Originally Posted by Tyrone Burton
...ferrite core would help against any image artefacts...
No. A ferrite core reduces common mode noise. The video and audio are transmitted using a differential circuit that essentially cancels out common mode noise. So, a ferrite isn't going to do much for those signals. And research has shown that a ferrite core will actually adversely affect the video and audio signals. IOW not only are ferrites pretty useless as far as HDMI goes, they are to be avoided unless you absolutely have to reduce interference with other devices.
HDMI uses digital signalling. A problem will not show itself as a subtle change in color, brightness, sharpness, contrast, or any of the other artifacts we might be familiar with in an analog environment. The first indication of a problem is sparkles, pixels that are just plain wrong. If you don't see sparkles, the picture is as good as it gets.