revisions to irradiance map

[dynaman]

i was wondering if this is possible:
let's say i have rendered an irradiance map at high settings for print resolution. then let's say something pretty minor gets changed in the scene, maybe the length of a desk or some furniture is added. is there any way to re-render the irradiance map for only the affected area of the image or would you have to re-render the whole image. i do realize that we're talking about global illumination here, but adding or moving a chair isn't going to have a noticeable effect on 85% of the illuminated space.

in more tangible terms, if i do a region render calculated as a single frame, will this be adding to the previously loaded irradiance map, or is it scrapping the rest of the image and only calculating the region area?

i guess the same question would apply for a saved vrlmap.

thanks! (hope this is clear??)

[Candelero]

Re: revisions to irradiance map

i was wondering if this is possible:
let's say i have rendered an irradiance map at high settings for print resolution. then let's say something pretty minor gets changed in the scene, maybe the length of a desk or some furniture is added. is there any way to re-render the irradiance map for only the affected area of the image or would you have to re-render the whole image. i do realize that we're talking about global illumination here, but adding or moving a chair isn't going to have a noticeable effect on 85% of the illuminated space.

You can use the < Incremental Add >

[b]Incremental add to current map[b] - in this mode V-Ray will use the irradiance map that is already in memory and will only refine it in places that don't have enough detail. This mode is useful when compiling an irradiance map to render multiple views of a static scene or a fly-through animation.

in more tangible terms, if i do a region render calculated as a single frame, will this be adding to the previously loaded irradiance map, or is it scrapping the rest of the image and only calculating the region area?

Yes, it will be added to the existing GI file (using the Incremental Add).


Best regards,
nikki Candelero

[dynaman]

thanks for the reply.
i have read about using "incremental add to current map" in the walk through tutorial in the help files. but here is the last line from the tutorial:

Note that if you make any changes in the scene (e.g. add/delete objects, change materials or lights etc) the irradiance map that is in memory will no longer be relevant to the scene and you will need to reset the irradiance map and start all over again.

a few weeks ago i was working on lighting a scene with some furniture hidden. once i was satisfied with the overall lighting i unhid the furniture and re-rendered (i can't remember whether i was using "add" or "incremental add"). but the result was lacking shadow definition around the furniture. could very well be that i was doing something wrong, so i will do some more testing on this. but i just wanted to double check that the incremental method does actually work when geometry changes.

[travistlo]

I think from a Semi-Accurate standpoint this cannot be done.

When you change any object in a scene the paths of lighitng change. Light gets block from on area, and added to another, etc etc.

Now, A good way to resolve this might be some type of merge option. Where you can use the Render Region option and overwrite that small portion of the Irr. map. Techincally the rest of the scene is incorrect, but no one really notices that.

[dynaman]

exactly! but can this be done? is this what would happen if you did a single frame region render, then re-saved your irradiance map?

[joconnell]

Well, the problem is that if you do a region render you're only doing a small area of the picture in terms of your irmap. The problem is as travistlo suggested that changing a model in one area that you render may block light in an other area of a scene and thus give you a wrong solution in another area of the image seeing as you're dealing with light that is bouncing all over the place.

Say for example you had a large black object in the scene which will kill all light that hits off it and suck light out of the scene. Now say you made the object smaller and did a region render - how can you be sure how much of an effect the black object had previously? It may have been pulling away light from an area outside your region render that you haven't thought of and you may end up with a weird situation where part of the scene gets suddenly darker or brighter because one part of the image s using the old irmap and another part is using the new changed irmap.

A lot of people have also reported that their renders have become really slow when they use the wrong irmap for a scene since vray is guiding samples to the wrong places. Personally I think for peace of mind to know that a render will look correct it's worth taking the hit on the time and calc a new one. Unless perhaps you're working only on stills and can paint out errors in photoshop but you might be causing yourself hours of problems for the sake of a few minutes saved.

[dynaman]

i see your points. i guess i was considering only trying this for some very minor geometry revisions - things that would not have a noticeable effect on probably +/- 80% of the rest of the image space. anyway, i think i'm going to test it out a bit to see what kind of results i get. i'll post back if i come up with anything conclusive.

[RePlay]

Best thing to do is put in your new object and matte it out.. or simply blowup render /region, and merge it in photoshop. I have to agree that the more you mess around with merging irr maps, the more time you will be spending on your scene.

Hence the pre-planning stages and rendering in layers

I have done a fair few renders that needed minor but significant tweaks and I would basically render to elements, both for the large image and for the section which has changes. This gives me a lot of control over GI influence/shadows etc.

If you have the time I suggest learning a comping package like Nuke or Shake or even Digital Fusion - my preference.

With node based control its mainly just a means of updating your image parts and a few slider controls.

Remember that with stills, photoshop will save your life. With animation, comping packages will save your sanity.

[dynaman]

thanks guys...i think i've got my answer...

the matte technique can definitely be a huge time saver. i've used it many times.
problem i'm trying to work around is the fact that i don't handle a lot of the final compositing. so i am trying to make the process as simple and straightforward as possible before handing off my files for someone else to render and composite.