Transfer Functions
A Transfer Function is the mathematical relationship between the image values and the values displayed on the computer display. Mira breaks image display into two parts: A transfer function and a palette:
The Transfer Function maps a range of image brightness into 256 levels.
The Palette maps the 256 levels into a spectrum of colors, which may be shades of gray.
The use of a transfer function has two main purposes:
To handle images having a dynamic range too great to be fully displayed on a computer screen. The transfer function compresses or expands the range of brightness that is mapped into the display.
To allow viewing of image details that span only a small part of the total range of image brightness. The transfer function can be adjusted to display certain features at the expense of others.
In decoupling the transfer function from the palette, Mira breaks ranks with many image processing software applications that simply allow transfer function adjustments or palette adjustments, but not both. Separating these image display concepts gives you greater power and flexibility in performing image enhancement because these two types of enhancement may be applied and adjusted independently.
The Transfer Function
Properties dialog allow you to interactively change
transfer function settings and apply the changes. This dialog works
independently with any Image Window shown. To open the Transfer
Function Properties dialog, use the View > Transfer
Function command or click 
on the Image
Toolbar. To work with another image window while this
dialog is open, bring the other image window to the top of the
stack (for example, click on its window caption or its the tab on
the MTI bar at the bottom of the Mira
screen). You can also change settings using the Transfer Function
Popup Menus.
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Note |
Mira splits image adjustment into two parts:
Transfer Function and Palette. Before beginning to make major
changes to the transfer function settings, it is best to start with
default palette settings. To reset the palette, right double click
on the Colormap of
the image window, or click the |
Mira manages all the transfer function settings using a profile control. A "profile" is a collection of parameters used by a function. The Transfer Function saves all the parameters as a profile with a name. You can load all the parameters at any time simply by loading the profile by name. One of the profiles is the default one used to open an image. After an image is open, you can change the profile or the settings of the profile for that particular image, an then use these settings to update the named profile or create a new one if you desire.
Transfer Function Properties, Transfer Function Popup Menus, Palette Properties, Displaying Images, Image Windows
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