
SkyCast

Introduction

Skycast is a new lighting utility for Animation Master 10.5.  It samples the colours of a spherical or hemispherical image and then applies those colours to a variety of spinning light rigs which allow fast, realistic rendering of diffuse light. The rigs themselves consist of a one or two light model and a corresponding action which can be loaded into your Animation Master projects.
Skycast lights can be used to light a scene quickly and very effectively.  In a traditional 3 point lighting setup they can effectively replace ambient and fill light. TwinSkycast lights can be used to quickly light a scene.

Theory

The rigs generated by Skycast are based on the spinning light trick popularised by Meni Tsirbas of Lightwave fame.
Rather than creating a skydome or sphere using 9 to 50 low intensity lights, Skycast rigs use one or two high intensity lights and repositions and rotates them rapidly in subframes. Because each subframe of a multipass render is averaged the bright lights create an effective dome or sphere of low intensity lights, without the rendering penalty associated with a large number of lights.
The path of the generated action is jittered rather than spun, minimising DOF and Motion blur artifacts. 

The Rigs
Skycast currently generates four different rigs for three different multipass settings

SkyDome
The Skydome light is designed to provide a hemispherical diffuse light source. Because the skydome light spends 50% of it's time shining from behind the object it can only provide an accurate colour at 50% intensity.
It's designed to replace/simplify ambient and fill light. 
Skydomes are generally used for objects on the ground which receive a large amount of difuse light from the sky.

Skysphere
But what happens if you're not on the ground. Diffuse light comes from all angles, and when we were approached to animate an aircraft for a set of titles for Australia's Royal Flying Doctor Service we created our first skysphere.
The Skydome light is designed to provide a spherical diffuse light source. Because the skydome light spends 50% of it's time shining from behind the object it can only provide an accurate colour at 50% intensity.
It's designed to replace/simplify ambient and fill light, including the light reflected back from the ground.
To use the skydome on a scene with a ground plane set the ground plane to no cast shadows.
 
Twin Skydome
Twin skydomes use two lights to enhance the intensity of the skydome.   
Unlike Skydomes and Spheres, Twin Skydomes and Spheres can be used as primary illumination. They also project twice as many shadows providing smother illumination.

Twin Skysphere
Twin skydomes use two lights to enhance the intensity of the skydome.   
Unlike Skydomes and Spheres, Twin Skydomes and Spheres can be used as primary illumination. They also project twice as many shadows providing smowother illumination. with a twin skysphere Light 1 rotates around the top hemisphere and Light 2 rotates around the bottom hemisphere. This allows you to quickly alter the intensity and shadow casting properties seperately.

To create a Skycast light.
*  Select a light model(dome, sphere, twinDome or TwinSphere) under the lighting rig options.
*  Select the multipass render option that you will use in AM from the multipass dropdown. 
*  Click on the load image to select an image as a base for the skycast rig. The image will appear in the image panel at the top of the application. ( A small selection of Dome and Sphere images is included with the beta).
* Click on the Create button and the image will be replaced by an approximation of the light colours, a file requestor will open for you to save the action file.  At this point you have to type in the .act file extension.

To use the Skycast model in Animation Master

In AM load the skycastlight.mdl or skycasttwin.mdl into your project and load the action generated in the previous step.
Depending on the type of Skycast action generated above add either the Skycastlight or Skycasttwinlight.mdl to your choreography at the centre of the scene. Import the Skycast action created above into your project and drop it onto the skycast model. Go to the file section under the properties of the model and action and embed them into your file. 
Under the action properties in the choreography set the cycle length of the action to match the motion blur setting you are rendering with.  Ie for 100%MB set the cycle length to 1 frame, for 50% set the motion blur to .5, for 20% to .2 and so on. Motion blur must also be turned on to a number which is evenly divisible into 100.(100,50,25,20,10,5,2 and 1 are valid motion blur settings.
Then set the number of repeats on the action to cover the length of your choreography.
Alter your light settings to the correct level under the item shortcuts. Depending on your scene you may want to scale the skylight model, change the type of the light(sun, klieg or bulb), and/or alter the light intensity and falloff.
Add addition key, rim, fill and specular only lights to complete your scene.  If your scene features reflective objects the skycast image can be wrapped onto a sphere to provide a reflection consistent with the skylight.
Render with multipass turned onto the appropriate setting.  

Generally the things that effect your render.

Single bone skylights are for ambient light only, they need a key light because as 50% of the time they are behind the object they come in at half the light level of the actual light setting. If you boost the light level above 100% it increases the level of illumination but greys the image.
Twin skylights can be used for general illumination and depending on need we may add triple's to the list.
If you alter the light type to kleig or bulb you may need to play with falloff.
The multipass render setting in Animation Master has to match the the Skycast multipass setting chosen.  Because each Skycast rig is designed for a particular rendering scenario, use of the wrong rendering settings can lead to unpredicable and downright ugly renders.

Creating Spherical Panoramas
Skycast uses spherical and hemispherical panoramas as input images.
We use two methods one for generating spherical panoramas from digital photographs and another for generating spherical panoramas from Animation Master Scenes.

Creating Panoramas using a Digital Camera
The most economical and easiest is with a digital camera, a chrome ball(available from good gardening/landscaping shops) Flaming Pears free Ornament plugin.

Creating Panoramas using a Animation Master
They can also be generated from an Animation Master scene using a rotating camera.


Bug Reports
Skycast has been used in production at Artbox for several months without issue, but it is still in beta. We will attemp to fix any bugs as soon as we find out about them.
Please email johnh@artboxanimation.com including skycast bug in the message.

