Rendering a Scene

More often than exporting, though, you probably want to render your scenes. Rendering is the process of taking your 3D data and creating one or more 2D pictures from the perspective of a camera. The 2D result can then be seen by nearly anyone using image viewers or movie players.

Creating a still image

Rendering single images, or stills, in Blender is remarkably easy. Blender actually offers three different ways to do it. The fastest way is to simply press the F12 hotkey. Alternatively, you can click the Image button in the Render panel of Render Properties or choose RenderRender Image from the menu at the top of each of the screen layouts that ship with Blender.

Viewing your rendered images in Blender

Any way you decide to do it, Blender uses its integrated UV/Image Editor to display the rendered output. If you don't have a UV/Image Editor already open in your screen layout, Blender takes the largest area in your screen layout and changes it to the UV/Image Editor while rendering. Of course, some people would prefer a different behavior for displaying renders. Fortunately, available options allow you to change that behavior. The control is a drop-down menu in the Render panel of Render Properties, labeled Display. By default, it's set to Image Editor.

Figure 14-2 shows the Render panel and the three different options you have for where to send your renders. I like to use the default Image Editor setting or Full Screen. Choosing Full Screen does the same thing as the Image Editor option, except it also maximizes the UV/Image Editor to the entire Blender window. If you choose the New Window option, Blender creates a completely new window, populated only with a UV/Image Editor that displays your image. For any of these render options, you can quickly toggle between your regular Blender screen and the render screen by pressing F11.

Figure 14-2: To view your renders, choose to use Full Screen, Image Editor, or Render Window.

Picking an image format

Now, you have your image rendered, but you still haven't saved it anywhere on your hard drive, so it's available for sharing with other people. This, too, is easy, but before you save, you may want to change the file type for your image. This is done in the Output panel of Render Properties, as shown in Figure 14-3.

Figure 14-3: Output panel in Render Properties.

The BW/RGB/RGBA buttons below the file type drop-down are always visible, and they're pretty important for both animations and stills. They control whether Blender, after rendering, saves a black and white (grayscale) image, a full color image, or a color image with an alpha channel for transparency. Typically, you use one of the latter two. RGB is the most common and is supported by all formats, creating a full color image. On occasions, however, you'll want to render with transparency.

As an example, say that you've made a really cool building model, and you want to add your building to a photo of some city skyline. You need everything that's not your building, including the background of your image, to be rendered as transparent. An alpha channel defines that transparency. The alpha channel is basically a grayscale image that defines what is and is not transparent. Totally white pixels are opaque, and totally black pixels are transparent. Gray pixels are semitransparent.

Setting dimensions for your renders

The Dimensions panel close to the top of Render Properties gives you control over the size of your final render. The X and Y values under the Resolution label set the width and height of your image in pixels. The X and Y values under the Aspect Ratio label are for determining the horizontal and vertical aspect ratio of your image. The ability to adjust aspect ratio is for certain circumstances where you want to render your image with rectangular pixels rather than square ones. Typically, rectangular pixels are necessary only for television formats, so unless you know exactly what you're doing or if you're using a preset, I recommend setting these to the same value. I use 1.000 most of the time.

Saving your still image

After you've adjusted all your settings, rendered, and chosen your output file format, you have just one thing left to do: Save your still. Saving is quick and painless. From the UV/Image Editor, press F3 or choose ImageSave As, and Blender brings up a File Browser. Here, you can dictate where on your computer you want to save your render. That's it!

Creating a finished animation

For rendering animations, the steps are similar to rendering stills (see preceding section), but you have a few more considerations. The largest consideration deals with the file type you choose. If, for example, you choose a still image format like JPEG, PNG, or OpenEXR, Blender creates an individual image for each frame in your animation. However, if you choose any of the movie options like AVI, QuickTime, or MPEG, Blender creates a single movie file that contains all the frames in the animation, as well as any sound you use for the animation. Note that Macintosh and most Windows users have the QuickTime option available, but Linux users do not.

