line down side/edge of bottle, too dark against background

[tom182]

Hi, Not so much a problem with Vray but the rendering is not what I want, so not sure if it belongs here, anyways I am rendering out a whitish bottle against a white background but I am getting a dark line running down the side of my bottle. how can I get rid of this without blowing out the white?
any ideas, I am think it is a reflection issue (but not using Fresnal) or an AA issue, I am using CM Rom
Thanks
Tom

[panthon]

Have u checked if u have "reflect on the back side" on the material properties ticked? Plus, u can increase your refraction depth to 10 or 12.

[tom182]

Initially I had 'reflect on back side' unchecked, so I checked it, I upped the refraction depth to 12 and it still appears,

everything else is 'perfect' (well in my eyes) on the render except for this agghh,

thanks,
Tom

[DaForce]

That is rather odd.
Have you tried different camera angles? Also whats the material setup?
Maybe just to be certain it isnt a depth problem, try changing the exit color on the material to red just to totally rule it out.

[tom182]

unfortunately I cant move the camera as it is matched up to a photo, I tried the exit colour (changed to white) -no luck,
Here is the screengrab of my material, scene is lit by 4 vray lights


will have to leave it for a day or so as I am away tomorrow, but will appreciate any help as I have to sort htis by Friday,
thanks again,
I will post scene if needed
Tom

[DaForce]

Please post the scene if you can.

Your material settings seem fine. Unless it some funny modelling?
Does that material have any reflection... is hard to tell by the color swatch.
Try increasing it to see if that exagerates the problem.

I was thinking to just try a different camera angle to test...

[Dynedain]

Is what you're showing visible in the frame buffer? It looks like it could be an alpha premultiplication issue.

[zoranm]

CHange Carmall-Rom to Mit-Net and it should be OK. CR can't, sometimes, handle a very high contrast

Zoran

[DaForce]

That could be it, i didnt think of that.

Will have to wait until he gets back to it

[tom182]

guys, have it sorted, The pic I showed was from PhotoShop, the scene renders onto a black background which I didnt think would affect the material. I genuinely didnt realise that when I specify a hdri in the environment slot of the material that it would overwrite everything else (i.e. max's background and enviro) it probably still does,
One of the first things I did was to change the AA to Mit-Net but that gave the same results in my case,

Thanks for help
Tom

[Dynedain]

black background which I didnt think would affect the material

It doesn't. But it does affect pixels that have alpha levels that aren't fully opaque or fully transparent. Thats what the premultiply alpha setting does when you save to targa/tiff. It multiplies the background color into the RGB so that you can get a "blurring" effect out of the antialiased pixels on the edges of alpha boundaries. There was a thread about 2 months ago where someone was trying to render a box and change out the background color. I think the technique he finally settled on would solve your problem

[panthon]

You can find a matting option in photoshop which should fix your problem. Remove black matte in your case.

[DaForce]

That would be me... and this would be the thread
http://www.chaosgroup.com/forum/phpB...ha+box+daforce

Yeah, you probabaly should have mentioned that you were rener out on a black BG and putting the white BG on in PS... then i would have fix ur problem straight away.

ah well atleast its sorted

[tom182]

cheers, I just didnt think it made a difference, i.e the alpha channel would sort it out regardless, oh well 'you live and learn'
Thanks,
Tom

[DaForce]

heheh no problems mate
Good you got it sorted out