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LOGARITHM

Section: C Library Functions (3)
Updated: 16 Mar 1998
Index

NAME

logarithm, fftDisplay - Take logarithm of BIFF band (compressdynamic range)

SYNTAX

#include <xite/arithmetic.h>

int logarithm( IBAND in_band, IBAND out_band,
double eps, double offset, double scale,
double minimum );

#include <xite/fft.h>

int fftDisplay( IBAND in_band, IBAND out_band,
double scale );

DESCRIPTION

Takes the logarithm of the magnitude of the pixelvalues of areal or complex band according to the algorithm

out_pix = (log10(eps + |in_pix|) + offset) * scale
out_pix = (out_pix >= minimum) ? out_pix : minimum

This mapping will compress the dynamic range of an image andmake small pixelvalues better visible (e.g. used to displayFourier transform magnitude).

epsequal to DOUBLE_MIN gives the default value
eps = 1 / (10 * xsize * ysize)

offsetequal to DOUBLE_MAX gives the default value
offset = -log10(eps)

scaleequal to 0.0 gives the default value 20.0.

minimumequal to DOUBLE_MAX gives the default value-10.0 * scale.

For an integral output pixeltype, the resulting pixel-valuesare rounded. The pixelvalues are limited to fit within therange of the output pixeltype.

fftDisplayis retained for compatibility with previous XITEversions. It is a macro call to logarithmwith epsequalto DOUBLE_MIN, offsetequal to DOUBLE_MAX and minimumequalto -DOUBLE_MAX. This will give the default values for epsandoffsetmentioned above. The call to logarithmis followedby a call to shift_band.

RESTRICTIONS

Input band may be any pixeltype, output may be double, real orunsigned byte.

RETURN VALUE

1 - bands have different xsize
2 - bands have different ysize
3 - out_band has wrong pixeltype
4 - in_band has unknown pixeltype

AUTHOR

Trond Sřrensen (wrote fftDisplay).

MODIFIED

Svein Bře (added output pixeltype real and double, fixed bugfor input pixeltype real, added lots of more input pixeltypes)when converting from fftDisplayto logarithm.

ID

$Id: logarithm.c,v 1.42 1997/05/27 14:44:03 svein Exp $

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