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4.2.2 Sky Images

There are five steps in converting a digital array into an image on the sky:

(optional) Transform from actual image pixel numbers to those that would be observed by an ideal instrument.
Transform from the origin and axes of the instrumental coordinate matrix system to the origin and axes of a set of projected sky coordinates.

Convert the scale along each axis from pixel to physical values, still in the projection plane.

Determine the projection of the sky onto the coordinate plane of the digital array and deproject from the array plane onto the sky.

Transform from sky coordinates derived by deprojection to a standard celestial coordinate system.