Binary maps and mass-ratio distribution for Boötes I. Left: Observed binary map (in blue), with the corresponding Δ_{F606W, F322W2} distribution shown in the top panel. The vertical dashed lines indicate the nine reference loci used to construct the map, including the fiducial sequences of binary systems with different mass ratios, q, whose values are labeled in the figure. Middle: Best-fit binary map (in gold). Right: Mass-ratio distribution derived from the best fit; the green line and shaded region indicate the linear fit and its associated uncertainty.