Portraits in Infrared, Visible and Ultraviolet light
— Nick Spiker
The Melanin in the freckles absorbs UV-light very well, making them show up black in the photo. Same thing is going on with sunscreen. You may notice the eyes are darker in UV light at well, another protection mechanism to help prevent UV damage. Melanin doesn’t absorb Infrared wavelengths as much — and IR-light penetrates further into the skin than UV — so the freckles/imperfections will show up less when you select for only those wavelengths in the photo.