Differential D1126 Diff 3570 motion_blur.rst

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motion_blur.rst

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	Blender's animations are by default rendered as a sequence of perfectly still images.	Blender's animations are by default rendered as a sequence of perfectly still images.
	This is unrealistic, since fast-moving objects do appear to be 'moving', that is,	While great for stop-motion and time-lapses, this is unrealistic, since fast-moving
	blurred by their own motion,	objects do appear to blurred by their own motion,
	both in a movie frame and in a photograph from a 'real-world camera'.	both in a movie frame and in a photograph from a 'real-world camera'.
	To obtain such a Motion Blur effect,	To obtain such an effect,
	Blender can be made to render the current frame and some more frames,	Blender can be made to render the current frame and some more 'virtual' frames,
	in between the real frames,	in between the actual previous and next frames,
	and merge them all together to obtain an image where fast-moving details are 'blurred'.	and merge them all together to obtain an image where fast-moving details are 'blurred'.


	The Human Eye
	=============

	Our brains process about 15 images from each eye in parallel each second.
	My brain cognates those images together and I perceive motion by comparing the two.
	If something is moving fast enough, I perceive it to be a blur
	(either because my rods have some latency in reacting to light, or my brain,
	in overlaying and differencing the images, somehow merges them in a mix sort of fashion).
	The POINT IS, I perceive a motion blur.


	In Film
	=======

	To keep us from seeing jumpy motion pictures,
	we simply doubled the frame rate to 30 frames per second (fps) (24 fps EU). So, the shutter is
	basically open for a 30th of a second and the film is exposed to the world for that length of
	time. As things moved in the real world during that time, the film exposure caused the image
	of the moving thing to be physically blurred or smeared on that frame.
	When developed and shown, we physically see an image that is blurred. The POINT IS,
	I see a blurred image.


	In CG
	=====

	In CG, when a frame is rendered, the computer knows exactly where everything should be,
	and renders it as such. From frame to frame, an object is location A in frame 1,
	and location B in frame 2. When we show you these two frames at speed (30 fps),
	the image appears jumpy to us, because somewhere between the eyeballs and the film,
	there isn't that same blurring as in the real world and film, and we can tell.


	Motion Blur in Blender	Motion Blur in Blender
	**********************	======================

	So, how can we make a blurry CG image? Blender has two ways to achieve Motion Blur:	Blender has two ways to achieve motion blur:


	Sampled Motion Blur	Sampled Motion Blur
	===================	-------------------

	This method is slow, but produces better results.	This method is slow, but produces better results.
	It can be activated in the motion blur section in the render options panel.	It can be activated in the motion blur section in the render options panel.
		It is done at render time.

	Motion Samples	Motion Samples
	Set the number of samples to take for each frame.	Set the number of samples to take for each frame. The higher the samples, the
		smoother the blur effect, but the longer the render, as each virtual intermediate
		frame has to be rendered.

	Shutter	Shutter
	Time Taken in frames between shutter open and close.	Time (in frames) the shutter is open. If you are rendering at 24 fps,
		and the Shutter is set to .5, the time in between frames is 41.67 ms, so the
		shutter is open for half that, or 20.83 ms.


	Vector Blur	Vector Blur
	===========	-----------

	:doc:`Vector Blur </composite_nodes/vector_blur#vector-based_motion_blur>`	:doc:`Vector Blur </composite_nodes/types/filter/vector_blur>`
	is faster but sometimes has unwanted side-effects - which can be avoided, though.	is faster but sometimes has unwanted side-effects - which can be avoided, though.
	Vector blur is a process done in compositing, by rendering the scene without any blur,	Vector blur is a process done in compositing (post-render time), by rendering the
	plus a pass that has movement information for each pixel.	scene without any blur, plus a pass that has movement information for each pixel.
	This information is a vector map which describes a 2d or 3d direction and magnitude.	This information is a vector map which describes a 2d or 3d direction and magnitude.
	The compositor uses that data to blur each pixel in the given direction.	The compositor uses that data to blur each pixel in the given direction.


	Examples	Examples
	********	--------

	To better grasp the concept, let's assume that we have a cube,	To better grasp the concept, let's assume that we have a cube,
	uniformly moving 1 Blender unit to the right at each frame. This is indeed fast,	uniformly moving 1 Blender unit to the right at each frame. This is indeed fast,
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	Hints	Hints
	*****	-----

	If Motion Blur is active, even if nothing is moving in the scene,	If Motion Blur is active, even if nothing is moving in the scene,
	Blender actually 'jitters' the camera a little between an 'intermediate' frame and the next.	Blender actually 'jitters' the camera a little between an 'intermediate' frame and the next.
	This implies that, even if Anti-Aliasing is off, the resulting images have nice Anti-Aliasing.	This implies that, even if :doc:`Anti-Aliasing </render/internal/antialiasing>` is off,
	MBLUR-obtained Anti-Aliasing is comparable to Anti-Aliasing of the same level,	the resulting images have nice Anti-Aliasing.
		Motion Blur-obtained Anti-Aliasing is comparable to Anti-Aliasing of the same level,
	but is generally slower.	but is generally slower.

	This is interesting since,	This is interesting since,
	for very complex scenes where a level 16 Anti-Aliasing does not give satisfactory results,	for very complex scenes where a level 16 Anti-Aliasing does not give satisfactory results,
	better results can be obtained using both Anti-Aliasing and MBlur.	better results can be obtained using both Anti-Aliasing and Motion Blur.
	This way you have as many samples per frame as you have 'intermediate' frames,	This way you have as many samples per frame as you have 'intermediate' frames,
	effectively giving oversampling at levels 25, 64, 121, 256 if 5,8,11,16 samples are chosen,	effectively giving oversampling at levels 25, 64, 121, 256 if 5,8,11,16 samples are chosen,
	respectively.	respectively.
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