Irradiance Maps and Photon Maps

[Envision]

I have a question regarding Irradiance Maps and Photon Maps. I understand that both of these can save rendering time if used correctly. My question is - when do I need to recalculate these maps? I am rendering single images of interior spaces so I do not use the same lighting in a space several times like in an animation.

How do I best use these maps to speed up rendering test until I get the final image that I like? Or do I need to recalculate after each time I try a different color on a wall, or add a piece of furniture, that will obviously cast new shadows in the space? What if I increase or decrease the intensity of a light or move it in the space?

Thanks for any advice. I really need to speed these test rendering up.

[flipside]

You need to recalculate the map if you move objects, lights, adjust materials etc... Anything that would change the lighting. If you make a wall red instead of green, this will have an effect on the GI. But if you're testing the look of for example a material, you don't need to recalculate as you are not focussing on the GI. Also for test, you can use very low GI settings. But if you move a light, this will have a really huge effect so it's best to recalculate after that.

[Envision]

Thanks for the response. I really appreciate the help. I figured I would need to recalculate the irradiance map after moving lights and objects or adjusting materials drastically. Does this also apply to the photon maps if I use it for the secondary bounces of the GI calculations?

I can reduce the DPI or size of the rendered image and the irradiance map calculations goes much faster. If I do a calculation at a lower resolution, about many times can I increase the final image size and still get good results from the smaller irradiance map? Does this also apply to the photon maps?

Thanks again for your help.

[flipside]

Don't know about photon maps and resolution.

But about the IR map you are correct. You can calculate that at eg half resolution and use that map on the full res. But the GI will be less detailed of course. The min max settings of the IR map actually do this for you: -3 means that it calculates the IRmap on the image with [full resolution/(2*2*2)]. 0 means IR map calculation on image with full res.

-3,0 means first pass at resolution/8, second pass at res/4, third pass at res/2, last pass at res/1. Each pass uses info of previous pass to know where to use more detail and where less detail is needed. That's the principle of the min max settings.

Search the vray.info site for a lot of info about IR maps and min max settings etc... Also search this forum because this topic has been discussed and explained many many times.

greetz,

flipside

[didjaja]

Photons are independent of resolution of render,they depend of geometry.Is the same calculate photon map to 100x100 that 1000000x1000000 (in time of calculation of course,not time in rendering )

[Envision]

Thanks That is very helpfull info.

[travistlo]

Photons are independent of resolution of render,they depend of geometry.Is the same calculate photon map to 100x100 that 1000000x1000000 (in time of calculation of course,not time in rendering )

So the calculation for a photon mapping at 100x100 will be the same amout of time as @10,000x10,000?

So if that is true, and you need to render something that is going to be very large, like a billboard, will it be better to use photons instead of IR?

Im sure this was probably discussed, but i was just reading through this post, and i wasnt really searching, so i figured i just ask quickly.

Thanks,
Travis

[didjaja]

For interiors the best combination is IR for first bounce and PHOTONS for secondary bounce
And of course photons are view independent You can calculate for one frame and use for all frames in your animations (with object movement dont work,only camera movement)

[travistlo]

but what is the answer to the question? Will the photon calcs stay the same at 100x100 and at 10000x10000

The reason i ask is because i may have to do a rendering for a billboard, its for exterior, and im not sure how long its going to take becuase of the size.

[didjaja]

Well,for exterior you have to use Irradiance (calculate for 500x500 and reuse for 1000x1000,work fine)
Photons for exterior arent useful because difusse ilumination is very much minor than in a interior