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:
EXR player: It is recommended to use this method in the ICVFX process, and it is much more convenient to read EXR files in UE5.1 and later versions. However, the biggest disadvantage is performance issues as EXR files are CPU-intensive. It is recommended to only have a maximum of 3 EXR players in the scene at the same time (maybe more in the future). You can refer to the following link for the actual process: https://www.youtube.com/watch?v=WLON4-lKQDM&ab_channel=On-SetFacilities
Flipbook: It has very lightweight performance and can exist in large quantities in the scene. However, since flipbooks use single-frame textures, the disadvantage is also obvious in terms of resolution and duration. The texture format will be further explained later.
How to create flipbook?
- Started with sequence images
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).
Create an Image Network in the Img menu.
In Image Network, use the Img menu to create an Image Network, and then use the file node to load your sequence image files. At this point, you should be able to see the animation playing in the file node.
Set the row and column numbers of your image sequence in the Mosaic node. Here, we use 64 frames as an example.
After setting up the Mosaic node, click on the "display" button to see the assembled sequence image. Sometimes it may not display properly, but switching between the 0th and 1st frames should fix the issue. Since it is a combined image, there should only be one frame (64 frames compressed into one frame).
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.
Add ROP node
Setup render settings
Finished
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.
Edited by Yi Chung Chen, Yung Jie Huang
Last Update: March 22, 2022
Software: Houdini 19.5
OS: Windows 10
Reference::
Houdini Mosaic Compositig Node https://www.sidefx.com/docs/houdini/nodes/cop2/mosaic.html
Make Animation Loop https://www.youtube.com/watch?v=RJ-CXK3B9WY&ab_channel=ChristianM%C3%B6hrle-ThePhlogPhotography