April 2006 Archives

I plan to make some dramatically-lit photos (combined with Maxwell renders). As a prelude to this work, I an experimenting with some issues related to photographic exposure. My goal in this experiment is to create the illusion of a spotlight illuminating a figure on an otherwise dark stage without actually having a particularly dark stage. It's nothing new, but I want to try it myself.

The photograph above represents a human figure on a stage under subdued window lighting.

Here's the same set, but now I'm "whacking" the figure with an overpowered key light. This adds even more light to the set.

When I expose for the new bright key light, it's as if I've effectively "darkened the room."

By going from a one second exposure to a 1/250th second exposure (for a given aperture) I have darkened the scene by 8 f-stops. I even seem to have reversed the lighting; the window light is no longer apparent at all. What's more, I can have the depth of field and short shutter speeds not normally associated with low light photography - if I choose.

Photograph doesn't always have to "mimic" how you perceive the scene to be. I remember one day I visited a taping of The David Letterman Show. I was struck by how pale, washed out and desaturated the set and everyone on it looked in person, and how richly contrasty and lustrously saturated it looked on the monitors.

When the Apollo astronauts were on the moon they took images suitable for stitching into panoramas. In fact, some have even created Quicktime panoramas from these images.

Did you know you can do this sort of work in 3D without actually stitching the images together? Here is a partial panorama I "stitched together" in 3D space directly within Maya. It is a practical example which builds upon ideas I laid out in 3 previous blog entries.

Prerequisite Reading

Nodal Point Pan and Tile Part 3

Nodal Point Pan and Tile Part 2

Nodal Point Pan and Tile Part 1

A Partial Apollo 17 Panorama

Map a photo onto a plane within Maya. Make sure the plane has a shape proportional to the resolution of the image so that in mapping the plane you neither stratch nor squeeze the image.

Set Maya up to show high quality texture maps in hardware preview.

Place the photo far enough away from a Maya camera so as to fill the resolution gate with the plane. Make sure the Maya camera is at the ORIGIN of the world space.

Group the image so that its parent is a group centered at the ORIGIN.

Make a copy of the first image group.

Put a second image on the plane which is part of the second group.

View both groups from your ORIGIN camera.

Use your eye to ROTATE the second group about the ORIGIN such that the second image seems to tile with the first image.

Here's what you should see. You may find it useful to make one plane semi-transparent in order to help alignment. BE CAREFUL when using transparency to look for this alignment, however. The planes WILL and SHOULD only line up at the edge where they meet.

Repeat the process with a third image group.

Did the photographer use an panoramic head to carefully level the camera as it pans across the horizon? No, he didn't? Who cares? It doesn't matter.

As long as the photographer only panned and tilted when he took his photos it doesn't matter if he was level or not, as you can see from the example above.

You can repeat this process until you have a faceted shell of desired coverage.

Why does a faceted shell work? Why don't we see the sharp corners? Why isn't this a continuous sphere?

All good questions -- and all answered here:

Nodal Point Pan and Tile Part 3

Nodal Point Pan and Tile Part 2

Nodal Point Pan and Tile Part 1

Idea for making a continuous single image panorama

You usually don't need a single image for pan and tile work. If you insist on having one, you might be able to use a Mental Ray lens shader to render out the faceted shell into a single lattitude/longitude image.

UPDATE 7/29/2006

Microsoft Photosynth

Paul Haeberli's early work on automatic merging