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ccdtypes noao.imred.ccdred



ccdtypes -- Description of the CCD image types


The following CCD image types may be specified as the value of the parameter ccdtype :

	""	- (the null string) all image types
	object	- object images
	zero	- zero level images such as a bias or preflash
	dark	- dark count images
	flat	- flat field images
	illum	- illumination images
	fringe	- fringe correction images
	other   - other image types defined in the translation file
	none	- images without an image type parameter
	unknown - image types not defined in the translation file


The ccdred package recognizes certain standard CCD image types identified in the image header. The tasks may select images of a particular CCD image type from image lists with the parameter ccdtype and also recognize and take special actions for calibration images.

In order to make use of CCD image type information the header keyword identifying the image type must be specified in the instrument translation file. This entry has the form

imagetyp keyword

where keyword is the image header keyword. This allows the package to access the image type string. There must also be a translation between the image type strings and the CCD types as recognized by the package. This information consists of lines in the instrument translation file of the form

header package

where header is the exact string given in the image header and package is one of the types recognized by the package. The image header string can be virtually anything and if it contains blanks it must be quoted. The package image types are those given above except for the null string, "none", and "unknown". That is, these types may be specified as a CCD image type in selecting images but not as a translations of image type strings.

There may be more than one image type that maps to the same package type. In particular other standard CCD image types, such as comparison spectra, multiple exposure, standard star, etc., should be mapped to object or other. There may also be more than one type of flat field, i.e. dome flat, sky flat, and lamp flat. For more on the instrument translation file see the help for instruments .


1. The example entries in the instrument translation file are from the 1986 NOAO CCD image header format produced by the CAMERA format tape writer.

    imagetyp			data-typ

    'OBJECT (0)'		object
    'DARK (1)'			dark
    'PROJECTOR FLAT (2)'	flat
    'SKY FLAT (3)'		other
    'COMPARISON LAMP (4)'	other
    'BIAS (5)'			zero
    'DOME FLAT (6)'		flat

The image header keyword describing the image type is "data-typ". The values of the image type strings in the header contain blanks so they are quoted. Also the case of the strings is important. Note that there are two types of flat field images and two types of other images.

2. One way to check the image types is with the task ccdlist .

    cl> ccdlist *.imh
    Zero.imh[504,1][real][zero][1][OT]:FOCUS L98-193
    Flat1.imh[504,1][real][flat][1][OTZ]:dflat 6v+blue 5s
    ccd002.imh[504,504][real][unknown][1][OTZF]:FOCUS L98-193
    oldformat.imh[544,512][short][none][1]:M31 V

The unknown type has a header image type of "MUL (8)". The old format image does not have any header type.

3. To select only images of a particular type:

    cl> ccdlist *.imh ccdtype=object
    cl> ccdlist *.imh ccdtype=unknown
    ccd002.imh[504,504][real][unknown][1][OTZF]:FOCUS L98-193
    cl> ccdlist *.imh ccdtype=none
    oldformat.imh[544,512][short][none][1]:M31 V

4. To process images with ccdproc :

    cl> ccdproc *.imh
    cl> ccdproc *.imh ccdtype=object

In the first case all the images will be processed (the default value of ccdtype is ""). However, the task recognizes the calibration images, such as zero level and flat fields, and processes them appropriately. In the second case only object images are processed and all other images are ignored (except if needed as a calibration image).



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