Scatter diagrams, or 'Concentration Histogram Images'
'TOOLS / 2&3 variable / scatter plots'
These are pixel by pixel value plots which show the value relationships between groups of pixels for two or three registered images. The spatial information in the image is discarded. For micrographs or x-ray maps of a crystalline material, clusters of points in the histogram correspond to phases in the material, while streaks of points between clusters correspond to the boundaries between the phases.
The coordinate system for the three dimensional diagram is right handed. The axes are labeled by small dashes continuing off the corner of the cube: x -, y - - , z - - -.
Choose X, Y, Z and Mask images by clicking on the image then clicking on the appropriate button.
The 2-D scatter diagram requires and X and Y image pair, and, optionally, a Mask image to select pixels for plotting.
To make a mask:
The color slider, a copy of which is made for each new image, makes a thermal-like color scale for displaying the histograms. Zero in a bin is shown as black, 1 count as bright red, then linear ramping through orange - yellow - to white, as controlled by the slider.
Each scatter diagram is actually an image with a histogram as the image array data. The two dimensional histogram is calculated this way:
The histograms have 256 bins for each axis. The scaled image values are used, instead of the actual image data, because the scaled values always are in the range 0 - 255, and because the data range of interest can be changed with the scaling method.