"Warp" <war### [at] tagpovrayorg> schreef in bericht
news:3ea1aab9@news.povray.org...
>   Actually if you want a photographically realistic result, the stars
> shouldn't be visible even if you are "photographing" (ie. in this case
> rendering) a planet (eg. Earth). Well, at least not if you want the
> details of the planet to be visible.
>
>   This is related to exposure time. The planet is brightly lit by the
> Sun, but the stars are rather dim. If you set the exposure time of your
> photographing device so that the details of the planetary surface are
> visible, the stars will be way too dim to be seen. If on the other hand
> you set the exposure time so long that the stars become visible, the
> planet will become overexposed, ie completely white (well, the lit
> part of the planet).
>
>   Space movies are always unrealistic in this matter. There planets and
> stars are perfectly visible all alike, which can't be achieved with any
> ordinary photographing device. (In theory you would need some kind of
> digital device which analyzes the image and corrects the exposure in
> different parts of the image depending on their brightness.)
>   On the other hand, space shots with completely black skies would be
> pretty boring, so we can forgive this artistic effect.
>
> --
> #macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb
M()}}
> N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
> N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  -
Warp -

i think you think too much, don't you think ;-)
it is true what you say, but imo if art was scientific correct it wasn't
called art anymore.

regards, lenx

Post a reply to this message

Lenx <len### [at] pandorabe> wrote:
> it is true what you say, but imo if art was scientific correct it wasn't
> called art anymore.

  I don't agree.
  There are many things which are most beautiful when they are completely
physically correctly modelled (fakes and shortcuts usually make them look
less pretty). For example water, fire, cloths, objects colliding with each
other, etc etc.
  For example a slow-motion animation of a rock thrown into a pool of
water is the most beautiful when its modelling is physically perfect.

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

Post a reply to this message

>   I don't agree.
>   There are many things which are most beautiful when they are completely
> physically correctly modelled (fakes and shortcuts usually make them look
> less pretty). For example water, fire, cloths, objects colliding with each
> other, etc etc.
>   For example a slow-motion animation of a rock thrown into a pool of
> water is the most beautiful when its modelling is physically perfect.
>

you won :-)
it is a scientific reproduction of nature, which is for me pure art
but i didn't mean it really in that way, i had something in mind like
'artistic freedom'.
lenx

Post a reply to this message

Among other things, Warp wrote:

>   This is related to exposure time. The planet is brightly lit by the
> Sun, but the stars are rather dim. If you set the exposure time of your
> photographing device so that the details of the planetary surface are
> visible, the stars will be way too dim to be seen. If on the other hand
> you set the exposure time so long that the stars become visible, the
> planet will become overexposed, ie completely white (well, the lit
> part of the planet).

I'd say scattering plays a role too here on earth, we don't see the stars 
when the sun is shining because the sky itself shines too (obscuring the 
sun with the hand is not enough). In outer space this doesn't happen and it 
should be possible to see the stars you cover the sun (and other bright 
bodies), but I've never been there to try.

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

Post a reply to this message

Jellby <jel### [at] m-yahoocom> wrote:
> In outer space this doesn't happen and it 
> should be possible to see the stars you cover the sun (and other bright 
> bodies), but I've never been there to try.

  As I said, it's perfectly possible to photograph stars in space. You
just need to set the exposure time of the photographing device so long that
it captures the light of the stars.
  And as I said, the problem with this is that if there's a much brighter
object visible, it will be highly overexposed, and will most probably
turn completely white in the image.
  Covering the bright object may be necessary if the object is extremely
bright because the brightness can overwhelm and bleed (at least if we are
using a photographic film), overexposing the whole image. I don't know
if this is necessary with a digital camera, though (does anyone know?).

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

Post a reply to this message

Many CCDs or digital cameras have enough dynamic range to get dim objects as
well as bright objects, but the images must be processed in a computer to bring
out all the features in most circumstances.  If the images showed the entire
dynamic range compressed to fit our human light range, they would look
unnatural, like our happy little space images with stars and planets all the
same.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip

Post a reply to this message

Among other things, Warp wrote:

> Jellby <jel### [at] m-yahoocom> wrote:
>> In outer space this doesn't happen and it
>> should be possible to see the stars you cover the sun (and other bright
>> bodies), but I've never been there to try.
> 
>   As I said, it's perfectly possible to photograph stars in space. You
> just need to set the exposure time of the photographing device so long
> that it captures the light of the stars.
> [...]

Yes, I agree. I was just pointing out that, under the atmosphere, it's not 
just a matter of exposure time.

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

Post a reply to this message

In article <3ea1aab9@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

>   Space movies are always unrealistic in this matter. There planets and
> stars are perfectly visible all alike, which can't be achieved with any
> ordinary photographing device. (In theory you would need some kind of
> digital device which analyzes the image and corrects the exposure in
> different parts of the image depending on their brightness.)

Well, they would be an unrealistic representation of what you would get 
from a present-day video camera, that doesn't make them unrealistic.

If I were designing a video camera for use in this kind of environment, 
I'd use multiple cameras with different settings and composite them 
together, or try to find a sensor with sufficient dynamic range. It 
could be as simple as a thin layer on the CCD that changes local opacity 
depending on the brightness of light on it. It could be passive, like 
today's color changing sunglasses, or an active liquid crystal filter. 
Or you could make a filter that varies in opacity evenly over the entire 
filter, and just take consecutive frames at different opacity levels, 
processing them together into the final image as you would with multiple 
cameras.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

Post a reply to this message

Christopher James Huff <cja### [at] earthlinknet> wrote:
> If I were designing a video camera for use in this kind of environment, 
> I'd use multiple cameras with different settings and composite them 
> together, or try to find a sensor with sufficient dynamic range. It 
> could be as simple as a thin layer on the CCD that changes local opacity 
> depending on the brightness of light on it. It could be passive, like 
> today's color changing sunglasses, or an active liquid crystal filter. 
> Or you could make a filter that varies in opacity evenly over the entire 
> filter, and just take consecutive frames at different opacity levels, 
> processing them together into the final image as you would with multiple 
> cameras.

  All this to simply get some white dots on the image?-)

  Space movies often exaggerate the beautiness of stars in space, but
I wouldn't be surprised if actually they were just extremely boring
white dots... :)
  The images of the Hubble telescope are marvelously beautiful... But those
images are photographind details thousands of light-years big. You don't
get that kind of colorful images when photographing a planet or a
spaceship...

  But anyways, the point is making a visually pleasant artistic image,
not a physically correct one. :)

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

Post a reply to this message

Warp wrote:
> I wouldn't be surprised if actually they were just extremely boring
> white dots... :)

Hundreds of years in the future, makind will send out a space probe
that will discover that the universe is, in fact, just a massive
spherical computer display surrounding the solar system.

-- 
Tim Cook
http://home.bellsouth.net/p/PWP-empyrean

-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------

Post a reply to this message