Line Profile Plot

A Line Profile is a graph of pixel values versus distance along a line drawn on the image. A Line Profile differs from a Column Profile Plot and a Row Profile Plot in that the sample line is drawn manually using the mouse, In addition, the Line Profile plots intensity versus distance on the x axis, whereas a column or row profile plots intensity versus position. To change the line ("marker") this command draws on the image, see Marker Properties. See Creating a Line Profile for details about the line profile plotting procedure.

World Coordinates

If the image has a World Coordinate System calibration, moving the pointer along the plot X axis reflects the world coordinates and pixel values along the drawn line.

Line Profile Toolbar

Below is shown the Line Profile Toolbar, which is a docking pane that controls most of the line profile plotting functions. Note: Additional options are available from the drop menu of the Line Profile button on the main Image Plot Toolbar. These are described in the topic Creating a Line Profile.

Additional properties may be set using the Line Profile drop menu described below. above adds options to those on the Line Profile Toolbar. It opens from the button on the main Image Plots Toolbar.

The Line Profile Plot

The line profile is drawn into a Plot Window like that shown below. Notice that the horizontal axis is distance, not an absolute position as used in Column Profile and Row Profile plots. The Plot Window below shows multiple parallel profiles on the head of a comet. These were made by switching to toolbar Move mode and repeatedly dropping the profile line further along the long axis of the comet head. The spike was caused by the profile line crossing a star.

The Line Plot Menu

The Line Plot menu contains several commands from the toolbar plus commands for changing the plot properties.

Drawing a Line Profile Plot

The procedure below uses two modes for creating line profile plots:

Mark mode creates a line profile plot in a new Plot Window. This creates the first plot of the window's plot series.
Add mode adds one or more parallel line profiles to the same Plot Window. These profiles add to the Window's plot series.

Procedure

Adjust the image to the desired scale, showing the region to measure.
Click the button on the Image Plot Toolbar or use the Plot > Line Profile Toolbar menu command to open the toolbar. Marking mode is automatically enabled when the toolbar is first opened. To reactivate Marking Mode it, click the (mark) button at the top of the toolbar.
Move the mouse to the starting point. Press and hold down the left mouse button.
Tip: To draw a line only in multiples of 45 degrees, press the SHIFT key and hold it before starting to draw. Do not release the SHIFT key until after releasing the mouse button at the end of the line.
Tip: If Centroid First Point is checked in the Marker Properties dialog, the position will lock onto the local centroid near where the mouse is released.
With the left button down, drag the mouse pointer to the endpoint and release the button.
Tip: If Centroid Last Point is checked in the Marker Properties dialog, the position will lock onto the local centroid near where the mouse is released.
Tip: The results are displayed in a new Plot Window.
To create additional line profile plots:
Tip: To create a new profile in a new Plot Window, repeat the previous two steps.
Tip: To add parallel profiles to the Plot Window containing the last plot marked (steps 3 -- 4), enter (add) mode and click on a point in the image. See Plotting Multiple Parallel Line Profiles, below.
When finished drawing profile lines, you can disable marking mode by clicking on the toolbar.

TIP:	To draw a line at a multiple of 45 degrees, press the SHIFT key and hold it before starting to draw. Do not release the SHIFT key until after releasing the mouse button at the end of the line

Plotting Multiple Parallel Line Profiles

Multiple parallel line profiles may be added to an existing Plot Window by repositioning the line plot vector at different image locations. The new profile will pass through the new point. Each time you draw a line plot vector using (mark) mode, the line profile plot is drawn into a new Plot Window.

Press (mark) and rubber-band the first line plot vector on the image. This draws the line plot in a new Plot Window as the first of a plot series of 1 or more profiles.
Press (add) and click on an image point through which you want the parallel line plot vector to pass. The line profile adds to the plot series started by the button.
Repeat step 2 to add parallel line profiles to the Plot Window.
To start a different line plot series in a new Plot Window, repeat step 1 and, optionally, steps 2 and 3.

Example

The picture below shows an Image Window with 3 parallel lines drawn using the (mark) and (add) modes. First, the middle line was drawn using the toolbar (mark) mode. After switching to (add) mode, two parallel lines were added by clicking on the image to the right and left of the first line. The two additional points were chosen so that the profiles would pass through bright stars.

The 3 lines drawn in the image created a plot series of 3 line profiles in the Plot Window shown below. The first profile created a new plot series whereas the additional profiles added members to the plot series. The picture below shows the profiles in Overplot mode. Switching to Animate mode displays each profile separately, each with a unique title that lists the line endpoint coordinates from the image.

In this example, the plot series members are drawn with equal line thickness in black, red, and green for series 1, 2, and 3, respectively. For example, notice the green spike around x=200 corresponding to the bright star near the beginning of line 3 drawn on the image. These properties can be changed before or after creating the plots:

Before the first profile is drawn in a new Plot Window, the series properties are set using the Image Plot Properties dialog in the View > Default Properties menu.
After the first profile is drawn, the series properties can be altered using the Plot Series Pane which is opened using Ctrl+Shift+A or by right-clicking in the Plot Window.