Digital Performance Institute

"I will do my utmost to be punctual with my postings"

I think that is a common misunderstanding of the inverse square law, I've heard it before. People ask if they get a short throw lens if it will make the image brighter because it's closer.
The answer is NO, it's not the distance it's the size of the image which the brightness is proportional to.

I see where the confusion happens, if you have two matching projectors (with the same lens) and one is 5ft away from the screen and the other is 10ft away from the screen: then the one that is 10ft way will be twice and high and twice as wide, therefore 4x the sq feet of image surface.
The same amount of light is spread over 4x the area making it 1/4 as bright.

It's the increased area that makes it dimmer, but it's the distance that makes the area larger, thus the mistaken connection.

So lets clear that up, by taking one of those projectors and putting in a wide angle lens, one that makes the image 5ft wide from 5ft away. The other has a long throw lens that makes the image 5ft wide from 10ft away.
Now both images are 5ft wide, from the same lumen projector and ... both images are the same brightness.

We move the short throw projector back to 10ft away, and it's now got a 10ft wide image, and is 4x the area and 1/4 as bright.

so we can change distance, or the beam spread of the lens, and both things change the area of the projection. Now distance is decoupled from area, but we see that it's area that is proportional to brightness not distance.

Now just for fun in case anyone needs it lets look at the inverse sq law and how it is about Area.So far that was nice and easy with 5ft and 10ft, lets put the long throw lens back in both projectors and put one at 5ft and one at 15ft. Away from the screen.

One image is now 5ft wide and the other 15ft wide.

3x as wide.but it's also 3x as high, meaning that it's area is 9x as large, and it's brightness is 1/9th less.

5ft vs 20ft 25x difference. 

in the likely event that that was not clear check out a more detailed explanation. 
http://en.wikipedia.org/wiki/Inverse-square_law

I've mentioned that I love Isadora, and I have a lot of patches that might be useful so I'm going to try and share a few here.   If you have any problems or questions about Isadora feel free to ask me, and I'll see if I know or can figure out how to help.

You will have to have "the newest" or close to newest version of Isadora to open my example files (1.2.9 on the Mac, or 9b51 on the PC)

One of the things I love the most about Isadora is the Quad Distort Actor.   I had been using my own cobbled together software in which this was the primary feature, and when I started using Isadora I though that it was so much better than everything I had tried, if only it had this one more feature.  Well Mark added the feature and I was hooked.

The simple explanation is that a Quad Distortion actor is just Like a Projector but you can control it's corner points to correct for even radical keystone distortions.

I think this is obviously useful, but I want to point out some of the great things that it makes possible.

• Your projector just can't quite go in the center of the screen.
  • use the Quad Distort to fix it in software
• You want to project behind actors, but don't have the space for rear projection
  • if you have a high grid put the projector up as high as possible, point the projector down onto your back screen at a very steep angle
  • this lets the actors walk up very close to the screen before shadwos apper
  • use Quad Distort to correct for the keystoneing, You can correct for much more radical keystonging than what is built into the projectors.
• your in a hurry on install, like all tour situations
  • just throw up the projectors in roughly the right spot, overshoot
  • and correct it in software with the quad distort actor.
  • (fix it after rehearsal if you have the time)
• you are projecting on scenerey that is not perpendicular to the stage, or not the same scenery from scene to scene.
  • use Quad Distport, hit the wall in this scene, and the park bench in the next scene
• You want to project on everything even actors
  • use a really big projector to cover the stage and quad distort to create multiple smaller "virtual projectors"
  • put a DMX mirror in front of a projector and recorde multiple focus settings, each with their own Quad distort settings.
• Your really tight on space and want to bounce the image off a mirror to cut the throw distance
  • Focus and alignment off a mirror is very tricky, but just get it as close as possible and use Quad Distort to do the final tweeks.

OK so back to the example patch:  here is the quick way to look at it, an explanation of the what and why of it all follows in more detail.

About the example patch.

1. unzip
2.  open patch
3. go to the second scene video 1
4.  show controls
5. show stages
6.  drag around the controls and see what happens

While the idea of replacing a Projector Actors is simple in theory there is more work to be done after that switch.  The main part of that is to actually set the values for the corner points, in fact it's very difficult to just correct those corner points directly on the actor, so I have made a patch with a bunch of controls hooked up so that you can simply drag around the corner points in what I hope is a simple logical way.

