Import your video to Photoshop. Create a new layer, and then paint an arch on it as shown. The color-coding makes it a lot easier to reference objects when the painting is later exported to modo. Create a blank layer on top of your painting. Then copy the painting of the arch to the clipboard, hide this layer, and highlight the blank layer on the Layers palette.

Choose Filter > Vanishing Point. Create your first plane so it’s in the correct perspective for the underlying video layer. Extend the right side of the first plane. Press Ctrl/Cmd + V to paste the arch into the perspective planes. Then drag the pasted bitmap into the perspective planes. Move it around until the colored sides are in the right places. Choose Export to 3DS or DXF (see your modeler’s documentation) and then put the saved file in a folder you can easily find later. Name the file Arch.3ds or Arch.dxf.

Bring the Photoshop model into modo and then build over the imported Photoshop model. Don’t worry: the proportions will be correct because they were correct in Photoshop. You might need to edit the texture maps for the components of the Photoshop exported 3DS or DXF file because Vanishing Point occasionally ignores transparency in PNGs. Bring them into Photoshop, erase superfluous image areas, and then save to PNG by unchecking the Save As Copy checkbox to force Photoshop to write transparency into the PNG file. Next, overwrite the PNGs that Vanishing Point wrote to keep the file names intact. You can now see that the arch is made up of two flat planes with the texture files applied correctly.

You’ll want to match the camera angle to the video scene. Often, this can be done by eye, by cool switching between the video footage displayed in Photoshop and modo’s workspace. At this point the arch is mostly made up of extrudes, and the pillars are a simple spline, a helix shape that I treated with Radial Sweep. You can experiment with different treatments. I used a dull marble texture to cover the arch model, then lit the scene to match the video clip. Finally, render the file to PNG format with transparency.

Drag the layer entry on the Layers palette for the arch into the video document window to duplicate it and then position it. Choose Layer > Video Layers > New Blank Video Layer. Unlike normal layers, video layers change over time. When you paint and clone them, your painting will disappear in the following video frame. Move the thumb on the Animation palette to the point in time when the arch clearly violates the foreground object (the green van in this example), and click the bottom video layer on the Layers palette. This is the layer from which you’ll clone.

Alt/Opt + click on an area where the pillar intrudes on the green van. It’s okay that you can’t see the target sampling point on the van. Photoshop can clone from one layer to a different one, even when you can’t clearly see the content of the source layer. Click the top video layer title to make it the current editing layer. On the Options bar, set the Clone Stamp brush size to 9 pixels diameter and make sure Current Layer is the Sample drop-down choice.

Hover your cursor before stroking and check Clone Source palette to make sure that X and Y Offset and Frame Offset are all at 0. You’ll want to clone the green van, matching position and frame number, at points in the video where the arch intrudes over it.

Carefully stroke over the pillar area, hiding it with the sampled van area.

Move on to the next frame by clicking the Selects Next Frame icon on the Animation palette; continue until the van clears the arch. It’s an investment of perhaps a half hour’s time and less than 30 frames.

When a car passes in front of a CG element, the object should be partially visible through the windshield for a truly realistic look. Instead of fussing with the Opacity settings for each frame you edit using the Clone Stamp, it’s more efficient to go back now and partially unhide the arch as seen through the van’s windshield. With the top layer as your current editing layer, choose Layer > Video Layers > New Blank Video Layer.

Choose the static arch layer on the Layers palette, and then, on the Clone Source palette, click the second Clone Source button. Up to this point, you’ve been using the default (first of four) clone source.

Using the Clone Stamp tool, Alt/Opt + click over the arch, starting at the frame where the windshield should show the pillar, and then switch to the new video editing layer. Set the Opacity on the Options bar to about 50%, clone the arch into the windshield, then move on to the next frame.

Gary David Bouton
Author and Web Host
www.theboutons.com

Gary David Bouton is the author of over 20 books on graphics applications. This tutorial is an excerpt from his forthcoming book, Adobe Photoshop CS3 Extended: Retouching Motion Pictures Amazon.com, published by Thomson Course Technology and available online at amazon.com.

Gary and his wife Barbara host a site devoted to all forms of multimedia, and offer user support through The Pixel Dust Forum, part of the Boutons’ site.

Gary says keep in mind…
If you want a rendered model to truly interact with a video clip, Photoshop CS3 Extended has the perfect feature: the Clone Source palette. Here’s how to add an arch to a street intersection and have a passing car or two actually drive through the modeled arch.