ITV: Interact with the Image on the TV

ITV enables you to interactively examine an image displayed on the video display. The mouse buttons and several keyboard keys are activated to perform functions when pressed:

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
E	EXIT ITV and return to VISTA (or resume procedure)
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
D	Print selected pixel row, column, and value.
	Load variables R and C with the location.
]	Clear boxes and stuff off the image display

The D key also loads the coordinates of the most recently selected pixel into VISTA variables R and C; the 0-9 keys load Rn and Cn, where n is the key struck. If the image had to be compressed to fit in the display window (auto or manual dezoom), the main display will not show every pixel, although the magnifying glass window will, so choose the pixel in that window.

You also have control of the color map (upper & lower contrast drag and color-map roll), see the X11 help page for details.

The ITV command is very useful in procedures for letting you use the D or 0-9 keys to extract position information from the image of interest needed elsewhere within the procedure. Recall that variables (or any arithmetic expression) may be used in place of a number in words of the form word=value. Here is an example of a procedure which draws a contour map of a section of an image located by the cursor. It draws at most a 51x51 box, but will draw a smaller section of an image if the cursor is placed near the edge of the frame.

   ASK 'DISPLAY WHICH IMAGE >> ' BUF        ! Get number of image
   MN $BUF; TV $BUF                         ! Display the image
   SROW=SR[BUF] SCOL=SC[BUF]                ! Note start row/col
   EROW=SR[BUF]+NR[BUF]-1                   ! Note end row
   ECOL=SC[BUF]+NC[BUF]-1                   ! Note end column
   PRINTF 'PLACE CURSOR ON CENTER OF THE REGION TO MAP'
   PRINTF 'THEN HIT THE D KEY, FOLLOWED BY E'
   ITV                                      ! Define center R and C
   NRSHOW=51 NCSHOW=51 DEL=IFIX[NRSHOW/2]   ! Default size
   LOROW=R-DEL HIROW=R+DEL                  ! Limits to box
   LOCOL=C+DEL HICOL=C+DEL
   IF LOROW<SROW                            ! Edge adjustment
      LOROW=SROW
   END_IF
   IF HIROW>EROW
      HIROW=EROW
   END_IF
   IF LOCOL<SCOL
      LOCOL=SCOL
   END_IF
   IF HICOL>ECOL
      HICOL=ECOL
   END_IF
   NRBOX=HIROW-LOROW+1 NCBOX=HICOL-LOCOL+1  ! Size of box
   BOX 1 SR=LOROW SC=LOCOL NR=NRBOX NC=NCBOX
   CONTOUR $BUF BOX=1
   END