Well,

You could use media, with a diminishing density toward the end of the tail,

define a macro that progressively scatters actual spheres as a function of the
distance from the head,

define a solid object that's textured with a gradient pattern, and a color map
that fades to fully transparent,

etc.

For the running figures, a naive but quick approach would be to iterate objects
to the side and slightly backwards, with a progressively increasing
transparency.

You could do the motion-line effect by sampling the [average] color at the
figure with eval_pigment, and then creating fading cylinders, rounded boxes,
etc.

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On 26/05/2018 16:36, Bald Eagle wrote:
> For the running figures, a naive but quick approach would be to iterate objects
> to the side and slightly backwards, with a progressively increasing
> transparency.

That reminds me of a technique posted here some time ago. Which was to 
make a short animation with the figure moving and averaging/combining 
the images into one. I am sorry but I can't remember the details.

-- 

Regards
     Stephen

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Le 18-05-26 à 10:07, Kima a écrit :
> There are some examples in this newsgroup for building a comet composed of a
> head and tail.
> 
> It is possible (in vector programs, for instance) to create a sense of moving by
> creating a series of the same object in which the tail is blurry.
> 
> I wonder if there is such possibility to gradually translate (and reduce the
> scale) an object and make blurry effects for the tail?
> 
> For this, blur should be something like that in vector programs rather than the
> focal blur of povray.
> 
> 

There is an experimental feature called blink that can be used when you 
run UberPov.

That feature allow you to make any object, light and even the camera act 
as if they are moving or not present all the time.
That feature effectively place several copies of the object and average 
them. Those can be stationary to make ghostly objects. They can have 
some path to make them blurry as if they are moving.

This have the advantage that any internal structure don't affect the 
image as they would if you use transparency.

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On 26-5-2018 18:07, Stephen wrote:
> On 26/05/2018 16:36, Bald Eagle wrote:
>> For the running figures, a naive but quick approach would be to 
>> iterate objects
>> to the side and slightly backwards, with a progressively increasing
>> transparency.
> 
> That reminds me of a technique posted here some time ago. Which was to 
> make a short animation with the figure moving and averaging/combining 
> the images into one. I am sorry but I can't remember the details.
> 

That is currently available as 'blink' in the UberPOV version of 
POV-Ray. It is one of the experimental patches. In the past, it existed 
in pre-3.7 iirc.

-- 
Thomas

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On 27/05/2018 07:49, Thomas de Groot wrote:
> On 26-5-2018 18:07, Stephen wrote:
>> On 26/05/2018 16:36, Bald Eagle wrote:
>>> For the running figures, a naive but quick approach would be to 
>>> iterate objects
>>> to the side and slightly backwards, with a progressively increasing
>>> transparency.
>>
>> That reminds me of a technique posted here some time ago. Which was to 
>> make a short animation with the figure moving and averaging/combining 
>> the images into one. I am sorry but I can't remember the details.
>>
> 
> That is currently available as 'blink' in the UberPOV version of 
> POV-Ray. It is one of the experimental patches. In the past, it existed 
> in pre-3.7 iirc.
> 


Alain mentioned blink but I did not know the technique was a feature of 
UberPOV. Nice. :-)

-- 

Regards
     Stephen

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Am 27.05.2018 um 08:49 schrieb Thomas de Groot:

> That is currently available as 'blink' in the UberPOV version of
> POV-Ray. It is one of the experimental patches. In the past, it existed
> in pre-3.7 iirc.

I think MegaPOV had a motion blur patch. Official POV-Ray? Not as far as
I know.

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On 27-5-2018 10:12, clipka wrote:
> Am 27.05.2018 um 08:49 schrieb Thomas de Groot:
> 
>> That is currently available as 'blink' in the UberPOV version of
>> POV-Ray. It is one of the experimental patches. In the past, it existed
>> in pre-3.7 iirc.
> 
> I think MegaPOV had a motion blur patch. Official POV-Ray? Not as far as
> I know.
> 

I stand corrected. It was MegaPOV indeed.

