This application combines up to three two-dimensional NDFs,  using a different primary colour (red, green or blue) to represent each NDF. The resulting colour composite image is available in two forms; as an NDF with an associated colour table (see Parameters OUT and LUT), and as an ASCII PPM image file (see Parameter PPM). The full pixel resolution of the input NDFs is retained. Note, this application does not actually display the image, it just creates various output files which must be displayed using other tools (see below).

The data values in each of the input NDFs which are to be mapped on to zero intensity and full intensity can be given manually using Parameters RLOW, RHIGH, GLOW, GHIGH, BLOW and BHIGH, but by default they are evaluated automatically. This is done by finding specified percentile points within the data histograms of each of the input images (see Parameter PERCENTILES).

The NDF outputs are intended to be displayed with Kappa application DISPLAY, using the command:

  display $<$out$>$ scale=no lut=$<$lut$>$

where “$<$out$>$” and “$<$lut$>$” are the names of the NDF image and colour table created by this application using Parameters OUT and LUT. The main advantage of this NDF form of output over the PPM form is that any WCS or AXIS  information in the input NDFs is still available, and can be used to create axis annotations by the DISPLAY command. The graphics device which will be used to display the image must be specified when running this application (see Parameter DEVICE).

The PPM form of output can be displayed using tools such as xv, or converted into other forms (GIF or JPEG, for instance) using tools such as ppmtogif and cjpeg from the NetPbm or PbmPlus packages. These tools provide more sophisticated colour quantisation methods than are used by this application when creating the NDF outputs, and so may give better visual results.

BADCOL = LITERAL (Read)

BHIGH = _DOUBLE (Read)

BLOW = _DOUBLE (Read)

DEVICE = DEVICE (Read)

GHIGH = _DOUBLE (Read)

GLOW = _DOUBLE (Read)

INB = NDF (Read)

ING = NDF (Read)

INR = NDF (Read)

LUT = NDF (Write)

RHIGH = _DOUBLE (Read)

RLOW = _DOUBLE (Read)

OUT = NDF (Write)

PERCENTILES( 2 ) = _REAL (Read)

PPM = FILE (Write)

colcomp m31_r m31_g m31_b m31_col m31_lut

Combines the 3 NDFs m31_r, m31_g, and m31_b to create a colour composite image stored in NDF m31_col. A colour look up table is also created and stored in NDF m31_lut. It is assumed that the output image will be displayed on the current graphics device. The created colour composite image should be displayed using the command:

  display m31_col scale=no lut=m31_lut

colcomp m31_r m31_g m31_b out=! ppm=m31.ppm

As above, but no NDF outputs are created. Instead, a file called m31.ppm is created which (for instance) can be displayed using the command:

  xv m31.ppm

It can be converted to a GIF (for instance, for inclusion in WWW pages) using the command:

  ppmquant 256 m31.ppm $|$ ppmtogif $>$ m31.gif

These commands assume you have xv, ppmquant and ppmtogif installed at your site. None of them are part of Kappa.

• The output image (PPM or NDF) covers the area of overlap between the input NDFs at full resolution. If the input NDFs are very large is is a good idea to compress them first (for instance, using COMPAVE) to reduce the size of the output images. Note, compressing the output NDF will normally produce spurious colours in the compressed image.

• The output image is based on the values in the DATA components of the input NDFs. Any VARIANCE  and QUALITY  arrays in the input NDFs are ignored.

KAPPA: DISPLAY, LUTREAD; XV; PBMPLUS; NETPBM.

• The HISTORY, WCS, and AXIS  components, together with any extensions are propagated to the output NDF, from the first supplied input NDF.

• Processing of bad pixels and automatic quality masking are supported.

• Only data of type _REAL can be processed directly. Data of other types will be converted to _REAL before being processed.