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Chapter 6: Image and Data Analysis

To facilitate image analysis, JHV provides tools that display pixel and digital values, that generate x-y plots or histograms from images, and that perform data transformations.
6.1 Image Values
6.2 X-Y Plots
6.3 Histograms
6.4 Data Transformations


6.1 Image Values

Digital Value and Pixel Value, on the image window View menu, display values of the data and pixels, respectively, of a single point of an image. After selecting either command, move the mouse around the image; a panel will appear displaying the coordinates and either the digital (physical) or pixel value of the point at which the mouse is pointing. If the data has dimension scales, the scale value as well as the index will be show. Select Default to unset the display.

The following figure illustrates both types of image value display. The digital value display is on the left; the pixel value display is on the right.


Figure 6.1 Image value

6.2 X-Y Plots

X-Y Plot, on the image window View menu, creates a line plot with image values plotted against horizontal corrodinate values.

Set Digital Value or Pixel Value and X-Y Plot. Dragging the mouse on the image will define a subsample of the image and open a window displaying an X-Y plot of the defined subsample.

Moving the X-Y plot window away from the image window allows you to watch a shifting plot while dragging the mouse across the image.

The following figure illustrates an X-Y plot.


Figure 6.2 An X-Y plot

6.3 Histogram

A histogram is a distribution plot of image values for a selected image area. To display a histogram, first set either Digital Value or Pixel Value then set Histogram. Dragging the mouse on the image will define a subsample of the image and open a window displaying histogram, or distribution plot, of the defined subsample.

Moving the histogram window away from the image window allows you to watch a shifting histogram while dragging the mouse across the image.

The following figure displays a histogram.


Figure 6.3 A histogram

6.4 Data Transformations

Convert Data, on the image window Data menu, allows the user to convert image data into another data set by the general power function Y = a + b * X^c, where X is the current data point and a, b, and c are user-defined values. The conversion function is applied to every point of the image data and the data type is preserved.


Figure 6.4 Data transformation control panel

Note that a backward conversion may not restore the original data. For instance, an integer data point whose value is 14 will become 1 if it is converted by the function Y = 0.1*X. The backward conversion, which is X = 10*Y, yields 10, not the orignal value. Use Undo, on the Edit menu, to restore the original data.


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