How to Render in Less Time

Decreasing render time

There are many ways for decreasing the render time of project, this tutorial will explain how I've textured, lit, rendered and composited my projects. This will be very useful for people who don't have powerful computers and also people that do.

I will be using and focusing on Maya for this tutorial, but I guess every 3D creation software has some kind of layer and attributes system.

About layers - part 1

Layer rendering is really useful, especially when you have many computers as you can assign different scenes to each one.

At the beginning of your project, assign a layer to every model or group of models in your scene. I've created a layer for a low-poly version as well as the high-poly version of the model, this is so I can turn off the low poly model and the high-poly models will remain visible. Also I've created a layer for the ground, and another one for the walls or other object in the scene.

About the Textures

When I create textures, I try to work to a size of 1024x1024 files for full shots, medium shots and close ups. It's not necessary you do this, so you could also create 512x512 texture files, so depending on the shot, assign either one or the other texture file. Also, I tend to always save my textures out as targa files.

Transparency mapped materials and close ups will increase render time and combine this with ray-tracing and your computer will be very busy for a very long time.

About the Lights

Animate your characters and then proceed to lighting your scene. Enter the Rendering mode in the menu.

By pressing the number 7 key, you will be able to see an illumination preview of you scene. This can help show you, more or less how your scene is illuminated, if you move a light you will see what is being illuminated by that light and how the illumination changes.

Without illumination preview

Without illumination preview

With illumination preview pressing 7 on keyboard

With illumination preview pressing 7 on keyboard

I have made only one or two of my lights, cast shadows. If you have many lights producing shadows your render time will also increase loads.

By adding more lights, the scene will become brighter and brighter, so I've assigned my lights to certain objects within the scene, which will then leave my shadow-producing light to illuminate all the objects. I've also disconnected the lights and objects apart by selecting both the light and the object, which I don't want this light to illuminate, and then click Break Light Links under the If Lighting/Shading menu. Just remember to have the object assigned to a light or it will be just a dark shape without volume

About previewing the final render

Before proceeding to your final render you will have to test with a single frame. This will show you how much time it takes to render every frame and how your scene really looks.

You can use the Snapshot and Render Region functions in the render view to preview the wireframe and, render only a region of the image.

This is useful because IPR doesn't support Mentalray and Raytrace. I use IPR mostly to see how the bump looks for my textures

About the Render Settings

Go to the Render Settings, if you are rendering with Maya Software, go to the Maya Software Tab and set Production Quality and Gaussian Filter Type options in their corresponding field.

With illumination preview pressing 7 on keyboard

With illumination preview pressing 7 on keyboard

Under the Common Tab, set the image and pixel size. If I was using this project for TV, I can use these setting to get the correct size required: 720x480 and Pixel Aspect Ratio to: 0.900. Remember to assign the camera you want to render, the image format, and the way you want sequenced file names to be created (I always render in my images as Targa files, because they include the Alpha Channel info).

Remember to check Alpha Channel to composite later

Now it's time to render : About layers (part 2)

When you are rendering your preview frame, you will notice that something is taking a long time to render. One of the best ways you can optimize time is by hiding some objects, you can then save different files to render these objects separately.

First save out a scene where all the scenery is visible, then turn off the character layers and then render it out again. Sometimes, I will only be requiring the ground, maybe just a wall or some other object, so render out each of these by going through the same process as above, but make sure you name each layer accordingly ground.mb, wall.mb or object.mb.

As well as the above, I will save a scene displaying only my characters, inorder to render them separately. The characters always take longer to render because they move and have way more textures attached to them than anything else in the scene.

About the Shadows

Sometimes, when the scenery render time is not too long, I render it out with the shadows, if by doing this it is affecting too much of the render time, render the shadows separately. This is how I do in both cases :

Case 1: Scenery includes shadows: To make the scenery, shadows and characters invisible:

  1. Access the object properties (in Maya press ctrl+A).
  2. In the 'render stats' section, uncheck the primary visibility stat of every character. Be sure the cast shadows stat is turned on

I will do this for every object that I want to produce shadows while they are invisible.

3. Render out the scene, and you will have your scenery with shadows moving in a single layer for your final composition.

Fig 10

Fig 10

Characters, shadows and background in one layer

Fig 11

Fig 11

Background and shadows only layer

Save a different file for your characters, this time turning the scenery layers off. Render the character layers and you will have another layer for your final composition.

4. Composite both layers in AfterEffects or any other similar software, capable of importing sequenced image files and reading the Alpha Channel of the Targa files.

If rendering the shadows and scenery together, is still taking too much time you can render your shadows in a separate layer. To render shadows separately follow the next steps.

Case 2: Shadows - only layer: To render shadows only

  1. The object that is casting the shadows should have the primary visibility stat unchecked. Maybe also you could uncheck the visible in reflections and visible in refractions stats too.
  2. The object that receives the shadows needs to have the Receive shadows and Primary Visibility stats checked.
  3. Assign a Use Background material to the object that receives the shadows, this material allows you to disappear the object but still receive the shadows.

Fig. 14

Fig. 14

If you view the alpha channel of the object you will see the shadows.

Alpha channel of shadows layer

Alpha channel of shadows layer

4. Import into your composite project between the scenery layer and the characters layer.

When you want to hide something behind an object, for example, if your character is holding an object and you want to render both character and object separately, you should set 0 reflectivity, reflection limit, and shadow mask in the Use Background material attributes. This will create a hole in RGB and Alpha channels.

Experiment and find which way of rendering best suits your needs.

If your camera doesn't move, you can always render just one frame of your scenery, a complete sequence of the moving shadows and a complete sequence of the moving characters.

About compositing

Now that you have your final rendered layers it's time to merge them together.

For this you will need any compositing capable software like Adobe After Effects or Adobe Premiere. This software can import image sequences and respect the alpha channels.
This step is really easy:

  1. Import your images as image sequence and premultiplied matted if asked
  2. Drag the sequences onto your time-line
  3. Place them in order
  4. Render again as a Targa sequence or movie file

Before rendering you will be able to correct the colour, brightness, contrast and other attributes of your layers, add effects or multiply a layer many times.

Combining your 3D and compositing softwares allows you to correct or create things that could lead to prolonged render times with your 3D software alone.

Hope you find this tutorial helpful

Fetching comments...

Post a comment