Multiplies red, green, blue, hue, saturation, or value in the image or selected region by some value to change the contrast. For grayscale images, only ``value'' can be changed.
NOTE***WARNING
Adjusting the brightness or contrast may invalidate the
correspondence between pixel values and the original optical
density in the image, making numerical results obtained by
subsequent densitometry scientifically invalid.
Changing brightness using the colormap palette bar
This method is very fast, but only works on 8-bit images that have a continuous colormap or with grayscale images.
Click on the top part of the bar and drag down to ``squash'' the colors downward, or click on the bottom part of the bar and drag up to squash the colors upward. This increases the contrast in all images of the screen.
Then, click in the middle of the bar and drag up or down to adjust the brightness as desired. The currently-selected image will be set to contain the new colormap.
If you change the colormap from the menu, or select ``restore original colormap'', the brightness and contrast settings return to normal.
Maximizing contrast
Clicking on the ``Maximize'' buttons in the Contrast dialog will automatically maximize the red, green, blue, or grayscale intensity contrast in the current image or selected region. In most cases, it is desired to maximize the intensity contrast; however, the red, green, and blue components can be maximized independently by clicking on the corresponding ``Maximize'' button. This may be useful, for instance, on images from confocal microscopes. For example, in a 24-bit image, if the red pixel values range from 50-100, maximizing the red will stretch the red range to 0-255.
For grayscale images, the display may not appear to change after maximizing contrast, because the grayscale mapping already maximizes the grayscale intensity range that is mapped to the screen.
On occasion, the image may not appear to become fully maximized. Usually this is the result of stray black or white pixels which must be removed manually or using image math.
In some cases, the display may temporarily appear incorrect until the OK button is clicked.