Hello, I am a newbie here and I don't know what this thing is, er..

Oops, wrong server.

Reallyy, what *is* persistence of vision? I know it's some phenomenon
but I don't know what it is (or, more likely I know, but can't match
the name with the thing). I know you guys, 80% of the replies will be
of the nifty smartass type :) but still...


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG      e-mail : pet### [at] tagpovrayorg

Post a reply to this message

Peter Popov wrote:
> 
> Hello, I am a newbie here and I don't know what this thing is, er..
> 
> Oops, wrong server.
> 
> Reallyy, what *is* persistence of vision? I know it's some phenomenon
> but I don't know what it is (or, more likely I know, but can't match
> the name with the thing). I know you guys, 80% of the replies will be
> of the nifty smartass type :) but still...

Not really the best question for this group but...

Let us use an example to describe the persistence of vision effect.
As you know it is possible to blink a light bulb or an LED and see
the individual flashes. As we speed up the flash rate it starts
to appear as though it is constantly lit even though we can verify
for ourselves that we are indeed still pulsing the light. This is
known as the persistence of vision effect. It is the same reason
why light bulbs that run on alternating current appear constantly
lit when we know that they are actually turned off and on 60 times
per second. The reason the light appears persistent is because
the light receptors in our eyes cannot react quickly enough to
resolve the individual on off cycles. There are other examples
of the persistence of vision effect but this is the best way
I know of to explain it.


-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

Post a reply to this message

> Not really the best question for this group but...

The povray.animations group would technically be o.k. though
because persistance of vision is the reason motion pictures
work...

-- 
Phil
...coffee?...yes please! extra sugar,extra cream...Thank you.

Post a reply to this message

Ken wrote:
..
> lit when we know that they are actually turned off and on 60 times
> per second. The reason the light appears persistent is because
..

Actually it's 120 times per second.. Ok I'll go away :)

Post a reply to this message

On Mon, 08 May 2000 23:48:16 -0700, Ken <tyl### [at] pacbellnet> wrote:

>Not really the best question for this group but...

Sure! I started posting it and just before sending it I noticed it was
the wrong group so I manually typed povray.gereral in the proper
header field but I probably hit the wrong button because it defaulted
to p.b.i. Happens.

<snip description>

Thanks, Ken. I know the effect you described, but I had no idea that
was what 'persistence of vision' meant.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG      e-mail : pet### [at] tagpovrayorg

Post a reply to this message

Ken wrote:

> Not really the best question for this group but...
>
> Let us use an example to describe the persistence of vision effect.
> As you know it is possible to blink a light bulb or an LED and see
> the individual flashes. As we speed up the flash rate it starts
> to appear as though it is constantly lit even though we can verify
> for ourselves that we are indeed still pulsing the light. This is
> known as the persistence of vision effect. It is the same reason
> why light bulbs that run on alternating current appear constantly
> lit when we know that they are actually turned off and on 60 times
> per second. The reason the light appears persistent is because
> the light receptors in our eyes cannot react quickly enough to
> resolve the individual on off cycles. There are other examples
> of the persistence of vision effect but this is the best way
> I know of to explain it.

Does the bulb immediately stop emitting light when the power is cut, or does
it "cool down"?
Sigmund's right, it's 120 times a second ;-)

Know what I hate? When I go into MS-DOS mode and the monitor goes to 60Hz.

--
David Fontaine     <dav### [at] faricynet>    ICQ 55354965
Please visit my website: http:/www.faricy.net/~davidf/

Post a reply to this message

David Fontaine wrote:

> Does the bulb immediately stop emitting light when the power is cut, or does
> it "cool down"?

I used the example for purely illustrative purposes. Obviously is does
take a filament time to cool down and in fact they are specifically
designed not to. But if we were to model the filament to have a perfect
heat discharge that followed the current cycle through it in the form
of a shape edged square wave the example would fit the explaination.
LED's in fact come much closer and that is why I also mentioned them
in my example. I just didn't expect you to come along and nit pick.
If you have a better example to offer I am sure Peter would be happy
to hear it.

