SHOWIMG(1)

NAME
showimg - display CCD-format images under X windows

SYNTAX
showimg [ options ] filename

DESCRIPTION
A CCD file or FITS-format file containing header information and 16-bit image data is read into memory and presented for display highlighting under the X window system. Mouse and cursor manipulations allow the control of several interactive functions. Besides the options listed below, the usual menu and window options as documented in the X and XMenu manual pages are available, either as inputs to the command line or in the .Xdefaults file.

OPTIONS

-planes n
    Allocate n planes to the display image. This will use 2**n colors or gray levels.

-rgb
    Default to red-green-blue color selection on startup instead of gray scale.

-neg
    Default to inverse video on startup.

-sqrt
    Default to square root mapping on startup instead of linear.

-threshold tnum
    Use tnum as the threshold level for scaling the 16-bit image instead of the one determined automatically.

-saturate snum
    Use snum as the saturation level for scaling the 16-bit image instead of the one determined automatically.

-fits
    Assume FITS format. Checks that `SIMPLE = T' and that `BITPIX = 16', and reads the size from `NAXIS1' and `NAXIS2'. The image will be read with 2880-byte reads and the 16tntegers byte-swapped if on a VAX.

-dfits
    Assume `disk' FITS format. On a VAX this assumes the integers do not need to be byte-swapped; otherwise this option is identical to -fits. Checks that `SIMPLE = T' and that `BITPIX = 16', and reads the size from `NAXIS1' and `NAXIS2'. The image will be read with 2880-byte reads.

-skip hbytes -nrows nr -ncols nc
    Do not read image size information from the header (either FITS or CfA CCD); skip hbytes bytes of information at the beginning of the file instead. The image is nc columns by nr rows of 16-bit pixels. This option can be used to read and display images in `foreign' formats.

Mouse Control
By default the picture comes up with a linear intensity gray scale. Pressing any mouse button, with or without mouse motion, causes the intensities displayed to change. Holding down the control button while pressing a mouse button causes a pop-up menu to appear, providing furthur choices. Releasing the button while pointing to an active selection chooses that selection.

The first pop-up menu selects other functions such as reinitialization to the default intensity map, display in red-green-blue or gray scale, and inverse versus normal video.

    Motion in the horizontal direction while holding down a mouse button down corresponds to a change in the threshold or background levels displayed. Motion in the vertical direction with a mouse button down changes the contrast. The center of the window is considered the default or null point.

    If the -rgb option is selected, either in the command line or via the pop-up menu, the left, middle, and right mouse buttons control the red, green, and blue intensity, respectively.

The second menu selects secondary cursor-activated options: printing, panning, and zoom-in. As each of these is selected, the mouse cursor changes to reflect the intended operation.

    Clicking any mouse button with the print option selected prints the 16-bit pixel value under that point, and the pixels atround it in an 11x11 grid.

    Under the pan and zoom options, the picture is redisplayed centered around the point under the cursor when clicked. If the point is too close to the edge of the display window, the point may not actually be displayed in the center. The zoom options (x2 and x4) magnify the picture via pixel replication.

The third menu select on of two functions to map the 16-bit intensities into the n-bit intensities loaded into the GPX memory: linear and sqrt. The latter is useful to relatively de-empahsize the contrast between background and bright pixels. After recalculating the mapping, the entire picture will be redrawn with the new pixels in the GPX.

BUGS

Needs a histogram display function to allow interactive setting of threshold and saturation values. Should have a true color palette instead of the rgb control to provide independent colors. Needs more types of mapping.

AUTHOR
William F. Wyatt, Smithsonian Astrophysical Observatory.