iraf.net

NUMBER:	178
MODULE:	images.fmedian
SYSTEM:	V2.9
DATE:	Tue Aug 18 11:31:49 MST 1992
FROM:	davis

BUG:	The fmedian task can crash with a segmentation violation or a
	floating operand error if image pixel to integer mapping is turned
	off (hmin = zmin and hmax = zmax) and the input image contains
	data outside the range defined by zmin and zmax. The bug is not
	seen often because for most ccd images the data is between -32768
	and 32767.

STATUS:	The bug is fixed in 2.10.1. The work-around is to either let zmin and
	zmax default to the image minimum and maximum or set hmin and hmax
	to numbers that are slightly different from hmin and hmax.

NUMBER:	276
MODULE:	imexamine
SYSTEM:	V2.8-V2.10.2
DATE:	Tue Jan 31 15:06:41 MST 1995
FROM:	valdes

BUG:	The standard deviation values returned by the 'm' key in IMEXAMINE
	can be inaccurate when the mean data value is large and the standard
	deviation is relatively small.  This is due to calculation
	of the standard deviation formula using the difference in the sum of
	squares and the square of the sum with real precision.  The
	workarounds are to use IMSTATISTICS with an image section or
	to first subtract something like the mean value from the image
	before using IMEXAMINE.

STATUS:	In V2.10.3 and after the calculation is done in double precision
	and the standard deviation is as accurate as IMSTATISTICS.

NUMBER:	450
MODULE:	imfilter.fmedian,imfilter.frmedian,imfilter.fmode,imfilter.frmode
SYSTEM:	V2.11
DATE:	Fri Nov 19 14:20:16 MST 1999
FROM:	davis

BUG:	The fast median / mode filtering tasks will overflow producing
	pathological pixel values if the size of the filtering kernel
	xfilter * yfilter > 32767 and the number of pixels in 1 histogram
	bin happens to be > 32767 as may happen in bad pixel regions.

	The problem was due to the fact that for historical reason the
	algorithm histogram was stored as a short instead of an int.

STATUS:	Fixed for 2.11.3. The workaround is to try and keep the filter size
	< 32767 pixels in size, or to use the much slower median task.