Time Vector Plotting

SRView 1.4c
Synergy Research, Inc.
17 June 2003
Introduction

Making Time Vector Plots

Opening a Plot Window
Y-Axis Scaling
Saving Plot Data to Disk
Plots from Rotated Images

Thresholds

Introduction

SRView understands and can work with images that have a time dimension.  A time vector is the set of pixel values for all points in time for a given point in space.  Plotting time vectors can be a helpful way to visualize the time dimension information in an image.  The Time Plot tool in SRView makes plotting time vectors very easy.

The time plot tool opens a separate Time Plot window in which graphs of time vectors are drawn.  You can interactively explore the time dimension for points displayed in SRView's three-view window.  When you click the left mouse button on the image, the time vector for the current cursor location is automatically plotted in the Time Plot window.
 

Making Time Vector Plots

To make time vector plots, you must have an image with a time dimension displayed in the three-view window.

Opening a Plot Window

Select Time Plot from the Tools menu. A separate Time Plot window will appear on screen, and the cursor will change to the Star Trek spaceship. The Time Plot window looks like this:
 
timePlot.jpg

Time vectors will be plotted whenever you click (left mouse button) with the cursor on the image. You can click in any of the three views.

By default, the Time Plot window contains a single time plot.  You can set the plot window to display a 3x3 array of time plots.  To do this, select Nine Plots from the plot menu of the Time Plot window.  Or open the Settings... dialog of the Edit menu of the three-view window (not the Time Plot window).  In that dialog, turn on the Time Tool: Nine Vectors toggle button, then click the OK button.  Then click on the image to see the time plot for the selected pixel and eight adjacent pixels.  The central graph in the 3x3 array is the one for the cursor location. The surrounding eight graphs have the same relation to the central graph as their corresponding spatial points have to the cursor location on screen.

The time dimension is plotted on the horizontal axis (x axis) and the pixel value is plotted on the vertical axis (y axis).  Time values are the point indices along the time dimension in the image data array, so the x axis always runs from 0 to (number of time points - 1).  To facilitate visual comparisons, all 9 graphs have the same x and y ranges.

Y-Axis Scaling

The y axis is automatically scaled to the minimum and maximum y values of the displayed data.  To set the y-axis range, select "Set Scale" from the Plot menu of the Time Plot window and enter the desired minimum and maximum y values.  To go back to automatic scaling, set the minimum and maximum y values to 0.

Saving Plot Data to Disk

At any time you can save the currently displayed time plot data to a disk file.  To do this, select Save from the File menu of the Time Plot window.  This will bring up a file selection dialog where you can select a directory and enter a file name for saving your data.

The data are saved to a text file.  For the single-vector display there is just one column containing the y-values of the plotted data.  For the nine-vector display there will be nine columns. The columns are ordered starting with the upper left graph, and run row-by-row to the lower right graph.  So the third column contains the data for the upper right graph, and the fifth column contains the data for the central graph.

Plots from Rotated Images

The time-vector plotting tool works on dynamically rotated images too. When making nine-vector plots from rotated images one needs to be clear about just where the eight surrounding points of the central point are located. SRView looks in the original image data array for the eight points. It starts at the location of the central point and moves outward in unit-interval steps measured in the image data space in directions that lie in the plane of the displayed slice where the cursor is located. The eight points are obtained by combinations of unit steps left, right, up and down. The nearest neighbors to the calculated floating point locations at those unit-interval steps are taken as the points from which to plot the time vectors.

Thresholds

The value of a 3D threshold mask can be displayed on the time plot of scaled 4D statistical data to show which points are above the threshold value or below the negative threshold value given by the mask.  To display the threshold value on the time plot, hold the Control key then click on the pixel to be plotted.  The positive (negative) threshold value will be shown as a red (blue) horizontal line on the time plot.  The minimum value of the y-axis is the smaller of the minimum value of the time vector and the negative threshold value; and the maximum value of the y-axis is the larger of the maximum value of the time vector and the threshold value. 

A single threshold line can also be displayed on a time plot.  Select "Threshold" from the Plot menu of the Time Plot window to open a Threshold dialog.  If you set the threshold value to something other than 0, then a horizontal cyan line will be drawn at that y-value on the plot.  If you are auto-scaling and the threshold value is above or below the data, the upper or lower bound will be set at the threshold.  If you set the y-axis scale values and the threshold is outside the scale range, the threshold will not be shown.