When you take an image, the CCD samples the continuous pattern of light and dark at the focal plane of the telescope, breaking the image into discrete pixels. In resampling, you treat the discrete pixels as points on a continuous flow of light and interpolate a new set of samples; that is, you create a new image by taking new samples—or resampling—the old one.
You can resample to create an image with more pixels than the original by supersampling, or with fewer pixels by subsampling. While supersampling does not create new information, the interpolated pixels give the image a smooth, rounded appearance, eliminating the blocky "square stars" that many people find
objectionable. Subsampling results in the loss of some information, but can squeeze the image into a smaller screen space and smaller file.
The procedure below resamples the image array old ( ) into an image new ( ) that is newwidth pixels wide and newheight pixels high.
PROCEDURE RESAMPLE (newwidth, newheight) xratio = newwidth / (xmax + 1) yratio = newheight / (ymax + 1) FOR xp = 0 TO newwidth -1
FOR yp = 0 TO newheight - 1 x = xp / xratio y = yp / yratio xf = x - INT(x) yf = y - INT(y) a = old(INT(x), INT(y)) b = old(INT(x), INT(y)+1) c = old(INT(x)+1, INT(y)) d = old(INT(x)+1, INT(y)+1) new(xp,yp) = a * (1-xf) * (l-yf)_ + b * (1-xf) * yf_
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