Render to elements transparency? (Vray 1.5)

[Xlars]

I have a problem getting the get Vray Render to Elements to show me any transparency in the Alpha map (with a VrayMtl material and Vray 1.5 R3). The alpha is pure black/white !? Here is my test render with some of the RTE maps. Any ideas / suggestions how to solve this would be much appreciated.



PS. The scene is just a few objects and a background the same image in both the Environment and in the Vray Render Environment override slots. Using Dome light and one standard omni light.

[dlparisi]

Check "Affect alpha" in the vray material refraction.

[Xlars]

Thank you very much dlparisi (i had missed that setting ). I have now turned it on in the refraction settings ... but strangely the Alpha is still just black/white !? I may be doing something totally wrong here?



Here is my mat settings:

[RErender]

The problem is with the fog, lower the saturation or the fog multiplier to get the alpha you are looking for.

Vlado - Looks like something odd with the fog/alpha in the alpha element, semi transparent alpha is rendering in the inverse color of the fog.

[Xlars]

Thank you RErender, I just tried your suggestion but I still can not get it to work .. even after setting the fog color to pure white, multiplier to 0 and also setting the refraction color to pure white

Here the changed material:


Image:


And resulting alpha !? (still solid black/white)


Tried also ajusting the fog, fog multiplier and refraction to differnet settings and colors but with no luck

Here is the max file (Max 8 SP3) if someone would like to see: http://www.xlars.dk/3D/Vray_test03_web.zip

[joconnell]

The problem is that you can't get an alpha for a raytraced object - the alpha sees the cylinder as a solid object, it just happens to be refracting what is behind it - there's no renderer that can raytrace a refraction and give you an alpha for it - you'll have to either use a faked non refractive material like the standard mat with the opacity turned down or generate an alpha using another material and render it as a seperate pass :/

[Da_elf]

vray used to do it though. why else would the effect alpha function be in there.

[Xlars]

The problem is that you can't get an alpha for a raytraced object - the alpha sees the cylinder as a solid object, it just happens to be refracting what is behind it - there's no renderer that can raytrace a refraction and give you an alpha for it - you'll have to either use a faked non refractive material like the standard mat with the opacity turned down or generate an alpha using another material and render it as a seperate pass :/

Ok, thanks for the info and hint. I will look into making a workaround this way (just got an idea: would be cool if Vray in the future could even do such a trick by it self, I mean have a look at the raytraced material and make a temp on the fly material substitution and make a suggestion of a more transparent alpha

vray used to do it though. why else would the effect alpha function be in there.

Ah yes, such a setting in the refraction section does indicate that it could be used for something along those lines.

[RErender]

The problem is that you can't get an alpha for a raytraced object - the alpha sees the cylinder as a solid object, it just happens to be refracting what is behind it - there's no renderer that can raytrace a refraction and give you an alpha for it - you'll have to either use a faked non refractive material like the standard mat with the opacity turned down or generate an alpha using another material and render it as a seperate pass :/

Not true, that is what "affect alpha" is for, it will affect the alpha for refraction.



Here are some examples just a simple mat with ior reflection and refraction, first with purple fog and alpha render element then again with the default fog setting of white.



note weird color alpha

[Xlars]

RErender: Wow, it works for you! .. are you using Vray 1.5? (and since you mention fog I assume it is a Vray material).
I wonder what it is that you different in your materials / settings than in mine. Hmm ..

[RErender]

yep using RC3

Not sure why yours isn't working. If you make a new mat, check affect alpha, turn up the refraction and leave the fog at default, does it work?

You don't have your background mapped to a matte plane do you? In that case the alpha would come out white no matter what.

[sv]

this is RC3, and it all appears to work fine here. I'm also using a fog bias of .22 like you, but this didn't kick up any problems...

sRGB:



alpha:



rawreflection:



rawrefraction:



reflection:



refraction:



reflection filter:



refraction filter:




I think the best thing to do at this stage, is just start with a clean scene, and set up another test material - sometimes strange things happen and a clean approach sometimes makes a difference.....

[joconnell]

I'd question how useful this is to be honest - In every case above you're all rendering over screen mapped backgrounds which isn't giving ou any real refraction effect. Take those spheres in rerenders examples - they aren't distorting the background in any way so to me it doesn't work. If you try comping them it doesn't do much either. Here's a sequence of pics:



As you can see above the alpha of the sphere should knock most of it out (the dark centre has an rgb value of 12,12,12) even though my material is totally refractive - we should be getting pretty much solid refraction here. the alpha itsel knocks out pretty much all of the sphere. Also note that you're not really getting any refraction at all from a screen mapped environment since there's no depth for the rendered to work with - it isn't a correct looking effect. If you ever see a ball of glass it'll warp the hell out of whatever's behind it which is no where near what we're getting here.

[joconnell]

Now next is using a spherically mapped environment - again not totally correct but looks a lot better:



In the top right we have the same image as below except spherically mapped and to its right we have the same sphere as above using a fully refractive material. We're getting a load more warping now. middle left is it's alpha channel and since it's a fully refractive material, this is the alpha that goes along with our refraction. You can see again that there's very little aside from a little bit of refraction along the rim. Again if we use this to comp over our background we get the middle right image which again is bugger all - it looks very like the screen mapped effect from above mainly as we're seeing right through our sphere object to the background since the alpha has so little strength in it. Last we have our sphere directly from vray and you can see a massive difference - there's no way using that alpha that you could comp the passes and get the exact same result - even if I generate my own alpha so that you get a lot more white / grey in the alpha so the sphere layer is more visible, you'd still end up with a blend of the non distorted BG and the distorted bg from the refractive pass which again would look totally wrong. In the last image I've made my own alpha using a photoshop gradient from black to white so I get a bit more from the sphere - as you can see it looks fake since the parts of the monitor in the background are getting no distortion at all mixed with other parts that are distorting.

I'm not sure what you'd actually want to be able to do with this any way - If you want to change the level of transparency of your object it'll look wrong due to the distorted bits blending over the non distorted bg. If you want to be able to control your level of transparency on a semi transparent object lke the examples above then you'll have to add back in the diffuse colour in the same amount you take from the refraction which is probably better done with generated masks anyway. If you want to be able to comp your transparent object over a different background then you'll need some way to distort your background correctly - probably using normap map renders and 2d displacement and then layering your glasses diffuse and reflection on top.

I'm just not sure what type of things you are expecting to be able to do using this - most of the bits I'd want to do could be done with a solid matte for the refractive object and maybe a seperate reflection pass. What was it you wanted to do?

[Xlars]

yep using RC3

Not sure why yours isn't working. If you make a new mat, check affect alpha, turn up the refraction and leave the fog at default, does it work?

You don't have your background mapped to a matte plane do you? In that case the alpha would come out white no matter what.

Thank you RErender when I create a new material (and keep everyting else the same it suddenly works - NOW i actullay see a greyscale Alpha and not just a b/w map). I have to study the first material more closely to see what then makes the difference ... strange (I so would like that to happen also to my material, I will have to change parameter for parameter until I see what it is .. and report back here when/if I find out).