Histogram Preferences

The Histogram page of the Mira Preferences dialog establishes rules for generating the frequency distribution shown in a Histogram plot. In this window you choose the histogram binning and range values. These are shown in the screen-shot below. The effect of varying histogram preferences are shown in this comparison.

Setting the Histogram Bins

The histogram bin is the "quantum" of the x-axis data in the plot. Each bin spans a range of image value so that pixels with value anywhere inside the limits of the bin are assigned to that bin. Their detailed values are lost in the plot. Choosing the bin width (or range of values) and the number of bins affects the way the data are displayed. The bin setting is a priority for generating the frequency distribution, because the other aspects follows. For example, setting the bin width affects the number of bins that are needed to span the range of the data. Conversely, choosing the number of bins controls the width of the bins. Mira provides 3 choices for setting the histogram bin priority:

Histogram Bin Priority Options


Mira chooses optimal settings for both the bin width and the number of bins.

Bin Width

You choose the bin width and Mira calculates the number of bins. There is one setting for integer type images and another setting for real type images, as integer type data should not be binned using a non-integral bin width.

Bin Count

You choose the number of bins and Mira calculates the bin width.

Setting the Histogram Range

The histogram range refers to the range of data values included in the histogram. Mira offers the option to use all the data or to select a range of upper and lower percentiles to exclude from the histogram. If the data are "well behaved" then you might choose to see the full range of data. Otherwise, you can exclude the extreme values to show more detail in a specific range of the frequency distribution.

Histogram Range Options

Full Range

The frequency distribution uses the full range of values encountered in the sample. The number of bins and the bin width are applied to the full range.

Upper Percentile

This setting specifies the upper percentile of values to be excluded from the binning process. For example, 1.0 specifies that the highest 1% of the values are excluded.

Lower Percentile

This setting specifies the lower percentile of values to be excluded from the binning process. For example, 0.5 specifies that the lowest 0.5% of the values are excluded.

Related Topics

Plotting Commands, Mira Preferences, Histogram Plot, Tutorial: Creating Plots from Images