Abstract images with Houdini

Discover how Niels Prayer’s creates abstract images with Houdini and Mantra…

Storm is an abstract piece created in Houdini and rendered in Mantra. The power in using a software like Houdini is that it’s an FX-oriented package. You can really control every step of process and procedurally modify and customize during the process of creation. It’s a really pleasant way to work, having the freedom to make modifications at every step without destroying anything you’ve built. This image is a great example of the power of this way of working. When I start a project like this one, I have an idea, but I know it will evolve thanks to the procedural approach of this software. The FX-oriented aspect allows you to easily generate really fun effects in combination with others; for example, having particles, curves, fluids and pyro effects in the same scene. It doesn’t matter if you don’t have any model or setup; you can go from scratch to an abstract piece in few hours, from idea to final render.

In this making-of, you will see how I’ve managed a particle system to create trails and metallic curves in conjunction with spheres to create an abstract flower shape. I’ve also played with effects such as smoke and detailed particles to frame the image and create the overall mood. Finally, we’ll cover the lighting and rendering steps and how I’ve put the final touches in compositing to fine-tune the atmosphere. Thanks for reading and I hope you like it!

Step 01: Particle SOP

For this particular scene, I wanted to have a dark, cloudy mood and play with the contrast of textures and shapes. The opposition of materials, such as clouds and metallic shaders for instance, is a great way to create detailed depth in an image. Playing with lighting, specular highlights, bouncing lights, and create eye-catching details will put your image in another dimension. The viewer is really sensitive to details in an abstract piece, so you have to create catchy elements! Even if it’s a poetic vision, in my opinion, you have to put a notion of reality that the viewer can identify with.

First, we start with a particle system done with a Particle SOP (Surface Operator). With some custom forces made with metaballs and turbulences (directly into the Particle SOP node), I’ve created this pattern to fit my composition. I wanted to create a squared ratio image, with an organic shape rising up, so I’ve generated my particle system more on the Y and Z axis than the X axis. With a really tiny focal length, it will be really effective when I add the depth of field in comp.

Particle system generation to create an abstract and organic shape fitting the framing questions

Step 02: Converting to curves

To create these trails, I converted my particles into curves. When I generated my points, I simulated some main particles and, with a Solver SOP, I merged the previous and next frames of the simulation to create nice trails of particles. In my simulation, I added an “id” attribute on my points so I could get the point numbers and generate curves on each trails. For that, I used an Add SOP in Polygons and “id” for attribute group method. I now have nice curves trails following my particle simulation.

Creation of curves trails following the particle system

Step 03: Converting to polygons

I knew for this image I wanted some rough metallic shapes for the curves. The problem was that my trails were just some NURBS curves, so I wouldn’t be able to apply the textures for roughness or reflectivity later in Mantra. I needed to convert them to polygons and create a basic UV system. So I used a Polywire SOP to convert the curves into polygons, and generated basics UVs with a UV Texture SOP. This meant I could add details to my trails’ material for the shading process later.

Convert the curve trails into polygons to add more details at rendering time

Step 04: Converting to polygons

At the beginnings of the trails, I wanted to have a sphere to give a floral look to this abstract shape. When I simulated the particles, I grouped the main ones with a Group SOP for this step. With a Copy SOP and a couple of random expressions (for the size, mostly) in the stamp attributes, I put some spheres randomly at the beginnings of my trails. This gave me the final flower-like appearance I wanted for these trails.

Adding some spheres at the beginning of the trails

Step 05: Creating extra details

For this type of image, I like to play with contrast of shape, textures and materials. I felt my composition was a little simple at this stage, so decided to generate some particles around my main shape, using spheres added with a Copy SOP, to get better framing. Later, to contrast with the solid aspect of the trail flower, I’ll put a glass shader on these spheres to add something light and fragile.

Creating of levitating spheres to obtain a better framing for the image

Step 06: Using Pyro FX

Now the fun part! Smoke! Since the beginning, I knew I wanted a dark, cloudy atmosphere for this image. To create these cloud shapes, I used Houdini’s Pyro FX, which is a really powerful tool. With a little tuning, you can make something really cool with a lot of control over your shape. I have two emitters (standard sphere) with a lot of turbulence at emission. On my Pyro FX, I have a lot of swirl with a large amplitude to get those nice rounded shapes. Of course, I put a heavy density in my smoke, to get a really opaque aspect later in lighting.

Creation of the clouds using the Pyro FX tool

Step 07: Shading and lighting

For the lighting, I used two kind of lights. First I set my environment with an HDRI map using the environment light tool. With that, I got an initial mood for the scene, ready to go further to adjust details. I added an area light on the top left to reveal a lot specular on my trails and spheres, and to get really good shadows in my smoke clouds.

For the shading, I used Mantra surfaces for every shader. I created a metallic one for the flower trail, with a little noise in Displacement and Roughness to obtain a really interesting render. As I mentioned earlier, I used a glass shader on the levitating spheres and finally a Billowy Smoke shader for the clouds with a colored ramp in the density attribute.

Lighting and shading the scene, and choice of materials

Step 08: Compositing and post-work

Final step, compositing! For the background, I used a custom HDRi map, really blurred to give a cloudy sky feeling in the scene. I put a glow on the really bright specular and desaturated the overall image a little bit. With the depth of field, I got a lot of nice bokeh in the front. In combination with a little flare, I use God Rays on the smoke to give a final stormy effect. Playing with the contrast and the size of the depth of field, I adjust the final mood of my scene to get this stormy abstract effect.