Katana Fastrack episode 04 by Xuan Prada

Katana Fastrack episode 04 is already available.
In this episode, we will finish the Ant-Man lookDev by tweaking all the shaders and texture maps created in Mari.

Then we will do a very quick slapcomp in Katana and Nuke to check that everything works as expected and looks good. We will do this by render a full motion range of Ant-Man walk cycle. And finally, we will write a Katana look file to be used by the lighters in their shots.

Check it out on my Patreon feed.

Nuke IBL templates by Xuan Prada

Hello,

I just finished recording about 3 hours of content going through a couple of my Nuke IBL templates. The first one is all about cleaning up and artifacts removal. You know, how to get rid of chunky tripods, removing people from set and what not. I will explain to you a couple of ways of dealing with these issues, both in 2D and in 3D using the powerful Nuke's 3D system.

In the second template, I will guide you through the neutralization process, that includes both linearization and white balance. Some people knows this process as technical grading. A very important step that usually lighting supervisors or sequence supervisor deal with before starting to light any VFX shot.

Footage, scripts and other material will be available to you if you are supporting one of the tiers with downloadable material.

Thanks again for your support! and if you like my Patreon feed, please help me to spread the word, I would love to get at least 50 patrons, we are not that far away!

All the info on my Patreon feed.

Katana Fastrack episode 03 by Xuan Prada

Episode 03 of my Katana series is out. We are going to be talking about expressions, macros and tools to take our look-dev template to the next level. Right after that, we will take a look at the texture channels that I painted in Mari for this character and then we will start the look-dev of Ant-Man.

We divide the look-dev in different stages, the first on is blocking, and we are going to spend quite a few time working on this today.

All the info on my Patreon feed.

Introduction to Redshift for VFX, episode 01 by Xuan Prada

I'm starting a new training series for my Patreon feed, it's called "Intro to Redshift" for visual effects. I'm kind of learning Redshift and trying to figure out how to use it within my visual effects workflow, and I'll be sharing this trip with you. In this very first episode, I'll be talking about probably the most important topics around Redshift and the base for everything that will come later global illumination and sampling.

I will go deep about these two topics, sharing with you the basic theory behind global illumination and sampling, and I will also share with you a couple of "cheat sheets" to deal with noise and gi easily in Redshift while rendering your shots.

Check the first video out on my Patreon feed.

Cheers,
Xuan.

Katana Fastrack episode 02 by Xuan Prada

Katana Fastrack episode 02 is now available for all my patrons. I cover how to create a proper look-dev template to be used in visual effects. Everything will be setup from scratch and at the end of this lesson we will have a Katana script ready to be used. In lesson 03 we'll be using this script to do all the look-dev for Ant-Man.

In Katana Fastrack episode 02 you will learn:

- How to create master look files
- How to use live groups to create light rigs
- How to create a look-dev template for production

All the info on my Patreon feed.

Katana Fastrack episode 01 by Xuan Prada

Here it is, the very first episode of my series "Katana Fastrack", available to all my exclusive patrons.
This is an introductory video where I'm going to give you an overview of what this course is all about. I hope you like it, it is going to be a lof of fun!

You will learn:

- Where Katana fits in the pipeline
- The most important concepts of Katana's workflow
- How to prepare assets for Katana
- The importance of look-dev recipes
- How to create a very basic recipe

Check it out on my Patreon feed.

Patreon: Houdini as scene assembler: Bundles, takes and rops by Xuan Prada

In this video I talk about the usage of Houdini as scene assembler. This topic will be recurrent in future posts, as Houdini is becoming a very popular tool for look-dev, lighting, rendering and layout, among others.

In this case I go trhough bundles, takes and rops and how we use them while lighting shots in visual effects projects.

You will learn:

- Bundles, takes, rops
- Alembic import
- Different ways of assign materials
- Create look-dev collections
- Generate .ass files
- Create render layers
- Create quick slap comps
- Override materials

Check it out here.

Katana, constraint lights to an alembic geometry by Xuan Prada

One of the most common situations while lighting a shot is attaching a CG light in your scene assembler to an alemic cache exported from Maya. This is very simple to do in Katana, let’s have a look at it.
I’m using this simple animation of a car spining around.

01.gif

In most cases you need an object within the alembic cache that has the animation baked into it. The usual approach is to use a locator. To do so, snap it onto one of the lights geometry of the car and parent constrain it to the master control of the car. Then bake the animation of the locator and export it with the rest of the alembic cache to Katana.

In Katana, create a gafferThree node but do not place any lights yet. It is better to do the constraints first, if not you might have to deal with offset issues later on.
Use a parentChildConstraint node indicating the gaffer node in the basePath and the locator of the car in the target.

Now place both headlights according with the model of the car. If you press play they should follow the animation of the car perfectly.

04.gif

In case you forget to do the parentConstraint before adding lights to the gaffer, you might have to control the offset and compensate for it. To actually see the values you can add constraintResolve and a transformEdit to check the transformations.

Houdini as scene assembler part 05. User attributes by Xuan Prada

Sometimes, specially during the layout/set dressing stage artists have to decide certain rules or patterns to compose a shot. For example let’s say a football stadium. Imagine that the first row of seats is blue, the next row is red and the third row is green.
There are so many ways of doing this, but let’s say that we have thousands of seats and we know the colors that they should have. Then it is easy to make rules and patterns to allow total flexibility later on when texturing and look-deving.

In this example I’m using my favourite tool to explain 3D stuff, Lego figurines. I have 4 rows of Lego heads and I want each of those to have a different Lego face. But at the same time I want to use the same shader for all of them. I just want to have different textures. By doing this I will end up with a very simple and tidy setup, and iteration won’t be a pain.

