LUTABLE - Manipulates an graphics device colour table

Description:

This application allows manipulation of the colour table  of an graphics device provided some data are, according to the graphics database, already displayed upon the device. A two-dimensional data array, stored in the input NDF  structure, may be nominated to assist in defining the colour table via an histogram equalisation. There are two stages to the running of this application.

1. The way in which the lookup table (LUT) is to distributed amongst the pens (colour indices) of the colour table is required. Some pens are reserved by KAPPA as a palette, particularly for annotation. This application only modifies the unreserved portion of the colour table.

2. The lookup table is now chosen from a programmed selection or read from an NDF.

The two stages may be repeated cyclically if desired. To exit the loop give the null response, !, to a prompt. Looping will not occur if the lookup table and the distribution method are supplied on the command line.

Usage:

lutable mapping coltab lut [device] ndf percentiles shade

Parameters:

DEVICE = DEVICE (Read)

Name of the graphics device to be used. [Current graphics device]

COLTAB = LITERAL (Read)

The lookup table required. The options are listed below.

"Negative" -- This is negative grey scale with black assigned to the highest pen, and white assigned to the lowest available pen.

"Colour" -- This consists of eighteen standard colour blocks.

"Grey" -- This a standard grey scale.

"External" -- Obtain a lookup table stored in an NDF's data array. If the table cannot be found in the specified NDF or if it is not a LUT then a grey scale is used.

FULL = _LOGICAL (Read)

If TRUE the whole colour-table for the device is stored including the reserved pens. This is necessary to save a colour table written by another package that does not reserve colour indices. For colour tables produced by KAPPA this should be FALSE. [FALSE]

LUT = NDF (Read)

Name of the NDF containing the lookup table as its data array. The LUT must be two-dimensional, the first dimension being 3, and the second being arbitrary. The method used to compress or expand the colour table if the second dimension is different from the number of unreserved colour indices is controlled by Parameter NN. Also the LUT's values must lie in the range 0.0-1.0.

MAPPING = LITERAL (Read)

The way in which the colours are to be distributed among the pens. If NINTS is the number of unreserved colour indices the mapping options are described below.

"Histogram" -- The colours are fitted to the pens using histogram equalisation of an NDF, given by Parameter IN, so that the colours approximately have an even distribution. In other words each pen is used approximately an equal number of times to display the two-dimensional NDF array. There must be an existing graphics deviceed. This is determined by looking for a DATA picture in the database. This is not foolproof as this may be a line plot rather an image.

"Linear" -- The colours are fitted directly to the pens.

"Logarithmic" -- The colours are fitted logarithmically to the pens, with colour 1 given to the first available pen and colour NINTS given to the last pen.

NDF = NDF (Read)

The input NDF structure containing the two-dimensional data array to be used for the histogram-equalisation mapping of the pens. The the data object referenced by the last DATA picture in the graphics database is reported. This assumes that the displayed data picture was derived from the nominated NDF data array.

NN = _LOGICAL (Read)

If TRUE the input lookup table is mapped to the colour table by using the nearest-neighbour method. This preserves sharp edges and is better for lookup tables with blocks of colour. If NN is FALSE linear interpolation is used, and this is suitable for smoothly varying colour tables. [FALSE]

PERCENTILES( 2 ) = _REAL (Read)

The percentiles that define the range of the histogram to be equalised. For example, [25,75] would scale between the quartile values. It is advisable not to choose the limits less than 3 per cent and greater than 97. The percentiles are only required for histogram mapping. All values in the NDF's data array less than the value corresponding to the lower percentile will have the colour of the first unreserved pen. All values greater than the value corresponding to the upper percentile will have the colour of the last unreserved pen.

SHADE = _REAL (Read)

The type of shading. This only required for the histogram mapping. A value of $-$ 1 emphasises low values; $+$ 1 emphasises high values; 0 is neutral, all values have equal weight. The shade must lie in the range $-$ 1 to $+$ 1.

Examples:

lutable lo co

Changes the colour table on the current graphics device to a series of coloured blocks whose size increase logarithmically with the table index number.

lutable li ex rococo

This maps the lookup table stored in the NDF called rococo linearly to the colour table on the current graphics device device.

lutable li ex rococo full

This maps the lookup table stored in the NDF called rococo linearly to the full colour table on the current graphics device device, i.e. ignoring the reserved pens.

lutable hi gr ndf=nebula shade=0 percentiles=[5,90]

This maps the grey-scale lookup table via histogram equalisation between the 5 and 90 percentiles of an NDF called nebula to the colour table on the current graphics device device. There is no bias or shading to white or black.

Notes:

• The effects of this command will only be immediately apparent when run on X windows which have 256 colours (or other similar pseudocolour devices). On other devices (for instance, X windows with more than 256 colours) the effects will only become apparent when subsequent graphics applications are run.

Related Applications :

KAPPA: LUTEDIT, LUTREAD, LUTSAVE, LUTVIEW; FIGARO: COLOUR.

Implementation Status:

• Processing of bad pixels and automatic quality masking are supported for the image NDF

• All non-complex numeric data types can be handled. Processing is performed using single- or double-precision floating point, as appropriate.