Operating Procedures: Optimizing Imaging
5-10
User Manual
C O N F I D E N T I A L –
limited rights
Feb 2018
Revision A
Scan Speed
To obtain a good imaging with acceptable signal to noise ratio it is necessary to find a balance among scan speed,
sample charging and/or damage.
A noisy image can be improved by decreasing the scan speed. If sample charging and/or damage is the limiting
factor(s), it is better to use a higher scan speed in combination with noise and charge reducing tools like
Average
or
Integrate
filter,
Line Integration
or
Scan Interlacing
.
Contrast & Brightness
The contrast and brightness can be set manually either by
adjusting the
Detectors
module controls, using the mouse (Ctrl +
click on & dragging – horizontal / vertical direction adjusts the
contrast / brightness) or by using the MUI (option):
1.
Select a medium scan speed in an active display.
2.
Reduce the contrast to zero. Adjust the brightness to a level
corresponding with the last gray level detectable by eye before
the screen goes black.
3.
Increase the contrast until the image of the observed structure appears.
4.
If necessary, adjust the brightness level to improve the image.
Videoscope (F3)
This tool can facilitate contrast and brightness optimization to utilize the full grayscale imaging range.
Three yellow horizontal lines (placed over the display) indicate white (top line), gray (middle line) and black
(bottom line) levels. The oscillogram signal amplitude / central position reflects the contrast / brightness of the
line just scanned. If the oscillogram is cut by the bottom / top line, the signal level is clipped in black / white. This
should be avoided, because imaging details are lost in the clipped areas.
Tuning the oscillogram exactly between the top and bottom lines for a feature of interest (using a reduced area)
results in full detailed imaging. Signal clipping may be used to obtain harder contrast conditions when more black and
white is needed. Lowering the signal amplitude decreases the contrast, i.e. the imaging looks softer.
1.
Select a slow scan in an active display.
2.
Activate the Videoscope in an active display (F3 / clicking on toolbar icon / Scan menu) or in all live displays
(Shift + clicking on the toolbar icon).
3.
Reduce the contrast to zero and adjust the brightness level to the lower dashed line (black).
4.
Increase the contrast so that the signal level just touches the upper dashed line (white).
5.
If necessary, adjust the brightness level so that the average signal level is roughly in the middle.
6.
The high and low peaks should just touch the dashed lines.
Repeating the contrast & brightness optimization helps improve the image quality.
Note
Use also the following functions to optimize the Contrast / Brightness: Auto Contrast Brightness (F9), Display Saturation
(Shift + F11).
