Sobel calculates a gradient image using a Sobel filter.

This method indicates gray value changes in the image. Large differences between neighbors are displayed as bright gray values, no changes are indicated by a value of 0 (zero). The pixels in the output image are calculated with the Sobel differential operator on the basis of a 3 x 3 x 3 fold of the input image.

Parameter

Description

Normalization

Defines how out-of-range pixel values are mapped.

The calculated pixel values of the output image may be out-of-range and are mapped into the available range.

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Clip

Values exceeding the pixel value range are set to the highest value available (white), values falling short of the pixel value range are set to the lowest value available (black). The effect corresponds to underexposure or overexposure. This means that in some cases information is lost.

-

Wrap

If a resulting value is larger than the maximum pixel value of the image, the difference exceeding the maximum pixel value is added to 0. Similarly, if a resulting value is below 0, the resulting pixel value is the maximum pixel value minus the difference falling below 0.

-

Shift

Normalizes the output to the value "pixel value + maximum pixel value/2". As a result, all resulting values are mapped to the available value range.

The middle value of the pixel value range remains constant. Values left and right of the middle value are changed progressively, so that values inside the pixel value range are changed only slightly. Values outside the pixel value range are changed strongly and mapped to the fringes of the pixel value range.

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Automatic

Normalizes the pixel values automatically to the available pixel value range. The highest resulting value is mapped to the maximum pixel value, the lowest resulting value to 0. As a result, the whole range of resulting pixel values is compressed evenly.