mkglbhdr: Make global header from keywords in images and reference

Package: proto

Usage

mkgblhdr input output

Parameters

input

List of input images.

output

Output global dataless image.

reference = ""

Optional reference image defining the allowed keywords, order, and blank cards. If no reference image is specified the first image in the input list serves as the reference image.

exclude = ""

List of keywords to be excluded from the global header even if present in the reference header and with common values in all the input images. The case of the keywords in the list is ignored and the are matched to the headers in uppercase. Typically the list would be specified as an @file; i.e. the contents of a file with keywords on separate lines. Note that one may use the output of a header listing without editing since only the first eight characters of each line are used.

Description

Mkgblhdr makes a global (dataless) header with keywords common to a set of input images. Common means present in all headers and with identical card records (value, formatting, and comments). The purpose of this thask is to allow appending the images using the FITS "inherit" convention into a multi-extension file.

The set of keywords which are allowed to appear in the global header are those in a reference image which are not in the exclude list and which have identical card records in all images. The reference image is that specified by the reference parameter. If the value of that parameter is a null string then the first image in the input list is used. The reference image also determines the order of the cards including blank cards.

The way the task works is that the header card records are read from the reference image. Keywords in the excluded list are eliminated. Then reference card records which are not exactly matched in the input headers, independent of position, are eliminated. Finally any leading blank cards are removed and consecutive blank cards are reduced to single blank lines.

Examples

1. An initial multi-extension file with inherited global keywords is split into separate images. The headers of the separate images are the union of the global and extension headers as is the convention for inheritance. After operating on the separate images it is desired to recreate a new MEF without having recourse to the original global header.

cl> type images
image1
image2
cl> mkglbhdr @images newimage
cl> imcopy image1 newimage[im1,append,inherit]
cl> imcopy image2 newimage[im2,append,inherit]

To check the headers separately use the "noinherit" flag.

cl> imhead newimage[0] l+
cl> imhead newimage[im1,noinherit] l+

Note that if the global header of the original MEF is available it is probably better to use that header instead of mkglbhdr as follows.

cl> imcopy mefimage[0] newimage
cl> imcopy image1 newimage[im1,append,inherit]
cl> imcopy image2 newimage[im2,append,inherit]

It is important to understand how inheritance works when appending extensions. The IRAF FITS "kernel" eliminates keywords from the extension header when they have the same value as the global header. If there are common keywords but with different values then they are both present and any task that read the union of the global and extension headers will see the value from the extension.

2. The following example uses an exclusion list.

cl> type exclude.dat
CTYPE1
CTYPE2
CRVAL1
CRVAL2
CRPIX1
CRPIX2
CD1_1
CD1_2
CD2_1
CD2_2
cl> mkglbhdr @images newimage exclude="@exclude.dat"

See also

mscsplit, mscjoin