[Sidefx-houdini-list] camera projection mapping

Phil Spicer PSpicer at bournemouth.ac.uk
Tue Jul 15 05:23:09 EDT 2008

Hi Jed,

1. ensure any projected image is a .rat image (this output type can be created using mplay)
2. In the Mantra Output Driver set a Output > Pixel Filter value of Gaussian 1.5 1.5
3. In the Mantra Output Driver set a Render > Rendering Engine value of Ray Tracing

This will ensure any projected image match the back plate source in terms of pixel quality. Without these values and settings specified, camera projected images will appear 'soft' in the rendered image. Tiff images for example will not project correctly, nor will a Gaussian value of 2 2.

When you project through a camera or a light, you get image curvature at the edges of the projection. If you need to correct this, you can create a custom VOP Surface Shader which takes Global P and converts it to Normal Device Coordinates using the To NDC VOP. The output of this VOP can then be utilised to drive the U and V inputs of the projection Color Map VOP (which is then assigned as a Material after the UV Texture SOP).

Kind regards,



-----Original Message-----
From: sidefx-houdini-list-bounces at sidefx.com [mailto:sidefx-houdini-list-bounces at sidefx.com] On Behalf Of Andrew D Lyons
Sent: 14 July 2008 22:08
To: sidefx-houdini-list at sidefx.com
Subject: Re: [Sidefx-houdini-list] camera projection mapping

Hi Jed,

You need to work with uv layering.

Look at:

group - prim grp by normal - backface from camera - if you only want to effects uv's on front faces.
uv texture sop - choose project from camera. (the camera you will render the still for painting from) layer sop - has all kinds of controls for blending uv layers using masks etc.
attribute - to rename (store) incoming uv attrs and reinstate them on output. Why? The uv texture sop will always work with uv layer 0. ie "uv". You will often want to add a new layer (or blend with another incoming uv layer). ie uv1 uv2 uv3 uv4 attrs. If you have all this in a HDA, then the attr sop will let you rename uv to:
uv`ch("../uv_layer_id")` etc tc.
In your shader, use the matching uv layer for each texture. Blend colors etc as needed.

Good luck!


2008/7/14 Jed Schwartz <jed at jedschwartz.com>:
> I'm exploring  the possibility of using camera projection mapping
> techniques (used quite successfully in a lightwave project) in our
> current production that calls for a bunch of extreme close up detail
> shots, mixed with broad sweeping moves across  very detailed martian
> terrain.  We have all our terrain built and a great set of very hi-
> res textures matching the DEMs we used to generate the terrain.
> Most of our shots are blocked out and approved for final render, so
> were to that stage where we're trying to figure out the most practical
> way to get detail into our shots where we need it- We have completed a
> few shots using Y projection maps with all the usual tiling, depth
> maps et-al- Very labor intensive and lots of extra detail generated
> that the camera will never see-
> My colleague who did this in lightwave breaks down his procedure into
> the following steps:
> 1. Finalize the camera move
> 2. Select "key" frames for terrain plate paintings
>   For a locked-off shot or a very small pan, one "key" painting
>   should be OK. For larger camera moves you may need to use several
>   paintings to cover the entire terrain seen by the camera. Instead
>   of using the (moving) final render camera I'll make a copy of it and
>   delete the motion so that each "key" painting camera is separate
>   and stationary.
> 3. Render a "screenshot" from the view of the plate camera
> 4. Paint on top of the screenshot
> 5. Project the final texture back through the plate camera onto the
>   terrain.
> The main reason to use this paint-projection technique is to get
> around the problem that ECU images never quite have enough resolution
> to look "photorealistic" for my typical MER shots. The disadvantage is
> the high amount of labor to set up each shot; the advantage is being
> able to put high-resolution detail exactly where it is needed for any
> given camera move.-
> I'd be most grateful if anyone who has explored this approach to
> projection mapping in Houdini and would be willing to share some
> insight into this process-
> Thanks!!
> Jed-
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Andrew D Lyons | Digital Artist | http://www.tstex.com =======================================
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