Boulder Laboratory for 3-Dimensional Electron Microscopy of Cells

ERASER(1)							   ERASER(1)

NAME
	eraser - to erase small flaws in image

SYNOPSIS
	eraser

DESCRIPTION
  This program replaces deviant pixels with interpolated values from
  surrounding pixels.  To use it, one first prepares a point list file
  (e.g. with WIMP) 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 specified 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 specified 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 theimages in the first place.
  
HISTORY
  Written by David Mastronarde, 2/27/89