Introduction to the X11 Image Display

VISTA provides a set of basic image display and interaction commands for X11 windows. The following commands setup and communicate with the display window. For more information see their individual help files.

A number of other commands (e.g., MARKSTAR) will also interact with the display for specific purposes, such as measuring image profiles.

The first time the TV command is given, VISTA opens an Image Display window on the console, and loads a color map as well as displaying the image. A "Zoom" window is also opened that shows a magnified section of the image under the current cursor location (a kind of "magnifying glass").

Once an image has been displayed, the Display window will accept interaction asynchronously of commands in the VISTA command window, provided that a wait for input, or any other I/O is not pending. To interact with the image, simply move the mouse onto the display window. The current pixel location of the cursor will be displayed in a frame at the base of the image display along with the pixel intensity. The arrow keys are used for find control (one pixel at a time) of the cursor position.

The following mouse buttons and keyboard keys are active while the mouse is located on the image display:

Mouse Buttons
Button Function
LEFT ZOOM IN, centered on the cursor
MIDDLE ZOOM OUT, centered on the cursor
RIGHT PAN, move the pixel under the cursor to the center

Keyboard Commands
Key Function
R RESTORE image to the original zoom/pan
+ BLINK Forwards through the last 4 images.
- BLINK Backwards through the last 4 images.
P Find the PEAK pixel near the cursor & jump the cursor there
V Find the LOWEST pixel ("Valley") near the cursor & jump the cursor there
# "Power Zoom" zoom at the cursor to the maximum zoom factor
H Toggle between small and full-screen cross-hairs
F FREEZE/UNFREEZE the Zoom window.
0-9 Mark the pixel coordinates and store in VISTA
  variables Rn and Cn, where "n" is the number key hit
] Clear boxes and stuff off the image display

Other commands may use additional keys, but this set is always available.

The ITV command is still useful in procedures for making VISTA wait for pixels to marked on the screen. If ITV or any other VISTA routine is waiting for screen input, the the INPUT status light is lit (which otherwise says ASYNC). ITV can also be used to print out pixel values in the VISTA window or for marking up features on the display with boxes or circles.

When VISTA is CPU bound (busy doing an intensive calculation), the display will be put into a wait state before any interactive commands to the display or ``damage'' from other windows can be serviced. A note for programmers: CPU intensive routines should have the LOOPDISP call inserted into them to permit occasional servicing of display window events. See the VISTA Programmer's Guide for details.

Color Bar Adjustment:

If you place the mouse on the color bar, these commands are available to adjust the contrast of the image:

The position of the mouse cursor displays the range of intensities represented by that color.

Pressing the R key while the mouse is on the color bar restores the original color map (undoing any change of the contrast or "roll" changes made with the mouse buttons).

X-Windows Resources:

The properties of the TV display window are defined by Resource variables that can be customized by making appropriate entries in your .Xdefaults file. The resource variables are of the form:

   xvista.variable:        value
where "xvista" is the resource name.

Vista Display Resource Variables
Resource Description Default
xvista.maxwidth Max width of displayed images 1024
xvista.maxheight Max height of displayed images 865
xvista.resize Auto-resize the window on display 1
  of large images up to the max size.  
  1=auto-resize [default]  
  0=no auto-resize  
xvista.autozoomout Automatically zoom out images larger 0
  than the max size so that the whole  
  image is visible.  
  0 = no zoom out [default]  
  1 = auto zoom out  
xvista.zoomsample Selects the de-zoom algorithm 1
  1 = fast pixel-sampling [default]  
  0 = slower pixel-binning  

The following are recommended values to place in your .Xdefaults file:

   xvista.maxwidth:        800
   xvista.maxheight:       800
   xvista.resize:            0
   xvista.autozoomout:       1
   xvista.zoomsample         1
These will keep the TV window from obscuring too much of the screen, and enable the fastest auto zoom mode.

Note that for changes to the .Xdefaults file to take effect, you either have to log out and log back in again (brute force), or load the changes to your .Xdefaults file with the Unix "xrdb -load" command.