NAME

overscan -- Simulate the effect of overscanning in an image.

USAGE

overscan image overscan xsteps ysteps

DESCRIPTION

This task modifies a 1-dimensional image to simulate the effects of overscanning. Each subimage in the image is affected by overscanning separately. The number of subimages in a group is controlled by the ysteps parameter. For example, if ysteps=2, both halves of the image are modified to simulate the effects of overscanning. Pixels that are closer to either end of a subimage than the value of overscan times xteps will have their intensity reduced by the factor {xstep/(overscan*xsteps)}, where xstep is the distance to the closer end of the spectrum (in units of xsteps). Suppose a spectrum is 1000 pixels long, the intensity at each pixel is 10.0, the value of overscan is 5, the X stepping factor is 2, and the Y stepping factor is 1. After this task is run, the spectrum will look like the following:

  1    2    3    4    5    6    7    8    9   10   ...
 2.0  2.0  4.0  4.0  6.0  6.0  8.0  8.0 10.0 10.0  ...

 991  992  993  994  995  996  997  998  999 1000
10.0 10.0  8.0  8.0  6.0  6.0  4.0  4.0  2.0  2.0

PARAMETERS

image [file name]

The name of the image to be modified.

overscan [integer, min=1]

The number of steps in the image that are overscanned.

xsteps [integer, min=1]

The X stepping factor of the image, e.g., 4 if the image is quarter stepped.

ysteps [integer, min=1]

The Y stepping factor of the image. This parameter controls the number of subimages that are stored as a single group, e.g., ysteps=2 if each group contains an object observation and a sky observation.

EXAMPLES

1. Simulate overscaning for all groups in the image yexample for the 40 pixels at the beginning and end of the group, and 80 pixels in the middle. The image is quarterstepped in the X direction:

  to> overscan yexample.d0h 10 4 2

2. Simulate the overscanning for only the second group in the image:

  to> overscan yexample.d0h[2] 10 4 2

BUGS

SEE ALSO

compspec