saveFITS does fail for uint8_t images

[jbOhland93]

Saving an image in shared memory to a fits file does not work anymore for UI8 images. Here's what happens:

• Have an image in shared memory, the datatype is uint8_t, displayed as "UI8" in milk_streamCTRL
• Start milk CLI

• readshmim

• saveFITS "myFits.fits"

• Get for following error:

  FITSIO error 412 [<MILK_ROOT>/src/COREMOD_iofits/savefits.c, saveFITS_opt_trunc, 660]: datatype conversion overflow
  WARNING [ FILE: <MILK_ROOT>/src/COREMOD_iofits/savefits.c   FUNCTION: saveFITS_opt_trunc  LINE: 665 ]
  No C error (errno = 0)
  data trucated

This does not happen for uint16_t and float images - I did not try other ones.

milk-branch: dev (commit 29f799d42126fac113d7bbebd9d45bb291f2820c) ImageStreamIO-branch: dev (commit 2ab382dd4bb774f7aaa9ef67385278e3b53ebca2)

[DasVinch]

Noted.

Seems that the int8/uint8 saveFITS is quite broken.

• If I saveFITS uint8 zero data, then load the file in astropy, I'm finding a float32 file of value 128.....
• If I saveFITS int8 zero data, the load, I'm getting Uint8 zero data...

[DasVinch]

Find the odd one out (from the cfitsIO manual)...

The following 4 data type codes are also supported by CFITSIO:
#define SBYTE_IMG 10
/* 8-bit signed integers, equivalent to */
/* BITPIX = 8, BSCALE = 1, BZERO = -128 */
#define USHORT_IMG 20 /* 16-bit unsigned integers, equivalent to */
/* BITPIX = 16, BSCALE = 1, BZERO = 32768 */
#define ULONG_IMG
40 /* 32-bit unsigned integers, equivalent to */
/* BITPIX = 32, BSCALE = 1, BZERO = 2147483648 */

I'm writing a PR.

[jbOhland93]

Now that's funky! Is the BZERO of the 8-bit signed int set to -128 rather than 0 because the unsigned counterpart is used more frequently and having a zero is more environmentally friendly? Feels like it's worth the confusion.