Orion 52083 - Manual (Page 27)

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Note: Before any color balance adjustment can be made, you must first
Combine Color to each individual LRGB or RGB images. Refer to “Combine
Color”.
Color images from CCD cameras typically require a background level adjust-
ment. This is accomplished by bringing the background level (or bias) in each
color plane down to zero. Each of the Background Level values is subtracted
from every image pixel in its color plane. Any pixel values that become nega-
tive are forced to zero. The Auto button automatically determines the settings
necessary to equalize the image background in all three color planes. The
Reset button resets the background level subtraction to zero on all planes.
Scaling adjustment (entered as a percentage) allows you to compensate for
transmittance differences between the filters used to acquire the three color
planes. Values of 100% result in no change. The scaling percentages can be
typed in or adjusted using the “spin” controls (small up and down click arrows
to the right of the scaling numbers). The Preview Image is particularly helpful
in monitoring the results when using the spin controls. The Reset Scaling but-
ton resets to 100% on all three planes.
The Click On White Area to Set Scaling check box enables the operation of
the mouse to set the scaling. Set the Background Level first (you can use
Auto), then click on a white object (e.g. a neutral-colored star) in the image (not
the Preview Image) with the mouse. The Scaling settings will automatically
be adjusted to make the selected point appear white. If an area of the image
is known to be white (or gray), this is an easier way to determine the scaling
factors, and can be used to instantly color balance the image.
Stretch
The Stretch command (located in the Process menu, Figure 16) modifies the
brightness and contrast, and optionally the range (maximum and minimum
pixel values) of an image. Unlike the screen stretch settings in the Screen
Stretch Window, which only affects the how an image appears on the com-
puter screen, the Stretch command actually changes the image data pixel
values in the memory buffer. In reference to the histogram, the Screen Stretch
Window changes how the histogram is displayed on the computer screen, the
Stretch command alters the histogram itself.
There are three elements which must be set: the Permanent Stretch Type, the
Input Range, and the Output Range. You can use the Preview Image to see
how changing these parameters will affect the resultant image (or click the
Full Screen button to see the changes applied to your actual image). You can
also open the Screen Stretch Window to see how changing these parameters
change the histogram.
For the Permanent Stretch Type, the Linear Only mode is useful for adjusting
the range of pixels to match a particular file format. The Log mode is useful
for compressing the dynamic range of the image, but can be rather harsh. The
Gamma mode allows you to selectively emphasize bright or dim parts of the
image by entering a suitable Gamma Value. A Gamma of 1 has no effect, less