COMPOSITE RENDERING AND EDITING WITH IMOVIE

These notes provide a relatively straighforward technique for overlaying separate renderings of the same scene and from the same camera. A backround movie file is created in jpg format, and an overlay movie file is created using an alpha channel in either tga or png format.

The notes are organized in three parts. In Part I the process used to create the background and foreground images is summarized along with compiling them in Quicktime Pro. In Part II the process to composite the two movies together is demonstrated with iMovie HD. As an alternative, in Part III the open source software “Open Shot” is used.

Using the Alpha Channel to blend to separate renderings.

     PART 1: Create the source image sequences.

1. Create a scene with a ground plane, two spheres, a spot light and an ambient light. Apply phong shader materials to the spheres.
   
2. Key -frame the spheres moving upward from the ground along the plus Y axis (vertically) over 48 frames.
3. For each sphere go to the attributes editor, go the “nurbsSphereShape tab” and “Render Stats” sub-tab and turn off “Primary Visibility”.

   

   

4. Render out the scene as a jpg series (which will not record an alpha channel).
5. Compile the movie with Photoshop.1. Launch the Photoshop software. Use the Photoshop menu to Open the first image of the image frame sequence and with the open file dialog box selected the check-box for “Image Sequence”.

   

6.  Set the import frame rate, such as 30 frames per second in the dialog box that follows.

   

7. Use the menu “Windows/Timeline tab at the bottom of Photoshop.

   

8. The video track will appear just below with standard play icons.

   

9. Use the menu item :File/Export/Rendered” to render video to a single file “mp4” video movie format (or alternative format).

   

10. With the file formatting dialog box that appears, select the export location folder and choose a filename with the “mp4” format extension. The other presets in the “Render Video” below are recommended, including Format “Quicktime” and the preset “Animation High Quality”. The Document Size of “960 x 540” should be the same resolution as the original renderings. Select the “Render” button in the right hand corner to compile the “background.mov” video. A “Progress” window will graphically display the progress towards completing the compilation.
11. The video can now be viewed within any number of standard video players on Windows or Mac OS, such as the Windows VLC Player.

    

12. Now, turn back on visibility for the ground spheres, and turn it off for the ground plan, ensure that the “alpha channel” check box is turned on in the Render Settings common tab, render the scene out as a series of “png” files, and compile them Photoshop, and save the movie to a file such as foreground.mov.
13. Similarly import the foreground images and open the timeline for viewing. However, the export video specifications will be different. Render to the “Preset” of “Animation High Quality” and to the “Alpha Channel” option of “Straight – Unmatted” and “3D Quality” of “Ray Traced Final”.

    

PART 2: Composite Sequence with iMovie HD

1. Begin with a new movie event.
2. Use the import media tool to import the foreground and background movie.
3. Place the background movie on the video track.
4. Place the foreground video in the work area just above the background video.
5. To complete the edit, use the menu” File/ShareFileSequnce” and confirm the video resolution.
6. Select the “Next” button (shown in the image above) and choose the appriate folder for placing the composite movie.
7. The mp4 file is created.
8. Open the file and playback to confirm the result.