CHAPTER 11 Digital Microscope Cameras 73
✔✔ the number of pixels
✔✔bit depth
✔✔whether binning is used or not (CCD sensors only)
✔✔whether a sensor sub region (Region of Interest Readout) is active (CCD
and CMOS sensors)
✔✔ exposure time
More pixels and higher bit depth mean that more data needs to be acquired per
frame, resulting in longer readout times and lower frame rates. CMOS sensors
can be read out much faster due to a more parallelized readout structure and
therefore
they can reach much higher frame rates compared to CCD cameras.
This faster readout only kicks in if the readout time is sufficiently short and negligible
compared to the exposure time. Just ask yourself: how many frames per second
can you get out of a camera if it is exposing for one second and the readout
time is 10 ms? Exactly: no more than one frame per second because the exposure
time is larger by orders of magnitude compared to the readout time. On the other
hand, the maximum achievable frame rate at a minimum exposure time would
be 100 frames per second as the sensor can be read out 1 s / 10 ms = 100 times
per second.
Example
term
Description
CCD A Charge Coupled Device. Proven reliable technology with a long
history of optimization offers high sensitivity, good dynamic range, very
homogenous image quality, low number of image artefacts; usable for
long exposure times with cooling.
CMOS A Complementary Metal Oxide Semiconductor. Successor to CCD
technology, recent breakthrough for mass production of quality
products, currently high innovation rate, fastest image readout due to
massive parallel readout architecture, highest dynamic range, high light
sensitivity, rolling and global shutter technology available, high-quality
mass production technology.
Resolution The spatial resolution of a digital camera is related to the pixel density,
which is defined by the pixel count per sensor area. The smaller the
pixel aperture, the finer the sampling of the presented structure. The
reproduction of fine structures (lines) requires at least two pixels per
structure sequence (line pair).
Table 11.1: Good-to-know terms for microscope cameras