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LogarithmImage

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Module: FoundationLite

Computes a natural logarithm of each pixel.

Applications

Transforms an image in such a way that a quotient on the input image becomes a difference on the output image. This can be useful for dealing with variable illumination.
Name Type Range Description
Input value
 inImage Image Input image
Input value
 inRoi Region* Region of interest
Input value
 inScale Real* Scaling factor (default: 255)
Input value
 inOffset Real 1.0 - Offset factor
Input value
 inNormalizeZero Bool Specifies whether the output range should be rescaled to start from 0
Output value
 outImage Image Output image
Diagnostic input
 diagLutProfile Profile Profile depicting the resulting look-up table of the logarithm transform

Requirements

For input inImage only pixel formats are supported: int8, uint8, int16, uint16, int32.

Read more about pixel formats in Image documentation.

Description

The operation applies logarithmic operator to each pixel of an image. Logarithmic operator is defined as follows:

\[inScale \cdot \frac{log(inOffset + |P(x,y)|)}{log(inOffset + M)}\]
where:

  • M is the maximum of the inImage type (i.e. 255 for UInt8, 127 for Int8).
  • inScale is the expected maximum value of the transformation. If set to Auto it will result in value 127 for Int8 image and 255 for other image types.
  • inOffset value corresponds to the camera's black level. Its default value is equal 1 and causes the strongest possible transform.

When inNormalizeZero is set to True, the result is not only scaled, but also normalized so that pixel value 0 is still transformed into value 0. This assures that the entire output value range is utilized.

Examples

Description of usage of this filter can be found in examples and tutorial: Fourier Analysis.

The LogarithmImage performed on the sample image with parameters inScale = 250, inOffset = 50. The middle image inNormalizeZero = False and the left image has inNormalizeZero = True.

Hardware Acceleration

This operation supports automatic parallelization for multicore and multiprocessor systems.

Errors

This filter can throw an exception to report error. Read how to deal with errors in Error Handling.

List of possible exceptions:

Error type Description
DomainError Region exceeds an input image in LogarithmImage.
DomainError Not supported inImage pixel format in AvsFilter_LogarithmImage. Supported formats: Int8, UInt8, Int16, UInt16, Int32.

Complexity Level

This filter is available on Advanced Complexity Level.