IPALOG Function (PV-WAVE Extreme Advantage)

Computes the natural logarithm of an image, excluding zero values.

Usage

result = IPALOG(image)

Input Parameters

image—An array of any data type except string.

Returned Value

result—The logarithm to the base e (the natural log) of image, excluding zero values. For double-precision floating-point and complex values result is returned with the same data type. All other valid data types are converted to single-precision floating-point and result is returned as a floating-point data type.

Keywords

None.

Discussion

The IPALOG function is useful for displaying images with wide dynamic range and is defined as follows:

y = log_ex

Values in image which are zero are left as zero.

The IPALOG function handles complex numbers in the following way:

IPALOG(image) º Complex(log_e(|image|, arctan(image)))

Note

When error messages regarding the handling of zero values in the input are not wanted, you should use the IPALOG function instead of the PV‑WAVE ALOG function.

Example

; Generate a test image.

x = DIST(256)

; Take the fast Fourier transform of x.

f = FFT(x, -1)

; Display the log magnitude of the image FFT, with zero values

; retained as zeros.

TVSCL, IPALOG(ABS(f))