2.4   Changing histogram apperance

The Options menu allows you to change the appearance of the histogram. You can open this menu in several ways:

From the menu bar:
  - either click on Options
  - or hold down the [ALT] key and type [O]
Mouse shortcut:
  Right-click on the histogram.

For histograms there are three 'options' in the drop-down menu:

1. Font opens a standard font dialogue window, which allows you to change the font, style, size and colour of the histogram text
2. Name opens a dialogue window, which allows you to enter a name for the chart, and give names to the plot axes.
3. Scale lets you rescale the axes, and switch between normal and cumulative histograms.

Changing the font

Select Font from the Options menu to open the Font dialog, and experiment with changing the Font, style, size and colour of the titles and axis numbering, until you find a suitable font and size for the histogram.

Note: At present you can only use one font definition for the whole histogram; there is no option for giving titles a different appearance for instance from axis labels and numbering.

Adding titles and axis labels

By default the histogram title includes the name of the image, the range of pixels from which the histogram was calculated, and some statistical information. You can change this by selecting Names from the Options menu.

The Names dialog ( figure (5K)) allows you to enter a chart name, and a description for each axis. Add a chart title, for example "Sea Surface Temperature (SST) January 1997", a description for the x-axis, such as the formula used to convert the data values to true temperatures, and a label for the y-axis.

If you do not want the default image name and range, you can remove this by unchecking the box to the left of this sub-title. Similarly you can remove the image statistics by unchecking the check-box that corresponds to this text.

Axis scaling

Bilko automatically scales the y-axis to fit the maximum pixel frequency in the histogram. However, sometimes you may want to change this - for instance when you want to compare several histograms from different images. This can be done by selecting Scale from the Options menu.

The Scale dialog figure (4K)) allows you to switch off the automatic scaling by typing new minimum, maximum and unit values in the relevant text boxes. Change the maximum value to 2000, the major unit to 500 and the minor unit to 100.

Cumulative histograms

The standard histogram gives you the frequency distribution of the pixels in the image. The data may also be presented as a cumulative histogram. To do this: