Sky Input - In Sketchup or Photoshop?

castromann · 14 Jul 2011, 15:51

thy so much for your quick answers, but unfortunately thats not true. in the png only the areas that are not covered by windows are transparent... at the moment i can still see the environment background from the render through them ;-( the transparency of the png is exactly the same as the alpha mask.

i now try to render a separate "background" channel and see what that will give.

any other ideas of what i´m doing wrong or can be done?

i own quite a few hdris already. i saw the ones from peter gunthrie - they are great! thx for your recommendations.

edit: btw - do you know if vray accepts .exr files in the environment slots?

castromann · 14 Jul 2011, 17:52

the background channel didn´t help either ;-(

andybot · 14 Jul 2011, 19:07

Here is an example of a png image rendered with the alpha channel. You can see the before and after, I have glass that has a slight reflection and is not 100% transparent. I can place the sky behind with no problems. Not sure what is different with your render. Do you want to post an image or perhaps your vismat?

castromann · 14 Jul 2011, 19:08

i found out how to do it - if someone else is interested - its explained by fernando in this video: http://www.youtube.com/user/asgvis#p/search/0/PjbrGcbzyjY

you have to check affect alpha in the materials refraction layer to make it work!!!

@andybot: thx for your example this is exactly the effect i was looking for, but it didn´t work because of the above.

andybot · 14 Jul 2011, 19:11

makes sense. I use a vismat for glass based on a version I've modified from the asgvis site. It must have that already checked. I think that's only an issue if you use a refraction layer. semi-transparent materials without refraction should work fine.

castromann · 16 Jul 2011, 22:31

ok - here´s a follow up to the last problem. as discussed before i got the alpha to be transparent behind the window with the "affect alpha" checkbox in the glass materials reflection layer.

unfortunatley i ran into an new problem with that kind of setting. to understand you maybe have to know i´m using the vray sun and hdri method trick with the unchecked reflection slot in the environment rollout. now when i try to put my backdrop behind the model in photoshop the glass seems to lose its reflections in the areas where the background shines through the window. looks not very nice and destroys the illusion of photorealism. in fernandos tutorial on youtube the reflections seem to stay. i tried so many things in the meanwhile that i think even if the solution was obvious i wouldn´t get it anymore.

another minor thing that happens when you save to png are the sharp white borders around the model you get in the alpha channel of the png. funny thing, if you crop the model to the alpha pass (not the alpha mask of the diffuse png)you can get rid of them easily.

if it´s uncelar what i´m talking about let me know and i´ll try to illustrate my problem with some pics tomorrow.

again thx for any pointing into the right direction!

fuzzion · 17 Jul 2011, 00:20

1)Get extremely high res commercial HDRI. VFSU sky isnt really as good as v.high HDRI for photo realism.
2)Use as sphere env.
3)VFSU 2.0 will have positional setting for env, current version = no so its trial and error. Hence Photoshop is prefered by some.

castromann · 17 Jul 2011, 08:28

thx fuzzion but the usage of hdris is not my actual problem. to clearify see the following pictures:

as you can see the lack of reflections in the second example makes it impossible to use an alternate BG in photoshop as it looks simply wrong.

grateful for your help!

andybot · 18 Jul 2011, 15:14

One thing you might try is to use material ID for the glass, and that way you get a channel you can control for the transparency of your glass/ background. You could mask your background with this channel and adjust the strength of how much you can see the background through the window.

Andy

castromann · 19 Jul 2011, 07:38

you´re right andybot. i now changed my glass material as i seem to have less problems when using a material without refraction (as you mentioned already). with creating a materialID it should be no big problem to get rid of this problem in photoshop.

thx a lot for your support.

apple85 · 5 Apr 2017, 18:56

where do you locate the alpha channel to turn on and off with vray 3 on sketchup?

I try to save as a tif or png with my sky but get a transparent background - jpeg I have no problems but you don't save in jpeg if you can help it.

Im pulling my hair out on this one looking for this needle