1. HI 1A - Raw Image

2. HI 1A – Shutterless/Flatfield Corrected Image (secchi_prep)

3. HI 1A – Bloom removed image

4. HI 1A – Background subtracted image

10. Starfield fitting for alignment

11. HI Calibration Parameters

12. HI Calibration Parameters

13. HI 1A – Star removal image

14. HI 2A – Milky Way

15. HI 2A – Magellanic Clouds

16. HI 1A – small-scale flatfield • Take series of images (at least 3) • Find the minimum value per pixel • Low-pass filter this background • Pixel-to-pixel variations are the difference between the two over small areas of the CCD • Do this many times to build up statistics for each pixel

17. HI 1A – small-scale flatfield

18. HI 1A – small-scale flatfield

19. HI 1A – small-scale flatfield uncertainties

20. HI 1A – large-scale flatfield • Identify stars in image • Wait for them to drift through the field of view • Measure the variation in their intensities as they do so. • Do this for many stars.

21. HI 1A – large-scale flatfield