HI 1A - Raw Image

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

HI 1A – Bloom removed image

HI 1A – Background subtracted image

Starfield fitting for alignment

HI Calibration Parameters HI 1AHI 2A Pre-flight StarsPre-flightStars HI x offset (°) ± ±0.02 HI y offset (°) ± ±0.02 HI roll (°) ± ±0.001 Distortion parameter (μ) ± ±0.002 Fparaxial (mm) Platescale (degrees/pixel) CCD x offset (bins) ± ±0.2 CCD y offset (bins) ± ±0.3

HI Calibration Parameters HI 1BHI 2B Pre-flightStarsPre-flightStars HI x offset (°) ± ±0.2 HI y offset (°) ± ±0.2 HI roll (°) ±8x ±0.4 Distortion parameter (μ) ± ±0.001 Fparaxial (mm) Platescale (degrees per pixel) CCD x offset (bins) ± ±0.8 CCD y offset (bins) ± ±2

HI 1A – Star removal image

HI 2A – Milky Way

HI 2A – Magellanic Clouds

HI 1A – small-scale flatfield 1.Take series of images (at least 3) 2.Find the minimum value per pixel 3.Low-pass filter this background 4.Pixel-to-pixel variations are the difference between the two over small areas of the CCD 5.Do this many times to build up statistics for each pixel

HI 1A – small-scale flatfield

HI 1A – small-scale flatfield uncertainties

HI 1A – large-scale flatfield 1.Identify stars in image 2.Wait for them to drift through the field of view 3.Measure the variation in their intensities as they do so. 4.Do this for many stars.

HI 1A – large-scale flatfield