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Rendering is the final process of CG (short of post processing, of course) and is the phase in which the image corresponding to your 3D scene is finally created. Rendering is a CPU-intensive process. You can render an image on your computer, or use a render farm which is a network of PC's that each work on a different section of the image or on different frames. This section provides a full explanation of the features in Blender related to the process of producing your image or animation.

Introduction

Rendering Buttons.

The rendering buttons window is accessed via the Scene Context and Render Sub-context (F10 or the Manual-Part-I-RenderingButton.png button). The rendering Panels and Buttons are shown in Rendering Buttons..

These buttons are organized into panels, which are:

  • Output - controls the output of the render pipeline
  • Render Layers - controls which layers and passes to render
  • Render - controls the actual rendering process of a still shot
  • Anim - controls the rendering of a series of frames to produce an animation
  • Bake - pre-computes certain aspects of a render
  • Format - controls the format and encoding of the picture or animation
  • Stamp - stamps the frames with identifying and configuration control item information
Tabs
To save screen space, some of the panels may be tabbed under another; for example, the Layers panel is a tab folder under the Output panel. To reveal it, simply click the tab header.
Yafray
If you have installed Yafray, options to control it will appear as two tabs under the Render panel once you have selected it as a rendering engine


Overview

The rendering of the current scene is performed by pressing the big RENDER button in the Render panel, or by pressing F12 (you can define how the rendered image is displayed on-screen in the Render Output Options). See also the Render Window.

A movie is produced by pressing the big ANIM animation button in the Anim panel. The result of a rendering is kept in a buffer and shown in its own window. It can be saved by pressing F3 or via the File->Save Image menu using the output option in the Output panel. Animations are saved according to the format specified, usually as a series of frames in the output directory. The image is rendered according to the dimensions defined in the Format Panel (Image types and dimensions.).

Workflow

In general, the process for rendering is:

  1. Create all the objects in the scene
  2. Light the scene and position the camera
  3. Render a test image at 25% or so without oversampling or raytracing etc. so that it is very fast and does not slow you down
  4. Set and Adjust the materials/textures and lighting
  5. Iterate the above steps until satisfied at some level of quality
  6. Render progressively higher-quality full-size images, making small refinements and using more compute time
  7. Save your images

Render Workbench Integration

Manual-Render-Pipeline.jpg

Blender has three independent rendering workbenches which flow the image processing in a pipeline from one to the other in order:

  • Rendering Engine
  • Compositor
  • Sequencer

You can use each one of these independently, or in a linked workflow. For example, you can use the Sequencer by itself to do post processing on a video stream. You can use the Compositor by itself to perform some color adjustment on an image. You can render the scene, via the active Render Layer, and save that image directly, with the scene image computed in accordance with the active render layer, without using the Compositor or Sequencer. These possibilities are shown in the top part of the image to the right.

You can also link scenes and renders in Blender as shown, either directly or through intermediate file storage. Each scene can have multiple render layers, and each Render Layer is mixed inside the Compositor. The active render layer is the render layer that is displayed and checked active. If the displayed render layer is not checked active/enabled, then the next checked render layer in the list is used to compute the image. The image is displayed as the final render if Do Composite and Do Sequence are NOT enabled.

If Do Composite is enabled, the render layers are fed into the Compositor. The noodles manipulate the image and send it to the Composite output, where it can be saved, or, if Do Sequence is on, it is sent to the Sequencer.

If Do Sequence is enabled, the result from the compositor (if Do Composite is enabled) or the active Render layer (if Do Composite is not enabled) is fed into the Scene strip in the Sequencer. There is is manipulated according to the VSE settings, and finally delivered as the image for that scene.

Things get a little more complicated when a .blend file has multiple scenes, for example Scene A and Scene B. In Scene B, if Do Composite is enabled, the Render Layer node in Scene B's compositor can pull in a Render Layer from Scene A. Note that this image will not be the post-processed one. If you want to pull in the composited and/or sequenced result from Scene A, you will have to render Scene A out to a file using Scene A's compositor and/or sequencer, and then use the Image input node in Scene B's compositor to pull it in.

The bottom part of the possibilities graphic shows the ultimate blender: post-processed images and a dynamic component render layer from Scene A are mixed with two render layers from Scene B in the compositor, then sequenced and finally saved for your viewing enjoyment.

