Grayscale images of greater than 8 bits/pixel often contain subtle details which would not ordinarily be visible. This option permits interactively changing the way the pixels are mapped to the screen, creating, in effect, a ``sliding scale''.
This sliding scale uses 4 parameters: the maximum and minimum values in the image to display, and the maximum and minimum values on the screen to which these are mapped (these latter 2 do not normally need to be changed). When a monochrome image is first loaded, tnimage automatically determines the maximum and minimum values in the image to allow the entire image to be viewed. By selecting ``Grayscale brightness'', you can use the mouse to select the actual range of values to be displayed.
For example, if the image has 12 bits of grayscale depth, it will be possible to set the maximum and minimum to any number between 0 and 4096. Setting the numbers close together enhances the contrast in that intensity range. Similarly, making the numbers small enhances the contrast in the darker areas of the image.
The maximum can also be lower than the minimum, creating an inverse image. Each image on the screen can have a different brightness/contrast level.
Note: Color images must be converted to monochrome before this feature can be used.
If a ``false color'' colormap is set, this option will change the mapping of false colors for the image (See Sec. 8.4).