[Tig] Phosphor persistence [was: Compression/Monitor calibration]

Chuck Harrison cfharr
Thu Jun 16 17:11:12 BST 2005


Peter,

On this one I am *very* suspect of your 10-msec-range numbers.

Think of what a motion picture camera pointed at a CRT sees:
a bright band proportional to the shutter angle of the camera.

Any readers out there can make a quick test with a digital
still camera, too.

My recollection is that the decay time of typical TV CRT
phosphors is several microseconds. FWIW the few long-persistence
applications I have bumped up against (typically caligraphic
ones, like radar or sonar displays) all seem to have green
phosphors.

Peace & light,
  Chuck

Peter Swinson wrote:
> 
> 
> 
> Thanks to James Braid of Oktobor for supporting the TIG
> --
> 
> >> a display CRT that has an afterglow of say 10-20mSec
> 
> Martin Euredjian wrote
> 
> > I guess I never thought of it being that long.  Is this typical for the
> BVM
> series?
> 
> Well I ball parked the figures.
> 
> Look at it like this, unlike a Scanner CRT, a display raster ideally, in a
> interlace world, should have 100% afterglow for at least one field. Bear in
> mind that it is still a spot (3 in color) that is drawing the raster across
> and down the screen. In NTSC world each field is around 16mSec and
> PAL/Secam  world 20mSec. In reality the afterglow can be longer as it takes
> another 16 or 20Msec for the second field to draw down the screen.  Also
> the spot is modulated by the video signal, so the instantaneous brightness
> is defined by the spot, no video no spot 100% video 100% spot. Now the
> instant the field is repeated the afterglow from the previous same field
> should clear. Impossible, therefore Display CRTs have  afterglows that hold
> well for at least one field but are gone by the end of the second field,
> such that the repeated "third" field can start again. If Display CRTs had
> short afterglow they would flicker horribly.  None of this applies to LCDs
> etc as they are, as far as I know,  basically "Splat" technology, like
> film; The whole image is presented at once and removed at once.
> 
> Or have I got it all wrong again !!!
> 
> cheers
> 
> Peter
> 
> 
> 
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