After Effects' Exposure control is a linear tool. It applies exposure multiplying the input image by a constant value, so it's useful to globally brighten or darken an image, but 3D artists usually think of exposure as a non linear control, aka a "tone mapper".
This simple Pixel Bender filter allows to compress highlights with a non linear curve, based on the well known Reinhard's Tone Mapper described in "Photographic Tone Reproduction for Digital Images". It's easy to use, reasonably fast, and especially useful when applied to images produced with a linear workflow. And it's free.
How to use this Simple Tone Mapper
Global tone mapping operators mimics film's logarithmic response curve. In short, they compress superbright pixels without darkening the image. Have a look at how the blown-up clouds are toned down by the simple tone mapper in this rendered sequence, straight out of Lightwave 11.
Tone Mapping reduces the harsh contrast in wood blocks and clouds
There are just two controls in this plugin: one is the White Level and the other the Input Gamma. The easiest way to use this filter is to apply it to an overblown rendering and do the following:
- Hover with the mouse over the highlights and look at the values in After Effects info palette.
- The largest value should be the one used as White Level. From there, it's only a matter of adjusting and refining the value to achieve a good balance of dark and bright tones.
- If your image is gamma corrected, make sure to set the proper gamma value. Otherwise leave it at 1.0 (linear gamma).
- Don't forget to set the project's depth to 32bpc, otherwise banding will ruin the image.
Here's the complete animation, a real quick render that uses just a direction light and a sky. Ninety percent of the final look is created by the Simple Tone Mapper plugin.
The remaining ten percent is a bit of color correction — a blurred layer added to the original — used to create an halo around the highlights. This energy diffusion step is important to preserve the illusion of really bright spots in the images (as explained in "High Dynamic Range Imaging" by Reinhard, Ward et al.). BTW, "energy diffusion" is the fancy term for Fast Blur.
Lighting in this scene is very simple: a directional light and an indirect HDR skylight
Math's boring, feel free to skip this section
The tone-mapping curve depends on the White Level adjustment, as shown by the sample curves for the tone mapper depicted below.
The dashed line is a linear mapping: the image is not changed. As the White Level parameter increases, brightness that approaches the highlight range is compressed. The low dynamic range (LDR) brightest value, one, will always be mapped to the original image's brightness closest to the value selected in the White Level parameter.
The Gamma control linearizes, if needed, the input image. Set it to 1, linear gamma, if you interpret After Effects footage with the "Preserve RGB" option. Set it to the current profile gamma (usually 2.2) to let the plugin linearize, then reapply, gamma correction. More accurate results can be obtained leaving the Gamma parameter to 1, and applying a Color Profile Converter after the simple tone mapper.
Important: Tone Mapping and "Linear Workflow" are meant to work together and Tone Mapping should always be performed on the linear image. Afterwards, the tone mapped picture should be gamma corrected.
Using a proper linear workflow does not mean we can skip the exposure adjustment (aka tonemap). The gamma correction is mandatory to adjust the monitor response curve, but the exposure step is just as important to produce pleasing images.
Download the Tone Mapping plugin: it's free
Download the filter here: After Effects Tone Mapper. If you have never installed Adobe Pixel Bender filters before, please refer to Adobe's instructions to install Pixel Bender filters for After Effects.
Otherwise, just copy the pbk file into your Pixel Bender folder and restart After Effects. The Simple Tone Mapper will be in the VFX Wizard menu group.
Max is a published author, has been producing commercial 3D animation since 1989, and his softwares have been sold in 31 countries around the world. He has taught compositing and animation both online and in classrooms. Anybody who has seen Big Bang Theory refers to him as Sheldon — he thinks it's a fair comparisons but doesn't quite get why it's supposed to be funny.