But there is one more wrinkle.  If you are building a show with only one file and just the one projector actor then there is no problem setting this up to match your installation.  But if you are using more than one scene then you would quickly notice that it is a pain to have to do the corner point correction on every scene, so what I do is set up the quad distort and the controls on scene 1.  
Then in each scene I "activate" the first scene and use a broadcaster and listener to send video to the same quad distort actor.
That's why you have to go to the second scene to see the video, but most of the actors are in the first scene.

That solves the problem but it does have it's won consequences.  For instance if you tend to use the Jump actor to switch scenes with a xfade value to crossfade between scenes then my using only one quad Distort won't work.
There are other solutions, but it just gets more complex as and I'm not sure what you need.  But I'd be happy to advise, or add things to this patch or your patch if you like.

Let me know if it's helpful or confusing.

DPI:

Would you be wiling to share any patches?

Hal Eagar:

Yes I would love to, It's always hard to find time to clean up and document something. And you are never sure if anyone will care, but if they do and it could save time for someone then I'd be really please to do so. I learn so much from looking at other peoples patches and code.
OK let me find some.

However, I was much more impressed by a product from the German company Woehburk, especially their Cristalline, glass projection screen. I thought that it showed a brighter image than the other products, with better contrast and color. Perhaps I was charmed by the small scale, as I wanted to design some kind of suspended 'chandelier' type array of small glass projection screens. I really like the way that the image is only visible from one side, which makes it appear quite magically, if you're just passing by...

In this video I compare three different Woehburk screens and then compare my favorite with an opaque rear projection sample from 3M's Vicuity range.

Participants:

PERFORMANCE: SOUNDING
February 17-March 13 2010  -  $18 8:30PM

HERE Arts Center at 145 6th Ave (entrance on Dominick Street).
http://www.here.org

I know this show has a lot more than the video design to offer, but so far the video aspect is all I've gotten to see.  It's a lush abstract immersive video that plays to the theatrical non cinematic.  In other words worth seeing.

It's nothing short of amazing the amount and variety of video surfaces and environments that can be packed into a small blackbox like HERE. 

Directed by Kristin Marting 
Written by Jennifer Gibbs
Video by Tal Yarden

Featuring Bessie Award-winning Okwui Okpokwasili* as Ledaand an ensemble cast featuringTodd d'Amour, Ana Kayne, Irene Longshore, Rudy Mungaray, Michael Pemberton*, Stephen Reyes*  
Music Kamala Sankaram Set Nick Vaughan Light Rie Ono Seo Costumes Elizabeth Bourgeois Sound Jane Shaw Technical Direction Nate Lemoine Stage Management Emily Rea Casting Judy BowmanAssistants Jane Jones, Jennifer Kraus, Elenna Mosoff, Zarrin Whyte, Taili Wu

DPI lost it's former space but thanks to our great friends become great partners at One Arm Red, we've got a new office at:

10 Jay St 9th Fl. suite 903
Brooklyn , NY 11201
Vox (530) 324-2701

The One Arm Red facilities are fabulous, it's nice to be our here where things are happing, and good things are to come.

There are many ways, from the brute force anolog.
Downsample your Montior output to Composite or S-Video and Capture it on another Computer with a frame grabber.
Or Output your Monitor to HDMI (or convert your DVI -> HDMI) and re-capture that on a HD capture card on another computer.

But that's a mess, uses 2 computers etc...

Or if your using Jitter there is a option to capture a portion of your desktop as a Matrix source. That's a perfect solution, but only for Max/Jitter.

I used to use Camtasia which included a live output driver. I've been using a venerable old V3 version for years. But I recently had to purchase V6 to edit some files for a client.
And I was disappointed to find that they had abandoned the live feature in V6 (v5 still has it)

I've never used the other features of camtasia much and it's seemed like an expensive solution, but I could never find another software option like it.
However this go round I did find a source for what looks like a better and free alternative!

http://www.splitmedialabs.com/vh-video-sdk/vh-screen-capture

Actually the features and performance of this tool are awesome, way better, though just as confusing as Camtasia ever was.
The multi-mix option is a whole new feature set to explore. I've needed those exact features in the past. (say to get multiple camera inputs into a VJ app.) Isadora my favorite application supports multiple inputs, and native capture drivers so I don't need this feature as badly now but it's still nice to have in a bag of tricks.

For instance you can change the video settings, and even some effects on the video input source in real time.
Scale and mix multiple cameras. (need a picture in picture this will do it with more options than you could hope for.)

Plus you can of course save your presets, a crucial feature.

Oh I'm giddy with the possiblites.

also if for some reason your software is not compatable with the drivers for your capture device (Skype crashes with my laptop's built in camera) you can run it through the multi-mix as a virtual camera and still use that device.

THANK YOU http://www.hmelyoff.com