Trevor G Quayle wrote:
> Best to have a camera with manual focus and shutter speed ability.
> (I also use these functions often for regular photography with my
> camera). Nowadays you can get digital cameras with these functions
> for fairly cheap. (Better yet you can go DSLR if you have the
> money...one day... one day...)

   I know very little about cameras: this is the first time I own a
camera in my life, believe it or not... the problem is that I didn't
have HDRI in mind when I purchased it, so following Murphy's law I
did chose the wrong one.

> Can you try averaging the images using a weighting appropriate to the
>  reltive f-stops and camera response curve?

   Very good suggestion, but I would have to learn *a lot* about
photography to be able to do this... Now that I remember, my brother was
into the photographic hobby some years ago and perhaps he still has some
basic books around (I only have to find the time to read them... :)

--
Jaime

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Perhaps it's just a coincidence, but some weeks ago they appeared over 
the autobahn:

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Attachments:
Download 'autobahn-060219-ufo.jpg' (91 KB)

Preview of image 'autobahn-060219-ufo.jpg'

Jaime Vives Piqueres <jai### [at] ignoranciaorg> wrote:
> > Can you try averaging the images using a weighting appropriate to the
> >  reltive f-stops and camera response curve?
>
>    Very good suggestion, but I would have to learn *a lot* about
> photography to be able to do this... Now that I remember, my brother was
> into the photographic hobby some years ago and perhaps he still has some
> basic books around (I only have to find the time to read them... :)
>
> --
> Jaime

Here is my attempt at doing this (I assume I know what you are doing, i.e.
you are trying to assemble a series of LDR images into an HDR image within
POV).  The difficult part is determining a camera response curve (similar
to monitor gamma) and the relative/absolute F-Stop values for the given
images. I'm not even sure I've applied the response curve correctly here,
but it seems ok even though the results are slightly different than that
obtained using HDRShop.

//start

#declare CamRsp=2.2;//Camera response curve
#declare NumMaps=5;

#declare
Maps=array[NumMaps][2]{{"Chateau-4","-4"},{"Chateau-2","-2"},{"Chateau+0","0"},{"Chateau+2","2"},{"Chateau+4","4"}}//{i
mage,
absolute FStop value}

#local PIMAGE = function {
  pigment{onion
    pigment_map{
    #local i=0;#while (i<NumMaps)
      [i/NumMaps     image_map {jpeg Maps[i][0] interpolate 2 map_type 1}]
      [(i+1)/NumMaps image_map {jpeg Maps[i][0] interpolate 2 map_type 1}]
    #local i=i+1;#end
    }
    phase -0.5/NumMaps
    scale<1,1,-1>*NumMaps
  }
}

#local FRd=function(x,y,z) {max(
  #local i=1;#while (i<=NumMaps)
    #local FS=val(Maps[i-1][1]);

pow(PIMAGE(i*x/sqrt(x*x+y*y+z*z),i*y/sqrt(x*x+y*y+z*z),i*z/sqrt(x*x+y*y+z*z)).red,CamRsp)/pow(2,FS),
  #local i=i+1;#end
0)}
#local FGn=function(x,y,z) {max(
  #local i=1;#while (i<=NumMaps)
    #local FS=val(Maps[i-1][1]);

pow(PIMAGE(i*x/sqrt(x*x+y*y+z*z),i*y/sqrt(x*x+y*y+z*z),i*z/sqrt(x*x+y*y+z*z)).green,CamRsp)/pow(2,FS),
  #local i=i+1;#end
0)}
#local FBl=function(x,y,z) {max(
  #local i=1;#while (i<=NumMaps)
    #local FS=val(Maps[i-1][1]);

pow(PIMAGE(i*x/sqrt(x*x+y*y+z*z),i*y/sqrt(x*x+y*y+z*z),i*z/sqrt(x*x+y*y+z*z)).blue,CamRsp)/pow(2,FS),
  #local i=i+1;#end
0)}


#declare Stops=0;

