User manual

Functional Descriptions 373

Applied filter: None Edge Sobel Horizontal Edge Sobel Vertical

In simple terms, the operator calculates the gradient of the image intensity at each point, giving

the direction of the largest possible increase from light to dark and the rate of change in that

direction. The result, therefore, shows how "abruptly" or "smoothly" the image changes at that

point, and therefore, how likely it is that part of the image represents an edge, as well as how

that edge is likely to be oriented. In practice, the magnitude (likelihood of an edge) calculation

is more reliable and easier to interpret than the direction calculation.

Mathematically, the gradient of a two-variable function (here the image intensity function) is at

each image point a 2D vector with the components given by the derivatives in the horizontal

and vertical directions. At each image point, the gradient vector points in the direction of the

largest possible intensity increase, and the length of the gradient vector corresponds to the

rate of change in that direction. This implies that the result of the Sobel operator at an image

point which is in a region of constant image intensity is a zero vector and at a point on an edge

is a vector which points across the edge, from darker to brighter values.

User Filter

Presently disabled.

Grid

Enable, (check), the Grid enable box to super-impose 7 horizontal lines and 7 vertical line, evenly

spaced over the Preview or Playback Panels to form an 8-row; 8-column grid.

Cross

Enable, (check), the Cross enable box to super-impose a horizontal line in the middle, and a

vertical line in the center, of the Preview or Playback Panels.

Default Button

Click the Default button to reset all the image processing Tools back to factory default settings.