These examples are only a small part of the possibilities in using Blender. Please read on to learn about all the options, and then exercise your creativity in developing your own unique workflow.

Sequencer from/to Compositor

To go from the Compositor to the Sequencer, enable both "Do Sequence" and "Do Composite". In the Compositor, the image that is threaded to the Composite Output node is the image that will be processed in the Scene strip in the VSE.

The way to go from the Sequencer to the Compositor is through a file store. Have one scene "Do Sequence" and output to an image sequence or mov/avi file. Then, in another scene, "Do Composite" and using an image input node to read in the image sequence or mov/avi file.

Render Window Options

Once you press F12 or click the big Render button, your image is computed and display begins. Depending on the Output Panel Option, the image is shown in a separate Render Window, Full Screen, or in a UV/Image Editor window.

You can render a single frame, or many frames in an animation. You can cancel the rendering by pressing Esc. If rendering a sequence of frames, the lowest number frame is rendered, then the next, and so on in increasing frame number sequence.

The Render Window can be invoked in several ways:

Render Panel->Render or F12
renders the current frame, as seen by the active camera, using the selected renderer (Blender Internal or Yafray)
3D View Window Header->LMB Template-LMB.png OpenGL Render button (far right)
Renders a quick preview of the 3D View window
Anim Panel->Anim CtrlF12
Render the Animation from the frame start to and included in the End frame, as set in the Anim panel.
3D View Window Header->CtrlLMB Template-LMB.png OpenGL Render button (far right)
Renders a quick animation of the 3D View window using the fast OpenGL render

Output Options needs to be set correctly. In the case of Animations, each frame is written out in the Format specified.

Rendering the 3D View Animation using the OpenGL is useful for showing armature animations.

Showing Previous Renders

If the Blender Internal render was used to compute the image, you can look at the previous render:

Render->Show Render Buffer
F11 - Pops up the Render Window and shows the last rendered image (even if it was in a previously opened & rendered .blend file).
Render->Play Back Rendered Animation
CtrlF11 - Similar as for the single frame, but instead plays back all frames of the rendered animation.

Render Window usage

Once rendering is complete and the render window is active, you can:

  • A - Show/hide the alpha layer.
  • Z - Zoom in and out. Pan with the mouse. You can also mousewheel to zoom
  • J - Jump to other Render buffer. This allows you to keep more than one render in the render window, which is very useful for comparing subtleties in your renders. How to use it:
  1. Press Render or F12
  2. Press J to show the empty buffer (the one we want to "fill" with the new image)
  3. Go back to the Blender modeling window. You can send the render window to the background by pressing Esc. Do not close, or minimize the render window!
  4. Make your changes.
  5. Render again.
  6. Press J to switch between the two renderings.
  • LMB Template-LMB.png - Clicking the left mouse button in the Render window displays information on the pixel underneath the mouse pointer. The information is shown in a text area at the bottom left of the Render output window. Moving the mouse while holding the LMB Template-LMB.png will dynamically update the information. This information includes:
    • Red, Green, Blue and Alpha values
    • Distance in Blender Units from the camera to the pixel under the cursor (Render Window only)

For Alpha values to be computed, RGBA has to be enabled. Z-depth (distance from camera) if computed only if Z is enabled on the Render Layers tab.


Step Render Frame

Step Frame Option.

Blender allows you to do faster animation renders skipping some Frames. You can set the step in the Render Panel as you can see in the picture.

Once you have your video file rendered, you can play it back in the real speed (fps). For that you just need to set the same Step parameter you used to render it.

If you play the stepped video in a normal speed in an external player, the general speed will be *Step* times faster than a video rendered with all the frames (eg. a video with 100 frames rendered with Step 4 @ 25 fps will have only 1 second. The same video rendered with Step 1 (the default value) will have 4 seconds of length).

If you want to use this parameter for rendering through command line you can use -j STEP, where STEP stands for the number of steps you want to use.

If you want to use this parameter for playing video files through the command line, you need to use the parameter -j STEP following the -a (which stands for the playback mode).

./blender -a -s 1 -e 100 -p 0 0 -f 25 1 -j 4 "//videos/0001.jpg"


  • Rendered stepped frames with output video format such as FFMpeg (always) or AVI Jpeg (sometimes) produce a corrupted video (missing end frames). in Blender 2.48a. Therefore the rendered video can't be played-back properly.

Therefore I suggest to work with the video output format of JPG, it works fine all the time.