rgbsun: Create a Sun 24-bit RGB rasterfile

Package: color

Usage

rgbsun red green blue rgb

Parameters

red, green, blue: Input image names for the red, green, and blue components. The images must all be two dimensional and of the same size.

rgb: Output file name for the Sun 24-bit RGB rasterfile.

rz1, rz2, gz1, gz2, bz1, bz2: Range of values in the input images to be mapped to the minimum and maximum intensity in each color. Image pixel values outside the range are mapped to the nearest endpoint. The values correspond to the input image intensities even when using logarithmic mapping.

logmap = no: Use logarithmic intensity mapping? The logarithm of the input pixel values, in the range given by the z1 and z2 parameters, is taken before dividing the range into the 85 display levels. Logarithmic mapping allows a greater dynamic range.

swap = no: Swap rasterfile bytes on output? Used when rasterfiles are being written to a computer with opposite byte-swapping from that of the home computer (e.g. between VAX and Sun).

Description

Rgbsun takes three input IRAF images and produces a 24-bit Sun rasterfile. Though this file type was developed by Sun Microcomputers it is a relatively simple format which may useful on other machines have software designed to use it. The color image may be display with a variety of tools such as xv (a very powerful and generic, public domain viewer for X-window systems), xloadimage (another X-window display tool), screenload (a simple displayer on Sun computers), and snapshot (a Open-Look tool). Also some color printers can be used with this format such as a Shinko color printer.

If one wants to display images which have a large dyanmic range it may be desirable to first take the logarithm of each image. This may be done with the logmap parameter. Other types of stretching may be accomplished by modifying the individual images first, say with imfunction.

If the output rasterfiles are being sent to a computer with opposite byte-swapping characteristics, set swap = yes (e.g., when running rgbsun on a VAX, with output to a Sun).

The rasterfile format produced is quite simple. There is a header with 8 integer values immediately followed by the data values. The header has the following values of interest:

Word 1: Magic numer = 1504078485 Word 2: The number of columns Word 3: The number of lines Word 4: The number of bits per pixel = 24

The data consists of triplets of 8-bit data values in the order blue, green, and red. The triplet pixels are ordered by varying the column elements first and then the line elements. The sequence is continuous except that each line is padded, if necessary, to maintain a multiple of 2 bytes per line (with 3 bytes per pixel this means that images with an odd number of columns will have an extra zero byte).

Examples

1. Three 2048x2048 images of the Trifid nebula are obtained in the B, V, and R bandpasses. These images are properly registered. Examination of the histograms leads to selecting the display ranges 1-500 in each band. The image is then displayed on a workstation running an X-window system using the xv utility. The file is also printed to a local color printer interfaced as a Unix printer (the Shinko at NOAO).

cl> rgbsun trifidr trifidv trifidb trifid.ras \
>>> rz1=1 rz2=500 gz1=1 gz2=500 bz1=1 bz2=500
cl> !xv -swap24 trifid.ras
cl> !lpr -Pclp trifd.ras

Time requirements

Example 1 takes 2:20 minutes (33 seconds CPU) on a SparcStation 2.