November l989

3.1	NCSA X Image

Display Options	3.1

National Center for Supercomputing Applications

November 1989




Chapter 3	Display Options



Chapter Overview
Displaying Your Dataset
Loading Image Data
Specifying Dimensions for Data
Generating a Cartesian or Polar Image
Generating a Contour or Shaded Data Plot
Generating Plots
Specifying Contour Levels
Creating a Histogram

Chapter Overview

This chapter explains the various data display options provided by 
NCSA X Image, and the procedures for performing image 
manipulation. The current version of NCSA X Image allows you to 
display your actual data values; generate full color cartesian and 
polar raster images, black-and-white contour and shaded data 
plots, and histograms of frequency distribution; and animate 
multiple raster images. 


Displaying Your Dataset

To display data in any form, you must first load the image data 
into NCSA X Image.


Loading Image Data
To load a dataset:

1.	Click the Image button in the control window. The directory 
window appears, displaying the current working directory.

2.	Enter the path to the directory in which your data file is stored in 
the text box labeled, Directory, and click Change or press 
RETURN to locate the appropriate directory. You may also 
locate a directory by entering a root path in the Directory text box 
and allowing the system to build the path. Click on the desired 
path that appears in the Filename text box, and repeat until you 
reach the desired directory and filename.

3.	Select the filename of the dataset. The filename becomes 
highlighted.

4.	Click Open. If the dimensions of the data matrix are not found 
in the file, several textboxes appear in the directory so that you 
may specify the dimensions of the image data (see Figure 3.1).



Figure 3.1	Specifying the 
Dimensions of an 
Image
                                   

To specify the dimensions for the data:

1.	Enter the width of the data matrix in the text box labeled Width of 
Image, and the height of the dataset in the text box labeled Height 
of Image.

2.	Click OK. The directory window disappears and an image 
control window appears, showing the pathname of the dataset in 
the title box (see Figure 3.2). This is the main control window 
for the dataset. All operations performed from this window will 
apply to this dataset.

If the file includes the proper dimensions of the data matrix, the 
image control window automatically appears (see  Figure 3.2).
Figure 3.2	Image Control 
Window
                                           

To display your data values in spreadsheet form, click the button 
labeled Display Data Set in the image control window. The image 
data is displayed as real data values in a text window, as shown in 
Figure 3.3.  The generation time of this window depends on the size 
of the dataset.
Figure 3.3	Data Window
                                   

NOTE:  Selections between data and image windows for a 
particular dataset are fully synchronized so that you may identify 
the data values that correspond to points on an image. Regions of 
data points cannot be selected.

When data points are selected in the Image window,  the value and 
location is also displayed in the Log Book. Thus, if you close the 
Data Value window, points selected on the image will still be 
identified in the Log Book.


Generating a Cartesian or Polar Image

To generate a cartesian or polar image from your dataset:

1.	Load the desired dataset (if you have not already) as instructed 
in the section entitled "Loading Image Data" above.

2.	Click the Display Cartesian or Display Polar button, 
respectively, in the image control window for that dataset (see 
FigureÊ3.1). The color image is displayed in an image window 
similar to that shown in FigureÊ3.4.

The Display Polar command generates a simple color image for 
datasets that have the array mapped in polar coordinates (r, theta), 
where theta ranges from 0 to 2¹.




Figure 3.4	Cartesian Image
                                        

For information regarding altering the color representation of 
your dataset, see Chapter 4, "Palette Manipulations."


NOTE: The speed of image generation is dependent on the size of 
the original data. A 300 x 400 polar image might take three to four 
minutes to complete (this may vary in relation to the speed of your 
system), whereas a cartesian image generally takes only a few 
seconds.


Generating a Contour or Shaded Data Plot

You can display your image data using contour or shaded data 
plots. A contour plot contains contour lines between areas of 
differing contour levels. A contour level is a range of data values 
that you want to distinguish from other ranges of values. A shaded 
data plot represents data values as eight different intensities of 
shading.

To generate a contour or shaded data plot:

1.	Load the desired dataset (if you have not already) as instructed 
in the section entitled "Loading Image Data" above.

2.	Click the Graph button in the dataset's image control window. A 
plot window such as that shown in Figure 3.5 appears.

Figure 3.5	Graph Control 
Window
                                     

3.	Specify whether you wish to produce a plot of a polar or cartesian 
image.

To specify the former, click the button labeled Plot Cartesian. 
This toggles the option to Plot Polar. Click the button again to 
return the option to Plot Cartesian.

	NOTE: Before plotting a contour or shaded data plot under the 
Plot Cartesian option, a polar image must be generated.

4.	Click the Contour, Shade or Histogram button to generate the 
desired graph. Clicking Shade generates a shaded data plot, 
similar to that shown in Figure 3.6.

Figure 3.6	Shaded Data Plot 
Window
                              

Specifying Contour Levels
Clicking Contour calls up the contour specifications window. In 
the contour specifications window, you can specify the number and 
spacing of contour levels and the range of data values to be 
distinguished (see Figure 3.7).

Figure 3.7	Contour 
Specifications 
Window
                                        


To use the contour specifications window:

1.	Click Evenly spaced or User defined levels to determine the 
spacing between contour lines.

If you select User defined levels, the window pictured in 
FigureÊ3.8 appears. Type in each contour level in ascending 
order, separating the values by a space.

2.	 If using evenly spaced contour levels, specify a number of 
contour levels and the minimum and maximum data value 
ranges.

Figure 3.8	User Defined 
Spacing
                                        

3.	Click OK. A contour plot of your data is drawn according to your 
specifications, either in a new window or over the appropriate 
image. A sample contour plot is shown in its own window in 
Figure 3.9.

Figure 3.9	Contour Plot 
Window
                                 



Creating a Histogram

To generate a histogram that represents the values in an image:

1.	Load the desired dataset (if you have not already) as instructed 
in the section entitled "Loading Image Data" in this chapter.

2.	Click the Histogram button in the graph control window for that 
dataset. A histogram, such as that shown in Figure 3.10, is 
plotted in a new window.

3.	Click the button labeled Done in the histogram window to close 
the histogram window.

The histogram represents the frequency of data values in the 
dataset. The y-axis denotes the number of instances of each 
particular data value in the dataset, while the x axis denotes the 
data values in ascending order from left to right.

Figure 3.10	Histogram Window
                                    

The box labeled Data Value reports the data value at the point in the 
histogram window on which your cursor currently rests. The box 
labeled Frequency Percentage reflects the relative percentage of 
occurrences of that data value within the dataset.

Drag the mouse within the graph area to see specific numerical 
values and percentages.