Houdini 19.5: Flipbook

Why do we use flipbook?

Real-time rendering is required in both VP and XR, but some special effects such as explosions, dense smoke, crowds, and water simulations have large file sizes and are difficult to render in real-time.

Referring to the traditional special effects production process, the huge files simulated by the special effects team are not passed to the compositing team, but are submitted in the form of an EXR sequence image file (only one layer). Therefore, in the case where the camera position is determined and there will be no major camera movements, it is a very efficient method to place sequence image files in the scene. 

Currently, there are two ways to use sequence image files:

flipbook01.mp4

How to create flipbook?

Sequence images can be rendered in any software or purchased online. Since flipbooks loop continuously, it is important to ensure that the head and tail of the video material can be seamlessly connected. This can be achieved by setting the loop parameters in DDC software or by using video editing software like AE to blend the head and tail together (usually done with alpha blending) (https://www.youtube.com/watch?v=RJ-CXK3B9WY&ab_channel=ChristianM%C3%B6hrle-ThePhlogPhotography). 

2. Image sequence formats

Common sequence image formats include the following 4 combinations:

3. Create image sequence in DCC software

Currently, the simplest way to combine sequence images is through the Mosaic node in Houdini (if there are simpler ways in the future, they will be added later).

DEBUG: There may be cases where the Mosaic node cannot read the combined image. In such cases, make sure that the sequence image files are numbered starting from 0, and also check if the image files can be read properly in other software. Some software, such as Nuke, may be more tolerant towards image formats, but they may not be read correctly in Photoshop or Houdini. In such cases, the image files may need to be converted to a different format.

Other examples

The use of flipbooks is not limited to explosion effects and sprites. Its essence is that of a Material and should be viewed as a low-performance consuming special effect creation method. Here is an example of its use in water simulation. 

ripple.mp4
water.mp4

Edited by Yi Chung Chen, Yung Jie Huang

Last Update:  March 22, 2022 

Software: Houdini 19.5

OS: Windows 10


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