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Ch. 5 - Viewing, Editing, and Annotating Images
Edit - Image Quality
User's Guide to the SPOT Cooled Color Digital Camera, 6/9/98
85
This one step process provides a quick and easy way to increase image contrast for low
contrast specimens. To use the Stretch Bright and Dark Level (RGB) option, select
Adjust RGB, Stretch Bright and Dark Level from the Edit menu. The picture
automatically adjusts itself.
Stretch Bright and Dark Level (HSL)
Like the Stretch Bright and Dark Level (RGB) option, the Stretch Bright and Dark Level
(HSL) option stretches the darkest luminance level in an image to 0 (black) and the
brightest luminance level to 100 (white). Unlike the RGB mode stretch, however, the
HSL stretch works
only
on the luminance value, and therefore maintains the original hue
and saturation of an image. As with the contrast and gamma adjust options using the
HSL color space to stretch images reduces the potential for washed out images and color
shifts.
To use the Stretch Bright and Dark Level (HSL) option, select Adjust HSL, Stretch
Bright and Dark Level from the Edit menu. The picture automatically adjusts itself.
Adjust Histogram (RGB)
A
histogram
is a graphical representation of the number of pixels at each brightness level
in an image. Our RGB histogram displays the red, green, and blue histograms on the
same graph. The SPOT program's RGB histogram serves two main purposes:
§
It is a point of reference for examining the distribution of brightness levels for the red,
green, and blue components in an image.
§
It can be used to reset the zero and full scale points for an image. This is known as
stretching
. Like the aforementioned Stretch Bright and Dark Level function, the
Adjust Histogram option enables you to stretch the darker areas of your image to pure
black and at the same time lighten the brighter areas of the image.
!
Note: Full scale for 8 bit monochrome and 24 bit RGB images is 255. Full scale
for 12 bit monochrome and 36 bit RGB images is 4,095.