Vrimg with multiple render chanels and proexr

[mfured20]

Hey Guys!

 

Hows everyone doing?

 

So check it, I am just now starting to legitimately use floating point images from vray, and I have found a problem that I hadn't anticipated. It has to do with the alpha map and putting my own backgrounds into images. First, let me give you a quick breakdown of how I have been rendering:

 

- save image as .vrimg

- convert to .exr using vrimg2exr

- import to photoshop using ProExr plugin

 

Pretty simple and straightforward. Now, when you go to import the exr ProExr gives you a couple of options. You can either have the background alpha as visible, but on a different layer, or transparent. I went with the transparent option, because I wanted to replace the vraysky with something else. Now I have 'fuzzies' around my tree branches.

 

I assume this is due to some alpha settings that I have going, but I cant figure out how to change them. It could also be how proexr imports the alpha map... I just dont know. Has anyone had a similar problem? And how did you get around it?

 

Thanks Guys!!

[BrianKitts]

what happens if you tick the "unmultiply RGB...." option when you open the EXR file?

 

Looks similar to the problem caused when you writeout a standard EXR in max with and without the premultiply alpha option.

[mfured20]

I did, but it didn't make a difference.

 

I think that I have found the answer tho!

 

The alpha map itself seems to look ok. There was no evidence of 'fuzzies'. so I looked at the rgb instead. My antialiasing is merging together the tiny tiny needles with the sky background so they hardly show up when they should. I have attached three closeup images to illustrate what I have seen.. the first is just the alpha, the next is the rgb channel with the transparency, and the third is the rgb channel with a black background behind it. you can see that the alpha is actually doing its and cutting out the right form, its the rgb itself thats off.

 

which brings me to my next question: what anitaliasing filter should i use to get a really sharp image? in all honesty I havent really experimented with them at all; I have a usual setup and I don't deviate from it.

 

setup right now:

Image Sampler: DMC, 1 - 4

Antialiasing: VrayLancos Filter @ 2.0

 

 

I guess I will play with some other settings to see if they offer better results and repost.

 

Thanks Brian!

[mhmd19732008]

hello

1-i had the same problem one day, if your scene contains textures with alpha maps, e.g. trees, figures, etc...., rendering to exr or vrimg makes such problems, because the output will be brighter, you have 2 soluotins, even replace alpha textured geometry with real 3d geometry (proxy), or, use double sided material for alpha textured maps, otherwise, simple materials will have the same problem with you.

2-for anti aliasing, choose adaptive subdivision instead of DMC, if your poly count is too high use QMC.

3-if you are rendering exterior scene, dont use LC for 2nd bounce, use None, in the other side, change color mapping to linear, increase fnumber of vraycam and adjust gamma to be (1.8-2.2).

4-why dont try using HDRI background instead of vray sky, because HDRI is an exr type?

all above is my trial and error.

hope works......

[mfured20]

hey Mohammed -

 

I am not using any alpha maps for these trees, only proxies, so I don't have to worry about that.

 

I am trying to work with adaptive subdivision, but I keep running out of memory and crashing. I am only on 32bit, 4 gigs with the 3gb switch installed and ramped up dynamic memory. With how heavy my geometry is, I think i have to keep working with qmc.

 

As for the .hdri / .exr background, I could use that for sure, but I want to figure out why what i am doing isn't working first.

 

really this is just an academic exercise at this point... I dont have a deadline on this image [or else I would have just thrown some image onto a plane in the background since im using vray sun/sky]. its like a problem that I can't solve, and its bugging me.

 

since my adaptive subdivision aa isnt going to work out, I plan on tweaking my dmc and the filters. Catmull-Rom is pretty good, but for the trees I am doing better with Mitchell-Netravali with a high ringing value even tho it makes the rest of the rendering look horrible. I think its just a matter of fine tuning the aa to get the trees to look just right and then pasting them in.

 

i'll repost later today.

 

 

Thanks for the responses guys!

[mhmd19732008]

hi

did you try lowering th LC sample size, LC cuases problems with sharp geometry edges, or try changing from screen to world?.

[mfured20]

Mohammed -

 

I havent tried that yet... i got caught up doing other things, i will try it tho first chance i get. thanks!

[mfured20]

Well guys, I gave up on it... even at 6000px wide I couldn't get the edges of those pine needles sharp enough to work well. The best luck I had was with Mitchell-Netrivali with a ringing value of 1.85, but it made the rest of the rendering look like crap. I decided that it would be a better move to just put a textured plane in the background. I am about to post it up to the WIP section for feedback on the rendering itself.

 

Thanks for the help gentlemen, I really appreciate it.

 

matt