#declare Tex1=
  texture{
    pigment{average
      pigment_map{
          [function{FRd(x,y,z)/10000} color_map{[0 rgb 0][1 rgb <1,0,0>]}]
          [function{FGn(x,y,z)/10000} color_map{[0 rgb 0][1 rgb <0,1,0>]}]
          [function{FBl(x,y,z)/10000} color_map{[0 rgb 0][1 rgb <0,0,1>]}]
      }
    }
    finish {ambient 3*pow(2,Stops)*10000 diffuse 0}
  }

//

-tgq

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Jaime Vives Piqueres wrote:

> Bill Hails wrote:
>> [...]
> 
> Very nice, Bill. I think it would look more "integrated" if the textures
> were less reflective, so you will see a bit of the shading of the object
> "matching" the real scene lighting.

Yes, I'll give it a try, but the least reflective part, the wing, is
imo the least integrated-looking part of the model. I think another
part of the problem was that the HDRI was only composed of 3 images
+/- 3 stops each, not a very H DRI :-)

> BTW, I purchased a very good mirror ball some months ago, but I found my
> camera only has autofocus, and it refuses to focus the on reflected
> environment, so I can't get a sharp HDRI. The lighting comes out very
> nice, but the reflections are always very blurred... anyone go a trick
> for this situation? Or should I buy a camera with manual focus?

Yes, that would help, but autofocus can sometimes be persuaded to
focus on a reflection.

There are some nice "creative compacts" that allow manual control,
and if you want to go the distance, a digital SLR is a wonderful
thing but tbh it was my sudden discovery of photography that has
kept me away from povray for so long, and you wouldn't want that
to happen to you would you? :-)

> P.S.: I tried to create the HDRI also with MegaPOV HDR output, without
> having to resort to external utilities, but I'm still polishing the
> method. It uses concentric spheres for each exposure shot, and
> successive transparency with increasing ambient values, but it's
> somewhat esoteric to adjust by now.
> 
> --
> Jaime

I've not tried that myself.

-- 
Bill Hails
http://billhails.net/

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Trevor G Quayle wrote:
> Here is my attempt at doing this (I assume I know what you are doing, i.e.
> you are trying to assemble a series of LDR images into an HDR image within
> POV).  The difficult part is determining a camera response curve (similar
> to monitor gamma) and the relative/absolute F-Stop values for the given
> images. I'm not even sure I've applied the response curve correctly here,
> but it seems ok even though the results are slightly different than that
> obtained using HDRShop.

   Thanks for sharing! I didn't try to understand what you done there, 
but it gives much better results than the simple linear approach I was 
using. And it's also much more practical to have it on a single layer, 
of course. Now, if I can convince the camera to focus on the reflection...

--
Jaime

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Bill Hails wrote:
> Yes, that would help, but autofocus can sometimes be persuaded to
> focus on a reflection.

   I tried some weird tricks, but none worked... :(

> There are some nice "creative compacts" that allow manual control,
> and if you want to go the distance, a digital SLR is a wonderful
> thing but tbh it was my sudden discovery of photography that has
> kept me away from povray for so long, and you wouldn't want that
> to happen to you would you? :-)

   That can't happen to me... I'm too lazy to change now! Anyhow, I will 
not try... ;)

--
Jaime

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Jaime Vives Piqueres <jai### [at] ignoranciaorg> wrote:
> Trevor G Quayle wrote:
> > Here is my attempt at doing this (I assume I know what you are doing, i.e.
> > you are trying to assemble a series of LDR images into an HDR image within
> > POV).  The difficult part is determining a camera response curve (similar
> > to monitor gamma) and the relative/absolute F-Stop values for the given
> > images. I'm not even sure I've applied the response curve correctly here,
> > but it seems ok even though the results are slightly different than that
> > obtained using HDRShop.
>
>    Thanks for sharing! I didn't try to understand what you done there,
> but it gives much better results than the simple linear approach I was
> using. And it's also much more practical to have it on a single layer,
> of course. Now, if I can convince the camera to focus on the reflection...
>
> --
> Jaime

