LBP2 User Guide
Document No: 50306-001
Rev G 3/12/2020
Page 81
Knife Edge 10/90
Legacy
Knife Edge Prog
Legacy
% Energy
Legacy
% Peak
Legacy
Moving Slit
Azimuthal (ISO)
The Ellipticity result is the ratio of the computed beam widths. The Minor (smaller)
beam width is always divided by the Major (larger) to produce a result less than or
equal to one. Thus, beams with Ellipticity values close to 1.000 are nearly circular.
Ellipticity:
M
m
d
d
z
)
(
The Eccentricity result will approach Zero as the beam becomes more circular.
Eccentricity:
M
m
M
d
d
d
z
e
2
2
)
(
5.11
Gamma Correction
If the camera has a gamma value less than or greater than 1, LBP2 can be set to
correct for the camera’s non-linear response. Enter the gamma of the camera in the
Gamma field in the Camera... dialog box. Each pixel of each new frame of data will be
automatically corrected as defined in the equation shown below. An entry of “1.0”
disables gamma correction.
P
P
Z
z
g
/
1
Where:
z
=
Gamma corrected pixel intensity
Z
=
Uncorrected pixel intensity value
g
=
Gamma
P
=
The maximum value for a pixel (255 for 8-bit
cameras, 1023 for 10-bit cameras, and 4095 for
12-bit cameras, etc)
Important:
Be sure of the Gamma correction value. If necessary, run a response curve on
the camera. Standard published gamma values are usually averages for
particular camera types and may not always be adequate for obtaining the
desired accuracy. Also, be wary of gamma values less than 1 published for
CCD cameras. These values are usually approximations obtained by using
two-piece linear fits to an exponential gamma curve. Whenever possible, use
CCD cameras which allow for a gamma setting of 1.0 and do the gamma
correction in LBP2.
