Color Spaces, Color Primaries, and Transfer Functions

Last updated 7 August 2026

Overview

What Is a Color Space?

A color space is a standardized way of describing color. It defines a mapping between numeric color values (for example, the red, green, and blue components in a digital image) and the color they represent in the real world. Common color spaces include:

  • sRGB – A standard for computer screens and the internet.

  • Rec.709 – Widely used in HDTV.

  • DCI-P3 – Common in digital cinema.

  • Rec.2020 – Defined for Ultra High Definition (UHD) and HDR workflows.

By specifying a color space, you ensure that the same numeric values (R, G, and B) refer to the same real-world color appearance, regardless of the display device—provided the device is correctly calibrated and respects that color space.

Color Primaries

Within a given color space, color primaries define the exact chromaticity (or coordinates) for the red, green, and blue channels. These primaries are typically standardized, so when someone refers to “Rec.709 primaries,” they mean the specific red, green, and blue coordinates defined by Rec.709. The shape of the triangle (or gamut) formed by these three primary points on a color diagram (usually the CIE 1931 or CIE 1976 chromaticity diagram) represents the range of colors that can be displayed or encoded under that standard.

Transfer Functions (Gamma, Log, HDR Curves, etc.)

A transfer function describes how numeric code values in a digital file (e.g., an image or video frame) are transformed into actual brightness/light levels. You can think of it as the mapping between the digital data and the perceived brightness on the display. In many workflows, these transfer functions are referred to as:

  • Gamma curves (e.g., gamma 2.2, 2.4) used in sRGB, Rec.709, etc.

  • Log curves (e.g., Log-C, S-Log) used in professional camera workflows to capture a wider dynamic range.

  • PQ (Perceptual Quantization) or HLG (Hybrid Log-Gamma) used in HDR (High Dynamic Range) applications.

By precisely defining the transfer function, you ensure that your displayed or rendered image has the correct brightness and contrast relationships.

Setting Color Parameters in Backstage

Color Parameters per Asset

In Backstage, each asset come with its own inherent color space, primaries, and transfer function. For instance:

Manually override automatically detected settings as needed. The values each of these can take are listed on Visual Assets Default Properties for assets and GPU Output for outputs.

  • Color Model: RGB, YCbCr

  • Color Range: Full, Limited

  • Color Primaries: BT_709, BT_2020, DCI-P3, Adobe RGB, BT.601-625, BT.601-525 or Manual

  • Color Transfer: Gamma, sRGB, SMPTE ST 2084, HLG, Log, Linear

For blended projections with Camera based Black Level Correction, the Gamma transfer function is required for assets.

Color Parameters per Output

Each output in your media server can also be set to a specific color space and transfer function.

Color Space

The options in the Color Space drop down are provided through the EDID by the sink of the output signal. “Default” refers to the default Colorspace in the settings (see below) - the default and always available option.

Understanding the "Color Space" setting of the output is crucial: it doesn't alter output values, but rather informs the output device (e.g., projector) about the color space of the signal. If you can manually adjust color space settings on your output device, you can select any value (or leave it at the default).

The conversion between Asset Color Space and Output Color Space is determined solely by their respective Color Primaries and Transfer functions, not the Color Space setting itself.

For blended projections, the Gamma transfer function is required for outputs.

Default Color Space

There are asset types that do not include any color space information, f.e. SBSM (our uncompressed format) or certain DPX files (with DPX, color space information is optional). For these assets, there can be setup a Default Color Space in the settings:

The default Color Primaries and Color Transfer will be used for Outputs, which Color Space is set to “Default” and for assets, that do not have any color space information embedded and which Color Space options are set to “Auto”.

Transformations Between Color Spaces

When an asset's color space and transfer function don't match the output's specifications, the media server automatically performs a color transformation. This three-step process ensures accurate color reproduction:

  1. Conversion to Linear Working Space: The asset is converted from its original color space and transfer function to a standardized linear working space.

  2. Gamut Mapping and Transfer Function Adjustment: Any necessary adjustments are applied to match the target output's color gamut and transfer function (gamma or HDR curve).

  3. Preservation of Color Appearance: This process aims to maintain the asset's original color appearance as faithfully as possible in the final output, considering both the target color gamut and the desired gamma or HDR curve.