will simply blank the top and bottom row of pixels... as they would surely tell you the most pixels the projector has from a salesman point of view.... so it seems the stats you have are for a 4:3 image.

 

Have Fun

Fletch

[Pete McCrea]

Most units I've come across when set in 16:9 with a Native 4:3 chip will simply put the unused top and bottom pixels to black (or dark grey with LCD....)

 

And as Fletch says do double check your brightness before you spend hours on creating artwork. Googling the Hitachi CP-X380 gives a 2000 lumen machine. Spread this over anything above a 8' screen and turn the lights on, and you ain't gonna see it due to spill. I'd doubt it'll work too well unless the stage is going to be dark.

[Johnno]

We used this projector in the last two shows projecting slides at 4:3 onto the cyc wall and the result was quite acceptable. The image would have been about 5m wide. The full cyc width is about 7m and the image is quite visible in the tests I carried out in semi-daylight. The shows will take place at night when the hall is darker. Incidentally the Drama Queen isn't the least bit upset about the shadows that the children throw onto the wall from both the lights and the projector. She prefers the idea of using projected slides to the disruption that shifting "proper" scenery entails. I think that's a bit sad since it loses some of the mystique of live theatre, especially at this low level.

 

I like the idea of doing 4:3 slides and masking the excess so I'll give that a try when the school re-opens.

 

Thanks for your suggestions.

[Pete McCrea]

Well if you guys are happy with the result, then that's good! Let us know how you get on.

[tlc]

In my experience a 2000 lumen projector is fine for backdrop projection up to 5 metres wide providing you take the simple precaution of ensuring no light spills onto the screen.

(A deep stage helps a lot of course)

 

Barndoor all overhead floods/fresnels and dont use front on FOH lighting.

Crossed side light (from just FOH) can usually give good clear lighting of principals without spill onto the back wall.

 

Of course a vastly bright (call lights at the musical) type of lighting will wash it out

However careful design to take account of the projection needs shouldn't equate to a darkly lit show.

 

Most projectors can be rigged upside down from the roof (swap picture via menu for roof mounting).

This means most of the shadows from the cast wont show on the projection.

Steep angles will need some keystone correction tho.

 

Roof mounting probably needs a longer cable to the laptop or whatever your image source is , make sure you use a good quality cable for long runs.

[Johnno]

In my experience a 2000 lumen projector is fine for backdrop projection up to 5 metres wide providing you take the simple precaution of ensuring no light spills onto the screen.

(A deep stage helps a lot of course)

 

Barndoor all overhead floods/fresnels and dont use front on FOH lighting.

Crossed side light (from just FOH) can usually give good clear lighting of principals without spill onto the back wall.

 

Of course a vastly bright (call lights at the musical) type of lighting will wash it out

However careful design to take account of the projection needs shouldn't equate to a darkly lit show.

 

Most projectors can be rigged upside down from the roof (swap picture via menu for roof mounting).

This means most of the shadows from the cast wont show on the projection.

Steep angles will need some keystone correction tho.

 

Roof mounting probably needs a longer cable to the laptop or whatever your image source is , make sure you use a good quality cable for long runs.

 

The image was washed out by the lighting quite a lot since all our lighting bar the cyc is FOH (this should be changed shortly)

 

The proj was high and close to the stage so the angle of projection was quite steep. Keystoning was at its extreme of correction.

 

I think that because we are a school and most of our audience are the doting parents of the cast members, and most of our cast members are complete beginners at acting, we can probably get away with technical levels that would be intolerable to an audience in a commercial theatre. This doesn't mean I'm happy with it though, and I expect to do at least one thing better in each new show at present.