如何使用熵转换（或缩放）FITS图像

Question

Using the Astropy library, I created a FITS image which is made by interpolation from 2 actual FITS images (they are scaled as " int16 ", the right format for the software I use : Maxim DL).

But the scale of this image is float64 and not int16 . And any astronomical processing software can't read it (except FITS Liberator)

Do you have an idea how to proceed ? Can we convert a FITS image just by changing the "BITPIX" in the header ?

I tried: (following this method : Why is an image containing integer data being converted unexpectedly to floats?

from astropy.io import fits

hdu1=fits.open('mypicture.fit')
image=hdu1[0]
print(image.header['BITPIX'])  # it gives : -64

image.scale('int16')
data=image.data
data.dtype
print(image.header['BITPIX']) # it gives : 16
hdu1.close()

However, when I check the newly-modified scale of "mypicture.fit", it still displays -64 ! No change was saved and applied!

Answer 1

If I understand your problem correctly, this should work.

from astropy.io import fits
import numpy as np

# create dummy fits file
a = np.array([[1,2,3],
              [4,5,6],
              [7,8,9]],dtype=np.float64)

hdu = fits.PrimaryHDU()
hdu.data = a

# looking at the header object confirms BITPIX = -64
hdu.header

# change data type
hdu.data = np.int16(hdu.data)

# look again to confirm BITPIX = 16
hdu.header