Film, HDR, and 32 Bit Compositing

True realism consists in revealing the surprising things which habit keeps covered and prevents us from seeing.

Jean Cocteau (French director, painter, playwright, and poet)

The most revolutionary and far-reaching change to After Effects 7.0 is also one that initially resonates with few artists, but in many ways it represents a paradigm shift in compositing. If 32 bit per channel floating point color mode, which allows high dynamic range (HDR) color adjustments, generates fear, uncertainty, or doubt, it's simply because we've trained ourselves to live without HDR, although it is in line with fundamental phenomena of the world around us.

The previous edition of this book contained a guest chapter written by Brendan Bolles, who helped create eLin, a third-party tool that allowed for linear floating point compositing in After Effects (if the meaning of this term eludes you, hold onit is drawn out thoroughly in the discussion ahead). That chapter forms the foundation of this discussion of HDR compositing with the new features in After Effects 7.0.

Destined to be a marginal tool, ignored by over 99% of After Effects artists, eLin made the After Effects workflow more complicated for the sake of benefits that seemed applicable only to the highest end projects. Although it's not true that the benefits would only be seen by feature film compositors, only they seemed to welcome the cumbersome addition to the pipeline.

HDR compositing in After Effects, as made possible by 32 bit per channel mode, may seem to begin its life in a similarly marginalized role; it changes the inner (and outer) workings of After Effects in ways that are not immediately obvious. Yet its benefits are within immediate reach of anyone, on virtually any kind of project. These benefits include

• Goodbye to clipping: If illuminations extend outside of the range of your monitor, their appearance remains as natural as in real life; highlights and shadows are not inadvertently crushed.
• There is no good reason to use the Glow filter, or a bunch of other imitations of natural light phenomena, ever again. Fewer Blending modes can do more of the work, more naturally, with an HDR pipeline.
• The world inside After Effects can represent the real world of additive color and light. Illuminate elements in the same way that you adjust a light or lens aperture, without having to compensate for strange results.
• Once you start combining light levels naturally, new techniques that would previously have been off-limits emerge as natural solutions to various lighting situations.
• Many benefits can be enjoyed immediately, without the need to convert to Linear Blending mode (explained further on) or to restrict effects use to 32 bpc compatible plug-ins (of which there are currently only a handful). You don't even need to begin with HDR source.

Of course, it would not be honest to tout the benefits without also acknowledging some limitations and challenges:

• 32 bits per channel requires more processor power than 8 or 16. It's twice as many bits, but 2 to the sixteenth power or 65,536x more numerical data per pixel. Multiplied by the previous capacity of 16 bit per channel values, we are talking trillions of colors per channel.
• A complete HDR pipeline is not possible. Presently there are very few digital HDR input devices (cameras) or monitors (the ones available now are extraordinarily expensive and could not simply be plugged into your PC). Of course, the analog medium of film has always been, and remains, an "HDR" format.
• The benefits of HDR are not difficult to grasp or use, but the other piece of the puzzle that truly completes the picturecompositing using linear valuesis a challenge to learn and understand, so unfamiliar are the underlying issues to most digital artists.
• Along with linear compositing comes the need to work between multiple color spacesan issue to which print digital artists have been accustomed for years, but which is virtual terra incognita, and for many, an unwelcome development, in video.
• No model yet exists to extend custom color spaces to other parts of the pipelineimage gathering (the camera) or output (conversion to the playback medium), so the benefits that print artists receive from color management seem elusive at this stage for their film and video counterparts. In some ways, Adobe's role is similar to what it was a decade ago with printto lead artists in a helpful new direction that nonetheless seems confusing at first.

But these points include concepts and terms that won't even be defined or discussed until later in this chapter. First, let's revisit Brendan's excellent primer to try to nail down why any of this is even worth the trouble in the first place.

Notes

The discussion first moves to issues associated with film, before covering the 32 bit compositing environment; film in many ways represents the analog standard against which digital HDR technologies are measured, which Brendan explains well.