Tuesday, September 30, 2008

exrdisplay for After Effects

When you work with linear floating point images in virtually any program, the standard conversion from the linear color space to your screen is usually some sort of gamma curve, a standard image operation. But a trained eye may notice that in some cases, OpenEXR files appear slightly differently. One example is the thumbnail previews shown by Mac OS X. In this case, the curve used is from ILM's exrdisplay program. In the sample below, standard gamma is on the left and exrdisplay is on the right:

Notice how in the exrdisplay version, the sky is not completely blown out. Overbright pixels have been brought into range and do not clip as harshly as they would with a standard gamma curve. ILM is using a modified gamma function and added an adjustable "knee" to make this happen.

Ordinarily this different curve was only of passing interest to me, but then I was helping out some friends put together a pipeline for an Inferno, and found that it also uses this curve, which made it necessary to replicate the same color operation in After Effects, which made me write this plug-in:

It has all the same controls as the exrdisplay command-line program, in addition to a few extras. For one thing, the dithering that exrdisplay always uses is optional in the plug-in.

But more interestingly, I've included a checkbox to apply the inverse function. This means you can take a regular image such as a JPEG and convert it to linear space using this plug-in, with control over the knee which will push some brighter pixels into overbrights. And then when you use the plug-in on the other end with the same settings, all values will round trip.

Anyway, I needed this for my personal use, so thought I'd share. Enjoy!

Mac | Win


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