Putting HDMI RS Sky in C4D: A Deep Dive into Redshift Sun & Sky and Sky Models

Redshift’s Sun & Sky system provides a physically based environment that integrates Sky models, horizon control, ground blur, and sun/moon rendering to create realistic outdoor scenes in Cinema 4D. This article weaves together the key concepts from the provided material to explain how to implement and optimize an HDRI-like sky, work with the PRG Clear Sky model, and leverage the Node Editor and interactive rendering for efficient results.

Sky models and the PRG Clear Sky framework

Redshift supports a Physical Sky environment shader based on the PRG Clear Sky model from the paper "A Fitted Radiance and Attenuation Model for Realistic Atmospheres" which improves upon the Hosek-Wilkie sky model. This option lets you pick between three different sky models. Each sky model has a unique sky rendering model, however, the two legacy sky models (Hosek and Preetham) share the same direct lighting model. PRG Clear Sky uses an updated direct lighting model. This describes the haziness of the air, or a measure of dust particle pollution. Only works with Hosek-Wilkie and Preetham et Al sky models.

The darkness or color of the sky is influenced by the ozone parameter, which describes the amount of ozone in the atmosphere, with values ranging from 0.0 to 1.0. The default is 0.35, which is commonly used for the Earth's atmosphere. Smaller values increase orange hues in the sun disk and glow; larger values push toward blue tones. The horizon can be adjusted to depict views from elevated locations, such as mountain tops.

Horizon, ground blur, and color controls

This section describes how you shape the boundary between sky and ground:

• The Horizon position control adjusts where the sky meets the ground, useful for elevated viewpoints.
• The Ground Blur control determines how much the ground blends with the sky at the horizon. The default is 0.1. A value of 0.0 yields a hard horizon line, while higher values blur the boundary for a more natural transition.
• The Ground Color control sets the ground’s albedo, influencing mood and overall GI without physically existing as a surface property, yet affected by atmospheric effects like the sun and air haze.
• The Night Sky Color control adjusts the color of the sky after the sun’s influence recedes. This is important for night scenes where the sky color remains even as daylight fades.

Color and saturation adjustments

The sky and sun can be tinted and balanced to achieve warm or cool atmospheres. The Sky Hue shift nudges the sky toward warm or cool tones. Saturation tweaks influence how intense the sun and sky colors appear, with a global saturation parameter that can affect red-blue shifts and sun tint. A subtle color-tint around the sun adds atmospheric glow, while a white tint results in no color shift.

Sun disk, glow, and sun/moon interaction

The sky shader includes a sun disk whose size and shadow softness can be tuned. A glow around the sun enhances atmospheric realism. The Sun & Sky system also supports both sun and moon rendering, with color tinting and a glow to add depth to daytime and night scenes. The Moon’s illumination is tied to the Sun’s intensity and phase, meaning the moon is bright but rarely sufficient to light the ground on its own in night scenes.

Positioning and rotation of celestial bodies

Position controls include:

• Sun altitude (vertical position) determining whether it is day or night.
• Sun azimuth (horizontal position) affecting the sun’s path and, correspondingly, the moon’s appearance when paired with moon direction.
• Moon directional vector controls and the moon’s intensity and size, which influence the softness of shadows on the Moon and its overall brightness.
• Time and Location settings with North Offset to align True North and time-based sky changes.

Interactive rendering and workflow optimizations

Redshift offers several pathways to speed up feedback while iterating scenes:

• Interactive Rendering (IPR) in the viewport from the Redshift menu provides real-time previews as you move the camera, objects, or tweak materials.
• Redshift RenderView can render in a separate window if preferred, with the ▶ button to start rendering.
• The Redshift Realtime engine (RT) is a faster mode than IPR, though it currently lacks full feature support (e.g., volume rendering) but can deliver lower noise for standard materials.

To begin, ensure Redshift is installed and enabled in Cinema 4D: check the Redshift Preferences in the Cinema 4D Preferences window, and set Redshift as the active renderer in the Renderer Settings window. Then create a simple scene to explore the Node Editor for materials, using the Jade preset as a starting point for the base material properties.

Node-based material creation and shader networking

Redshift uses a Node Editor to build materials. The Material Editor can be opened from the material’s preview or via the Node Editor, which appears in a separate window with the primary nodes (Material node, Output node) visible. The Asset Browser provides access to all Redshift nodes; you can double-click a node to add it to the Node Editor and connect ports by dragging connections between left (inputs) and right (outputs) ports. This allows you to tweak color, texture sampling, and lighting contributions by routing nodes through the graph.

Practical tips:

• Access full material options by opening the Node Editor and the Asset Browser.
• Adjusting the Diffuse, Specular, and other material properties is done by selecting nodes and editing parameters in the Attribute Manager.
• Use texture sampling nodes to bring in external textures and plug them into the RS Material’s inputs for base color and other channels.

Lighting and camera setups for realistic scenes

For proper exposure in daylight, reduce the camera exposure (EV) to compensate the sun’s strong intensity. The default EV of 0 often results in blown-out renders; around EV -4 to -5 yields more natural daylight. The Sun & Sky system provides a physically accurate light intensity that can be scaled or toggled between physical and non-physical intensity modes. When Non-Physical Intensity is enabled, you may avoid extreme adjustments to exposure while retaining a visually pleasing result.

The Sun & Sky system behaves similarly to a Dome Light in terms of practical workflow, offering the same light parameters like contribution scale and light linking. The horizon, ground blur, and atmospheric haze interact to deliver believable outdoor lighting, with the ability to render both day and night conditions seamlessly.

Tables and practical considerations

Practical tips for HDMI RS Sky in Cinema 4D

- Start with the PRG Clear Sky model if you seek a physically grounded daylight scenario and adjust ozone and haze to taste.

- Use horizon and ground blur judiciously to avoid a too-soft seam between sky and floor, especially on distant landscapes.

- Balance sun tint, disk size, and saturation to achieve the desired mood; remember the sun’s color shifts with horizon position.

- Leverage the interactive rendering features (IPR and RT) to iterate quickly on lighting, material, and camera settings without long re-renders.

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