SOBEL Function

Performs a Sobel edge enhancement of an image.

Keywords

Col

Computes the column gradient (horizontal line enhancement). (Default: Col = 1)

NOTE: For horizontal line enhancement only, set the keyword Row = 0 to disable the vertical line enhancement.

Edge

A scalar string indicating how edge effects are handled. (Default: 'zero') Valid strings are:

'zero'

Sets the border of the output image to zero. (Default)

'copy' Copies the border of the input image to the output image.

No_Clip

If set, the result data type is greater than the image data type so that overflow values in result are not clipped.

TIP: Use the No_Clip keyword to avoid overflow conditions.

Return

A scalar string specifying a mathematical function to apply. Valid strings are 'abs', 'phase', and 'value'. The Return keyword is used with the Row and Col keywords per the following table. (Default: 'abs')


	*Return* = `'abs'`	*Return* = `'phase'`	*Return* = `'value'`
Col = 1,Row = 0	ABS(col grad)	Invalid Condition	column gradient
Col = 0,Row = 1	ABS(row grad)	Invalid Condition	row gradient
Col = 1,Row = 1	ABS(row grad)+ABS(col grad)	ATAN(row grad ÷ col grad), data type is double	Invalid Condition
Col = 0,Row = 0	Invalid Condition	Invalid Condition	Invalid Condition

Row

Computes the row gradient (vertical line enhancement). (Default: Row = 1)

NOTE: For vertical line enhancement only, you must disable the horizontal line enhancement by setting the Col keyword to 0.

Same_Type

If set, the result is the same data type as image; otherwise, the result image data type is always integer.

Scale If set, each gradient is scaled by the factor 0.25; otherwise, no scaling is performed.

Zero_Negatives If set, all negative values in the result are set to zero.

Discussion

The SOBEL function supports multi-layer band interleaved images. When the input array is three-dimensional, it is automatically treated as an array of images, array(m, n, p), where p is the number of m-by-n images. Each image is then operated on separately and an array of the result images is returned.

SOBEL implements an approximation of the 3-by-3 nonlinear edge enhancement operator:

G(j,k) = |X| + |Y|

where

X = (A₂ + 2A₃ + A₄) - (A₀ + 2A₇ + A₆)

Y = (A₀ + 2A₁ + A₂) - (A₆ + 2A₅ + A₄)

and where the pixels surrounding the neighborhood of the pixel F(j, k) are numbered as follows:

CAUTION: Because the result image is saved in integer format, large original data values will cause overflow. Overflow occurs when the absolute value of the result is larger than 32,767. Use the No_Clip keyword to avoid overflow.