Floating Point


A common misconception is that if you work solely in the domain of video you have no need for floating point. But just because your output will ultimately be restricted to the 0.0 to 1.0 range doesn't mean that overbright values above 1.0 won't figure into the images you create.

In the Figures 11.12a, b, and c, each one of the bright Christmas tree lights is getting severely clipped when shown in video space, which is not a problem so long as I'm only displaying the image. In the center image, I followed the rules and converted the image to linear before applying a synthetic motion blur. Indeed, the lights are creating pleasant streaks, but they are not reflecting their true overbright nature. In the third image, I processed the HDR image in floating point, and the lights have a realistic impact on the image as they streak across. Even stretched out across the image, the streaks are still brighter than 1.0. Considering this printed page is not high dynamic range, I think this example shows that HDR floating point pixels are a crucial part of making images that simulate the real world through a camera, no matter what the output medium.

Figure 11.12a, b, and c. An HDR image is blurred without floating point (11.12a) and with floating point (11.12b), before shown as low dynamic range in 11.12c. (HDR image courtesy Stu Maschwitz.)


Floating point's benefits aren't restricted to blurs, however. Every operation in a compositing pipeline will gain extra realism from the presence of floating point pixels. The simple act of floating one layer over another with a transfer mode also potentially sees big benefits.

In Figures 11.13a, b, and c, I took an HDR image and performed a simple composite once in video space and once using linear floating point. In the floating point version, the dark translucent layer acts like sunglasses on the bright window, revealing extra detail exactly as a filter on a camera lens would. The soft edges of a motion-blurred object also behave realistically as bright highlights push through. Without floating point there is no extra information to reveal, so the window looks clipped and dull and motion blur doesn't interact with the scene properly.

Figure 11.13a, b, and c. A source image (11.13a) is composited without floating point (11.13b) and with floating point (11.13c). (HDR image courtesy of Stu Maschwitz.)


And now you might have noticed another red flag: After Effects 6.5 does not support floating point.

So how can you hope to work in linear color space or retain Cineon values over 1.0 in After Effects if it has no floating point? The answer is you have to cheat.



Adobe After Effects 6. 5 Studio Techniques
Adobe After Effects 6.5 Studio Techniques
ISBN: 0321316207
EAN: 2147483647
Year: 2006
Pages: 156

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net