eraser(1)                                                            eraser(1)



NAME
       eraser - to erase small flaws in image

SYNOPSIS
       eraser

DESCRIPTION
       This program replaces deviant pixels with interpolated values from sur-
       rounding pixels.  To use it, one first prepares a point list file (e.g.
       with model2point) containing a point for each area that one wishes
       to erase.  Best results will be obtained if the point is the most
       extreme value in the area.  (For elongated areas, one might want to to
       enter more than one point).

       The program works by building up a list of points around the specified
       point that need to be replaced.  The list starts with just the speci-
       fied point.  A rectangular box is defined by a placing a border around
       the points on the list; e.g. for a border size of 3, there will be at
       least 3 pixels between any point on the list and the edge of the box.
       Then the mean and standard deviation of density is computed for pixels
       that are in the box but are not on the list or adjacent to a point on
       the list.  Then, all of the adjacent points are examined, and they are
       added to the list if they deviate from the mean by more than the speci-
       fied criterion number of standard deviations (and in the same direction
       from the mean as the original specified point).  This process is
       repeated until no further points get added to the list, or until the
       box reaches a limiting size.  After the list is stable, the pixels in
       the box and not on the list are fit to a polynomial function of x and
       y, and the pixels on the list are replaced by values computed from the
       polynomial.

       The inputs are:
       Input image file
       Output image file, or <Return> to place modified sections back into
             the input file.  USE REPLACEMENT OPTION WITH CAUTION
       Point list file
       Criterion # of standard deviations for adding a pixel to the list
             of points needing replacement  (try 2)
       Border size around points on list (default 3 pixels)
       Maximum # of pixels to include in box (default 400)
       Order of polynomial (default=2, terms in x, y, x**2, y**2 and x*y)

       At each position, the program outputs a map of the pixels in the box,
       with the initial specified point marked by a 2 and other replaced
       points marked by a 1.

       This program doesn't always do a good job.  It could be improved, but
       it is better to keep dirt off of the images in the first place.

HISTORY
       Written by David Mastronarde, 2/27/89

BUGS
       Email bug reports to mast at colorado dot edu.



BL3DEMC                              4.7.3                           eraser(1)