Link [2021]: Pixinsight Lerar

You cannot use LinearFit on stretched images (images you have already processed with HistogramTransformation or Curves).

When an image exits the stacking process, it is "linear." In this state, the pixel values are directly proportional to the number of photons captured. This is physically accurate but visually abysmal to the human eye—appearing jet-black save for a few faint star cores. More critically, in this linear stage, the background sky glow (light pollution or airglow) dominates the dim signal of nebulae and galaxies. If a photographer applies a simple stretch without linking the channels, the channel with the highest background noise (often the blue or red channel, depending on the sky conditions) will balloon out of control, resulting in a green or magenta cast across the entire image. pixinsight lerar link

However, after analyzing common user errors and forum queries, we believe you are looking for —or more specifically, how to use LinearFit to link the black and white points of your images to a reference frame. You cannot use LinearFit on stretched images (images