Separating a color image into its luminance and chrominance components is a fundamental task of image processing in astrophotography. To calculate luminance and chrominance values, PixInsight uses a colorimetrically defined RGB Working Space (RGBWS). Such a RGBWS is defined by the following parameters:

• Luminance coefficients. These are the relative weights of red, green and blue used to calculate the luminance of a pixel.

• Chromaticity coordinates. The x, y coordinates of the red, green and blue primaries. These colors are the fundamental colorants of the RGB color space.

• Gamma. A function used to linearize RGB components when converting them into a linear transformation space, such as CIE XYZ or CIE L*a*b*. Usually, the gamma function is just the raise function and the value of gamma is the exponent used.

Each image window can use its own, local RGBWS. For images that don't have their own RGBWS (as is by default), there exists a global RGBWS.

Note that the concept of RGBWS has nothing to do in PixInsight with color management or ICC profiles. Color management is used to achieve consistent color through different imaging devices. A RGBWS is used strictly for pure image processing tasks. At this point, it is important that you take the time to read why we decided to implement color processing this way in PixInsight.

You probably already know this, but perhaps you might be also interested in a small document that explains why processing luminance and chrominance separately is so important.

::Index

Defining RGB Working Spaces

Why RGB Working Spaces

Why Separate Luminance and Chrominance