Comparison between the color magnitude diagram of the target field and that of the background region. Top panel: Color-magnitude diagram of the 18 651 sources (black dots) selected according to their shape. The plot shows the g′₀ magnitude as a function of the (g′−i′)₀ color. The red dots represent the sources after the selection on colors and magnitudes. Bottom panel: Color-magnitude diagram of the background region. The plot shows the g′₀ magnitude as a function of the (g′−i′)₀ color for the 1639 compact sources (8.79% of the total sources in Field 1) located in the rectangle region of 11.10 × 6.95 arcmin² (11.87% of Field 1) used to calculate the background level (see green rectangle in Fig. 3).