What I did was not too difficult.
1) First I mapped the images using the onion pattern to enable being able to
use loops to simplify the code for varying numbers of input images.
2) Then for each onion layer (representing each LDRI) convert the image
colour (for each r,g,b channel) by COL^CamRsp which converts the pixel
colour to the corresponding real world colour according to the camera
response.
3) Divide the resulting colour by 2^FStop, this coverts the colour of the
corresponding image to its equivilant at 0 stops.
4) Use the max colour found.  Any colours that were clipped in the
corresponding LDRIs (i.e. values of 0 or 1) get dropped out.  (Any colours
that were still clipped at the lowest and highest fstop values will still
be clipped however)

This is a very rough method and assumes that you know the camera response
and the FStop values of each LDRI.  Programs like HDRShop can do a much
better job of estimating these sorts of things.

There is no need to add the successive images together, (as it wouldn't give
the proper result anyways). What HDRI creation is trying to achieve, is find
the real world brightness of every pixel in the image.  If you had only one
image, but there were no clipped colours, then it could act directly like
an HDRI.  However, due to photographic and image storage restrictions,
colour do get clipped.  rgb values are limited to 1, but brightnesses of
lights tend to be much higher, especially as the FStop value gets higher,
and they get clipped to 1 in the image file.  On the other hand, dark
shadow areas can get clipped to 0 due to decimal place truncation at lower
FStop values.

So basically if you take a low FStop image and a high FStop image, convert
them to an equal FStop level, then you just need to check for the greatest
pixel valuebetween the two.  Ideally, for pixels not clipped in either
LDRI, the values should be the same.  For any pixel that was clipped in one
LDRI but not the other, the clipped one will get dropped out.  And for any
pixel clipped in both, well it'll stay clipped, as there is no easy way to
determine the actual value, there isn't enough information.

Hope this helps you understand HDRI and what I did a bit more and I didn't
bore you to death.  I don't profess to be an expert, but I have been
working with HDRI a lot lately so have had to get to understand it myself.

(FYI: in case you don't know, FStops double (or half) the light let in, so
an increase of an image of n Stops will result in an image 2^n times
brighter.)

-tgq

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High!

Bill Hails wrote:

> I guess a sensible answer is in order :-)
> It's pointed at the floor so it can't be pointing at the sun.

As an amateur stargazer myself, I would like to ask what aperture do you 
have there - seems to me it's a 6-incher, isn't it?

See you in Khyberspace!

Yadgar

Now playing: El Greco, Movement 2 (Vangelis)

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> High!
> 
> Bill Hails wrote:
> 
>> I guess a sensible answer is in order :-)
>> It's pointed at the floor so it can't be pointing at the sun.
> 
> As an amateur stargazer myself, I would like to ask what aperture do you
> have there - seems to me it's a 6-incher, isn't it?

11cm Russian-made TAL-1, I can see the rings of Saturn on a clear night :-)

> See you in Khyberspace!
> 
> Yadgar
> 
> Now playing: El Greco, Movement 2 (Vangelis)

-- 
Bill Hails
http://billhails.net/

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High!

Bill Hails wrote:

> 11cm Russian-made TAL-1, I can see the rings of Saturn on a clear night :-)

Ah, the TAL-1! The mounting looks quite massive, it surely would carry 
an additional camera... unlike my somewhat flimsy EQ-2 with my Bresser 
Mizar (11.4 cm/900 mm focal length). Saturn's rings are generally no 
problem, I even was able to spot Titan one night... but as I until 
recently had to watch under a metropolitan area sky, this is far from 
the best results possible with a 4.5-incher - under optimal conditions 
(Afghan mountain desert sky with no scattered artificial light within a 
200-km radius) at least Rhea, Iapetus, Dione and Tethys, perhaps even 
Enceladus would be also visible...

Yes, astronomy (as well as programming) is one of the best excuses to 
turn night into day! Unfortunately, my telescope now is with my parents 
in the dark but remote countryside, about 60 kms from here, so that I'm 
able to observe only on weekends - and during recent months, the weekend 
weather over Germany was a complete failure, just LRCC (Lower Rhenanian 
Cloud Cover)...

See you in Khyberspace!

Yadgar

Now playing: Esthematique (Serge Blenner)

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