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Jar Contents: Filters

Camera Filters are 2-D image processors that AoI applies to images at the end of the rendering process. To be honest, it's probably better to do this sort of post-processing outside of AoI. It's easy enough to throw together a script that processes the frames produced by AoI, and then assembles them into an animation or video file, using any of a number of free and commercial tools (I tend to favor netpbm and the GIMP for image processing). But sometimes it's more convenient (and fun) to just have AoI apply the filter automatically --especially when rendering a test animation directly to a Quicktime file.

The filters included here are probably more fun than they are useful. But hey, fun is what AoI is all about!

To apply a filter, select it from the FILTERS menu in the AoI camera dialog. Note that the order in which the filters are added is important. The output of the first filter is the input to the second, and so on.

One more thing; most of these filters can't be controlled via Pose tracks. This means what whichever parameters you set in the filter will remain in effect throughout an animation.
ColorEdge Filter
This is an implementation of Prewitt's Compass edge detection algorithm. The algorithm works by detecting intensity changes, and so is really intended for grayscale images. But I like the effect it has on color images as well. Because it is an edge-detecting filter, you may find that aliasing is more noticeable after running this filter.

Emboss Filter
This is an implementation of the emboss algorithm that's used in the GIMP, which I believe is itself based on something in one of the Graphics Gems books. As with other edge-detecting filters, you may need to turn the anti-aliasing up in AoI to achieve satisfactory results.

Invert Filter
This is probably the simplest image filter there is. It just inverts the color of each pixel in the input image, resulting in a "color negative" of the original image. For some reason, I continue to like this effect (I think it's kind of spooky!), so I added it.

Highlight Color RGB Filter
This filter converts all colors in the image to shades of gray except for the specified "highlight color".

Add Text Filter
This filter superimposes the specified text over the bottom of the image. This feature may be useful for annotating test renderings and animations, and even for adding "subtitles".

The latest version of this filter allows the user to specify an input file containing a "script" of caption text that should be added to the output frames at the specified times.

The format for the captions file is very simple. Each line in the file contains a start time, followed by a single space, followed by the text of a caption. Once a caption is activated, it will remain "on" until the animation ends or until it is explicitly replaced by another entry. To remove a caption, just add an entry with no caption text at the desired time.

The following example was used to generate the caption in my Talk To The Hand IRTC animation. Note that at the beginning of the animation, an empty caption is specified, so no text is displayed until the 27 second mark, at which time the letter Y is added. This text is added to every frame until the 31 second mark, at which time it is replaced by the text YO, etc.. Check out the animation to see the effect of this.

Example file
000.000
027.000 Y
031.000 YO
035.000 YOU
041.000 YOU H
045.000 YOU HA
049.000 YOU HAV
053.000 YOU HAVE
059.000 YOU HAVE W
063.000 YOU HAVE WO
065.000 YOU HAVE WON


A note about fonts
The current version of this filter uses the system default font. Because different systems may be using a different default font, different physical fonts may be used depending on the system on which the image is rendered. This can lead to unsatisfactory results when rendering the frames of an animation across multiple machines, say via a render farm.


Spotlight Filter
This filter simulates a spotlight focused on the center of the image.


Camera Filter Examples:

Unfiltered Image Color Edge Filter Example
Unfiltered Image Color Edge Filter
Emboss Filter Example Invert Filter Example
Emboss Filter Invert Filter
HLC Red Filter Example HLC Green Filter Example
Highlight Color Red Filter Highlight Color Green Filter
HLC Blue Filter Example Add Text Filter Example
Highlight Color Blue Filter Add Text Filter
Spotlight Filter Example Another Spotlight Filter Example
Spotlight Filter Another Spotlight Filter Example

The sample scene used here is by Nathan Ryan.