FG and GI maps 3dsmax??

melviso

I wanted to ask if one generates a fg and gi map.If u make changes to the GI settings and generate a new map,do u need to generate a new fg map again or the one u generate before is still usable?
Also with fg and gi maps generated,do u need to generate them again everytime you tweak the diffuse, reflective, bump parameters of ur materials?I read in the 3dsmax docs ,that as far as u do not move ur objects,or change ur lights or move them.U can continue to use them for a frame.
I am using Mental Ray.

JamesTKirk

1. FG map relies on GI to get information about multiple light bounces so yes you need to recompute FG after changing GI.
But you don't have to recompute GI if you just made changes to FG.

2. Both FG and GI maps contain light intensity and color. So if you change some shader parameters saved maps wouldn't reflect those changes.

melviso

Thanks for replying, JamesTKirk.

Also if u generate a photon map file and u were rendering at say 720p and u want to render at 1080p,do u need to generate another photon map for that resolution or the map is resolution independent?

Also in 3dsmax, u can specify the average caustics photons and GI photons per light.Is the light generating seperate photons for caustics or its the same being used for GI? If u specify say 600,000 for GI and 300,000 for caustics, Does this mean Mental Ray will generate 900,000 photons in total?

JamesTKirk

Think of GI map as of a 3d point cloud in which every point contains light information taken from bouncing photons. It doesn't rely on rendering resolution. And because it is used as secondary solution with FG being primary you don't want this point cloud to be too dense anyway.

What kind of scene are you working on? Is it interior or exterior?
GI is considered to be an outdated technology as it has number of flaws. Irradiance particles and importons were intended to replace it but they never made it.
It would probably be better to just use multiple bounce FG for now. It may be a bit slower but much more predictable and controllable. 2 bounces should be enough for most cases.

JamesTKirk

Caustic photons are generated in a different way and they doesn't sum up with GI.
But yes in total it would generate 900.000 photons.

melviso

Interior scene,I have a mr sun and sky with portal light through a window.I was considering using GI over fg bc of flickering that seems to come with animated objects or moving camera.
I also gather sometimes it might be due to sampling issues when using mental ray.I am guessing unlike GI, fg maps are resolution dependent?

JamesTKirk

So you are trying to use GI only without FG? You won't be able to get nice lightning solution this way.

mental rays lightning techniques are like stone age so there is no one button solution for every possible case. But I still suggest you to try FG only with 1 or 2 bounces. Turn off speckle reduction(it actually makes it worse). Set interpolation like 100 or even higher and rays per point like 500 and see if it works. You should get smooth lightning this way.
Use additional lights to light dark areas of your scene.
There are also special settings in case the only thing moves is camera.

Tune one thing at a time. Be sure what causes flickering. It may be area shadows, not FG. Use single grey material for all objects to see lightning better (Use material override option).

FG map itself is actually a 3d point cloud like GI. What is different is how those points are distributed in scene. GI creates sample point when photon generated from light source hits scene geometry. FG sample grid are projected from camera and distance between grid points can be set in pixels which makes it resolution dependent.
But I think it's safer to tune it in final resolution if you are not sure what you are doing.

melviso

Okay,I have been reading u can downgrade the resolution and size of your fg map.Say if u were rendering at 1080p,can u use a fg map of 960 x 540p?or 720p will be the best res to use.

I have heard flickering is mainly caused by not having enough inital fg density points, hence Mental ray has to compute additional ones.I have been reading up on it. It seems if u run diagnostics on fg sampling.If ur image has only green dots,it means there will be no flickering,if there are red ones,then its probably going to flicker.Another problem might be the sampling setttings as well.So far, my image shows completely green when I run diagonistics,I am thinking of rendering the animation but kinda worried it might flicker without the fg maps and the fg map takes a very long time to render.

melviso

Testing out photon mapping only:



Btw,does anyone know how to blur a hdri image?Can u do this in photoshop or u need another software?I am also wondering if u can blur a hdr image in 3dsmax material editor.