English-speaking claim for the origin of the term "K correction" is Edwin Hubble, who supposedly arbitrarily chose
to represent the reduction factor in magnitude due to this same effect and who may not have been aware / given credit to the earlier work.
[2] [3] The K-correction can be defined as follows I.E. the adjustment to the standard relationship between absolute and apparent magnitude required to correct for the redshift effect.
The exact nature of the calculation that needs to be applied in order to perform a K correction depends upon the type of filter used to make the observation and the shape of the object's spectrum.
[5] It has been shown that K corrections in many frequently used broad-band filters for low-redshift galaxies can be precisely approximated using two-dimensional polynomials as functions of a redshift and one observed color.