Naked Science Forum

General Science => General Science => Topic started by: neilep on 06/05/2007 15:41:12

Title: Blue Flouresent Edge To Objects On A TV Screen !!..what is it ?
Post by: neilep on 06/05/2007 15:41:12

This may only apply to conventional TV's ie: not plasma, not LCD, Not Progressive scan or HD models ...(but I'm not 100% sure on tat)

....but why when watching films (mostly on DVD) do I very often see a blue/purpley edge to objects and people and stuff ?

Have ewe seen it ?...do ewe know what I mean ?

Title: Blue Flouresent Edge To Objects On A TV Screen !!..what is it ?
Post by: Seany on 06/05/2007 17:36:24

Sorry! I don't understand! LOL!

Title: Blue Flouresent Edge To Objects On A TV Screen !!..what is it ?
Post by: neilep on 06/05/2007 17:48:29

Quote from: Seany on 06/05/2007 17:36:24

Sorry! I don't understand! LOL!

Sometimes, I can see a clear blue/purple edge to objects when watching DVD's...be it the edge of a tree or a person !!...you don't see it ?...it's obvious....even when pausing !

Title: Blue Flouresent Edge To Objects On A TV Screen !!..what is it ?
Post by: Soul Surfer on 06/05/2007 23:33:00

It could be a result of the analogue filtering to increase the perceived sharpness of the image.  In an analogue TV signal the colour signals have a rather poor bandwidth and colours tent to wash into each other.  the black and white information has the best resolution but sharp edges are often slightly enhanced by having a slightly rising frequency response to blot out this colour blurring and make the picture appear a bit sharper than it really is.  some TV sets allow you to change this emphasis (a bit like a treble control in an audio system and call it the "sharpness" or "noise reduction"  control  because having it turned up will also enhance high frequency noise in the signal.

Title: Blue Flouresent Edge To Objects On A TV Screen !!..what is it ?
Post by: Seany on 06/05/2007 23:41:15

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.progressive-av.com%2Fflat_screens%2Fimages%2FFujitsu_Plasmavision%2FFujitsu_Plasma_TV_Screen.jpg&hash=72b2920ba39212df64e8cd9dfd747a44)

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thewarehouse.co.nz%2Frexcomposer%2FuserImages%2F100010305.jpg&hash=839da8eb70de9f6832b9ba074491feab)

What blue line? [:P]

Title: Blue Flouresent Edge To Objects On A TV Screen !!..what is it ?
Post by: JimBob on 07/05/2007 00:15:18

It could also be due to a poorly synchronized signal processing.

Title: Blue Flouresent Edge To Objects On A TV Screen !!..what is it ?
Post by: another_someone on 07/05/2007 00:20:59

On still photographs, what you describe is what is often referred to as purple fringing (usually only happens when you have a very high contrast), and is a consequence of chromatic aberrations; but I am not at all sure that this is the case for what you are describing with movies (not that I have had cause to see it happen with movies - and I would be very disappointed if they allowed significant chromatic abberation with any professional photography, even professional movie photography.

Title: Blue Flouresent Edge To Objects On A TV Screen !!..what is it ?
Post by: neilep on 07/05/2007 00:31:34

THANK YOU all for your answers...what I will do is next time try and photograph the phenomena and post it here for you....hmm..I wonder if it can be photographed !

Your mention of high contrast George may be it though..........it happens on old Black & White movies too.

In fact Ians response rings true too..THANK YOU IAN ...as does JimBobs !!..LOL...could you ALL be right ?

Title: Blue Flouresent Edge To Objects On A TV Screen !!..what is it ?
Post by: another_someone on 07/05/2007 01:13:33

You cannot get chromatic aberrations on monochrome film.

Another possibility I would add is a poorly focusedelectron gun (if you have a 3 gun tube - not relevant if you have a single gun tube), or a slipped colour mask on the tube.