Partial-area render window

Partial-area render window

Edit: 4-20-2016
Please see New Improved process in reply below. Photoshop is good for saving and manipulating layers, but it's expensive and uses computer resources best devoted to C3D. Preview is cheap, lightweight, and can work alongside C3D.

Using Cheetah 3D and Photoshop simultaneously

The request for a partial-area render tool has been a “Must-Have” on the forum Wish List thread for around seven years. Here is my best guess at a work-around, by having Photoshop open while working in C3D. The idea for the window originated with Frank Beckmann. I have extended the idea by incorporating Photoshop, and tried to reduce the implementation down to step-by-step directions, primarily for the benefit of beginners. It takes a few minutes to set up the first time, but then it will be ready whenever you face the all-too-typical situation where you are doing test renders and only need to inspect or tweak a small area of the render. By having this capability you can save hours of wasted time waiting for high-resolution whole-picture test renders. Usually there is a trade-off between high quality and fast speed. Until C3D incorporates a partial-area render tool, this allows you to effectively utilize Photoshop as a side-tool to get fast feedback on work in progress, because it practically automates the process. It also enhances quality, by stacking multiple test renders in layers, so that you can click back and forth to compare them, zoomed in if you want.

It may be that Version 7 will be released in the near future, and have this tool built in. But meanwhile, for anyone using Version 6, this might serve the purpose. Suggestions and corrections are welcome. I’m posting it in the Tutorials thread, but it’s more like a time-saving tip, broken down (so you won’t waste time trying to use a time-saving tip).

Frank Beckmann’s Passe-partout Rendering window:

Cheetah 3D:

One-time easy preparation of the Window plane:
Collapse a 1 X 1 plane, inner extrude, delete the center polygon
Material: White (or other color that doesn’t appear in the partial render): Diffuse & Emissive
Black: Specular, Reflection, & Transparency
Mode tag: Visible in editor; Visible in renderer, Editor shading = Wire
Render tag: only check Visible for primary rays (uncheck to render the entire picture)
Copy and paste the camera’s coordinates into the plane’s coordinates
Rotate the Y axis 90°, adjust the distance from the camera
Make the window plane the child of the camera
Save the file: Users/[you]/Library/Application Support/Cheetah 3D/Samples/Rendering

Re-use it in every future C3D picture

Open the Window.jas file before starting a new picture, copy the camera/window,
Open the new file; paste the camera/window
All settings and materials will be ready to use, with the window “attached” to the camera

In Edge mode, ring select the edges of the window opening
Use the Transform tool to frame the area to be rendered
Save the full-picture render, then copy the partial render to the clipboard


Open the full-picture render
Paste the partial render copy over it; Blend mode = Normal
Name the layer according to the C3D settings so you remember what you tried out
Use the Magic Wand selection tool: tolerance around 0 (white) to 8 (red, etc.); Anti-alias unchecked, contiguous checked
Select surrounding color — make sure the selection is uniform and complete, with no excluded “sparkling” pixels
Select/Modify/Expand: one pixel (the edge of the partial render has a one-pixel blur)
Delete the surrounding color; maybe use command-H to hide the selection outlines
Stack multiple partial renders in Layers, click the “eyes” to compare different partial renders
Save the layers in a Photoshop file, or Flatten the layers for a finished picture
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Partial Render using Preview

It's not unusual to finish a 20-minute render and notice a detail that you want to tweak. It would be nice if C3D had the partial render capability built in, but meanwhile here's a fast, cheap, easy process that runs Preview concurrently with C3D. It combines Hiroto's Camera Mask script, a Solid white material, and Preview's "Instant Alpha" tool.

1) Download Hiroto's Camera Mask script:
Place it in the Polygon scripts folder.
Open script in C3D, drag camera into "target cam;"
Click "add render tag"
Mode tag: Not visible in renderer (shown: Editor shading = Wire)
Add Solid shader material (white) to Camera Mask
2) Make first (full) render — Copy from Render Manager
In Preview: File -- New from Clipboard
3) Select partial area with Camera Mask
Mode tag: Visible in renderer
Make second (partial) render — Copy from Render Manager
In Preview: File -- New from Clipboard
4) In Preview, select the "Instant Alpha" tool:
OS X 10.6: it's with the selection tools
OS X 10.10: click Markup Toolbox icon, then "Instant Alpha" icon
Drag a little rectangle in the white area; orange = selection
Note that the edges of the rendered area have a one-pixel anti-alias
5) Result of step #4
6) Delete (creates a transparent background)
7) Select All — Copy — Paste into #2
OS X 10.10 pastes high; I don't know why. Quirky.*
Click on the pasted copy to get the blue dots, lower with arrow key
9) To avoid anti-aliased one-pixel border, select inside rendered area
Use either the rectangle or lasso
10) File — Invert Selection — Delete — Select All — Copy
11) Paste
12) OS X 10.10: lower with arrow key

*Why is this? Please post an explanation/fix.

Wish List requests for partial render:


Preview app, not preview function

It frequently happens that after many preliminary renders I will get an over-all render that is just about perfect except for one small detail. Rather than have to wait through a high-resolution render of the entire picture, the technique I described above ("Partial render using Preview") lets me quickly fix the problem area and use Preview to add the revised detail to the larger completed render.

To clarify; I'm not trying to preview the render, just using the app named Preview for the cut-and-paste since it does the job and everybody has that app, as compared to Photoshop. This saves me time at the end of the creative process, not the beginning. I would prefer to have this capability built into C3D, but at this point that seems unlikely to happen.