Defining RGB Working Spaces

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Global and Local RGBWS

Default RGBWS Parameters

The RGBSpaceParameters Process

Global and Local RGBWS

The global RGB working space (RGBWS) is used for luminance/chrominance separations and color space conversions by images that don't state their own local RGBWS, as happens by default.

The global RGBWS parameters are stored in the Windows registry and restored on startup, so changes made to the global RGBWS are remembered between successive executions of PixInsight.

An image window can have its own RGBWS parameters, which are then used instead of the global RGBWS.

Default RGBWS Parameters

The default RGBWS parameters correspond to the sRGB color space:

sRGB Space
















where x, y are chromaticity coordinates, and Y values are luminance coefficients. Numerical values have been converted from the D65 reference white used natively by sRGB to the D50 reference white used by PixInsight. The Bradford algorithm for chromatic adaptation has been used.

The gamma function defined by the sRGB standard is also used as part of the default RGBWS parameter set. The sRGB gamma function is similar to a simple gamma 2.2 curve.

The RGBSpaceParameters Process

To define and assign RGB working spaces the RGBSpaceParameters process is used. Instances of RGBSpaceParameters can be executed globally and on images, but not on previews.

When RGBSpaceParameters is executed in the global context, the global RGBWS parameters are established. When applied to an image, a local RGBWS is created and will be used in color space conversions and luminance/chrominance separations for the target image instead of the global RGBWS.

The standard interface for RGBSpaceParameters is the RGB Working Space Parameters window, which is shown here loaded with the default RGBWS parameters:

To load the default parameters (which correspond to the sRGB space) click the Load Default RGBWS button. The current global RGBWS parameters are loaded in this window on startup; however, you always can reload them by clicking the Load Global RGBWS button.

To load an image's local RGBWS parameters, select it in the view selection list at the top of the window. If the selected image does not have a local RGBWS defined, the global RGBWS is loaded instead.

If the Apply Global RGBWS check box is checked, other process parameters are ignored and the process will just apply the current global RGBWS parameters.

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