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Chapter 15 Menus and Dialog Boxes 221
Function Type
Linear:
Pixel values are linearly mapped to display gray levels.
Log:
This option changes the display of the image from linear, where changes
in intensity of the image are mapped equally to the display gray levels, to
logarithmic, where changes in intensity on the dark end are more pronounced.
This is helpful for an image with a very high dynamic range. Since CCD
detectors can have three orders of magnitude more dynamic range than a
computer display, this option can map both faint and bright signals.
Square Root:
This option computes the square root of each pixel value before
mapping to the display gray levels. The effect is similar to that provided by the
log selection but less pronounced. Note that the function is labeled “Square” in
the Brightness/Contrast dialog box.
Histogram:
Uses the “histogram equalization technique” to give the best
mapping between data intensity and display gray level or color. Result depends
on setting of brightness and contrast. Takes longer than other methods since it
must build the histogram from the data.
Gaussian:
Takes the equalized histogram and modifies it with a Gaussian
function, which tends to compress the representation of bright values and expand
darker ones.
Save As Default:
When this box is checked, the Brightness/Contrast settings will be
saved as the default. These settings will be automatically established the next
time the software is booted.
Palette Type
Grayscale:
Image is mapped into 256 levels of gray. Luminance range extends
from black to white.
Color:
Image appears as 256 color false-color display. In Pseudo Color mode
colors are mapped to the 256 levels of the monitor. It does not show actual color.
Only one color mapping is available. However, the color appearance of the
image can change dramatically depending on the Function Type selection.
Inverted:
This option reverses the mapping of grayscale or pseudocolor images.
When Inverted is not selected the pixels with the lowest intensities are black.
Pixels with the highest intensities are white. With Inverted selected, pixels with
the lowest intensities are white, and pixels with the highest intensities are black.
In Pseudo Color mode, low intensity pixels are normally black-blue, while high
intensity pixels are red-white. When inverted, low intensity pixels are black-
blue, and high intensity pixels are red-white.
Control Buttons:
OK:
Applies the settings and closes the dialog box.
Cancel:
Closes the dialog box without applying any changes.
Help:
Accesses context-sensitive help for the Brightness/Contrast dialog box.