This is a part of a Physics paper I just want to know what d

This is a part of a Physics paper, I just want to know what does it mean the letters \" g, and r, and i\" when they say \"electronic sustraction in g & r\" what these letters represent?

All images underwent preliminary data reduction that included bias subtraction, flat fielding, sky background subtraction and an electronic pattern subtraction (in g & r) or a fringe pattern subtraction (in i). We will briefly describe each technique but refer the reader to the escribe each technique but refer the reader to the ini- al data release papers for more detailedd descriptions (Wang, L. et al. 2013; Oelkers et al. 2015).

Solution

SDSS (Sloan Digital Sky Survey) filters have five band transmission filters , namely u, g, r, i and z

g- band filter has central wavelength 4686 amstrong, r-band filter has central wavelength 6166 amstrong and  i - band filter has central wavelength 7480 amstrong.