FSOBEL

Description

Performs Sobel edge detector filtering on image data. The Sobel edge detector filter creates an image where edges (sharp changes in gray-level values) are shown.

Parameters

Name	Type	Length	Value range
Input: Input raster channels *	Raster port	1 - 1024
Output: Output filtered image channels *	Raster port	1 - 1024
Mask: Area mask	Bitmap port	0 - 4
Port Settings: Resample mode	Raster port	1 - 1024	Nearest | Bilinear | Cubic Default: Nearest
Gain Factor	Float	0 - 1	Default: 1.0

* Required parameter

Parameter descriptions

Input: Input raster channels

Specifies the input channels to filter.

Output: Output filtered image channels

Specifies the output channels to receive the filtered result.

The output channels (DBOC) can be the same as the input channels (DBIC). If a mask is specified, only the area under the mask is written to the output channels.

For more accurate results, it is recommended that the output channels be 32-bit real channels. If an 8-bit channel is used, all generated values greater than 255 are truncated to 255.

Mask: Area mask

Optionally specifies the bitmap that defines the area to be processed within the input raster. If this parameter is not specified, the entire layer is used by default.

To define a bitmap mask, you must specify the bitmap segment that you want to use. All of the pixels within the specified segment, having a pixel value of 1, define the area to be processed.

Only the area under the mask is written to the output. Pixels that are outside the mask but within the filter size window will be used to determine the output pixel values.

Port Settings: Resample mode

Specifies the type of image resampling desired.

Gain Factor

Specifies the gain factor applied to the filtered input channel. The default value is 1.0.

Values of 0.0 or negative real numbers are not allowed.

Details

FSOBEL performs Sobel edge detector filtering on image data.

Sobel edge detection produces an image where higher gray-level values indicate the presence of an edge between two objects. The Sobel edge detector filter computes the root mean square of two 3x3 templates. For more details about the filter, see the Algorithm section.

The input channel (DBIC) can be the same as the output channel (DBOC). You can apply a gain factor (FACTOR) to each filtered input channel before averaging. A factor of 1.0 (the default) implies no gain.

Algorithm

The Sobel edge detection filter uses the two 3x3 templates to calculate the gradient value.

-1   0   1           1   2   1
-2   0   2           0   0   0
-1   0   1          -1  -2  -1

     X                   Y

Consider the following 3x3 image window:

+---------+
| a1 a2 a3|
| a4 a5 a6|     <---  3x3 filter window
| a7 a8 a9|
+---------+

All pixels are filtered. To filter pixels located near the edges of an image, the edge pixel values are replicated to provide sufficient data.