rgbdisplay: Display an RGB image

Package: color

Usage

rgbdisplay rgb

Parameters

rgb

Image name of the 8-bit RGB dithered composite image to be displayed.

frame = 1

Image display frame.

Description

Rgbdisplay displays an 8-bit RGB color mapped or dithered image produced by the tasks rgbto8 or rgbdither. This task is a simple script calling the display task with parameters fixed appropriately for the images. The actual display command is:

display rgb frame fill- ztrans=none

where rgb and frame are the parameters of this task.

In addition to loading the image with the rgbdisplay task it is also necessary to adjust the image display server. Either SAOimage or IMTOOL may be used. SAOimage is to be prefered because it is possible to make some adjustments in the color mapping while with IMTOOL one must modify the composite image by varying the z1 and z2 values for the three images.

Both display servers must be set so that there is no contrast stretching. This is how both programs start initially but it may be difficult to return to this state if you adjust the contrast with the right mouse button in IMTOOL or the contrast adjustments in the (COLOR) menu of SAOimage.

You must first determine where the special color maps are located. For the images produced by rgbto8 the color map will be in the same directory as the image and have the same name with either the extension ".sao" or ".imt" depending on the target display server. Since the display servers are host programs they require host pathnames.

For the images produced by rgbdither you can determine the host pathname for the special color map from within IRAF using the command

cl> path colorlib$saorgb.lut
puppis!/ursa/iraf/extern/color/lib/saorgb.lut

                or

cl> path colorlib$imtoolrgb.lut
puppis!/ursa/iraf/extern/color/lib/imtoolrgb.lut

You can either remember these names (without the node prefix) or more simply copy the one you need to your IRAF home directory (or any place else you like) with the command

cl> copy colorlib$saorgb.lut home$

                or

cl> copy colorlib$imtoolrgb.lut home$

With SAOimage load the appropriate color map look up table by entering the (COLOR) menu, then the (CMAP) menu, and then pushing the (READ) button. When you are prompted for the map enter the pathname for the file saorgb.lut. For IMTOOL you need to call up the setup menu and set the pathname for the file imtoolrgb.lut in either of the user look up tables and then select the appropriate map.

For IMTOOL that is all you can do. Beware, don't adjust the contrast (the right mouse button) since this destroys the mapping between the composite image values and the look up table.

In SAOimage there are a couple of things you can do to make adjustments to the display. If you select (GAMMA) in the (COLOR) menu you can then move the mouse with a button down and vary the linearity of the color maps. This may be used with either of the 8-bit algorithms.

For the pixel dithered images you can also directly manipulate the color map. Bring up the color editor by clicking on the color bar. Even if you don't adjust the look up table this can be instructive. You can also adjust the individual colors by clicking the left (red), middle (green), or right (blue) buttons to either move the shown points or add and move points in the middle. Note that the abrupt discontinuity between the colors can cause sudden jumps in the color map if one point is moved past the other but you can recover by bring the point slowly back. If the map gets too messed up you can always reload the color map.

Examples

1. Display a dithered composite image.

cl> rgbdisplay tucana!/d1/testdata/rgb/trifid8
<Load the color map tucana!/d1/testdata/rgb/trifid8.sao or
<tucana!/d1/testdata/rgb/trifid8.imt. Because the display
<server is a host program you may need to copy the map
<first.

See also

rgbto8, rgbdither, color.package