Hi Max,
I generally need a non-linear strech to add Luminence to the image.
Of course. This is because LRGBCombination works in the CIE L*a*b* and CIE L*c*h* color spaces. Both are nonlinear spaces. For this reason you need to stretch (nonlinearly) the RGB and luminance images prior to combine them.
I wish could find a way to put a total linear LRGB together
Yes we can
Do the following:
- Open your luminance and RGB images. We assume both are linear images.
- Open the RGBWorkingSpace tool and define a linear RGB color space. A linear space has a value of gamma equal to one. So expand the Gamma section, disable the "Use sRGB gamma function" option, and set gamma = 1.0.
- In addition, if you're working with a deep sky image, you may want to define custom RGB weights. On the Luminance Coefficients section, my advice is to set equal weights for the three channels (for example R=G=B=1).
- Apply this instance of RGBWorkingSpace to the RGB and luminance linear images.
- Open the ChannelCombination tool. Select the CIE XYZ space. Disable the X and Z components. For the Y component, select your linear luminance image. Apply this instance to your linear RGB image.
Now you have a YRGB linear image
Don't forget to apply the linear RGB working space that you defined above to your YRGB image each time you open it, or otherwise all luminance/chrominance separations will be incorrect! Also, to apply a process to the luminance, use the linear luminance option with the tools that support it, notably Deconvolution, ATrousWaveletTransform, and RestorationFilter.
