Edge Blending Content Setup

so have a pretty basic question about how to setup content for an intended edge blending setup.

first of does anyone have an opinion on an optimum percentage of overlap? 10%? 25%

does catalyst put the feathered transparency in or do i do that in after effects?

it is as basic as i think right? meaning if you are going to stitch two projectors running 1024x768 then i create two pieces of video which have the same exact content in the shared 102 pixel overlap region (10% overlap)

any advice would be greatly appreciated.

Render your movies to 2048 x 768 or somewhat more narrow, as your overlapped picture will be a bit smaller. IÂ´ve found it quite easy to use corner pinning in the mixes when setting up two beamers, and the Catalyst will do the blending nicely. You might want to adjust the gamma on the ramps a bit to make the blending all seamless...

ItÂ´s easier than youÂ´d think, and IÂ´ve been surprised by how good it looks, even on quite big areas of overlap.

Generally a 20% minimum overlap is preferable.

I have a few answers as edge blending is about 99% of my Catalyst work. I've done all kinds of systems 5%, 8.33%, 10%, 12.5%, 15%, 16.67%, 20%, 25%, 33%, and 50%.

Quote:

Originally Posted by craigglow

....does anyone have an opinion on an optimum percentage of overlap? 10%? 25%

When I first started doing edge blending, it was using Blend Pros from Folsom and Spyders from Vista. These solutions are rock solid but hella expensive.

When using those systems, I used a pixel by pixel overlap. I use 1024x768 projectors mostly.

Since 10%, 15%, or 20% of 1024 are not a whole numbers, I didn't use them. I do 64 pixel overlaps, 128 pixel overlaps, or 256 pixel overlaps mostly for 1024 x 768. These equate to 6.25%, 12.5%, 25%, or 50%.

In these cases though, I had projectors with long throw lenses I was shooting on to curved screens at far distances with long throw lenses, and each projector was perfectly on axis with its respective piece of the screen. Therefore, except for imperfections in the lenses, each pixel was almost exactly the same size and my edge blend was perfectly overlapped.

In this method, I was able to get an image that worked great. In the real world though, we have other concerns.

For productions or any application where things are changing are do not stay exactly the same, always use larger blend regions. 10% is almost too small. I suggest 25% at least if you can get it but never less than 20%.

There are two major problems you will run into with smaller blends.

Perceived intensity of a blend region.
Distortion of a moving screen.
The perceived intensity
If your projectors are very close together and far away from the screen this will not be a problem. Basically what happens is that your eye on the reflected axis of the screen perceives the greatest amount of light. Therefore if you are House left and look at the blend, the right side will look brighter and the left darker. The opposite is true if you are on the House right side. You will end up seeing a line of the blend area where the side of the blend on the same side of the room as you appears brighter and the opposite edge appears darker.

The solution to fix this is to put the projectors a close together and hope and adjust horizontal keystoning proportionately. Sometimes I'll even cross projectors to eliminate this problem.

In any case the larger the blend, the less you notice this.

Visual Distortion
Basically, there is wind everywhere. Every screen moves (unless it's a solid wall). When the wind blows, AC turns on, or anything the like, the screen moves and the blend no longer stays overlapped. With a small blend, this is very noticeable. The larger the blend, the more forgiveness.

I can't tell you how many times I've been in an arena where the AC was off during the day and at showtime, the screen moved almost 2 feet from air movement.

Quote:

Originally Posted by craigglow

does catalyst put the feathered transparency in or do i do that in after effects?

The whole edge blend feature in Catalyst is about the feathered black. Richard even included a wonderful bezier curve tool that allows you to adjust the curve parametrically to achieve the best results.

Quote:

Originally Posted by craigglow

it is as basic as i think right?

It is very simple.

Create the offset for each mix. Pick the blend overlap size. Then turn blending on and adjust.

It takes practice to learn as it is not logical in a step one step two process but it makes perfect sense once you figure it out.

The hard thing is remembering that if you set your overlap to 25% then you need to make your offset between mixes a difference of .75 and so on.

Quote:

Originally Posted by craigglow

shared 102 pixel overlap region (10% overlap)

If you just blend 2 screens, then subtract the blend percentage from one projector and count (1024 + 1024 x 0.9 = 1945.6) to get your image width. Yes, the blend pixels are 204.8 which means your blend region will be 102.4.

If you use more than two screens, remember that any screens in the middle will have two blend regions. For example, three screens would be:
1024 x 0.9 Left
1024 x 0.8 Center
1024 x 0.9 Right
The total would be 2867.2 wide from the total of 3072.

These are important when calculating your content creation.