Typically you render in passes to render various attributes, such as color, shadows, highlights, of your scene separately. You can fine-tune a scene without re-rendering it by modifying different passes in a compositing program.
It produces a complete rendering of the components produced by a shadow pass and a color pass. Because the color pass produces a complete rendering of the components produced by a diffuse pass and a specular pass, a beauty pass ends up producing a complete rendering of all possible components.
Only specular shading is performed. The specular component is modulated differently depending on the type of material associated with the object. Phong, PhongE, Blinn, and Anisotropic materials produce specular contributions differently. On a Phong material, the specular pass can be modulated using cosine power, and specular color.
You can also create custom shadow and reflection passes with the useBackground material which catches shadow and, or reflections. When the shadow pass is rendered, a black image is created with mask channel that contains the shadow information. A compositor can work with this channel to blur, lighten, darken, and so on, the look of the shadows. When the reflection pass is rendered, an RGB image is created with a white mask in the mask channel.
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