Houdini Week4
Render in Houdini
Render in Houdini will use the linear workflow, the image below shows how the workflow will look like, it can be divided into 5 parts, input, conversion, calculations, outputs, and viewing.
the input data will be your assets source image. and the ACES is a color system that’s meant to standardize how color is managed from all kinds of input sources. and provide a future-proof working space for artists to work in at every stage of the production pipeline.
ACES color system contains a larger gamut than the old SRGB color system, and it closer to how much color human’s eyes can see. (the black gamut belongs to the human’s eyes, and the purple gamut belongs to ACES, and the red Gumat belongs to SRGB)
the LUT viewer, ACESCG has its own viewer, we need to define the ‘viewing’ space, that we could view our object color like the color it will be rendered to. You’ll need to make sure that when you’re viewing or compositing your renders that you’re looking through the right viewer LUT that transforms your renders from ACESCG to sRGB or Rec. 709 or Rec. 1886 or whatever you’re into.
the next step is to convert your texture, we need to make sure the texture we use, is converted into ACESCG, You’ll need to apply what’s called an “input device transform”, or “IDT”, to these textures. because most of the texture we download online is SRGB.
when we are converting there is the main thing need to know is that only color can be converted don’t convert the normal or displacement and roughness.
to set up ACES in the application, you will need to download an OpenColorIO (OCIO) configuration,next part is to configuration your application. the writer introduce some common application like Maya and Houdini.
Render testing
first is to create geometry and create a testing object inside, go back to the geometry panel, and create light. you will get a scene like this.
go to the output panel and will see a mantra node be created. this node is used to check the render parameter.
To let the UI easier to control is to split the panel bottom and top, and drag the scene view down, and you will see the changes you made in the scene will react on the render view, like real-time.
if you want to lock your render view, is to create a new camera, and select the camera you create in render view. and the perspective will be locked.
HDRI light
using HDRI light in Houdini is to create an environment light. this node can use the HDRI file.
Click the Environment Map and import the HDRI file. but only Mantra can use the rat format file when using Arnold rendering should avoid the’. rat ‘ HDRI file.
the usual HDRI file will be ‘. hdr’, Houdini can read the hdr file as well.
In Houdini, we can make a point light into the spotlight. in the light parameter, you will see an option, enable spotlight.
Click that option it will turn the point light in to spotlight.
and we can also change different light types in type, the gird light(like the area light),
and the area attribute is to control your shadow opacity, the smaller the number is, the sharper your shadow will be.
the direction light like sunlight, spotlight, Distance light, and disk light, will take less time to be rendered in Houdini, is because the light only comes from the limited zone.
mostly we will use both light and environment light and remember setting the light come from the same direction.
from now the grid don’t have any texture, so we can create a material node under the grid.
and then go to the material interface
different render engine will use their own shader and mantra will use principle shader.
and then drag and drop this node to the grid. and we will see the result updating. this is one of the ways to add material to an object. another way to add an object material is to go to the obj and paste your node on the material blank, or you can go to the material node, and paste your shader node. the priority choice will be the shop matertial path.
Arnold rendering
To using Arnold rendering, will need to download and install the right version for the Houdini. After setting up everything, Arnold rendering option will showup on this place.
In the second render way we will use the ACES color to render the view, so installed the config of colorIO, now can render view in ACES color area.
Jump to the out panel and create an Arnold node, and click render. but the render view showing the toy is completely white, is because of the material. the shop material path not working with Arnold. It uses the principle shader which only works in mantra rendering.
we need to delete the unreadable material, create the attribute delete node, the principle shader is in the primitive attribute, so select it in the delete attribute node, the texture will go.
and then go to the obj option and right-click, another network, and select material to the toy. the material Arnold using, will need the Arnold material builder node.
what we need is to create a standard surface node. and then drag the material to the toy. now the material is successfully been applied.
The next step is to create the light, Arnold rendering will only using Arnold light.
we can choose what type of light we want and setting the angle to get a soft shadow.
the quad light also named area light, you can set it visible or invisible in your scene. in the camera, setting the number to 0, it won’t show up in your render view but still can illuminate the mesh.
How to use HDRI file in Houdini Arnold rendering
To using the HDRI file in Houdini Arnold rendering is to attach the hdr. file to the skydome light. select the color type to texture. and attach the hdr file to the color texture.
and we will see the light been set up.
how to attach jpg. texture in Houdini
create the image node in the material panel.
and then select rgba, and what I choose is the base color file so I going to choose the base color. remember to turn the auto-generate TX texture file.
but the texture still can’t show up normally, because my grid doesn’t have UV.
Create a UV project mode under the grid. to check the UV create or not, we can go to the UV view and click the display point to see how things go.
and now the wood material showup correctly.
another thing is to check the color display correct or not. because we are using ACES workflow, so there will be something that needs to be set up.
we can check the color information in the material, select the color space to Utility and Utility SRGB texture. but my image doesn’t have any change so it has the right color.
How to render the image
go to the output panel, and select output
we need to rename the output picture name. So I am going to call it. the main thing at this point is remembering to call it .exr
and then click render to disk, click the + button, I can check the render schedule in this place.
using Mplay to check the exr file, because when I am using Photoshop, the image color isn’t in the aces area. and this is how my render view looks like.
particles Arnold render testing
the first step to render the scene we will need to name the geometry. and make sure we using file cache.
and the next step is there are only particles we need the main character. create a geometry node. then go back to the particles geo, and grab the crag. copy it, then create an object merge node, and paste the file path in the object 1 box.
go to the output panel and create an Arnold render node.
and same as before we need to create Arnold light and Arnold material builder.
now the texture can be illuminated by the environment light.
at this time crag and hammer have the same material, Mehdi taught us how to use the group to apply different materials to the same object. go back to the object panel, and create a material node under the crag object node.
we can use the spreadsheet to check the name of the model has. we can select the group in this place. things can be set up like this.
to set up material in the same place. we can delete the material name here and then go back to the material panel.
create one more material, and type* ^before the hammer name, * means ‘all’, and ^ means ‘except’.
the interesting thing is about the crag material setup. Mehdi shows us how to use the node curvature. and add the ramp RGB to set up the color. and it can attach to the standard surface as the base color.
moving to the particles, connect the attribute vop to the out render node. at this time the particles don’t have the arnorld renderable shader so we need to give it a material like others.
and then copy this node and paste to the material block.
and we can setup the particle material. in the attribute panel. there is an attribute called IOR. I don’t know what is IOR means. and I found some good explanations in the SideFX community.
so I set the particles as 1.
The next thing is to use user data to set up the particle’s age, color, life.
the color needs to use user data RGB node.
motion blur
using Arnold to set up motion blur is in the output network. in the motion blur panel and select the transform keys and deform keys.
but the particle motion blur will need to set up in the geo node. and we can create a velocity node for adjust the motion blur.