Ferrite cores are most effective in providing attenuation of unwanted noise signals above 10 MHz. ... For low-frequency cable emission problems, typically below 10 MHz, ferrite chokes have not been very useful, since their impedance is too low, at these frequencies, to be effective.

Do I need a ferrite core?

Assuming that the devices being connected, and the cable itself are not defective, ferrite cores are going to have zero effect on picture quality. The primary intent of the ferrite cores is to prevent the cable from behaving like an antenna that radiates EMI from the devices connected to the ends of the cable.

How effective are ferrite beads?

For effective power supply noise filtering, a design guideline is to use ferrite beads at about 20% of their rated dc current. As shown in these two examples, the inductance at 20% of the rated current drops to about 30% for the 6 A bead and to about 15% for the 3 A bead.