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Old 01-21-2014, 06:03 AM   #1
jibadajaba
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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.
 
Old 01-26-2014, 05:43 AM   #2
everlite
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David Edwards
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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 : 01-29-2014 at 04:10 AM.
 
Old 01-27-2014, 10:47 PM   #3
norbertoidiart
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Hey Dave. Nice answer.
thanks for sharing knowledge.
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Old 01-27-2014, 11:12 PM   #4
jibadajaba
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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.
 
Old 01-27-2014, 11:12 PM   #5
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