implot: Plot lines and columns of images using cursors
Package: plot
Usage
implot image [line]
Parameters
- image
- List of images to be plotted. If more than one image is in the list then the 'm' and 'n' keys are used proceed to the previous and next image.
- line
- If given, the number of the image line to be plotted, otherwise the central line is plotted.
- wcs = "logical"
- The world coordinate system (wcs) to be used for axis labeling.
The following standard world systems are predefined.
- logical
- Logical coordinates are image pixel coordinates relative to the image currently being displayed.
- physical
- The physical coordinate system is invariant with respect to linear transformations of the physical image matrix. For example, if the reference image was created by extracting a section of another image, the physical coordinates of an object in the reference image will be the pixel coordinates of the same object in the original image. The physical coordinate system thus provides a consistent coordinate system (a given object always has the same coordinates) for all images, regardless of whether any user world coordinate systems have been defined.
- world
- The "world" coordinate system is the current default WCS. The default world system is the system named by the environment variable defwcs if defined in the user environment and present in the reference image WCS description, else it is the first user WCS defined for the image (if any), else physical coordinates are returned.
- step = 0
- Step size for stepping through lines or columns in an image with the 'j' and 'k' keys. If zero or INDEF the step defaults to ~10% of the image axis length. This parameter may be changed interactively with a colon command.
Description
Implot is an interactive, cursor driven task for examining images by plotting the lines and columns or the averages of lines and columns. An image line is plotted when the task is first run, then cursor mode is entered and keystrokes may be used to generate additional line and column plots. 'q' is typed to exit cursor mode and implot and 'n' is typed to proceed to the next image in the input image list.
The following single character keystrokes are recognized by Implot. Note that numerous additional keystrokes are provided by "cursor mode" itself, i.e., by the graphics system. These additional keystrokes provide such standard facilities as stepwise cursor motion, plot expansion, movies, disposal to a batch plotter or metafile, and plot annotation facilities. Cursor mode is documented elsewhere.
? print help and other info
a plot the average of a range of lines or columns
c plot a column
e expand plot by marking corners of viewport
j move down within image (moving section)
k move up within image (moving section)
l plot a line
m proceed to the previous image in the list
n proceed to the next image in the list
o overplot next vector
p measure profile (mark region and bkg with 2 pos)
q quit
s print statistics on a region
w change world coordinate system
/ scroll status line
<space> print coordinates and pixel value
The single character keystroke commands use the position to the cursor to determine what region of the image to plot. If the plot is examined carefully one will note an extra scale on the right hand edge. This scale gives the "other" axis of the image in units of pixels. For example, if the current plot is a line plot (rather than a column plot), the X axis of the plot will correspond to the X axis of the image, and the right Y axis of the plot will correspond to the Y axis of the image. Both axes will be scaled linearly in units of pixels. The left Y axis is scaled in either linear or logarithmic pixel intensity units. In the case of a column plot the bottom axis will correspond to image Y and the right axis to image X.
The 'l' and 'c' keystrokes, used to plot lines and columns, take image coordinates from the bottom and right axes of the plot. In the case of a lineplot, the cursor would be positioned in Y and the key 'l' typed to plot a new line. Extrapolation of this convention to the other cases and keystrokes is self evident. The 'a' keystroke is used to mark an X or Y region to be averaged and plotted. This mode of averaging is independent of the ':a' command discussed below.
Successive vectors may be overplotted by typing an 'o' and then any other command. A range of linetypes are used if the device supports them to make the curves easier to distinguish. The position of each line is marked on the right axis with a small tick to document the coordinates of the curves.
The 'j' and 'k' commands are used to step through an image in either the upward (k) or downward (j) directions, relative to the current line or column plot. Each new vector is plotted in place of the previous one without clearing the screen, making it easy to compare successive vectors. The step between vectors may be defined by a task parameter and changed by a colon command.
The 'm' and 'n' commands are used to step through the input image list. This is the same as using the 'i' key to switch images and the 'l' key to plot the same line or column as the previous image.
