[AstroPy] unexpected pyfits behavior float32 converted to float64
Phil Hodge
hodge at stsci.edu
Wed May 9 12:38:59 EDT 2012
Erik,
On 05/09/2012 11:49 AM, Erik Bray wrote:
> As a followup: I did a little more digging on this issue, and found out
> that despite the deceptive documentation, this has actually been the
> behavior of PyFITS for quite a long time:
>
> If the raw data is 16-bit ints they are scaled up to 32-bit floats. And
> if they're 32-bit ints (or 64-bit I think) they're scaled to 64-bit
> floats. I think this is so that one can generally expect the size of
> their data to double when reading scaled data.
No, this is so you don't lose any precision. A 32-bit float has
something like 22 bits of precision, which is fine for a 16-bit integer,
but you would lose around 10 bits if you converted a 32-bit integer to
32-bit float.
Phil
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