-- 
Thomas

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On 05/26/2018 10:07 AM, Kima wrote:
> There are some examples in this newsgroup for building a comet composed of a
> head and tail.
> 
> It is possible (in vector programs, for instance) to create a sense of moving by
> creating a series of the same object in which the tail is blurry.
> 
> I wonder if there is such possibility to gradually translate (and reduce the
> scale) an object and make blurry effects for the tail?
> 
> For this, blur should be something like that in vector programs rather than the
> focal blur of povray.
> 
> 

For a comet I'd probably first try a media solution.

I played some with a blob based, 2D image processing framework in early 
2016 which might do for a 2D motion blur effect(1). See:

http://news.povray.org/povray.binaries.images/thread/%3C56ca69e1%40news.povray.org%3E

POV-Ray can duplicate pretty much any 2D gimp/photshop result. However, 
given it's a 3D rendering tool and so carries extra overhead - it's 
almost always slower than a 2D/2.5D alternative. A way of saying a 2D, 
layer based, image tool might be the expedient path - especially if it 
already has the canned effect you want.

Some have implemented motion blur by blending multiple images from an 
animation of the moving parts into a single final image. This can be 
done entirely with POV-Ray today though not in a single render. 


Bill P.

(1) - A comet is a moving object where you don't need the associated 
blurred shadows, reflections, an uberpov 'blink' like feature offers.

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A comet's tail is actually composed of tiny particles or gases (blown off the
comet by the Solar wind, I think), so the tail effect isn't actually
motion-blur-from-movement (although it *looks* like that from a distance.) As
others mentioned, media might be a more appropriate way to create the tail;
perhaps media within a transparent cone object(?). Plus some turbulence.

However, your running-man example made me think of a 'solid media' idea,
something I posted years ago. It might be helpful, to get the effect you're
after. Take a look at the image example I posted there, a kind of step-by-step
guide...

http://news.povray.org/povray.binaries.images/message/%3Cweb.4436e54a72fe66658ad7a9060%40news.povray.org%3E/#%3Cweb.443

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On 26-5-2018 16:07, Kima wrote:
> There are some examples in this newsgroup for building a comet composed of a
> head and tail.
> 

In 2012 I built a scene of the Early Earth with meteor/comet showers. I 
looked up the code and found I used the following for building them:

//------------------------------------------------------------
#declare C_STAR = rgb <1.000, 0.477, 0.154>*1; //3000K
#declare fn_Disc = function (x) { 1 / (1 + pow (x, 3)) }
#declare fn_Spike = function (x) { 1 / (1 + pow (x, 2)) }

#declare Disc =
cylinder {0, y, 50
   hollow
   pigment {rgbt 1}
   interior {
     media {
       emission C_STAR * 10
       density {
         function {fn_Disc (sqrt (x*x + z*z))}
       }
     }
   }
}

#declare Diffraction_spike =
box {
   <-100, 0, -0.5>*4, <100, 1, 0.5>*4
   hollow
   pigment {rgbt 1}
   interior {
     media {
       emission C_STAR * 2
       density {
         function {fn_Spike (abs(x))}
       }
     }
   }
}

#declare Meteor_trail =
box {
   <0, -2, -2>*4, <10000, 2, 2>*4
   hollow
   pigment {rgbt 1}
   interior {
     media {
       emission C_STAR * 2
       density {
         function {fn_Spike (abs(x))}
       }
     }
   }
}

//---------------------------Meteor1
#declare star_pos = vaxis_rotate(SunPosition,x,10);
#declare star_pos = vaxis_rotate(star_pos,y,-170);
#declare YAxis = CamLoc - star_pos;

object {Disc
   scale 1800
   Point_At_Trans(YAxis)
   translate star_pos
}

object {Meteor_trail
   scale 1800
   rotate -100*y
   Point_At_Trans(YAxis)
   translate star_pos
}

object {Diffraction_spike
   scale 1200
   rotate 45*y
   Point_At_Trans(YAxis)
   translate star_pos
}

object {Diffraction_spike
   scale 1200
   rotate -45*y
   Point_At_Trans(YAxis)
   translate star_pos
}

//------------------------------------------------------------

A visualisation of this work canbe found here:
http://news.povray.org/povray.binaries.images/thread/%3C4ff1b4cc%40news.povray.org%3E/?ttop=422387&toff=1050

-- 
Thomas

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