There are three keys which print various quantities of interest. The space bar key will read the cursor position, find the nearest pixel, and report the image line and column, the coordinate along the current axis, and the pixel value. The line and column are in logical pixels (that is the coordinates in the current image section) and the coordinates are in the selected world coordinate system and printed in the current coordinate format. If the selected world coordinate system is "logical" then the coordinate will be the same as the line or column.
The 's' key requires two cursor positions and then computes statistics of the region. The values are the median, mean, sigma, sum, and number of pixels. The 'p' key also requires two cursor positions with the x positions defining a region and the y positions defining a linear background. Within the defined region the peak departure from the background (either above or below the background) is found and the full width at half maximum of this peak is measured. The linear background, the peak position and distance from the background and the widths at half the peak value are overplotted on the data. In addition to the profile quantities the moments of the background subtracted data are measured. The moments computed are the centroid, the integral (or flux), the width, and the normalized asymmetry. The width reported is the square root of the second central moment multiplied by 2.35482. For a gaussian profile this corresponds to the full width at half maximum which can be compared with the direct measure of the profile width. The normalized asymmetry is the third central moment divided by the 3/2 power of the second central moment. The various measurements are printed on the status line. There are multiple lines of results which are scrolled using the '/' key.
In addition to the single keystroke commands, the following : escape commands are provided:
:a N set number of lines or columns to average
:c N [M] plot column N [average of columns N to M]
:f format set the x coordinate numerical format
:i imagename open a new image for input
:l N [M] plot line N [average of lines N to M]
:o overplot
:log+ log scale in Y
:log- turn off log scale in Y
:step N set step size for j,k
:solid overplot with solid, not dashed, lines
:w wcsname change world coordinate systems
:x x1 x2 fix range in X (call with no args to unfix)
:y y1 y2 fix range in Y (call with no args to unfix)
The 'c' and 'l' commands are identical to the keystroke commands except that the column or line position is explicitly entered rather than taken from the cursor. An averaging factor entered with 'a' will apply to all subsequent line and column plots, as well as plots generated by 'j' and 'k'. The input image may be changed at any time using the 'i' command; only one image may be open at a time. Log scaling on the Y axis may be turned on and off with the 'log' commands. The default step size of 1/10 the height of the image may be changed with the 'step' command. Finally, the 'solid' command may be used to draw all overplotted curves using solid, rather than dashed, line segments.
The 'x' and 'y' commands may be used to fix the plotting scale in either X or Y, i.e., to disable autoscaling. Once the scale is fixed on an axis it remains fixed until either the fix scale command is repeated without any arguments, or the 'e' option is used to expand the plot (this causes the fixed scale to be lost). Plotting different lines or columns or even changing images does not cause loss of fixed scaling. If the X scale is fixed to a range less than an entire line or column Y autoscaling, if enabled, will only pertain to the displayed range in X.
The numerical format for the coordinate labels are set with the 'f' command. The values may be "" (an empty string), %f for decimal format, %h and %H for xx:xx:xx format, and %m and %M for xx:xx.x format. The upper case %H and %M convert degrees to hours. Some images have a recommended x coordinate format defined as a WCS attribute. If the format value is "" (the default) the WCS attribute format will be used. Any other value will override the image attribute.
Examples
1. Enter cursor mode, plotting line 240 of the 300x480 image 'crab':
cl> implot crab
(plot appears)
Type '?' to get the list of recognized keystrokes. Move the cursor and type 'l' to plot the line at the Y position of the cursor. Try typing 'c' to plot a column (note that a column plot will take longer than a line plot since the entire image must be read). Go back to a line plot and try several 'k' keystrokes to step up through the image. Try a cursor mode 'E' to playback a movie of a small region, then type 0 (zero) to restore the original plot.
Bugs
It should be possible to use the image display cursor to mark the lines or columns to be plotted. This capability will be added when the image display is interfaced to GIO (the IRAF graphics subsystem).
See also
imexamine, cursor