Postage Stamps

In Staggered Frame mode, there are multiple windows containing data in a single raw FITS file. This information has to be transferred to the AQLC efficiently. Instead of sending the entire FITS file, a postage stamp is extracted from each raw FITS file for the AQLC to use. Only 1 postage stamp is extracted for each raw FITS file regardless of the number of windows that file may contain. The following is a summary of the steps involved in creating the postage stamp files:

1.

Read in average bias and convert to long integer. Saturated pixels are converted to NaN's

2.

Read in raw FITS image and convert to long integer. Saturated pixels are converted to NaN's

3.

Subtract bias from raw image and do over-clock correction as in photon counting event list.

4.

Sum all the windows together.

5.

Apply gain corrections for each node (convert to real numbers).

6.

Extract a region about the user input centroid (program can determine/adjust centroid if desired).

7.

Write out a FITS postage stamp image.

8.

At end, write out a total postage stamp image from all the data.

The advantage is that these images give a quick turn around on the quality of the data and are good for computing centroids. The disadvantage is that the time scale for each image is the total time of the raw FITS image (about 6sec), and if the user selects too small a postage stamp to extract, useful data may be lost.