problem with photons

[themaxxer]

my problem are these white splotches on the grey objects...



my settings are:
min/max: -3/0
HSph.sub: 60
Interp. sub: 30
clr: 0.4
nrm: 0.5
dist: 0.1

any ideas for the right settings?

thanks for your ideas and help
best regrads

[marc]

Try lowering the treshhold values (dr/nrm). What are the photon settings?
Maybe lowering the noise treshhold in the qmc rollout could also be an issue...


marc

[GoncaloP]

Hi Manuel,

Photons are never enough to fix problems in small areas like this, so you have two options:

1- Hide the small objects that doesnt contribute much to GI, and calculate the photon map. This will allow you to use less photons (subdivisions) and get a better photon distribution,

2- Increase the retrace treshold, you can see it effect doing a small test:
with the photon map from file, change the first diffuse bounces to direct computation, with only 3 subd. then with AA at Fixed 1, press render. You will notice that near the corners, more visible at right side of the image, if you increaase the retrace threshold amount, some small white points will appear, and getting biger each time you increse this value, this means raytraced points to be able to get detail in small areas like this one.

here is an example:




Gonçalo

[marc]

Hello you two

Just some further questions because the master of photons is speaking :

As far as I understand the retrace treshold parameter, it just blends from photon to IMap in detailed areas. The higher the retrace treshhold the bigger the amount around the edges which will be done with Imap.

You wrote: "..., this means raytraced points to be able to get detail in small areas like this one." What exactly is meant with that?

In the past I tried to increase the retrace value just if I don't get enough photons to have a nice contribution. In fact I just used it to speed up my renderings, because I can lower the photon amount and get nice edges anyway.
For a perfect result I would rather have increased the diff subdivis as increasing the retrace treshold.

In your photon "tutorial" I saw that you set this value to 0. I thought that was done to receive a "only photon map" in the first pass (where you hide the small objects). Is there another reason?


thanks in advice


marc

[GoncaloP]

I ve set the retrace threshold value to 0.0 mainly because I didnt undertand the real effect of this until now!

But yes it usualy slows the irradiance map a lot, and the retraced points are from the photons (I guess), irradiance map will take this points to store the samples, instead of looking for photons...

Rizing the amount of subdivisions its a way to get a good solution for the edges, but also takes some more time to trace them, and the irradiance map will be a lot faster. For animations thats a good solution, even for stills if you want to have more than one image...

I like to trace a lot of subdivisions because it will rize the dinamic range for reflections and refractions, it will work mostly like a HRDI base, but for interiors.

The small objects can be hidded because they dont contribute much to GI, so you can have a cleaner solution to work with, with less subdivisions.

Gonçalo

[didjaja]

Gonçalo,Vlado says in "a basic guide to photon map" "The Retrace threshold parameter controls what "near corners" means to VRay"
Its mean that my scene is in centimetres and retrace threshold is 2,the retrace distance is 2 centimetres nears the cornes??
I know is my scene is in centimetres and max density is 1,it means 1 centimetre,but with retrace threshold i dont know
And Vlado says "computing GI with Monte Carlo methods instead of the photon map near corners"
If retrace threshold is more than 0 the cornes are calculated by direct computation not irradiance map.Is this right?
Very thanks master

[pengo]

another technique???

To Goncalo
another technique???

do u render now with direct computation in the first diffuse bounce and photons in the second??

or do u use it (direct computation) only to make visible the retrace threshold value effects??

bye and thank again TEACHER

[GoncaloP]

Hey please stop calling me those names My name is Gonçalo

To Didjaja - I´m not sure about the correct answer to your first question, but I think that is units independent, so the best way to see its reall effect is with testing it with direct computation...

"If retrace threshold is more than 0 the cornes are calculated by direct computation not irradiance map.Is this right?"
Vlado is the one how knows vray, not me

To Pengo - Yes, this image was only to see the effect, but you can use direct coputation in first diffuse bounces and photon map for second diffuse bounces too...

Gonçalo

[pengo]

yes your name is goncalo but

yes your name is goncalo but you are our teacher

But do u use direct computation and photon for final image?

bye goncalo

[GoncaloP]

No, I use to change it for irradiance map

Gonçalo

[pengo]

OK I stop me

thank u

OK I stop me!!

I don't ask to u more on it


........................I can't resist but is it beter for rendering time to use treshold value or not and upper than 2 or only for some solution do u use non 0 value?

and with this question I really close

[Zero One 010110]

Hi Gonçalo, i got another question that has buggin in my mind, in your "a basic guide to photon map" i found an ies sun system aligned with a direct target light, but the ies sun is off, is there any reason then to have it in the scene?

Thanks G!

[marc]

Hey Gonçalo... just want to thank you for your patience
...and your answers of course

cheers

marc

[pengo]

TO oblivion

TO oblivion

I reply for him
I hope it doesn't offend him

He put it because he can put a direct light (that vray supports) in the same correct place of the sun at specific date and time and geographic location !!! So the lighting is more realistic
But if u are interested on using sunlight with vray directly u must search in this forum (with search function) goncalo eplained in old thread how to use it in conjunction with dreamscape

bye