Window Reflections

Become a member of the CGSociety

Connect, Share, and Learn with our Large Growing CG Art Community. It's Free!

Thread Tools Search this Thread Display Modes
  01 January 2014
Window Reflections

Any good ideas on adding window reflections to a city at night that has been projected and animated? Appreciate any tips or tricks anyone has.
  01 January 2014
Yup, you have to set up a reflection pass and comp it back over the projection.

You can do this a few ways, some more accurate than others depending on the distance from the windows. If you're very close, then you'll want to have the reflection objects pretty accurate, so this may involve building the surrounding environment in 3d and rendering off a reflection pass with a shader applied to the reflecting geo. Plug a a black and white map into the shader/reflection slot that matches the position of the original projections, white being reflective areas which means you need to cut out all the windows, black equals non reflective. Noting to just render the reflection pass/element/AOV then screening this layer over the final animation in After effects or Nuke (comp program)

Sadly this involves cutting out lots of windows if its from a live plate/photography, but the results look cool!

You might also want to just add a slight grunge map to the white reflective areas. Windows usually have a layer of grime, stains, etc from weathering, so something to break up the perfect reflection will help to add realism. Perfect reflections are bad

Also note, on buildings with lots of windows you will see that not all the glass is perfectly aligned to each other. There's usually slight differences from one pane of glass to the next. This tends to break up the reflecting when looking over all the windows together. I typically address this in 3d, by making sure there's a polygon face for each window, then selecting all the windows and doing something that will displace them all slightly in a random direction; though just a little. This might involve rotating each face in a random direction, or applying a noise modifier to them all with a small value. Whichever technique is used, it's important to only apply small values, to displace only a little. If you want to avoid 3d, you can do a similar technique in comp, that involves applying a gradient to each window in a random direction for each window, then using this to drive a displacement.

Usually for a lot of shots where the reflections dont need to be too clear, you can get away with minimal detailed reflections. Sometimes this may be just a city HDR applied to a sphere or a few cubes with buildings mapped to them, duplicated a few times and moved around the focused object.

Another technique, usually for less windows, ie the camera's pointing towards an actor with a glass door in the background, involves using the reverse image (behind the camera), then tracking it to the camera, then flipping the track/camera move so it goes in the opposite direction to the reflecting window. Of course you will then need to screen the layer and roto it to sit into the window. I've used this technique a few times in shows to remove camera crews. Though if the original camera move is in 3d then you don't need to track it in.

Anyhow, it's all pretty simple, think about how much you'll be seeing and don't put in any more work than you need to

- Dave

Last edited by everlite : 01 January 2014 at 04:10 AM.
  01 January 2014
Hey Dave. Nice answer.
thanks for sharing knowledge.
Norberto Idiart
Digital Matte Painter / Environment Artist
  01 January 2014
David, first off thanks for the response. Second thing...thanks for the awesome response. This is exactly what I was looking for. Definitely appreciate the input.
  01 January 2014
Thread automatically closed

This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.
CGTalk Policy/Legalities
Note that as CGTalk Members, you agree to the terms and conditions of using this website.
Thread Closed share thread

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Society of Digital Artists

Powered by vBulletin
Copyright 2000 - 2006,
Jelsoft Enterprises Ltd.
Minimize Ads
Forum Jump

All times are GMT. The time now is 08:58 PM.

Powered by vBulletin
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.