def aperture_mask(fnlist, axcen, aycen, arad):
"""Opens a series of images and masks pixels outside a circular aperture.
The images are overwritten with the new masked image. The values of axcen,
aycen, and arad are added to the FITS headers as keywords 'fpaxcen',
'fpaycen', and 'fparad' respectively.
Inputs:
fnlist -> A list containing strings, each the path to a fits image.
axcen -> The aperture x center
aycen -> The aperture y center
arad -> The aperture radius
"""
for i in range(len(fnlist)):
print ("Masking pixels outside aperture for image " +
str(i+1)+" of "+str(len(fnlist))+": "+fnlist[i])
image = FPImage(fnlist[i], update=True)
rgrid = image.rarray(axcen, aycen)
image.inty[rgrid > arad] = 0
image.badp[rgrid > arad] = 1
image.axcen = axcen
image.aycen = aycen
image.arad = arad
image.close()
