Antoine,
Here is the process for doing what you were trying to do, and it is an important step to get the Lum and RGB fluxes the same before doing the LRGB Combination:
This is the basic procedure (from Juan himself):
- Apply the initial nonlinear histogram transformations to your RGB and L images. Adjust the L image first, to the desired brightness and contrast. Then try to match the overall illumination of L when you transform RGB. Do it roughly by eye using the CIE L* display mode (Shift+Ctrl+L, Shift+Cmd+L on the Mac). Don't try to do a particularly accurate job here; it will get much better in the next steps.
- Extract the CIE L* component of RGB with the ChannelExtraction tool (select the CIE L*a*b* space, uncheck a* and b*, and apply to RGB).
- Open the LinearFit tool (ColorCalibration category) and select the L image as the reference image. Apply to the L* component of RGB that you have extracted in the previous step.
- Reinsert the fitted L* in the RGB image with the ChannelCombination tool.
Now your RGB and L images have been matched very accurately. Use the LRGBCombination tool with them. You shouldn't change the luminance transfer function, nor the channel weights, as LinearFit has already done the matching job much better than anything you could do manually.
Hope that helps,
Jim