Doing this in Maya is quite straightforward and I explained the process some time ago in this blog. What I want to illustrate now is another common situation that we face in production. Layout artists and set dresser usually do their work in Maya and then pass it on to look-dev artists and lighting td’s that usually use scene assemblers like Katana, Clarisse, Houdini, or Gaffer.

In this example I want to show you how to handle user attributes from Maya in Houdini to create texture and shader variations.

  • In Maya select all the shapes and add a custom attribute.

  • Call it “variation”

  • Data type integer

  • Default value 0

  • Add a different value to each Lego head. Add as many values as texture variations you need to have

  • Export all the Lego heads as alembic, remember to add the attributes that you want to export to houdini

  • Import the alembic file in Houdini

  • Connect all the texture variations to a switch node

  • This can be done also with shaders following exactly the same workflow

  • Connect an user data int node to the index input of the switch node and type the name of your attribute

  • Finally the render comes out as expected without any further tweaks. Just one shader that automatically picks up different textures based on the layout artist criteria

Houdini as scene assembler part 04 by Xuan Prada

Let’s talk a little bit about cameras in Houdini. Most of the time cameras will be coming from other 3D apps or tracking/matchmoving apps. The most common file format then it would be alembic. Apparently alembic cameras are not very welcome in Houdini, don’t ask me why, but there are certain issues that might occur. In my experience most visual effects companies have their own way to import alembic cameras.

I have never used fbx cameras in a professional environment but I have done a few tests at home and it seems to work fine. So, if you get weird issues using alembic maybe fbx could be a solution for your particular case. Go to file -> import to do so.

To create cameras in Houdini use the camera node. Here are some important features to consider when working with cameras in Houdini.

  • If you need to scale the camera, not very common but it can happen, do not scale the camera itself, just connect a null to the camera and transform the null instead.

  • Render resolution is set in the camera attributes. It can be overwritten in the ROP node but by default it uses the camera resolution.

  • There are different types of camera projection, perspective, orthographic, etc. There is also a spherical lens preset in case you need to render equirectangular panoramas.

  • Apperture parameter is pretty much the same as sensor size, this is very useful when matching real cameras (always in vfx)

  • Near/far clipping, same as every 3d app, important when working with big/small scales.

  • Background image: It places an image in the background that actually gets render. Usually you don’t want this to happen for final rendering. If you disable this option, the image won’t be visible during render time but it still will be visible in the viewport. Use the below icon to disable it.

  • To see safe areas go to display -> guides (display is d key).

  • Sampling parameters

    • Shutter time: Controls motion blur

    • Focus distance and f-stop: Control depth of field

    • To see focus distance, select the camera and click on show handle

Houdini as scene assembler part 03 by Xuan Prada

In this post I will talk about using texture bitmaps and subdivision surfaces.
I have a material network with a couple of shaders, one for the body of this character and another one for the rest. If using Arnold I would have a shop network.

To bring texture bitmaps I use texture nodes when working with Mantra and image nodes when working with Arnold. The principled shader has tabs with inputs for textures. I rarely use these, I always create nodes to take care of the texturing. At the end of the day I never use only one texture per channel. More of this in future posts.
In Mantra, textures are multiplied by the albedo color. Be careful with this.

With Mantra, this is the UDIM tag textureName.%(UDIM)d.exr with arnold textureName.<UDIM>.exr

There is a triplanar node that can be used with Arnold and a different one called UV triplanar projection for Mantra. I don’t usually work without UVs, but these nodes can be useful when working with terrains or other large surfaces.

To subdivide geometry, at object level you can just go to the Arnold tab and select the type of subdivision and the amount. If you need to subdivide only a few parts of you alembic asset, create an unpack node (transfer attributes and groups) and then a subdivide node. This works with both Mantra and Arnold, although there is a better way of doing this with Arnold. We will talk about it in the future.

Houdini as scene assembler part 02 by Xuan Prada

In the previous post I showed you how to load alembic caches using the file node and then change the viewport visualization to bounding box. This is good enough if you are let's say look-deving a character. If you want to load a heavy alembic cache, like a very detailed city with a lot of buildings, or a huge spaceship, you might want to use a different approach.

Instead of using a file node, it is better to use the alembic node to load you assets, and then set the option Load As: alembic delayed load primitives, and display as bounding box. This isn't actually loading the geometry in memory and it will be way more efficient down the line.

In this post I'm just talking about shading assignment in Houdini.
The easiest and more simple way to assign shaders is by selecting the asset node in the /obj context and assign a shader in the render tab. Your Mantra shaders should be placed in the /mat context and your Arnold shaders in the /shop context as /mat is not fully supported yet.

In the /mat context you can just go and create a Mantra Principled Shader. For Arnold, it is better to create an arnold shader network and then any arnold shader inside connected to the surface input.

Houdini doesn't have an isolation mode for shading components like Maya (as far as I know) but you can drag and drop shaders and textures onto the viewport or IPR while look-deving. This only works in the /mat context (again, as far as I know).

Another way of assigning shaders is creating material nodes inside of the alembic node. This material nodes can be assigned to different parts of your asset using wildcards. To assign multiple materials you can create different tabs in the material node or you can just concatenate material nodes (which I prefer). This technique works with both Mantra and Arnold.

You will find yourself most of the time creating material networks (Mantra) or shop networks (arnold) containing all the shaders of your asset. In a lighting shot you will end up with different subnetworks for each asset on the shot.
This subnetworks of shaders can be place at the /obj level or inside of the alembics containing your assets.

Another clever way of assignment shaders is using the data tree -> object appearance. This only works at object level. If you want to go deeper in your alembic asset, you need to add first a node called packed edit. Then in the data tree you will have access to all the different parts of your asset.

There is another way of controlling looks in Houdini, and that is using the material style sheets. We will cover this tool in future posts.