Fit Curve to Scatter Plot

Fit Curve to Scatter Plot

This option determines a least squares curve which approximates the scatter plot of the intensities of two images. The intensities of the first image are considered an independent variable. For each such intensity in the first image, the mean intensity for the corresponding pixels in the second image is calculated and used as the dependent variable. Finally, a least squares fit relates the two.

First source buffer (intensities used for independent variable) ?

This entry specifies the buffer from which the independent variable intensities are determined. Any DigImage buffer may be specified.

Second source buffer (intensities used for dependent variable) ?

This entry specifies the buffer from which the dependent variable is constructed. Any DigImage buffer may be specified.

Scatter plot using Window or whole Screen ?

The plot may be generated from data in the entire buffer (<S>), or a subwindow (<W>).

{If window selected}

Window Selection: Region for Scatter Plot

If the plot is to be made for a window, then the DigImage Window Selection submenu will be produced to enable window specification. For help on the selection process, consult the [H Help] option within the submenu.

Name of file to write plot data to (blank to suppress, .PLT default extension) ?

DigImage produces a plot and performs the least squares fit using DigiPlot. Specifying a file name here will allow the plot file (which also contains the data) to be kept.

Place scatter plot in which buffer ?

This entry specifies the buffer in which the scatter plot is produced. The buffer will be made the current output buffer. The scatter data between the independent intensity variable and the corresponding mean dependent variable will be plotted as plus marks. The least squares fit will be plotted as a line.

Erase scatter plot buffer first ?

Answering yes (<Y>) will erase the contents of the buffer to contain the scatter plot prior to rendering the scatter plot.

Basis functions for least squares fit (use DigiPlot colon-separated list for functions as a function of P) ?

The basis functions should be expressed in terms of the independent intensity P. Each function should be separated from the next by a colon. The fitted coefficients will be available through the !!R0, !!R1, ... variables on completion of the plot.

Name of output PostScript file (blank to suppress; .PS for printable PostScript .EPS for encapsulated PostScript, or .DPS for data only PostScript) ?

Specifying a file in response to this prompt will cause a PostScript description of the output to be placed in the file. The file will subsequently need to be transfered to a suitable PostScript printer to enable the hard copy to be produced. Entering a blank line suppresses the production of the PostScript file.

Encapsulated PostScript (.EPS) and Data Only PostScript (.DPS) can not be printed directly, except using DigiFile. Normally they would be included within some other package (eg. a word processor) to be printed. The .DPS file is a special version of .EPS which does not contain the normal DigImage\PostScr\Header.PS and DigImage\PostScr\GraphVDU.PS header files. These may need to be added to the PostScript prolog used by the application into which the .DPS file is inserted.

If no extension is specified, then the default PostScript type specified in [;P Printers] in CONFIGUR.EXE will be produced, and the appropriate extension added.

This file may be sent to the printer immediately by specifying PRN as the file name.

{If PostScript file specified} Default, Line, Greyscale or Colour printing ? DigImage is able to produce either grey-scale or colour PostScript files. The Default option is controlled by the setting in the Configur.EXE utility. If colour is selected, then the file MUST be printed on a level 2 (or higher) PostScript printer. 

        Default                 Colour type specified in Configur.EXE
        Line                    Greyscale images and dashed line types
        Greyscale               Greyscale images and greyscale lines
        Colour                  Colour images and colour lines - requires
                                Level 2 PostScript

Fitted coefficients:

Coefficient for term !!S2RM0: !!R!!RM0=!!GRM1 ; Basis function :!RM1

RMS error in fit : !!R!!RM0=!!GRM1

The above list shows the fitted coefficients and the rms error in the fit. These values may be accessed through the indicated !!Rn return variables.

Errors, Warnings and Messages

Error Message: Unable to open output file

DigImage was unable to open the (possibly temporary) output file required to plot the scatter data.

Parent menu

Main Menu

DigImage User Documentation

Stuart Dalziel, last page update: 19 February 1996