This topic describes how to use 2D scatter plots with an ENVI Classic display group. See Scatter Plots for the recommended method for using scatter plots in ENVI.

Use 2D Scatter Plots to interactively classify two bands of image data. If desired, you can have multiple scatter plots active simultaneously. Two-dimensional scatter plots use only the data in the Image window so quick interactive response is provided. You can select ROIs in the scatter plots and save them for use in other full band processing techniques. Dancing pixels show how the distribution of pixels under a box changes as you move it interactively in both the scatter plot and image. You can also show the density distribution of the scatter plot.

For complete details on using the Scatter plot window, see the topic "Using 2D Scatter Plots" in the ENVI Classic Help. Here are some basic instructions for using the dialog.

  1. From the Display group menu bar, select Tools > 2D Scatter Plots. The Scatter Plot Band Choice dialog appears.

  2. Choose the x and y axes for the scatter plot by selecting the desired bands in the Choose Band X and Choose Band Y columns. Click OK.

  3. To zoom to an area within the scatter plot, select Options > Scatter:Zoom. In the Scatter plot window, middle-click and drag the box outline that appears. To return to normal viewing, middle-click in the window.
  4. To interactively view the distribution of image pixels, select Options > Scatter:Dance. Place the cursor anywhere inside the scatter plot and middle-click to plot a colored box on the scatter plot. Any image pixels that fall within the data range selected in the scatter plot are plotted in color in the Image window. Press and hold the middle mouse button while moving the cursor in the Scatter plot window to automatically update the corresponding pixels in the Image window.
  5. You can also view, in the scatter plot, the distribution of pixels that are highlighted in the Image window. Select Options > Image:Dance. Place the cursor anywhere inside the Image window and click to mark pixels in color in the scatter plot. This shows the distribution of pixels falling within a pre-defined box the same size as that used in the scatter plot. Click and drag inside the Image window to interactively highlight the pixels in the scatter plot.
  6. Many image pixels can have the same data values within bands and will lie in the same place in the scatter plot. The density distribution is color coded from purple (low density) to red (high density). To show the density distribution of the scatter plot, select Options > Density On.
  7. To change the color table used to define the density distribution, select Options > Select Density Lookup.