56 replies to this topic

[michael]

I'll bet that's how most 'art of ...' books are made  

[Marc]

Day 2:

Well, after the initial tragedy that day1 was turning into it was ultimately saved by the timely and fortuitous intervention of Mario (who has now entered the tale as the hot-blooded latin hero, and is nicely juxtaposed against the comic relief of Jason and Arctor).

So day2's diary entry is all about caustics. Whether they can be done, should be done or are even worth doing at all. I believe that caustics are definitely worth the effort.

So here is the first image using 500 000 photons and Mario's wonderful new (and working) glass shader. You'll notice that it looks slightly different to the reference image. The caustics look slightly different in the center and I'm not getting any bounce on the wall. I'm not too concerned about the shape of the caustics since that could be attributed to a number of things, and besides... it looks pretty.

I followed (mostly) the steps outlined in this video :  Caustics


  


In the last one I added photons to the chrome sphere too.

  

ah yes, here is the hip file :  cornell_day2_v1.hip.gz   42K   342 downloads

M

[Mcronin]

Hey! Where's the Day 2 hip file?


I am riveted!

[Marc]

Day 3 :

Well since day2 went rather well, I've left it at that and moved straight into day 3. If the reference material is to be believed then my render should take somewhere along the lines of 15 seconds to render. According to my mplay window my render started at 11:32 am... it's now 1:56pm PST.
Something, somewhere seems to have gone wrong.

I notice now that I may have used too many photons (100 000 global photons and 500 000 caustic photons), but I'm too far along now to stop.
As soon as the current render is done I will fire off another one with the desired 200 000 global and 50 000 caustic photons.

Image1 : 100 000 global, 500 000 caustic
Image2 : 200 000 global, 50 000 caustic

Both were rendered with a sampling quality of 8, and are pretty noisy. I also realised that I had my irradiance cache set to "write only" and that's why they were so slow. I'm rendering another one now and its going alot faster.



It's interesting to note the sharpness of the glass caustics in the first render.

M

P.S. I donated blood this morning, so I'm a little woozy and slow today. Day3 may in fact spread out to more than one day.

[Mario Marengo]

Marc, on Sep 14 2004, 04:08 PM, said:

According to my mplay window my render started at 11:32 am... it's now 1:56pm PST.
Something, somewhere seems to have gone wrong.

Uh oh  
Guess that doesn't bode well for the question of "Whether they can be done, should be done or are even worth doing at all"...

If it doesn't turn out to be a simple thing (like just too many photons or something),  and caustics are in fact pigs, then maybe it'll be woth looking at what can be done (if anything) by using point clouds; maybe in conjunction with the auto-gen'd photon maps.... just a thought.

But hopefully it's just a bad setting  

[Marc]

Forgive me, I wasn't clear. The exceedingly long render times are caused by me hitting the "Full Irradiance" button.
Caustics aren't that long in this controlled test. Longer than the 12 seconds HWJ claims to have made them in, but not long enough to put me off.

[Mario Marengo]

Marc, on Sep 14 2004, 04:52 PM, said:

The exceedingly long render times are caused by me hitting the "Full Irradiance" button.

Ah. OK... whew!

Yeah, 12 seconds does sound a little too snappy... but 15 seconds for full GI?

Can't wait for the Day3 results. Bring'em on!

[Marc]

Day 4:

And so we begin day 4 with an interesting turn of events. For some esoteric reason, no matter how hard I tried, I could not get rid of the noise in the render regardless of how high I turned up my irradiance sampling quality. In fact, I could not detect a noticable difference in the prettiness of the render at all... all it did was take longer (8, 64, 128, 256 settings).

So I discussed this with someone here at work (Erich) and was told that you cannot have the full irradiance and photon maps activated in the same shader. Apparently Houdini/mantra doesn't approve of those sort of shenanigans.
Fair enough, thought I, I'll do some testing in this new direction.

With all this in mind, I have a new render on the go using only caustic photons and global photons, no irradiance. I have also turned up the "Global photon sampling" up to a seemingly massive number of 500. Admittedly I have no idea what a good number for this should be, but the default is set to 50, so 500 seems like alot (although we've learnt the folly of paying attention to Houdini's defaults haven't we?)

As soon as the render is done I shall post it here. I'll be following it up with one that only uses full irradiance, and another combining the two using multiple lights/shaders.

Image1 photons only (global/caustic)                                 image2 irradiance only.
                                

Last one for today. Irradiance and photons, two seperate shaders and lights. Only 16 irradiance samples though, and it took forever.

M

Here is the hip file, in case anyone is interested.
 cornell_day4_v2.hip.gz   45.49K   381 downloads

[TheDunadan]

On the noise problem... I might be terribly wrong here, but usually there is something like "photon radius". I know from Mental Ray that renders can turn out terribly noisy if the photon radius is too small,... I'd be very surprised if Mantra hasn't got a similar option. Have you tried playing around with these settings yet ?

Btw. Does anyone know if ray-labels are planed for mantra or already available in H7 ? They could make life much easier I reckon  

Jens

[Marc]

I believe the 'photon sampling' setting is the radius. I could, however, be mistaken.

M

[Jason]

From my previous experience with Irradiance Caching - unless you blow away your cache file, nothing you ever do will change the sampling quality of the irradiance rays.

BEWARE THE CACHE, MY FRIENDS.

[Mario Marengo]

TheDunadan, on Sep 15 2004, 03:54 PM, said:

On the noise problem... I might be terribly wrong here, but usually there is something like "photon radius".
... I'd be very surprised if Mantra hasn't got a similar option.

You know what?... strange... I haven't used GI in Mantra yet (did quite a bit of it with Entropy back in the day), and I can't check this out right now (swamped with work), but I don't think there is a gather radius for irradiance. I'm pretty sure there is for photons (from looking at the images), but for irradiance?.... nnnnnnn-I-don't-think-so... could it be?!?    

I certainly don't see it as an option for the irradiance() function. There is an error metric in the ROP, but that's not the same; and number-of-samples is definitely not the same as a gather radius... very strange...

It should be pretty trivial to scatter a few thousand points in the scene as a point cloud, call irradiance() on each one, and do your own filtering over a given radius (the occlusion sample shader that Mark E. submitted does this with occlusion(), and the SS shaders do something similar as well). I'd imagine it should render pretty fast and not look that noisy...

Mario Puzzled-In-Toronto Marengo.