Monday, May 28, 2012

Perspective Tomfoolery part 2

I mentioned in my last post that the previous example did not cover the axis on the top and bottom of the page. If you ignore the convergence coming from the Z axis (up and down), you might draw things in perspective like this:

What would the world look like if the z axis didn’t visually converge onto vanishing points as the X and Y axis do? Duke Nukem 3D, and many other early 3d videogames, answers this question. Due to the nature of primitive corridor shooters, and the technical limitations of a 1996 home computer, the z axis in such games were not programmed to converge. I found two screen-shots showing this quirk off for those of you who haven’t seen it before:

You may recognize this nuance in other media. For example, for a long time, photographers have used special lenses (and Photoshop filters) to ‘correct’ the perspective on buildings:

I’ve included the uncropped version so you can see how much artificial distortion is happening to the picture. Here’s the original:
For arguments sake, what is the perspective in this shot really doing? Or rather, what would be an accurate way to simulate the perspective converging east to west and up and down at the same time? That’s where 5-point perspective comes in:

Here’s a building drawn on top so you can see this in application. In most scenarios, you would most likely want to crop in so the distortion around the edges is lessened:

Understandably, you might not want to use this in every one of your layouts/projects. We usually abstract this into ruler-made three-point perspective, if z axis distortion is required. When do you know you should be using it? The further up or down you’re looking, the more likely you should be introducing a third vanishing point. This chart I made demonstrates:
Coincidentally, this also explains, as a guideline, how to fib two-point perspective if you don’t want to warp it like with the last post I made. Just flip the chart on its side and you’ve got shorthand for the other axis. Something I found useful is not even plotting distant vanishing points at all- just eyeball two slightly converging lines on either side of the horizon line and interpolate some lines in between. That way you don’t have to use a two metre long piece of paper to plot some awful vanishing point far away from your centre of interest.

Again, I hope someone out there has found this informative!

Sunday, May 27, 2012

Perspective Tomfoolery

Hi there, Blogviewers! I thought I would share a few observations I've made about pespective. This post deals specifically with calculating the distance between multiple vanishing points, panned perspective and warped perspective. We start our journey with these photos my brother took with multiple lenses. The first was taken using a 24 mm and shows very little perspective warping. This kind of layout would be easy to replicate using only 1 pt perspective.
The second is using a 10 mm. This would be a bit more difficult to replicate on paper, since the lines are now obviousley bent. Of course, it could still be fudged and look great in 1 pt perspective.
As you can see from my third image, the perspective on the two photos are the same, one is just zoomed out more. From these two images, we can start to see a pattern of distortion develop (see the blue line I drew overtop). What would it look like if we zoomed out even more? or even panned the camera?
This is a panorama that I rendered a long time ago in 3ds Max. This type of warped perspective is used in photography pretty much every time someone wants to do a breathtaking panorama, wether it consists of only two pictures, or you're creating a 360 degree masterpiece, like the photography of Sam Rohn ( http://www.samrohn.com/)  I say 'pretty much' because this abstraction breaks if you tried to keep all three axis ( X Y and Z) reletivley undistorted ( notice that the upper and lower areas are totally unrecognizable). computers use this type of image to create skyboxes for games, creating an undistorted 360 degree image, so long as you're looking througha virtual camera to limit the field of view to something more human. (Again, check out that Sam Rohn guy- his website does what I'm talking about)
A crop of the above panorama, showing that a smaller field that produces normalized looking results.
Here, I've superimposed the three images together in as accurate a perspective as I could throw together on Photoshop in 20 minutes. You can see that instead of radiating out from the vanishing points linearley, a la one and two point perspective, we have the two axis, X and Y, curving around the horizon line into their opposite poles. Facinating! This means that we can easily calculate how far apart each vanishing point is ( a 360 deg pan divided by 4 poles- 90 degrees) and also, we have a good way to estimate what FOV we would want in any given scene, as well as how distorted the perspective would have to be in that scenario. 50 degree field of view? great, just crop 50 degrees into this image, like the inset photos, and theres your perspective, wether its one or two points!
"But Chris, what does this have to do with DRAWING perspective?"
I'm glad you asked. Armed with this knowlege, you now know a bunch of new things:
> this is another checkmark to ensure that you're drawing accurate perspective. If you have two vanishing points on a page, make sure you know why you're placing them there; are you absolutley sure your layout wouldnt look more accurate if they were farther apart? 90 degrees apart?

> This trick works horizontally, or vertically (again with the elevator shaft) no more guessing what warped perspective looks like!
>reverse engeneer photos, and match BG plates easier, if you're into matte painting
>Fool-proof panoramas and wideshots for 2d layout. some fudging required if you have to move horizontally and then vertically in the same camera move.

I hope you all find this as fascinating as I did. I want to talk about rotating objects in perspective as well as 3 pt perspective if I ever do another one of these blog posts.

Monday, May 21, 2012

3d year Film Previs Art Dump

Whew! Third year is wrapped up! I thought it would be a good time to dump all these concepts I was working on during first semester while we were trying to find the look of our group film. All in all, I enjoyed the year far more tan i had expected to, and not only that, every group finished their film on time, despite the usual setbacks and delays. Possibley more film-related artwork to come, but I'm waiting for its online debut to happen (more on that later)