Input transform

A formula or LUT mapping the values from a camera or stored in a file into the ACES colour space. Also known as the IDT.

Output transform

A formula or LUT mapping values from the ACES colour space to the output of a specific device or device specification, e.g. to PQ or HLG or rec709. The output transform is the collective name for the RRT and ODT.

By using transforms, you can ensure that your content will be displayed correctly on the displays.

 

For video inputs it is possible to enter a number to specify a gamma transform (in Input Gamma field), or enter an amount in stops (in Input Exposure field) to make an image more or less exposed.

1. Open a Video layer

2. Right click on the media clip used on the layer

3. Open the video clip editor

4. Enter the number for Input Gamma or Input Exposure

All content inputs (i.e. video files, RenderStreams, anything that is coming into Disguise software that has color & has image data has an “Input Transform” field. Upon configuring the input, you will see a dropdown list with the ACES standard list of colour spaces that are supported for input. This includes both scene-referred content derived from cameras (such as ARRI LogC), and display-referred content mastered to an output standard (such as ST 2084).

All display outputs have an “Output Transform” field. You will see a dropdown box with the ACES standard list of colour spaces that are supported for output; and you simply choose the appropriate one for your display.

 

Output Transform - ACES ODT (added on virtual devices such as camera and projector: Output → OT) Input Transform - ACES IDT (beneath: Video → Media → Edit media menu → Colour Shift → IT)

 

For video module: 2 fields were added: Beneath: Colour Shift - on video editor: Input Gamma-

Input Gamma Transform (IGT) - control the brightness (user can set less or more contrast using numbers) Input exposure -

Input Exposure Transform (stops) - (IET) - changing the brightness of the image accordingly: less exposure darker, more expose: brighter, user can specify it by entering the number)

A given piece of content will have both a relationship to a colour space, which will be independent of intensity, and a function of some kind that describes how intensity is encoded into the colour values. So a colour transform will affect how colour is represented relative to the CIE colour diagram, while a transfer function will not. A transfer function will change the perceived intensity or contrast of an image, where a colour transform will not.

In addition to this, there are specifications such as rec709 and sRGB that define a colour space as well as a transfer function, as well as transfer functions that are independent of colour space and colour spaces that are used independently of transfer functions.

Linear Transfer Function

When we say an image is ‘linear’, we mean that the transfer function is linear, i.e. there is no curve applied and a value that is twice another value will be twice as intense. This is useful for mathematical accuracy in visual effects, but is inefficient for display.

Curves

The sRGB and rec709 curves are closely related but different, although they’re often used interchangably with each other as well as with a 2.2 gamma curve. This is the most common curve in graphics and is the current ‘default’ curve in Disguise software, which content is assumed to be in if no other choice is specified.

The PQ and HLG curves are for displaying HDR content on HDR displays.

Camera-specific formats, as well as ACEScc, are “log” formats that use a log curve on intensity.