Dave,
Substitute the RGB for BVR. B&R in BVR are photometric bands, different from the non standard R&B in the RGB.
I use the BVR 3 input images to produce 1 output image, which is the merged BVR image.
I use min value and max value parameters control the placement of the "black point" and the "white point" in the luminance values of the input images. When merged into the output BVR image, all pixel values lower than the min value are assigned "black" and all pixels above max value are assigned "white". These values do not need to be the same for each of the images. Typically they may be different if the images have different background signal or inherently different contrast. The particular values you use affect the overall brightness of the BVR image as well as its contrast and colour balance.
The luminance is the added values of the exposures of BVR images.
Eamonn A
  