Eyeon:Manual/Fusion 6/Look Up Tables

A Look Up Table is a table of values used to transform an image. This is generally used to correct for variances in the monitor or the source color space of the image. It is possible to apply a LUT to all displays (regardless of type), or individual LUTs for each 2D display view. Multiple LUTs can be chained together, making it possible to apply a standard Log / Lin color space transformation followed by a 2D LUT curve.

A wide range of LUTs are supported, including industry standard 2D and 3D LUTs, shader fragments embedded in Fuse tools, and macros assembled from standard Fusion tools. Generally LUT processing is performed on the graphics card's GPU in realtime. Macro based LUTs will not process in realtime, taking as long to render as the tools they contain.

Image LUTs

A different image LUT can be applied to each view, including separate LUTs for the A and B buffers in the view. These LUTs can only be applied to 2D images. Multiple image LUTs can be chained together.

Buffer LUTs

The buffer LUT is applied to all of the view, regardless of contents, including 3D scenes, 3D materials, and sub-view types. Only one buffer LUT can be applied. If a 2D image is being displayed with an image LUT applied, then the buffer LUT is applied to the result of the image LUT.

LUT Processing Order

When a tool's output is displayed in the views the data produced is processed before it is shown in the displays. The processing order is applied as follows.

2D images first have the image LUT is applied (if any), and the result composited over the checker underlay. 3D scenes are instead rendered with OpenGL.

For either 2D or 3D, the result may be drawn to an offscreen buffer where a buffer LUT can be applied, along with dithering, a full-view checker underlay, and any stereo processing.

The final result is then drawn to the view, and any controls are drawn on top.

Enabling and Editing Image LUTs

The LUT button in the display view toolbar can be used to toggle the image LUT on and off. The default LUT type is a standard Fusion View LUT which is initially flat, so there will be no apparent change to the image. To select a different LUT type click on the small arrow to the right of the button and a LUT menu will appear with a list of all known LUT types, including applicable macros and fuses.

The LUT menu can also be found as a sub-menu in the display view's context menu.

Selecting the Edit option from the LUT menu will display a dialog showing a control panel to set the options for each LUT applied.

Enabling and Editing Buffer LUTs

To enable a buffer LUT for all the display views right click in the display view and select the Global Options -> Buffer LUT -> Enable option. The Global Options -> Buffer LUT sub-menu will contain a list of all known LUT types, including applicable macros and fuses.

Buffer LUTs are often useful for applying monitor corrections, which do not usually change between projects.

Stacking LUTs Together

The display view context menu can be used to stack image LUTs into a processing chain. For example, when loading a Cineon in Log color space, the artist may wish to first apply a Log->Lin conversion, followed by a Fusion View LUT to apply a color calibration.

To insert a LUT after the current one in the processing chain select the type from the LUT -> Add new sub-menu in the display view's context menu. To remove a LUT from the stack select the LUT from the LUT -> Delete sub-menu.

A complete stacked LUT configuration can be saved to and loaded from a .viewlut file, as described below.

Types of LUTs

Fusion View LUT

The Fusion View LUT is the default and most frequently used LUT type provided by Fusion. A filename selector can be used to load any one of the 2D and 3D LUT formats supported by Fusion. See the File LUT tool for details.

It also provides an RGBA curve which can be used to assign IN/OUT value pairs. This control is identical to that provided by the Color Curves tool. Since the purpose of the display LUT is to provide an unchanging correction for the monitor or the file's color space, however, these splines cannot be animated.

In addition to the ability to modify the separate color channels, the LUT has Gain and Gamma sliders. The Gain slider is helpful for temporarily brightening or darkening the viewed image, allowing easier examination of shadow or highlight detail. The Gamma and Alpha Gamma sliders are used to duplicate the gamma values of the eventual output device. Video monitors, for example, commonly have a gamma of 1.7, while computer monitors can range anywhere from 1.6 to 2.2. Alpha Gamma is only applied when viewing the alpha channel of an image, or when viewing masks.

Log-Lin View LUT

Similar to the Cineon Log tool, this LUT allows linear image data to be converted to logarithmic data, or vice versa. This can be particularly useful when used in conjunction with supplied LUT files that expect logarithmic data.

Macro LUTS

Any Macro tool can also be used as a LUT, simply by saving the macros .setting file to one of the directories specified by the LUTs: pathmap in the global pathmap preferences. On Microsoft's Windows Vista this is usually the C:\Users\Public\Documents\eyeon\Fusion\LUTs\ folder, or the equivalent. Fusion may need to be restarted before macros added to the folder will appear in the menu.

The macro must have one image input and one image output. Any controls exposed on the macro will be available when the Edit option is selected for the LUT.

Fuse LUTS

A Fuse of type CT_ViewLUTPlugin can be applied as a LUT to a display view. Shaders can be written and embedded into the LUT for real time processing. See the Fuses chapter for more information.

Fuse LUTs require shader-capable graphics hardware, and can not be applied in software.

Save and Load LUT Settings

The LUT -> Save and LUT -> Load display view context menu options can be used to save the current LUT settings to disk or to load previously saved LUTs from disk. The settings are saved as an ascii file with the extension .viewlut in the LUTs: folder. Any files with this extension found in that folder will appear in the image LUT menus, for ease of loading.

Setting a Default LUT

The default LUT applied when a new composition is created can be assigned in the Global -> View Preferences panel.