> Sigmund's right, it's 120 times a second ;-)

Not on a 30hz system.

-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

Post a reply to this message

Not only does an incandescent bulb cool down, it also does a shift toward
orange-red as it cools.

David Fontaine wrote:

> Ken wrote:
> Does the bulb immediately stop emitting light when the power is cut, or does
> it "cool down"?
> Sigmund's right, it's 120 times a second ;-)
>

--
Bryan Valencia
Software Services - Making Windows Scream
http://www.209software.com
mailto:bry### [at] 209softwarecom

Post a reply to this message

On Tue, 09 May 2000 16:25:15 +0200, Sigmund Kyrre Aas
<as### [at] studntnuno> wrote:

>Actually it's 120 times per second.. Ok I'll go away :)

Actually, a common houshold lamp can't flash that quickly. The
filament won't cool off enough between the rapid pulses of current. So
this isn't purely a simple case of Persistence Of Vision, it's also
partially a case of "Persistence of Illumination" as well.

Later,
Glen Berry

( Remove the "7" from 7no### [at] ezwvcom to email me. )

Post a reply to this message

Glen Berry wrote:
> 
> Actually, a common houshold lamp can't flash that quickly. The
> filament won't cool off enough between the rapid pulses of current. So
> this isn't purely a simple case of Persistence Of Vision, it's also
> partially a case of "Persistence of Illumination" as well.

Go to the movies for a better effect ;) Actually I had a lab project with a
light sensing thing and an oscilloscope some years ago. We could easily
identify the variation of the light from a light bulb. A gas lamp produced a
very weird noise curve.

sig

(followup to off-topic)

Post a reply to this message

Dear Folks,

Peter wrote:
[snip]
> what *is* persistence of vision?

Ken wrote:
[snip]
> Let us use an example to describe the persistence of vision effect.
> ...The reason the light appears persistent is because
> the light receptors in our eyes cannot react quickly enough to
> resolve the individual on off cycles.

This is a very clear explaination of this effect.  But, to continue this
off-topic discussion, why did the creators of this renderer choose this
name for the program that is mostly used to produce still life
snapshots?

This is a question that people have asked me after I've explained
ray-tracing.

Blessings,
          Brendan

-- 
Michael Brendan Hurley
POV: http://www.geocities.com/mbrendanh/
FAMILY: http://www.saber.net/~mbhcgc/
mbh### [at] sabernet

Post a reply to this message

Brendan Hurley wrote:

> This is a very clear explaination of this effect.  But, to continue this
> off-topic discussion, why did the creators of this renderer choose this
> name for the program that is mostly used to produce still life
> snapshots?

A good question. I'll see if I can find out.

-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

Post a reply to this message

Ken wrote:

> I used the example for purely illustrative purposes. Obviously is does
> take a filament time to cool down and in fact they are specifically
> designed not to. But if we were to model the filament to have a perfect
> heat discharge that followed the current cycle through it in the form
> of a shape edged square wave the example would fit the explaination.
> LED's in fact come much closer and that is why I also mentioned them
> in my example. I just didn't expect you to come along and nit pick.
> If you have a better example to offer I am sure Peter would be happy
> to hear it.

IMAX projector
how's that ;)

> Not on a 30hz system.

-?- where do you have 30Hz?

--
David Fontaine     <dav### [at] faricynet>     ICQ 55354965
Please visit my website: http://www.faricy.net/~davidf/

Post a reply to this message

Brendan Hurley wrote:

> This is a very clear explaination of this effect.  But, to continue this
> off-topic discussion, why did the creators of this renderer choose this
> name for the program that is mostly used to produce still life
> snapshots?

Artistic license.

--
David Fontaine     <dav### [at] faricynet>     ICQ 55354965
Please visit my website: http://www.faricy.net/~davidf/

Post a reply to this message

David Fontaine wrote:

> > Not on a 30hz system.
> 
> -?- where do you have 30Hz?

