PM usecase tutorial, Red Kitchen

[_Mo_]

Hi guys!

Here's the first draft of the photon-mapping tutorial I'm writing. Link to PDF & scene. I would like to hear what else could be put into it (have I forgot any important things?), if I made any big mistakes so far and generally what you think. It's still missing some test renders imagery to better show the influence of some parameters & caustic examples, but roughly this is it.

Scene was donated by Yaroslav Lebidko, I just re-tweaked the materials for Blender 2.6, added curtains and set up lighting. Two things still bother me; why is the aluminum material behind glass so dark (EDIT; solved, see at bottom) and what is causing the fireflies you can better see in the second picture:

The noise gets cleared a bit after a few passes, but still its an anomaly. It appears mainly in this region:

Here are the settings I used for the above "final" render (I forgot to save the packed .blend with them).

EDIT: lol, forget about the "dark aluminum" thing, it was insufficient raydepth. Such a noob mistake, o the shame!
hm, I used raydepth (&shadowdepth) of 4, the curtains are solid (2 sides), and the glass also (another 2 sides), so 4 should be enough? (there is no window glass)

[Samo]

Hi Matej

The tutorial is good. I would like to point out a couple of things though. First, I believe the standard term is 'patch' rather than 'spot' when talking about photons averaging points.

Secondly, I would explore in more details the current posibilites of using photon lamps and BGportals at the same time we disable backgrounds as a source of photons, and also photon lamps in support of arealights to produce caustics while still keeping the arealight soft shadows and lighting. Also I believe photons only lamps could be interesting to produce a fast 'indirect lighting only' pass in case users want to play with render passes.

I would be interesting also to point out how arealights that we put on windows as photon emitters usually should reproduce background color and power, so users might be interested in disabling the background as a source of light.

[Samo]

another important question is the fact that many times glass is not intended to produce any caustic effect because it is a prismatic mesh like windows panes, however photons will make themselves caustics as soon as they get through the glass and will produce a bad effect, unless we activate fake glass for such cases.

[_Mo_]

Thanks for checking it and for reminders. I will correct that and add additional content:

* a separate scene (a bottle, or something) for examples of caustics use (arealights + photon only spotlights)

* an example of portals use with the kitchen scene. IIRC for portals is better to use a sunsky environment and not a sunlamp?

* a warning on caustic troubles (had in mind this one) and explanation why it's better to use fake glass in archviz

Only the 'indirect lighting only' pass part I'm not sure I understand - do you mean to create a PM clay-render which would be then used for "lightening" the scene in compositing?

[Samo]

Thanks for checking it and for reminders. I will correct that and add additional content:

* a separate scene (a bottle, or something) for examples of caustics use (arealights + photon only spotlights)

* an example of portals use with the kitchen scene. IIRC for portals is better to use a sunsky environment and not a sunlamp?

* a warning on caustic troubles (had in mind this one) and explanation why it's better to use fake glass in archviz

Only the 'indirect lighting only' pass part I'm not sure I understand - do you mean to create a PM clay-render which would be then used for "lightening" the scene in compositing?

bgportal can be used, or are intended to be used with background you can disable as photon sources, which at the moment are texture IBL and sunsky 2

if you use a 'only photons' spot lamp in a scene, you basically would get an 'indirect lighting only' result. I have not tested this that much.

[_Mo_]

OK, will do some tests on the "indirect pass".

[condar]

...
if you use a 'only photons' spot lamp in a scene, you basically would get an 'indirect lighting only' result. I have not tested this that much.

it's great to improve caustics or Photon Map where blotches are too evident without changing the main lighting setup

[Samo]

...
if you use a 'only photons' spot lamp in a scene, you basically would get an 'indirect lighting only' result. I have not tested this that much.

it's great to improve caustics or Photon Map where blotches are too evident without changing the main lighting setup

Yes that's true, but apart from that the point I am trying to make is this

directindirect.jpg (27.82 KiB) Viewed 23028 times

If you enable 'photons only' in a scene you get an indirect lighting pass

indirect.jpg (69.73 KiB) Viewed 23028 times

This could be useful to use in compositor with other passes from Yafaray or from other engines, for people who likes using this kind of workflow

[_Mo_]

I've updated the draft. See sections Rendering caustics & Using fake glass.

I have problems presenting a good use case of portals. Using portals produces a much noisier photon map (note: texture env has IBL disabled)), resulting in longer render times / noisier render. As it's visible on the various photon maps, the one without portals, but with area lights instead is the best one:

Any suggestions? Someone who has experience with portals could take a look at the scene (link to files in the first post) and rig a good solution, but I kinda doubt it would be a better one than spot lamp + area lights.

[Samo]

about portals, maybe has to do with the way the photon count is balanced between the sunlight and the portal. When you use portals, do you disable photons emision from the background? can you share the scene please?

[_Mo_]

When you use portals, do you disable photons emision from the background?

With texture background IBL is not used, sunsky 2 is used with default settings (no add sun or add skylight enabled).

blend file

20th layer: area lights + spotlight
19th layer: bg portals + spotlight
18th layer: spotlight only

[_Mo_]

I think I tried all possible lighting combinations (sunlamp, spotlamp, IBL, sunsky with skylight & sun...) and BG portals settings, but the photon map with BG portals is always worse than when using arealights. With area lights you get smooth & clean p.map, but with BG portals the brightness of neighboring patches varies a lot more (=more noise).

If anyone has any real project experience with BG portals (with PM), that resulted in better quality, then post some examples. Else I would rather not include BG portals in this tutorial, because it seems they are inferior to sun / spot + area-lights technique.

It seems to me that portals are useful with unbiased pathtracers like Lux Render, but in PM you will always get better results using specific lamps.

[stoneage]

I had similar trouble a long time ago with my 'Stairwell' render. I found the quality of the photon map got better the more you increase intensity for the portal, though by the time you get a good photon map the render is hugely over-lit.

This was with an earlier 0.1.2 and Blender 2.49