ISOCAM Interactive Analysis User's Manual Version 5.0 - ISO - ESA

240 CHAPTER 20. ADVANCED DATA CALIBRATION
3. It is important to mark the boundary of the image beyond which the pixel values are
invalid due to the shift. Given the (x, y) positions determined previously, flag edges will
generate a mask with 1 where pixels are valid and 0 elsewhere:
CIA> raster_pds.npix = $
CIA> flag_edges(x1, y1, x2, y2, raster_pds.nscd)*raster_pds.npix
When the raster MOSAIC is created the invalid pixels will not be included.
4. Now correct the library flat with register flat. This routine will shift the optical flat and
multiply it by the detector flat.
CIA>
my_flat = register_flat(x1, y1, raster_pds)
5. Supply the corrected flat to corr flat:
CIA> corr_flat, raster_pds, inflat=my_flat
That completes the flat-field correction.
20.2.7 Small mirror and unilluminated pixels
To avoid straylight, for the 3 ′′ PFOV normally the small Fabry-mirror was used. However,
this results into an incomplete illumination of the detector. For raster observations, standard
treatment leads to an uneven .MOSAIC, as illuminated and unilluminated pixels are averaged
(left picture in Figure 20.1). In order to produce a publishable .MOSAIC (right picture in
Figure 20.1), the unilluminated pixels should be masked out before the .MOSAIC is generated,
as shown in the example script below.
CIA> x3d, raster_pds.image
CIA>
Cube(4,28,4) = 14.8355
CIA>
Cube(31,0,4) = 13.7431
CIA> stat, raster_pds.image(4:31,0:28,*)
-------------------------------------------
Image dimensions: 28 29
Number of frames: 9
Total number of pixels: 7308
-------------------------------------------
Minimum Maximum Mean Median RMS
11.7170 15.5912 14.0292 14.0416 0.248977
CIA> x = where(raster_pds.image lt 14.0292 - 6*0.248977)
CIA> raster_pds.npix[x] = 0
CIA> raster_scan, raster_pds