As an electronics engineer I can create just about any duty cycle I
want :)

-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

Post a reply to this message

Ken wrote:
> 
> Brendan Hurley wrote:
> 
> > This is a very clear explaination of this effect.  But, to continue this
> > off-topic discussion, why did the creators of this renderer choose this
> > name for the program that is mostly used to produce still life
> > snapshots?
> 
> A good question. I'll see if I can find out.

Here follows two quotes on the subject.  The first is a reply by 
Chris Young, after I told him about Varley's "Persistence of Vision"
I found on a flea market.

************************************************************************************************************
Varley is one of my favorite authors and I've owned that book long
before POV-Ray existed.  POV-Ray was originally going to be called
Starlight or StarLite or something similar but somebody else, I don't
know who, said we'd get in trademark trouble over some existing
product.  Drew Wells was team leader and he picked Persistence of Vision
based on the properties of the human visual system. I also felt there
was a double meaning in that POV-Ray was the continuation (or
persisence) of David K. Buck's DKB-Trace.  I warned Drew about Varley's
book but book titles aren't as messy as product names.  Note also that
Public Broadcasting System has a documentary series called POV but that
stands for Point Of View which is the filmmaking term for hand-held
camera, cinema-verite style used in many documentaries.

I wanted to take our team name from the Fractint Stone Soup Group and
call us the Crystal Soup Group but I got voted down.
        Chris Young, POV-Team Coordinator

************************************************************************************************************
After the recent thread on the starting time I POV-Ray I did
a search and found this post to this very news group from
David Buck himself. The message places the birth of the POV-Ray
project to be in May of 1991. A very historic event!

I hope I'm not stepping on toes by re-posting
it  :-)

Harold

Sun, 19 Feb 1995 19:14:44 GMT
(STEERPIKE) says:
>        I had always presumed that Persistance of Vision was a
>pun on the name of Salvador Dali's painting "The Persistance of Memory".
>Is this right, and if not, how did POV-Ray come to have such a poetic
>name? :)

The POV-Ray project started in May 1991 when I first proposed the idea
to a group of people on CompuServe.  They liked my DKBTrace raytracer
but didn't like the fact that I was too slow adding new features to
it.  They were going to re-write a raytracer from scratch, but I
suggested that after version 2.12 of DKBTrace, they could take the
code as is and develop it from there into a new raytracer.  The first
name was STAR - an acronym for something or other.  Then someone in
the group came up with "Persistance of Vision".  We liked it because
of its reference to Dali (I believe the painting was actually called
Persistance of Vision - am I mistaken?).  Moreover, it seemed to
symbolize the team who "Persisted" to achieve their "Vision".  The
third reference was to the phychological effect that seeing an image
flashed on a screen causes you to retain that image in short term
memory.  Thus, your memory was a representation of reality but not
really reality.  They all seemed to fit together to make a nice name.
Early on, we were abbreviating the name to PVRay, but we were
concerned about a commercial product called PV-Wave.  We agreed to
change the abbreviation to POV-Ray and standardize on the spelling.

>David Buck dbu### [at] ccscarletonca
************************************************************************************************************

Post a reply to this message

Fabien Mosen wrote:
> 
> Ken wrote:
> >
> > Brendan Hurley wrote:
> >
> > > This is a very clear explaination of this effect.  But, to continue this
> > > off-topic discussion, why did the creators of this renderer choose this
> > > name for the program that is mostly used to produce still life
> > > snapshots?
> >
> > A good question. I'll see if I can find out.
> 
> Here follows two quotes on the subject.  The first is a reply by
> Chris Young, after I told him about Varley's "Persistence of Vision"
> I found on a flea market.

Thank you for posting this. It's amazing what people will archive away
waiting for that obscure moment at some future time when it might be
needed.

-- 
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

Post a reply to this message

Ken wrote:
> 
> Brendan Hurley wrote:
> 
> > This is a very clear explaination of this effect.  But, to continue this
> > off-topic discussion, why did the creators of this renderer choose this
> > name for the program that is mostly used to produce still life
> > snapshots?
> 
> A good question. I'll see if I can find out.

Yes. When I first heard of POV-ray, I thought the POV stood for
Point Of View. Still seems more appropriate than Persistence Of Vision.

Post a reply to this message