Linear Match
Linear matching is the process of finding a linear function that matches best (in the sense of Least Squares) the intensity of pixels from one image to those of a reference image. This is a quick and easy way to balance the histograms of different images.
Linear match dialog
The Reference allows you to pick the reference image.
The Reject low and Reject high sliders allows to exclude pixels values in the left and right tails of the intensities distributions. They are defined as quantiles, in the range [0, 1]. For instance, default for high is 0.92, meaning that the 8% brightest pixels will be excluded from the fitting to find the linear match coefficients.
Warning
The image and reference must be aligned prior to applying a linear match. Otherwise, there is no reason to assume that their pixels intensities are correlated.
Siril command line
linear_match reference low high