Zoomed-in view of the Perseus ERO focusing on a region that lies 17 kpc southwest of NGC 1275. The ground-based seeing-limited CFHT i′ -band image (left panel) is comparable in wavelength to the Euclid I_E-band image (middle panel). However, the superior spatial resolution in I_E reveals numerous GCs, which are encircled in white. Euclid’s resolution decreases with wavelength because of diffraction and undersampling of the PSF, such that most of the GCs cannot be identified in the J_E band (right panel). Black and white correspond to a surface brightness of µ = 22 and 21 mag arcsec⁻², respectively, in the left and middle panels, and µ(J_E) = 23 and 22 mag arcsec⁻² in the right panel.