The image may saved in four formats, the Pyxis native format ("*.PXI"), the Flexible Image Transport System ("*.FIT" extension) format, in a 16-bit grayscale Portable Networks Graphics format ("*.PNG") or as a 24-bit colour Windows bitmap (".BMP").  The Windows bitmap format should only be used once the image has been processed (dark background removed etc.) to avoid loss of information.  Bitmap images can be loaded into Pyxis, however they will be converted to 16-bit grayscale by summing the R, G and B channel pixel intensities and scaling so that the brightest pixel has intensity 65535.  The bitmap is then displayed using Pyxis's current default palette.

The FITS format was developped as a means of sharing tabular astrophysical data across a wide range of platforms.  It consists of a header containing a number of keywords that describe the manner in which the data is stored ("primary" keywords) as well as auxilliary information about the image itself ("secondary" keywords).  Most astronomical image processing programs accept the FITS format and free readers are available from numerous sources.  When saving images as FITS, all of the information for the image is kept except for the data necessary to reconstruct the palette used in Pyxis.  Therefore, if you need to preserve palette information, do not save to this format.  Also, for very small images the FITS format is expensive in terms of disk space due to its limitation that the header and data blocks must be written as integer units of 2880 byte sized blocks.

The composite image editor uses a variant of the PXI format; composite images use the extension "ADI" (...you probably don't care, but this derives from "AstroDarkroom Image", the original name of my processing application).  If you create a composite using Pyxis and you want to save all of the raw image information, you must use this format.  Once you're satisfied with the processed image, the composite can be saved as a Windows bitmap for printing, converting into a JPEG, etc.  Pyxis provides minimal support for image formats because applications that can perform many image format conversions are plentiful.

The PXI format consists of a text header which contains all of the image descriptor keys (similar to the FITS format).  The header is terminated with the string "END_HEADER******************".  The header is followed by a binary data section containing the parameters used to construct the palette.  This is followed by the pixel data.  A typical PXI header might look like;

PYXIS_IMAGE_FILE
VERSION: 3.1
FILENAME: C:\CCD Images\July 23 2004\north america_g_3
SYSTEM_CREATE_DATE: Saturday July 24, 2004
SYSTEM_CREATE_TIME: 08:20:22 (GMT)
DESCRIPTION:
FILTERS: Green
INTEGRATION_TIME: 1.000e+02
CCD_TEMPERATURE: -20.4
BRIGHTEST_PIXEL_VALUE: 65535
DIMMEST_PIXEL_VALUE: 6021
CCD_MAX_N_COL: 796
CCD_MAX_N_ROW: 512
X_BIN: 1
Y_BIN: 1
X_LO: 0
X_HI: 795
Y_LO: 0
Y_HI: 503
TOP_DARK_LEVEL: 5.29e+2
BOTTOM_DARK_LEVEL: 1.85e+2
OFFSET_LEVEL: 6.019e+3
SKY_LEVEL: 6.1e+1

END_HEADER******************

Unless extensive use of a commercial image processing package is to be used, it is recommended that all images be saved in the PXI format because it is more compact than the FITS format and it preserves the palette information.  To convert several PXI images to FITS or vice-versa, the multiple file processing tool can be used with an effectively void process setting.  For example, a bias subtraction with a bias of 0 can be performed on the list of images to convert.