On 4-11-2012 15:30, Christian Froeschlin wrote:
> Reuben Pearse wrote:
>
>> Here's my latest Lego render. I've used focal blur in this scene but I
>> think I need to use motion blur. Is motion blur available in latest
>> version of POV-Ray
>
> no, but you can simulate it by rendering an animation moving the
> object in "sub-exposure" steps and then averaging the frames. This
> also gives you the artistic freedom to give more weight to the final
> frame if you want a more comic-like asymmetric blur for this scene.

Ah! A little trick I might need. The animation ng is not regularly open 
on my system, but I should give it a look once in a while :-)

Thomas

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Reuben Pearse <reu### [at] pearsecouk> wrote:
> On 04/11/2012 14:30, Christian Froeschlin wrote:
> > Reuben Pearse wrote:
> >
> >> Here's my latest Lego render.

cool!

> >> I've used focal blur in this scene but I
> >> think I need to use motion blur. Is motion blur available in latest
> >> version of POV-Ray
> >
> > no, but you can simulate it by rendering an animation moving the
> > object in "sub-exposure" steps and then averaging the frames. This
> > also gives you the artistic freedom to give more weight to the final
> > frame if you want a more comic-like asymmetric blur for this scene.
>
> Thanks for the info. Can you point me to any websites or tutorials that
> explain this technique in more detail? Some example POV code would be
> useful.

Here's the scene I use when averaging a number of pre-rendered frames:

#version 3.7;
global_settings{assumed_gamma 1.0}
#default{finish{ambient 1}}

camera{
 orthographic
 right x up y
 location -z
}

#declare n_frames = 80;
#declare image_name_ = "superman"
#macro image_type_() png #end

plane{z,0
 pigment{
  average
  pigment_map{
   #for(V, 1, n_frames)
    [1
     #declare image_name = concat(image_name_, str(V, -(log(n_frames)/log(10) +
1), 0))
     image_map{image_type_() image_name}
     translate -(x+y)/2
    ]
   #end
  }
 }
}


Memory requirements can become pretty high when using large numbers of images,
especially if they are in the HDR format (but they work really well, especially
when rendering star fields).

Sam

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Hm, I'm not quite sure, if this alone solves the issue of having motion blur
with POV 3.7. Should this wonderful superman not having decreasing transparency
during the flight? If you only average pictures of the flight, you will probably
get more blur than expected, since POV doesn't know the sequence of the
pictures. May be, proper weights in the average map will help. But you are still
limited to 256 entries. An other approach is to have copies of the blurred
object with decreasing transparency in the scene. But to find the correct
positions and transparencies is the hard job. Christian Froeschlin gave an
example with his entry "glocken" at the IRTC april 2006, which shows the idea
but the difficulties likewise (rendered at a higher resolution then the original
entry).

Best regards,
Michael

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> Ah! A little trick I might need. The animation ng is not regularly open
> on my system, but I should give it a look once in a while :-)
>
> Thomas

Ah! That is why I get no comment from you to my first (very technically) entry
there. And I value your comments very much ;-)

Best regards,
Michael

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> Hm, I'm not quite sure, if this alone solves the issue of having motion blur
> with POV 3.7. Should this wonderful superman not having decreasing transparency
> during the flight? If you only average pictures of the flight, you will probably
> get more blur than expected, since POV doesn't know the sequence of the
> pictures. May be, proper weights in the average map will help. But you are still
> limited to 256 entries. An other approach is to have copies of the blurred
> object with decreasing transparency in the scene. But to find the correct
> positions and transparencies is the hard job. Christian Froeschlin gave an
> example with his entry "glocken" at the IRTC april 2006, which shows the idea
> but the difficulties likewise (rendered at a higher resolution then the original
> entry).
>
> Best regards,
> Michael
>
>

For the comicks like decreased transparency.
In this sample scene, all frames have the same weight, but it can be 
changed:
    #for(V, 1, n_frames)
     [V // the weight goes from 1 to n_frames.
      #declare image_name = concat(image_name_, str(V, 
-(log(n_frames)/log(10) +
1), 0))
      image_map{image_type_() image_name}
      translate -(x+y)/2
     ]
    #end

By replacing the [1 by [V, the first image have a weight of 1, the 
second a weight of 2,...
You can also use V/n_frames if you want to keep the weight parameter no 
larger than 1.
You can increase the last image further in a few ways:
Add some number to the last image's weight.
Use pow(V,2) or pow(V/n_frames,2) for the weight. You can use a power of 
3, 4 or some intermediate value if you want.
This assume that each frame is created in the direction of the movement 
and that you want the last frame to dominate.

The limit of 256 entries is not a problem unless you have a very long 
motion blur trail. If you use decreasing transparency, it's even less of 
a problem, even with rather long trails.



