Plot Window Controls

Use the following to control and change the plot display.

General Plot Controls

• To zoom in and out of the plot, click in the plot and roll the mouse wheel back and forth, or click and drag the middle mouse button to draw a box around the area to zoom into.
• Click and hold on a curve in the plot to show the X-Y line crosshair. As you move the cursor over the curve, the crosshair snaps to the closest data point. The X and Y values of the point appear below the plot.
• The X-axis (Wavelength) is determined by the first spectra that is plotted. By default, the plot automatically rescales the Y-axis (Data Value) to the data minimum and maximum when you add or update plots. To toggle off rescaling and keep the current Y-axis range, right-click the plot and select Auto Scale Y-Axis. If auto scaling is toggled off and a plot is added outside the current Y-axis range, that plot is not visible until the Y-axis is rescaled.
• If the Z plot range header value is set in the ENVI header, then the X- and Y-axis is set to the Z plot value and the Y auto scale value is turned off.
• To offset the plots in the window so that data does not overlap, toggle on the Stack Plots button .
• To reset the plot range to the original view, click the Reset Plot Range button .
• Click the Show arrow on the right side of the window to expand the panel and show the plot key and plot properties.
• To hide data in the plot, disable the check box for the curve in the plot key.
• To remove data from the plot, select a curve in the plot key and click the Remove Selected Curve button , or click the Remove All Curves button . You can also right-click a curve in the plot key and select a Remove option from the menu that appears.
• To edit the plot X-values if a plot has anomalous points, click the Edit Data Values button to open the Edit Plot Values dialog.

Select Statistics Plot

If the plot is being shown in the Statistics View, the initial view of the plot window contains the minimum, maximum, and mean values for each band in the raster. Use the Select Plot drop-down list to change the display to the standard deviation, eigenvalues (if the covariance was generated), or histograms (if the histograms were generated) for each band, or for all bands. If the statistics are for a classification image, you can also change the display to a specific class.

Change Plot Functions

To change the data display in the plot, select from the X and Y drop-down lists as follows:

X:

Available for all profiles:

• Index: Plots Y values of the curve against equally spaced integers ranging from 1 to number_of_elements in the curve. For example, the "wavelength" of an AVIRIS spectrum will range from 0.4 to 2.5 microns, and the "index" of an AVIRIS spectrum will range from 1 to 224 bands.

Available for the Spectral Profile, Statistics Profile, Spectral Library Viewer, and ENVI Plot window:

• Wavelength: (default) Plots the data as wavelengths, if wavelengths are in the image header.
• Wavenumber: Plots the data as the wavenumber (1/wavelength), if wavelengths are in the image header. For example, a spectrum that ranges from 0.4 to 2.5 microns will have wavenumbers that range from 25,000 down to 4,000. Because the wavenumber is an inverse relationship to wavelength, smaller wavelengths will have larger wavenumbers.

Available for the Horizontal Profile:

• Column: (default) Plots values of the curve as the column width.

Available for the Vertical Profile:

• Row: (default) Plots values of the curve as the row length.

Available for the Arbitrary Profile:

• Transect: (default) Plots values of the curve as the transect length.

Y:

• Data Value: (default) Plots the data in the original values.
• Continuum Removed: Plots the data with its continuum removed. The continuum is the convex hull that fits over the top of a spectrum. It is divided into the original data values to produce the continuum removed values. The continuum is calculated using the first and last data points displayed in the plot, so for plots that have been zoomed, the continuum is calculated based on the displayed data range only.
• Binary Encoding: Replots the data as a spectrum of 0s and 1s. It calculates the mean of the data and encodes each value as a 0 if it is less than or equal to the mean and as a 1 if it is greater than the mean.

Edit Plot Values

You can edit the Y-values of a plot, for example, if a plot has anomalous points. Expand the plot properties panel, then select the spectrum to edit in a plot window and click the Edit Data Values button . The Edit Plot Values dialog appears.

1. The left column in the Edit Plot Values dialog contains a list of the X-values for the selected spectrum. The right column contains the Y-values. Click on a single value to edit, or use Ctrl+click or Shift+click to select multiple values.
2. Enter a value in the field and press the Enter key, or use the + and - keyboard keys to increment the value.

3. Click OK to accept the changes.

   To return the values to the actual data value, click the Revert button.

Options Menu

Available for all profiles and plots:

• To keep the crosshair visible at all times, select Crosshair Always On.
• To toggle on a legend for the plot, select Legend.

• To toggle on a wavelength color along the X axis of the plot, select Wavelength Color. This applies only when the X axis has valid Wavelength or Wavenumber units.

• To apply a boxcar average smoothing of plotted data, select Curve Smoothing. A slider control will display, allowing on-the-fly adjustment of smoothing levels.

Available for Spectral, Horizontal, and Vertical Profiles:

• To open the data in a new ENVI Plot window, select New Window with Plots.

Available for Spectral Profiles:

• To show a vegetation index for the selected pixel, select Vegetation Index.
• To change the bands displayed in the plot, select RGB Bars to display RGB bars on the plot. Click and drag to move the RGB bars, then select Load New Band Combination from the Options drop-down list to display the new band combination in the plot.
• To extract the spectrum for the selected pixel from an additional file, select Additional Profiles > Add Files, from the Options menu, then select the input file. The input file must be the same spatial size as the as the original input file. The curve is added to the Spectral Profile.

Available for Horizontal and Vertical Profiles:

• By default, the Horizontal and Vertical Profiles show data for only the area of the band that is visible in the Image window. To show the profile for the entire band, select Use Full Band. You can change the default in the General properties for the plot.

Available for Series Profiles:

• To display a specific series frame in the view, select the Series Index Bar. A gray vertical line will appear on the Y-axis, and can be dragged to the desired series index. The associated image will load once you release the mouse button.