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tv filename [span] [zero] [box=] [l=] [z=] [zoom=] [xo=] [yo=] [hist] [dither] [nofork] [invert]

DESCRIPTION This program displays the image in the file specified in the command line onto the TV display. The data are processed as follows:

pixel = (data - zero)*NCOLOR/span

where NCOLOR is the number of colors that the monitor can display.

If no span or zero are specified, then a few pixel values are sampled, and the span and zero are adjusted automatically (their values are printed on the text screen). The span and zero are either the third and fourth arguments, or can be specified anywhere in the argument list via the l and z parameters.

The data are shown starting in the upper left hand corner of the display unless modified by the xo and yo switches.

The zoom modifier can be used to show an expanded or shrunken view of the data. Non-integral values are rounded to the nearest integer. If the zoom value is less than 0.5, then the reciprocal of the value (rounded to the nearest integer) is used as a binning factor; thus, zoom=0.24 yields an image binned by a factor of four.

TV usally spawns a background process and returns your prompt. If you wish to wait until the window is terminated before getting the prompt, use the nofork option.

The invert option changes blacks to whites.

If the hist parameter is used the image is displayed using the technique of "histogram equalization". Note: the histogram must be computed first using the hist.

To present pictures more satisfactorily on monochrome monitors use the DITHER switch. If possible, use a zoom factor greater than one to yield "superpixels" which may have several different intensity values.

If you get a message like:

read_property: XGetWindowProperty returns wrong number of items you must run the propinit command.


As each image is displayed, a new process is created to run inside the window. Thus, control will pass immediately back to the shell after the "tv" command is typed, even before the image is fully shown. You can use any X-Windows Manager functions to move, hide/show, or cancel an image window. In addition, both the mouse and the keyboard may be used to affect the image whenever the cursor is within the image window, as follows:



Pressing the following keys causes the image to react in some way. Other keys are ignored (including Control-C).


tv crab - displays the file `crab' in the upper left-hand corner of the screen. Automatically finds the span and zero by looking at some pixels from the file.

tv virgo 500 200 zoom=2 box=1 - starting at 200 units to the right of the upper left-hand corner of the screen, displays the part of the image `virgo' which is within box 1. The zero value is 200, and span 500. The file is displayed so that each pixel in the image covers a two-by-two pixel area on the screen.

tv virgo zoom=0.5 - Displays the image in `virgo', using automatic zero and span, in the upper left-hand corner of the screen. The image is crunched down so that each pixel on the screen represents a two-by-two pixel area on the image.