Realization of Realistic Wave Effect in Houdini
under the Overlooking Angle
Jiani Zhou, Tae Soo Yun
Department of Visual Concents
Graduate School, Dongseo University
Busan, South Korea
This paper analyzes and summarizes the process of making realistic marine special effects through Houdini. According to the different position of the camera, the wave effect can be simulated by 2D plane when making the wave special effect with the overlooking angle. Compared with the traditional way of marine 3D, it simplifies the production process and effectively shortens the time required for later rendering.
Keywords-component; wave effect; the overlooking angle; Houdini
As a part of special effects, marine special effects play a very important role in many film and television works all the time. Because of its randomness and complexity, marine special effects require a lot of computation time to render through later software. In view of this phenomenon, this paper shows that when making realistic wave special effect under the overlooking angle, the three-dimensional effect of the waves can be expressed by the whitewater and mist visual effects. By changing the marine model from a 3D container to a 2D plane, this dimension reduction can effectively reduce the computational time required for rendering and maintain a high level of realism in visual effects. Through the use of special effects software Houdini to make realistic marine special effects under the overlooking angle, this paper analyzes and summarizes the workflow of marine special effects and brings the concept of overhead view angle into the production process, it further streamlines and refines the original production process, and puts forward an innovative marine special effects production idea.
2. Prior study of marine special effects
2.1. Marine special effects and production software
Nowadays, Maya and Houdini are the main after-effects software to make marine special effects. Maya can use built-in fluid systems and third-party plug-ins to make marine effects. However, due to the complexity and intelligence of the Maya fluid system, the third-party plug-in has become the first choice for Maya to make marine special effects, where Maya Bifrost is widely used as a simple and visually realistic plug-in. Maya Bifrost's production process can be divided into 1. creating liquid; 2. adding collisions and accelerators; 3. adding whitewater; 4. adjusting water material; 5. final rendering. From the making process of Maya Bifrost, it can be seen that the focus of this plug-in is to simulate the true texture of marine water, but there is no good solution to the details of marine fog, whitewater diffusion and so on, and it often needs to be assisted by other software . For example, Maya Bifrost does not have a wet map generator, it needs to use the echo special effects in after effect to make the effect of wave trailing. Maya Bifrost offers a solution for controlling the visual effects of waves by adjusting attribute values. This approach is easy to use, but it can be overstretched in response to complex marine scenarios.
Fig. 1 The Schematic Diagram of Marine special effect by Houdini
As a professional special effect software, Houdini has unique advantages in making marine special effects. Maya Bifrost has the same function as Houdini for creating the texture of the waves, at the same time, Houdini can also provide more abundant force field, as well as superimposed marine fog and whitewater splash to enrich and enhance the visual effects of the marine. This series of adjustments only needs to be done in the Houdini software (e.g., “Fig. 1”), in terms of the completeness of the production process and the richness of the final marine special effects, Houdini is more professional than Maya Bifrost, which is the reason for this paper to select Houdini as the after-effects software for making marine special effects.
2.2. Wave effects and lens angle
In the shooting of marine special effects, the camera lens angle can be roughly divided into two angles: side angle shot and high angle shot (e.g., “Fig. 2”). The high angle shot shows the vastness of the marine, while the side angle shot shows the surging waves. As can be seen from the figure below, the marine is divided into four parts: the volume, the surface, the whitewater, and the mist(In Fig. 3 red line is the marine surface, Dark blue under the water surface represents the ocean volume, light blue is whitewater, above the whitewater is mist).
Fig. 2 Real view of side angle shot(left) and high angle shot(right).
The distance between the camera and the marine surface is long in high angle shot, and the marine surface is made up of three parts: surface wave, whitewater, and mist. At the angle of the side shot, the camera is closer to the marine surface, so the camera will record not only the three parts of the surface but also the deep volume below the marine surface, especially when the waves immerse themselves in the camera, all levels of the waves will be recorded. It is precisely because of the difference in the recorded content caused by the difference in lens angle, in this paper, it is proposed that the special effects of marine waves do not need to have all the details as side shots, but can be simulated by making surface waves, whitewater and mist. In other words, only the surface of the marine is made and the depth volume of the marine is omitted, and the processing process is simplified by using the characteristics of the lens angle, thus reducing the time of making marine special effects.
Fig. 3 Camera position diagram of side angle shot(left) and high angle shot(right).
3. Using Houdini to make realistic wave effects under the overlooking angle
3.1. The process of making the special effect of the realistic wave under the overlooking angle
In Houdini, the process of making wave effects can be divided into nine steps, including 1. adding waves; 2. adding the motion of waves; 3. adding whitewater; 4. adding wind; 5. adding mist; 6. marine textures; 7. whitewater gridding; 8. mist textures; 9. final rendering (e.g., “Fig. 4”).
Fig. 4 The Schematic Diagram of Our Method.
3.2. Innovation in production process
In the traditional process of making marine special effects, it is often necessary to make the overall depth of the marine. Due to the particularity of the overlooking angle mentioned above, it is only necessary to understand the marine as a 2D undulating plane, and not to make the marine into a 3D shape with depth, the volume of the marine model has therefore been greatly reduced.
The three-dimensional sense of the marine at the overlooking angle depends on the whitewater.
Therefore, in the experiment, the distribution and simulation of whitewater have also been studied and explored. The marine surface material is also changed to basic liquid. And change the value of the refraction color and attenuation, so that the fluid gives people the visual experience in line with the size of the water created.
In addition, in order to meet a variety of environments, such as the shoal, the ground will be exposed through fluids such as the bottom of the beach, and Fig. 5 uses simple planes and textures to simulate this visual effect.
Fig. 5 The surface test result(left) and the top view(right).
This paper shown the marine special effects of the overlooking angle as the starting point, and proves by the example in Houdini that the deep volume of the marine can be neglected when making the special effect of overlooking angle, a 2D plane is used to simulate the effect of the marine, and marine surface, whitewater, and mist are added to the 2D plane to create a three-dimensional sense of the marine, and the texture of marine water and mist is further enhanced by the addition of shader. Because the overhead view is a commonly used camera angle, the process proposed in this paper is practical and innovative, which can not only simplify the original process of making marine special effects, but also save the time needed for rendering, and provide a new way of thinking for the making of marine special effects. In the future research, the research and exploration of ocean special effects and game engine connection made by Houdini will be carried out, and the realistic marine effects created by Houdini will be imported into the game engine. Since the application scene of the game engine in CG industry is increasingly abundant, if the ocean special effects made by Houdini can be successfully imported into the engine, it will be a very significant supplement to the special effects board of game engine.
 E. Darles, B. Crespin, D. Ghazanfarpour and J.C. Gonzato, “A Survey of Ocean Simulation and Rendering Techniques in Computer Graphics,” The Authors Computer Graphics Forum © 2010 The Eurographics Association and Blackwell Publishing Ltd. 2010.
 K.H Lee and J. Park, “A Survey of Ocean Simulation and Rendering Techniques in Computer Graphics,” Journal of the Korea Contents Association 14(8), 2014, pp. 13-21.
 H. Lee, Il-S. Koh, J. S. Yoon and T. H. Kim, “Criterion to Choose Efficient Far-Field Approximation of Dyadic Green’s Function for Impedance Plane like Ocean Surface,” Journal of Korean Institute of Electromagnetic Engineering and Science 28(2), 2017, pp. 147-154.