COMPOSITING IN PS

[Cesar R]

I have not figured out how to composed a max rendere that was slip into the different elements (reflctions, shadows, alpha, z-buffer) in photoshop. can someone give me a little lesson ?

[Wolf]

hey there cesar

 

i dont think photoshop does the best job with alpha channels, but lets give it a go and see what happens....

 

render your elements and save them as 32 bit alpha targa files

make sure that premultiplied alpha is on, as that makes the antialiasing for the alpha channel.

 

in photoshop, click on channels and you should see the alpha channel there.

CTRL click on it, and it should only select the alpha

now choose the move tool

and Shift Drag the Alpha to your new image, and it should drop in with the alpha nicely masked out.

(holding shift makes sure the image stays in position like the original)

 

gimme a yell if this doesnt work out for you

and ill send a file.

 

btw after effects is really ideal for this,

it even knows straight away when you load that the image has alpha,

and asks you wether to treat the image as premultiplied or not.

[Cesar R]

hey wolf thanx , that worked, for what if I want to compose something that has glass where are going to see through (window) on top of a picture, how would I treat that, what about reflections ?

[Jeff Mottle]

Cesar,

 

It depends on what exactly you are doing, but let's assume you have a background plate that has glass already and you are adding a new composited element that needs to relfect in the original glass.

From MAX you would need to place your new element and a reflective surface located in the same relative location as it would be in the final image. Then render out the reflection render element.

 

In Photoshop place the element over top of your image and set the layer to "Screen" you can then adjust the layer transpareny to control the strenht of the refection. It's best to make the reflective surface in MAX 100% reflective that way you have full control in Photoshop over the reflection strength.

 

I'm sure there are other, possibly better ways to do this, but that's how I've done it in the past. Last week to be exact.

 

Hope that helps,

[Cesar R]

what if I have a plate (picture I took), and will like to make it the background seen though a glass window ? how would I do this is PS or set up the rendered in max so the alpha of the glass surface, which will be somewhat transparent with some reflections, is preserved and usable in the compositing proccess ? I ask this quesiton because this is something I am actually trying to accomplish is LS. help Jeff

[Jeff Mottle]

Hey Cesar,

 

Hmmm, that is a problem. Can you post the image that you took? There might be a solution, but if for example you have an interior room with downtown Detroit outside the window and you want to replace it with downtown Los Angeles, this might be difficult if no impossibel to pull off successfully. If however the picture you took has reflections on the window ans it is completly black outside, I think I can suggest a few things.

[PI]

try going to this site..lots of photoshop compositing techniques..also one of my favorite sites...have fun

 

http://www.computerarts.co.uk/tutorials/2d/

[Cesar R]

thanks PI, ill check them out,

[PI]

i would also like to add that there is a section in a book about compositing images

 

title:digital lighting and rendering

author: jeremy birn

publisher: new riders

 

check it out!