Alain

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Alain <kua### [at] videotronca> wrote:

> > Hm, I'm not quite sure, if this alone solves the issue of having motion blur
> > with POV 3.7. Should this wonderful superman not having decreasing transparency
> > during the flight? If you only average pictures of the flight, you will probably
> > get more blur than expected, since POV doesn't know the sequence of the
> > pictures. May be, proper weights in the average map will help. But you are still
> > limited to 256 entries. An other approach is to have copies of the blurred
> > object with decreasing transparency in the scene. But to find the correct
> > positions and transparencies is the hard job. Christian Froeschlin gave an
> > example with his entry "glocken" at the IRTC april 2006, which shows the idea
> > but the difficulties likewise (rendered at a higher resolution then the original
> > entry).
> >
> > Best regards,
> > Michael
> >
> >
>
> For the comicks like decreased transparency.
> In this sample scene, all frames have the same weight, but it can be
> changed:
>     #for(V, 1, n_frames)
>      [V // the weight goes from 1 to n_frames.
>       #declare image_name = concat(image_name_, str(V,
> -(log(n_frames)/log(10) +
> 1), 0))
>       image_map{image_type_() image_name}
>       translate -(x+y)/2
>      ]
>     #end
>
> By replacing the [1 by [V, the first image have a weight of 1, the
> second a weight of 2,...
> You can also use V/n_frames if you want to keep the weight parameter no
> larger than 1.
> You can increase the last image further in a few ways:
> Add some number to the last image's weight.
> Use pow(V,2) or pow(V/n_frames,2) for the weight. You can use a power of
> 3, 4 or some intermediate value if you want.
> This assume that each frame is created in the direction of the movement
> and that you want the last frame to dominate.
>
> The limit of 256 entries is not a problem unless you have a very long
> motion blur trail. If you use decreasing transparency, it's even less of
> a problem, even with rather long trails.
>
>
>
> Alain

Yes, your proposal is much more detailed than mine. In fact I only mentioned the
general idea that simply averaging pictures of a flight will not yield a motion
blurred picture and proper weights are needed. But I think you have to play
around a lot with the weights and the number of images to find a proper image.

Best regards,
Michael

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Am 04.11.2012 20:46, schrieb MichaelJF:

> Yes, your proposal is much more detailed than mine. In fact I only mentioned the
> general idea that simply averaging pictures of a flight will not yield a motion
> blurred picture and proper weights are needed.

As a matter of fact, for /realistic/ motion blur simple averaging of the 
images /is/ the proper method. Whike the "opaque object with transparent 
trail" look is a common staple - probably invented to give the 
impression of motion while at the same time preserving object detail - 
it is outright wrong.

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On 4-11-2012 20:02, MichaelJF wrote:
>
>> Ah! A little trick I might need. The animation ng is not regularly open
>> on my system, but I should give it a look once in a while :-)
>>
>> Thomas
>
> Ah! That is why I get no comment from you to my first (very technically) entry
> there. And I value your comments very much ;-)

<blush> I shall have to experiment with this then... ;-)

Thomas

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clipka <ano### [at] anonymousorg> wrote:
> Am 04.11.2012 20:46, schrieb MichaelJF:
>
> > Yes, your proposal is much more detailed than mine. In fact I only mentioned the
> > general idea that simply averaging pictures of a flight will not yield a motion
> > blurred picture and proper weights are needed.
>
> As a matter of fact, for /realistic/ motion blur simple averaging of the
> images /is/ the proper method. Whike the "opaque object with transparent
> trail" look is a common staple - probably invented to give the
> impression of motion while at the same time preserving object detail -
> it is outright wrong.

Thanks, clipka... I knew I wasn't going crazy :) Maybe MJF is confusing motion
blur with tracers?

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clipka wrote:
> Am 04.11.2012 20:46, schrieb MichaelJF:
> 
>> Yes, your proposal is much more detailed than mine. In fact I only
>> mentioned the
>> general idea that simply averaging pictures of a flight will not yield

>> a motion
>> blurred picture and proper weights are needed.
> 
> As a matter of fact, for /realistic/ motion blur simple averaging of th
e
> images /is/ the proper method. Whike the "opaque object with transparen
t
> trail" look is a common staple - probably invented to give the
> impression of motion while at the same time preserving object detail -
> it is outright wrong.
> 
	The "opaque object with transparent trail" is also what you get
with a flash light synced on the rear curtain and a long(ish)
exposure time (if you don't sync on the rear curtain, the "trail"
will be in front of the object, or sometimes on both sides).

	For example:
http://www.apnphotographyschool.com/wp-content/uploads/2010/12/358x500xni
kon-speedlight-rear-curtain-sync.jpg.pagespeed.ic.qeHOKzR258.jpg

		Jerome
-- 
mailto:jeb### [at] freefr
http://jeberger.free.fr
Jabber: jeb### [at] jabberfr

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