Adjusting Image Brightness and Contrast
MultiTracer automatically adjusts the brightness of images when files are loaded. However, it is
often helpful to manually adjust the image brightness and contrast for optimal viewing. It should be noted
that adjustments to image intensity have no effect whatsoever on the brightness or contrast of image volumes
saved from MultiTracer using the "Save First Volume" or "Save First Volume As ..." menu items; they simply modify the display
for your convenience.
Brightness and contrast can be adjusted using the "Image Intensity" window. This is a tabbed
window with a "Master" tab and numbered tabs for each loaded image. By default, this window is
originally positioned at the lower right hand corner of the main image window after the first image
volume is loaded.
To brighten or darken an image, select the image's tab in the "Image Intensity" window and adjust
the slider. Alternatively, you can enter a new scaling factor into the field labelled "Scale".
Entering a new scale factor also adjusts the range of values accessible by the slider.
To alter image contrast, enter a pixel value into the field "Values < __ are black". This value is
subtracted from the input voxel value before scaling. As the field label implies, voxels less than
this value are displayed as black. Setting this value too high can cause the entire image to appear
black. You may need to increase the brightness of the image when entering larger values in this
To link the brightness and contrast settings of two or more images, select the tab for each image
and click the "Use Master" checkbox. Select the "Master" tab and use the controls on this tab to
adjust the brightness and contrast of all the images. You can use the "Add All" button on the
"Master" tab to put all currently loaded images under the "Master" tab control. The "Remove All" tab
returns control to the individual image tabs.
©2001-2003 Roger P. Woods, M.D.
Modified: January 18, 2003