SimplePic app

Thursday, November 27, 2014

More on tattoos

Here is a nice little graphics project: tools for optimizing illusion tattoos like these:
Here is the article that is from.

I suggest if you and some friends do this you all agree to get a tattoo using the tool at paper submission time.  I guarantee that is a strong incentive for software quality!

Radiosity on an iPhone

I went to Brad Loos' PhD defense earlier this week (and it and the work presented was excellent; congratulate Brad and remind him that "Dr. Loos" sounds like a James Bond villain).  One of the things Brad talked about was modular radiance transport (MRT).  This was one of the most important works in rendering to my mind because it was a serious attempt to "make radiosity work" and in my opinion was the most successful one so far.   The basic idea is to divide the world into boxes with some number of open interfaces.    By some muscular linear algebra and clever representation they make this work very well for environments that are not exactly mazes and have clutter and details and characters.  Brad mentioned in his talk that Kenny Mitchell spearheaded an MRT tech demo game that is free on the apple app store.  This was done at the time of the work and it even worked on my generation 0 iPad, and here's a screen shot:

It is fluid on that old hardware, and REALLY fluid on my newer phone.  Interactive radiosity really does look good (and the underlying approximations can be seen if you pay careful attention, but I would not have guessed this wasn't just a full solution except for how fast it was).  Try it-- it's fun!

Here is a video of it running.

Also, there is a full report on all the tech behind it.

Wednesday, November 26, 2014

Secondary light source

One of the most useful assumptions in graphics is that there is "direct" lighting and "indirect" lighting.  Mirrors always mess that up.  Here is an example of a shadow cast by "indirect" light:
The shadows on the ground are from the Sun which is well above the horizon.  The dimmer shadow in the doorway is from a bright "secondary" light.

The light comes from a car:
The shadow is cast from the highlight on the red car.  Interestingly the iPhone camera makes all these bright hightlights about the same, whereas in real life one is MUCH brighter.  Clamping FTW!
For games and historical visualizations it is probably best to just pretend those secondary specular lights are not there.  However, for predictive applications they should be tracked.    Dumping the whole concept of "direct" light is not irrational in such cases.

Tuesday, November 25, 2014

Photo processing tattoos

Our app extension fixes to SimplePic went live last night (we solved the app store search bug of Pic! by just changing the name.  Crude, but effective.  The fix to app extension was replacing some of the Swift code with Objective-C... old technology has more warts but fewer bugs).  I tested it on Tina Ziemek's tattoo as that is one of the things SimplePic is designed for:

Top: original image.  Bottom two output of SimplePic
The middle picture is a good example of the tradeoff in changing colors without messing with skin tones too much.  Some of the hues change a little as some of that tradeoff.  There is most definitely a few SIGGRAPH papers to be had in this domain, and I am not going to pursue it, but if anybody does please keep me apprised on what you find (there is a correlation between tattoos and iPhones so there's a specialized app to be had as well).  The posterization I personally use when I want to exaggerate contrast (like a photo of a sign where the colors are blah) so I wouldn't probably do that there.

PS-- Many of you who know Tina, and FYI she's started a game company and has a crowd-funding campaign going.  Sign up!

Monday, November 24, 2014

Strange looking reflection

This one looks to me like a bug in real life. 

(I don't mean insect).  It is a reflection of this lamp:

Friday, November 21, 2014

And a mistake in the original ray tracing paper

More fun trivia on the original ray tracing paper.  Whitted put in attenuation with distance along the reflection rays:


This is a very understandable mistake.  First, that radiance doesn't fall off as distance squared is confusing when you first hit a graphics class, and there were no graphics classes with ideal specular reflection then; Whitted was inventing it!  Second, the picture with the bug I think probably looks better than without: the fading checkerboard in the specular reflection looks kind of like a brushed metal effect.  So it's a good hack!
Whitted's famous ray tracing image.  From wikipedia
There are two lessons to draw from this: when bugs look good think about how to make them into a technique.  Second, when you make a mistake in print, don't worry about it: if somebody is pointing it out decades later you probably wrote one of the best papers of all time.  And if the paper is not great, it will disappear and nobody will notice the mistake!

Thursday, November 20, 2014

Another fun tidbit from the original ray tracing paper

The paper also used bounding volume hierarchies (built by hand).    It's amazing how well this paper stands up after so long.