Does HDTV also give off the "strobing effect"? (1 Viewer)

[Carlos Garcia]

Hi everyone. I remember reading that the strobing effect (when someone on the tube is wearing stripes and you can see a moire effect) was a phenomenom that was exclusive to the NTSC standard. However, I've watched a few ballgames broadcast in HDTV on my set, and I can still see the strobing effect when someone wears stripes. Can somebody explain to me if this is supposed to happen with HDTV also?

 

[Joseph DeMartino]

No, it happens with PAL, too, for instance. What you're seeing is an interference pattern and it happens anytime a display system made up of discreet lines or pixels (unlike the continuous image of a photograph) tries to display any pattern where the distance between elements of the pattern is smaller than the distance between vertical rows of pixels or horizontal scan lines. HDTV has more lines of resolution, smaller and closer together, and some display technologies associated with HDTV have less distinct scan lines (plasma, for instance), all of which reduce the appearance of moire patterns, but which won't eliminate it. At least if I understand what I've read on the subject. It seems that if the line pattern in a garment or what-not in a given shot is sufficiently small, it will display the phenomenon.

Regards,

Joe

 

[Carlos Garcia]

Thanks Joseph, for that in depth explanation.

 

[Joseph DeMartino]

Thanks. It strikes me that you'll see much the same thing looking through a fine-mesh screen at someone wearing a striped shirt - when and if they are in a position where the apparent distance between stripes approaches the visible area defined by the vertical and horizontal "grid" imposed by the screen. No electronics involved at all, just looking at one pattern through a grid that defines aother pattern. The phenomenon is purely a visual artifact.

Regards,

Joe

 

[Steve Berger]

If I remember correctly from an Engineer's comment, it's usually caused by moving the camera too far away from the subject and using zoom to bring the image in closer. If the camera was closer the artifact might disappear but that makes it hard to switch the camera from person to person (and I don't think Jay Leno would want to displace audience members to stick a camera right in front of himself).