At the bottom right corner of the opening menu is a set of 4 mouse buttons.
These activate:
- The algorithm that optimizes the hardware video pre-scaler.
- The software ABC.
- Frame Averaging
- The collection resolution of a full screen 'fast capture'.
Scale
The Scaling "button" at the bottom of the opening screen provides a
quick and easy method for getting the image brightness within the range of the
video digitizing circuitry. SCALE controls a hardware based video level
adjusting circuit on the SEM-PC interface. Clicking on SCALE causes a software
based algorithm to seek the setting of the video pre-scaler which causes
maximum utilization of the input range of the video digitizers. This is
a hardware controlled ABC.
ABC (Auto Brightness Contrast)
the ABC algorithm scans the beam over the sample and records the maximum and
minimum gray levels encountered. Next, the ABC algorithm checks whether the
maximum and minimum gray levels in the raw data fall within the range of the
ABC and whether the minimum amount of contrast required for successful ABC
exists. If signal saturation or insufficient contrast exist, ABC does not
attempt to change the contrast, and the 16:1 ratio is used. If the
aforementioned criteria are met, a linear curve fit is calculated so that the
maximum and minimum gray levels sampled are reassigned to gray levels 10 and
245 respectively. ABC then calculates a "lookup table" (LUT) which
the image digitization algorithm uses to convert 4096 values to 256. The LUT
itself is an
array 6 X 4096, that is, there is a separate LUT for each signal source. The
SE and BSE input channels are modified by a Y = m X + b curve fit where X is
in the range of 0 - 4095 and Y is limited to the range of 0 - 255. If the ABC
algorithm needs to modify the lookup table, a small bar appears at the
lower-right corner of the CRT indicating the progress. For 486 or faster
systems, this process takes just a few seconds.
Frame Averaging (Avg off or Avg on)
To activate frame averaging, click the mouse cursor on the AVG (on or
off) button at the
bottom of the CRT. The button will appear to "depress", and frame
averaging will occur when a GET function is selected. Pressing ESC will terminate collection at the end of the current
pass. Frame averaging utilizes multiple frame weighted averaging with the
hardware controlled signal integration time constant in effect. That is, if
the user had selected a long dwell time with a fast preview mode, that dwell
time would be utilized during the frame averaging operation. Maximum speed is
generally desired during frame averaging operations, and using a short dwell
time results in the maximum apparent speed. It should be noted that unless
frame averaging must be used due to sample damage or charging considerations,
single frame image collection results in the most noise free image in the
shortest time.
640
This button changes the screen resolution mode for the full screen
capture. This allows us to accommodate a variety of thermal and other video
printers that capture the PC's monitor image directly. The selections are
640x480 (default), 800x600, and 1024x768.
