Comping in Photoshop

[Marshall_Craft]

Hi, I have a small project that I want to use to learn how to composite a final image using Photoshop C2. I'm working in VIZ 2006 with Vray 1.46.xx. I've just gone through a few threads regarding basic comping techniques, but I am hoping someone can clarify a few simple things that weren't covered in those threads:

When you save from the Vray VFB window, are you somehow saving all these G-buffer channels into a single file, or are they each saved separately? which file type should I be using? (I see no settings for "EXR" and have no idea what program might open it.)

Has anyone come across any links for tutorials explaining compositing in Photoshop? Searching these forums hasn't been too fruitful for me yet on that subject, but I figure more Vray experts will understand me than those in Adobe's forums.

That's it, I'd love to learn how the masters go about compositing stills (not ready to composite a video, nor do i have the software for it.) Thanks in advance for any help/answers/screaming/etc.

- Alex

[joconnell]

Heya Marshall,

I don't use the channels myself - most of the stuff I do is all in the one render but just as a rule of thumb for compositing layers, anything that removes light like shadow or ambient occlusion passes is set to multiply in your compositing program or photoshop, anything that adds light such as a keylight / direct light pass, reflection or specular pass are normally added over in add, screen or linear burn mode. If you render out a depth pass for the scene too, you can use this to apply depth of field in post - admittedly it wont look as nice as the in camera rendered version but it's pretty much free in terms of render time and used subtlely, the fake composite version is often better than not having it at all.

Christopher Nichols has a quick breakdown at the top of the following thread too - http://www.chaosgroup.com/forum/phpB...ic.php?t=13818

[Marshall_Craft]

joconnell,

thank you for the response and the link (i've gone through that link a few times, but it's good to see that other users are referencing it.) any good links for learning about ambient occlusion? i feel like i have only a slight grasp of the terminology used in Vray and in rendering, and I've tried the help file online and its terminology section.

anyone else out there have any advice? thanks.

- Alex

[joconnell]

Ambient occlusion is a term used to describe parts of a model where light gets trapped and thus they render darker like corners of a room for example. Another type of pass which is very similar is a dirtmap pass - dirt would normally collect in the same areas as ligh gets trapped - again in corners of rooms or the grooves of objects or places sheltered from the elements. What happens though is that a dirtmap / ao pass looks very very similar to a skylight pass with no bounced light so a lot of people end up substituting an ao pass for global illumination to give a soft diffuse look to your lighting.

Ambient occlusion is raytracing based and because of that it doesnt depend on the same undersampling methods that are often used to accelerate global illumination. If you are rendering an animation where things are constantly changing such as character animation, you dont have the option of baking global illumination or using cached irradiance maps or light cache and so your global illumination can often flicker and look bad. Ambient occlusion isn't doing half as much as global illumination since it doesnt take into account the light bouncing from one object to another so it isn't half as accurate, but it does look like soft diffused light and might be a good enough substitute to replace gi in cases where you don't have the render time to use full gi (Though that's rarely a problem with vray).

If you are mainly doing arch viz projects and fly throughs where you are dealing with a moving camera in a static scene, you are far better off learning as much as possible about vrays cached irradiance maps and light cache which are extremely fast and won't have the same flickering problems as mentioned. If you are doing animated things such as character animatin or visual effects work, the undersampling methods don't work as well so ao / dirt mapping and qmc based global illumination work far better (though again may be slow)

[Marshall_Craft]

wow, thank you so much for taking the time to answer me with such an extensive response. now i KNOW how little i understand about rendering, but you gave me some good leads. thanks!

- Alex

[joconnell]

To be honest I'm only getting to grips with how vray works in terms of its sampling etc now - It's always changing and quite difficult to keep track of all of the various methods that people use so it's just a case of learning enough about something to get the results you need in the time you have - I still haven't a clue about loads of vray and wouldn't have a breeze about mental ray and i'm using 3ds max 10 years