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[edit] Chapter 13: Render Settings: Discussion

By Roland Hess

There are only a few useful settings for the renderer that are not related to compositing.

RSD.01: The Render Buttons.

The Render buttons are accessible from any buttons window, and can be found by clicking on the Scene context and Render sub-context on the header, or by pressing F10.

When rendering, there are several things you need to specify: the render size, where and in what format to save the finished product, and the quality options you would like the renderer to use.

[edit] Render Size

The finished size of the render is chosen in the Format panel, with the SizeX and SizeY controls. The column of buttons to the right contains preset values for different rendering tasks.

RSD.02: Setting render size and preset buttons on the Format panel.

[edit] Output Format

Rendered images are not automatically saved. You must press F3 to save them, or select "Save Image..." from the File menu. When Blender saves the image, it uses the format specified on the Formats panel.

RSD.03: The different image formats available for saving.

The default image format is Jpeg, but, as Jpeg compression can leave ugly artifacts, you should probably change it to PNG, and set the Quality spinner to 100. With this menu, you can also choose from the animation formats appropriate to your computer (Quicktime, AVI codec), which will bring up your operating system's animation saving dialogue.

If you want to save an image's Alpha channel along with the rest of the render, you need to select the "RGBA" button at the bottom of the panel, as well as an image format that supports Alpha channels (Targa, PNG, OpenEXR and MultiLayer).

If you are rendering an animation and have chosen a still image format (PNG, Targa, Jpeg, etc.) instead of an animation format (.avi, Quicktime), Blender will save a series of numbered image files, one for each rendered frame. It is then up to you to put the images together into a playable animation, using either Blender or some other program.

Animated image sequences are saved automatically to the folder specified in the top file selector of the Output tab.

File:Figure RSD.04.png

[edit] Oversampling

The render is basically a system that looks at the 3D scene for every pixel of the final image and asks "What color should this be?" In the simplest case, it just takes the object nearest to the camera on that pixel, figures out the location on the object that the pixel covers, and calculates the final color based on lamps, shadowing and the object's material. What should it do, though, if one of the pixels in the final image happens to show the edge of an object? Should the renderer use the color and shading for the closest object, or the one showing from behind it?

This is the problem that anti-aliasing tackles. If the renderer only chose the foremost object, final renders would look like this:

Figure RSD.05: Jagged edges anywhere one object ends and another begins.

However, the renderer could actually pretend that that single pixel is made up of, say, four smaller pixels. Then, it could calculate a color for each of those, giving a more accurate picture of what's really going on at that object's edge. After those four values are calculated, the results could be averaged, giving the final color for the image's pixel. This process is called oversampling, which is one method of anti-aliasing. For images to look natural, it must be enabled.

Figure RSD.06: The same scene, with anti-aliasing.

Anti-aliasing is enabled with the "OSA" button, which stands for "oversampling." Different levels of OSA can be set: 5, 8, 11 and 16. Lower levels give a less nice, though often acceptable, result. The higher levels will take longer to render, but give smoother edges. Always start at the bottom and only raise the level if the edges of your objects still show the kind of "stair stepping" visible in the first sample image.

Figure RSD.07: The Oversampling buttons.

[edit] Rendering Controls

The large Render button on the Render panel triggers a render. That's kind of obvious, but it must be said. A render may also be triggered from any window type or screen within Blender by pressing F12.

If you will be rendering an animation, the large Animation button on the Anim panel does the trick. Blender will render all the frames in the range between (and including) the Sta (Start) and End values at the bottom of the panel.

At any time during either a single frame or animation render, the rendering process may be stopped by pressing the Esc-key.

Figure RSD.12: The Render and Animation render buttons.

[edit] Technical Details

If you have a computer with a dual core processor (or more), you can have the renderer take advantage of it. The "Threads" spinner on the Output tab tells Blender how many different render processes to run at once. Dual core processors will be able to efficiently run two threads at once, while quads or two duals could run four at once.

Note: If your computer has an Intel Core Duo or Athlon X2 processor, you can set Threads to 2. If you have a different multi-processing architecture than those two, you probably don't need us to tell you what you have.

Figure RSD.08: The Threads spinner set to 2 for use with a Mac Dual G5 computer.

[edit] Speeding Up Test Renders

You don't always want to wait for a full quality render. Sometimes, it's good enough just to see how a moved lamp or tweaked material looks in place with the rest of your scene.

If you don't want to use the Shift-P Preview Render panel in one of the 3D views, your only option is to actually trigger a full render. There are several ways to speed it up, if you are willing to compromise certain aspects of the result.

• Disable OSA: Turning off OSA will give a drastic speedup, as each pixel in the image will only go through a single round of calculations.

• Disable Shadow: Disabling the Shadow button on the Render panel tells the renderer to entirely skip shadow generation and mapping. If there are several lamps that cast shadows, this will give the render a nice speed boost. This button disables both buffered and raytraced shadows (see Chapter 11).

• Disable Ray: Disabling the Ray button on the Render panel skips all raytracing calculations, including ray shadows, transparency and reflection. For test renders that don't directly involve raytraced objects or effects, turn it off. In fact, unless you really need it, Ray should be disabled as a general principle.

• The percentage buttons: If you don't need to see your render at full resolution, you can use these buttons to tell the renderer to work at a percentage of the set output resolution. For example, setting this to 50% would generate a 400 x 300 pixel image if the output size on the Format panel was 800 x 600. Remember that a reduction to 50% in dimension means that the renderer only has 1/4 of the full number of pixels to calculate, which could give you a great speed increase.

Figure RSD.09: A test render ready to go at 50% size, with no shadows, raytracing or oversampling.

One final way to speed up test renders is to render only part of your image instead of the entire scene. Pressing Shift-B in a camera view brings up the same sort of marquee selection mode as using the B-key for border selection. LMB drag a box around the portion of the view you would like to have rendered. When you release the LMB, a dashed red box describes the area.

Figure RSD.10: Setting the area for a Border render.

When you activate a render, only the outlined area is rendered.

Figure RSD.11: The selected area is rendered.

This border render mode will persist until turned off by disabling the "Border" button on the Render panel.

Figure RSD.13: The "Border" render button.