Image - Motion Blur

Motion Blur provides a streaked blur effect as if the RGB or RGBa image were dragged along the direction indicated. In cartography, the main purpose of Motion Blur is as a directional "filter." It also may be used to create artistic effects to give a sense of motion to images.

Direction	A number from zero to 180, showing the direction in degrees around a circle to use for the blur.
Amount	Number of pixels to blur.
Preview	Check to see effect in action.

This command is also available on the Transform Toolbar for images as the Motion Blur transform operators:

Motion Blur Diagonal 1	Blurs the image as if moved diagonally on the upper left / lower right axis by the specified number of pixels.
Motion Blur Diagonal 2	Blurs the image as if moved diagonally on the upper right / lower left axis by the specified number of pixels.
Motion Blur Horizontal	Blurs the image as if moved horizontally by the specified number of pixels.
Motion Blur Vertical	Blurs the image as if moved vertically by the specified number of pixels.

However, when used from the transform toolbar the effect is immediate with no preview possible. In the transform toolbar version the parameter specified is used as the amount of pixels to blur.

Uses

The obvious artistic usage of Motion Blur is to annoy people by making them think their eyes are out of focus:

$images\img_bronze_motionblur.gif$

A more responsible use of Motion Blur is to create a blurred version of the image that may then be placed underneath the unaltered image in a map layer. If we take the image shown above and place a cutout of the unblurred monument on top we can give the impression that the monument is moving.

$images\img_bronze_moving.gif$

To create this example we made a copy of the bronze image and selected all pixels except the monument. We then deleted those pixels to leave just the monument. This appears in a layer above the blurred image.

A Cartographic Example

As much fun as it is to ruin people's eyesight with blur effects, Motion Blur does in fact have great utility in vectorization. We use it to extract lines that run in particular directions.

$images\img_motionblur_eg01.gif$

Suppose we have a raster image that contains horizontal and vertical lines as well as many other lines. We want to extract just the horizontal lines.

$images\img_motionblur_eg02.gif$

Applying Motion Blur twice with maximum Amount setting and a Direction of 90 in both cases blurs everything but the horizontal lines. These don't appear to change because their pixels are moved onto each other. Everything else is blurred into various shades of gray.

$images\img_motionblur_eg03.gif$

We can now use Threshold to extract only those lines by setting the threshold range so that everything except the lines is made white.

Had we set the Direction to any other value we could have extracted features oriented in any other direction. Since raster images are rarely very accurate it is rare that we have the opportunity to use Motion Blur in this way. However, when we can do so the effect is like magic.