POV-Ray : Newsgroups : povray.binaries.images : Progress on anniversary scene Server Time
3 Mar 2024 13:12:58 EST (-0500)
  Progress on anniversary scene (Message 1 to 4 of 4)  
From: Cousin Ricky
Subject: Progress on anniversary scene
Date: 10 Feb 2024 16:36:02
Message: <65c7ec42@news.povray.org>
Of the 4 unfinished elements that were part of my POV-Ray 30th
anniversary tribute scene, 3 have been published: DeskLamp, RC3Wood, and
ShapeOfTheDay.

Unfortunately, there are a couple of lighting problems that showed up in
the interaction between DeskLamp and ShapeOfTheDay.  Most obviously, the
caustics are out of control.  More subtly, the light bulb emission is
too low; this can be seen as the dark spot in the reflection of the lamp
at the lower right corner of the wood block.  I have not figured out
what the problems are.

Image povray_30th_anniversary.20230605.jpg was rendered right after I
completed RC3Wood, and that is when the caustics bug first manifested.
This bug has diminished the usefulness of ShapeOfTheDay with refractive
and, to a lesser extent, metallic objects, but there are workarounds.
The easiest is to use one of the outdoor settings, which don't use DeskLamp.

An indoor workaround for image povray_30th_anniversary.20240207.jpg was
possible because I rendered it with separate photons and radiosity
passes.  For the photons pass, I used Declare=sotd_Quality=0, which
de-implements the lamp fixture, then re-enabled the lamp for the
radiosity passes.

The new image applied my light bleeding technique.  It is noticeably
darker than the 2021 render; I do not yet know why this is.


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Attachments:
Download 'povray_30th_anniversary.20230605.jpg' (423 KB) Download 'povray_30th_anniversary.20240207.jpg' (261 KB)

Preview of image 'povray_30th_anniversary.20230605.jpg'
povray_30th_anniversary.20230605.jpg

Preview of image 'povray_30th_anniversary.20240207.jpg'
povray_30th_anniversary.20240207.jpg


 

From: Alain Martel
Subject: Re: Progress on anniversary scene
Date: 11 Feb 2024 10:29:21
Message: <65c8e7d1$1@news.povray.org>
Le 2024-02-10 à 16:35, Cousin Ricky a écrit :
> Of the 4 unfinished elements that were part of my POV-Ray 30th
> anniversary tribute scene, 3 have been published: DeskLamp, RC3Wood, and
> ShapeOfTheDay.
> 
> Unfortunately, there are a couple of lighting problems that showed up in
> the interaction between DeskLamp and ShapeOfTheDay.  Most obviously, the
> caustics are out of control.  More subtly, the light bulb emission is
> too low; this can be seen as the dark spot in the reflection of the lamp
> at the lower right corner of the wood block.  I have not figured out
> what the problems are.
> 
> Image povray_30th_anniversary.20230605.jpg was rendered right after I
> completed RC3Wood, and that is when the caustics bug first manifested.
> This bug has diminished the usefulness of ShapeOfTheDay with refractive
> and, to a lesser extent, metallic objects, but there are workarounds.
> The easiest is to use one of the outdoor settings, which don't use DeskLamp.
> 

In povray_30th_anniversary.20230605.jpg, my guess would be not enough 
photons being shot. If you use a count, I suggest switching to spacing.
When using count, remember that it's spread across all light_source and 
all target objects. ALL non-shadowless light will emit photons unless 
they have this photons block :
photon{refraction off reflection off}
as the default is :
photon{refraction on reflection on}

You may use a non unit value for the target attribute of an object. That 
will be used as a spacing multiplier.
target 0.2 will DIVIDE the spacing by 5 (meaning 25 times more photons), 
while target 2 will double the spacing (meaning 4 times less photons), 
used when shooting photons at that object.

Maybe also increase the jittering of the photons. It looks like there is 
none.

The dark area in the reflection of the desk lamp look credible. I often 
see something similar IRL. You may try to give the interior of the shade 
an finish that include a moderate amount of emission. That should make 
the darker area less obvious.


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From: Cousin Ricky
Subject: Re: Progress on anniversary scene
Date: 19 Feb 2024 12:20:41
Message: <65d38de9@news.povray.org>
On 2024-02-11 11:29 (-4), Alain Martel wrote:
> 
> In povray_30th_anniversary.20230605.jpg, my guess would be not enough
> photons being shot. If you use a count, I suggest switching to spacing.
> When using count, remember that it's spread across all light_source and
> all target objects. ALL non-shadowless light will emit photons unless
> they have this photons block :
> photon{refraction off reflection off}
> as the default is :
> photon{refraction on reflection on}

I stopped using photons count many years ago, probably in 2006, when I
bought a computer with a decent amount of memory.  Both images used
photons spacing, and they used the same spacing value.

> You may use a non unit value for the target attribute of an object. That
> will be used as a spacing multiplier.
> target 0.2 will DIVIDE the spacing by 5 (meaning 25 times more photons),
> while target 2 will double the spacing (meaning 4 times less photons),
> used when shooting photons at that object.

That is just side-stepping the issue, because the '30' object uses the
identical photons block in both images.  All that changed was the light
source.

> Maybe also increase the jittering of the photons. It looks like there is
> none.

Jitter is turned on permanently, and as recommended in the POV-Ray
reference, I have not changed the default value.  (I neglected to
mention this in the DeskLamp user manual.)  Are you attributing the
discrete rainbow stripes to non-jittering?  That is most likely due to
imperfect anti-aliasing (interpolate 2) in the image map used to define
the glass '30'.

To be clear, the changes between these images, including the one I
posted in in 2021, were in the include files, not in the scene
definition itself.  The bottom line is that there is something about the
lamp fixture that causes the caustics to go haywire.

> The dark area in the reflection of the desk lamp look credible. I often
> see something similar IRL. You may try to give the interior of the shade
> an finish that include a moderate amount of emission. That should make
> the darker area less obvious.

An emitting object cannot be darker than the surface it is
illuminating--in this case, the interior of the lamp hood.  The problem
is that the emission on the light bulb object is too low.  I will not
put an emission on the lamp hood interior, because it does not emit
anything.


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From: Cousin Ricky
Subject: Re: Progress on anniversary scene
Date: 19 Feb 2024 12:34:00
Message: <65d39108$1@news.povray.org>
On 2024-02-19 13:20 (-4), Cousin Ricky wrote:
> On 2024-02-11 11:29 (-4), Alain Martel wrote:
>>
>> Maybe also increase the jittering of the photons. It looks like there is
>> none.
> 
> Jitter is turned on permanently, and as recommended in the POV-Ray
> reference, I have not changed the default value.  (I neglected to
> mention this in the DeskLamp user manual.)  Are you attributing the
> discrete rainbow stripes to non-jittering?  That is most likely due to
> imperfect anti-aliasing (interpolate 2) in the image map used to define
> the glass '30'.

I just realized I confused photons jitter with area light jitter.  But
since I have not used the jitter keyword in the photons global_settings
block, the default carries.  Since the same photons global settings were
used in both images, this cannot be the problem anyway.


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