Motion Blur Tutorial - Anyone for a game of tennis

Here we have three children standing with their bikes and tennis racquets in front of dads gleaming new car.  It looks blurred, so the first thing is to zoom into the image and look for point sources which become streaks of light for motion blur or circles for out-of-focus blur.

The image has a whole lot of "double point sources" at 45 degrees and a few pixels apart as shown by the arrows above.  This is another type of motion blur even though it looks like some sort of double exposure.  The camera was travelling more slowly at the two ends of the blur.  This type of blur can happen if the photographer jerks the camera as the shutter release is pressed.

Lets suppose the the unthinkable happens, and there are not a single point source on the image - there are no shiny little dots to help us diagnose the type of blur.   This can happen, so we need to look at edges in various directions to determine the motion blur direction.

The parts of the tennis racket as pointed to by the yellow arrows are a lot sharper and narrower than the parts pointed to by the blue arrows.  The parts pointed to by the yellow arrows have edges which are parallel to the motion while the parts pointed to by the blue arrows have edges which are at right angles to the motion.  If edges are blurred the same amount in all directions then the image has out-of-focus blur.

By lining up the blur direction indicator in Focus Magic with the blur of the image we get a direction of about 130 degrees.  The blur distance can normally be found by trial and error.  To do this, slowly increase the blur distance until the streaks (or double dots in this case) become one dot.

The image will be fixed as shown below.

If you want to experiment, you can download the whole image from here.

For an audio-visual presentation of this tutorial, click here.