Intensity Histogram

This facility allows the intensity information contained within a window or buffer to be summarised in the form of an intensity histogram. As options, this information may be plotted on one of the frame buffers and/or written to a file.

RETURN VALUES The following return values are available through the !!Rn mechanism (note that you will normally require a E, F or G modifier to return the floating point representation of these return variables):

           !!R0    Mean intensity
           !!R1    Standard deviation of intensity
           !!R2    RMS intensity.
           !!R3    Minimum intensity
           !!R4    Maximum intensity

Note that all of these are calculated only within the range specified for the high and low intensities.

Histogram of what buffer ?

The histogram may be evaluated on the image contained in any valid buffer.

Histogram of Window or whole Screen ?

The histogram may be evaluated on the image contained within a window (<W>) or on the entire contents (<S>) of the buffer specified by the previous entry.

Window Selection: Region to evaluate histogram of

If the answer to the previous question specified that the histogram was to be produced on the contents of a window, then the window selection submenu is produced to enable the window to be specified. Information on operation of DigImage windows may be found under the [H Help] option within the submenu.

Instantaneous, Cumulative or No histogram plot ?

This question allows the type of plot required to be specified. If <I> is selected, then a probability density histogram will be produced on one of the buffers. Pressing <C> will produce a cumulative probability histogram, while <N> suppresses any plotting.

Use lInear or lOgarithmic scales ?

This question is produced only if a probability density histogram plot is selected from the options in the previous question. The probability scale for the histogram may be either linear (<I>) or logarithmic (<O>) in nature.

Plot histogram in what buffer ?

This entry specifies the buffer in which the histogram is to be plotted. Any valid buffer may be used; the buffer selected will be made the current output buffer. Note that this question will not be asked if no plots are to be produced.

The histogram will be scaled between LowInten and HiInten to make full use of the available plot space. Use what intensity as LowInten ?

The range of intensities over which the plots are scaled, and the average and standard deviation of the intensity are calculated, may be specified using this and the following entry. Only intensities equal to and exceeding the value specified by this entry (and less than or equal to that in the next entry) will be used.

Use what intensity as HiInten ?

The value specified here is used in conjunction with the previous entry to restrict the range of intensities used in calculating averages, scales etc.

Write data to which file (blank to suppress, .DAT default extension) ?

The histogram data will be written to the file specified at this prompt. A blank name indicates that no file to be created. The format of the file is:

       Intensity, nPixels, CPixels, CFraction

where nPixels is the number of pixels of intensity Intensity in the specified window, CumulativePixels is the number of pixels of the specified intensity or less, and CumulativeFraction is the fraction of the window occupied by Intensity or lower intensities.

Statistics based on selected intensity range: Mean intensity : !!R0 = !!GR0 Standard deviation: !!R1 = !!GR1 RMS intensity : !!R2 = !!GR2 Minimum intensity : !!R3 = !!R3 Maximum intensity : !!R4 = !!R4

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Stuart Dalziel, last page update: 19 February 1996