Depending on the movie format you choose, an Encoding panel appears in Render Properties in which you have a second set of choices that enables you to pick the codec, or compression format, you want to use. QuickTime has its own interface, dependent on whether you're on a Windows computer or a Macintosh, whereas the other movie options work from the Encoding panel. Figure 14-4 shows the options in this panel.

Figure 14-4: The Encoding panel in Render Properties.

The Encoding panel lets you choose which codec you would like to use, and it also offers you the ability to tweak how the actual video gets compressed. More often than not, though, the default settings tend to work pretty well.

Like in the Dimensions panel, a presets drop-down menu appears at the top of the Encoding panel for commonly used configuration. Using this menu automatically enables the proper settings to render for outputs such as DV, DVD, and VCD.

The Audio Codec drop-down menu lower down the panel gives you similar control over the sound that Blender renders (if the file type supports audio), but arguably the most important thing to remember is to make sure that the Audio Codec drop-down isn't set to None if you want audio to be included with your rendered movie file. The PCM option gives you the best results, but also yields the largest file sizes.

The other consideration to make when saving an animation is where on your hard drive you intend to store it. Enter this information on the first field of the Output panel. By default, Blender saves your animations to the /tmp directory on your computer. However, you may not have a /tmp directory, or you explicitly may want to save the animation to a different folder on your hard drive. Left-click the file folder icon to the right of this text field and use the File Browser to navigate where you want to save your animation.

So, to render animation, the steps are pretty similar to rendering a still:

1. Set up your render resolution from the Dimensions panel and your file type from the Output panel.

   If you've been working on your animation, hopefully you've set it all up already. Although changing the output resolution (the width and height) of the image after you animate isn't too bad, changing to other frame rates after the fact can get to be a pain. The frame rate is set with the FPS value in the second block of buttons of the Dimensions panel.

2. Confirm the start and end frames from the Frame Range values in the Dimensions panel.

   You probably already made this setting while animating, but double-check these start and end frames to make sure that they're correct.

3. Verify where you want to save your file in the Output panel.
4. Animate by pressing Ctrl+F12.

   Also, you can press the Animation button in the Render panel or choose RenderRender Animation. Your animation immediately starts being created. Now go get a cup of coffee. Rendering an animation can take quite some time.

Creating a sequence of still images for editing or compositing

In a couple of situations, rendering out a sequence of still images rather than a single movie file makes a lot of sense. One of the biggest reasons for rendering a sequence of stills is for compositing, or combining multiple images together. When you do compositing, you often rely on having an alpha channel that makes everything transparent except for your rendered subject. Most video formats simply don't support an alpha channel, so to accommodate this shortcoming, you render out a sequence of still images in a format that does support alpha, such as PNG.

Another reason that you may want to have a still image sequence rather than a movie file is for editing, or sequencing multiple video and animation clips. To get smaller file sizes, many video codecs throw out large chunks of image data from one frame to the next. The result is a small file that plays well, but is pretty difficult to edit because in editing, you may want to cut on a frame that doesn't have very much image data at all. Using a sequence of still images guarantees that all image data for each and every frame is completely there for smooth editing. Chapter 15 covers both compositing and editing in more detail.

The third reason you may want to render a sequence of still images is largely practical. When rendering to a movie format, what happens if you decide to stop the render and change a small part of it? Or what happens if Blender crashes in the middle of rendering? Or if an army of angry squirrels invade your office and shut down your computer midrender? Well, you have to restart the whole render process from the start frame. Starting over, of course, is painful, especially if you have to wait multiple minutes for each frame in your sequence to render. If you render by using a sequence of still images, those images are saved the second that they're created. If your render process gets stopped for any reason, you don't have to start rendering again from the beginning. You can adjust the Start value in the Dimensions panel of Render Properties to pick up where you left off and resume the render process.