Level 2 Help for CORNER

CORNER uses the portion of the input image defined by the SIZE
parameter, minus any border specified by the BORDER  parameter.  
If the SIZE field is not entered, the image size is obtained from the
VICAR label.

The WIDTH parameter determines the size of the interval over which the
gradient and second derivative are computed.  The larger the WIDTH parameter,
the less the program pays attention to noise and fine detail.  CORNER ignores
most features that have a diameter much less than the WIDTH parameter.
In the initial search for edge pixels, CORNER looks through a line for a pixel
for which the average brightness of the preceding M pixels differs from 
the average brightness of the succeeding M pixels by at least the GTHRESH
value, where M is the WIDTH value.  The default value for WIDTH is 4.

The GTHRESH parameter is used roughly as a gradient magnitude threshold for
edge detection.  If GTHRESH is defaulted, the program automatically computes a
threshold based on the brightness variation in the image. 
In the initial search for edge pixels, CORNER looks through a line for a pixel
for which the average brightness of the preceding M pixels differs from 
the average brightness of the succeeding M pixels by at least the GTHRESH
value, where M is the WIDTH value.  

This parameter can have a major effect on the number of corner locations
found.  For images with very low contrast, it may be more reliable to
explicitly specify a small value for GTHRESH, such as 5.

CORNER divides the input image into NAV rows (and NAH columns) of rectangular
cells.  For each rectangular cell, CORNER finds the corner of greatest quality.
The default for NAH is 5.

CORNER divides the input image into NAV rows (and NAH columns) of rectangular
cells.  For each rectangular cell, CORNER finds the corner of greatest quality.
The default for NAV is 5.

In some applications, only non-zero pixels are considered to be image data.
In such cases, the default value of 1 for THRESH can be used.  CORNER considers
any pixel with a DN less than THRESH to not be image data.  This parameter is
used so that the edge of image data will be ignored during the corner search.
Use THRESH=0 if 0 is to be included as image data.  (Negative halfword values
are always considered to not be image data by CORNER.)

CORNER uses the portion of the input image defined by the SIZE
parameter, minus any border specified by the BORDER  parameter.  
All corner locations found will be more than the BORDER value of pixels 
from the edge of the image so that these locations can be used for 
FFT correlation by another program.  

The default is for CORNER
 to print a list of corner locations found.
'NOPRINT supresses printed output.