The current microscope image acquisition marketplace is filled with new products, each one promising excellent images at a variety of price points
By William G. Hand, Ph.D., General Manager, Optronics
current microscope image acquisition marketplace is filled with new
products, each one promising excellent images at a variety of price
points. What do you really need to know when you get ready to buy?
first priority should be to look at your application requirements. You
should answer the following questions:
fluorescence microscopy is used, can you see the latent fluorescent
image through the eyepieces? If you can't see an image, you will
need a camera that integrates the image past a few seconds (integration
is the digital camera equivalent of extended or time lapse exposure
in a film camera).
field of view does the application require? This can be measured as
a percent of the field of view as seen through the eyepieces. You
can use a stage micrometer to determine this.
you feel comfortable with integrating image processing boards in to
your computer? If you have not had experience doing this, you should
work with a dealer who has an imaging department or consider purchasing
a camera that uses an existing interface (Serial, Parallel, or if
newer USB or IEEE 1394).
you really need a digital camera? There are still some applications
where film is the best medium for image acquisition, especially if
you require special lighting. Remember that you can post-process a
photo image through a high quality scanner to get digital results.
about the price/performance issue in digital cameras? As with any
product, you get what you pay for. A lower price means some sacrifice
in performance. Make sure that the performance hit does not effect
that you have a idea of what your requirements are, make a features
list and use it to select your ideal camera. Stay true to your list.
The following description will provide you with some overview areas
to consider when composing your camera "wish list".
When selecting a camera for microscope imaging, you have the following
Film Cameras (Leica, Zeiss, Olympus, Nikon, Polaroid)
standard emulsion, or Polaroid formats, film cameras provide the necessary
high resolution and color fidelity required by microscopy.
are several drawbacks to film cameras:
can not preview the image you are saving to film.
the film and providing prints or slides is cumbersome and expensive.
learning curve for successful application of film technology is extensive.
direct computer interface.
high latitude of film light sensitivity makes the medium ideal for
some low light and high speed applications.
emulsion formats provide unequaled resolution.
(Optronics, Sony, Hitachi, Javelin, Toshiba, Panasonic, Cohu, Dage)
has emerged over the past 10 years as a viable alternative to film.
With CCTV high resolution imaging, video provides:
(What you see is what you get) capability.
resolution for high magnification, fine structure characterization
3 chip (RGB) technology, excellent color rendition.
digital conversion for computer input, storage and manipulation.
sensitivity for low light level applications, marginal sensitivity
for high speed applications.
has some down sides too. These include:
microscope interface issues (image magnifiers, adapters, filters,
complex computer interface issues (image processing board configurations,
software compatibility issues).
image display issues (RF interference, color balancing, display resolution,
video tape storage resolution, video duplication image loss).
Imagers (Optronics, Kodak, Diagnostic Instruments, Roper)
the past 5 years, technology applied to video has been modified to provide
high quality, high resolution digital images. By creating new imaging
"chips", and ignoring standard video image standards (NTSC,
PAL), it is possible to produce an electronic format camera that has
high resolution, a simple direct computer interface, and excellent color
rendition. The advantages of digital imagers are:
resolution with excellent field of view (where chip format is 1K x
1K pixels, or "megapixel" quality).
digital "mapping" of the image into a computer, eliminating
the need for image processing boards (but you still may require dedicated
image transfer boards).
high sensitivity and image integration for low light applications
such as fluorescence imaging.
newer models have near "real time" image viewing.
image cameras have some inherent disadvantages as well. These include:
image creation and transfer provide little or no WYSIWYG capability.
integration times, often coupled with multiple image captures (for
color imaging) make the use of these devices impractical for some
high sensitivity fluorescence applications.
physical size makes the mounting on some microscopes (especially tissue
culture or other "inverted" optics microscopes) cumbersome
(Examples: Optronics, SONY, Cooke)
These cameras feature the ease of use of a video device with a method
of taking a digital "snap shot". Most transfer the digital
image over an existing computer interface (serial, parallel, or USB).
These cameras provide the following benefits:
WYSIWYG functionality at standard video rates (NTSC, PAL).
Resolution 3-CCD imaging with real time image enhancement rivals the
image quality of megapixel imagers.
digital input without image processing boards.
compliance for direct input into image manipulation and storage programs.
sensitivity and cooling provide short duration integration times for
low light (fluorescence) requirements.
remote-head design provides a simple, low mass microscope mount.
disadvantages of the hybrid system are few:
field of view when compared to megapixel digital imagers .
color mis-registration when compared to color wheel megapixel imagers.
table below summarizes the features of each camera type with respect
to the nature of the microscope application:
Application Table I: General Issues
to make digital image
to reproduce image at or beyond the resolution of the microscope.
the resolution of the microscope without image enhancement.
Does not match the microscope image in one or more ways.
separate hardware device which copies (digitizes) the printed film
image to the computer.
board-level addition to the computer that converts analog video
images to digital images in real or delayed time.
a digital image to be stored in a computer without a scanner or
image processor. This method may require a proprietary interface
board and/or a parallel or serial cable, or proprietary cable.
Application Table II: Low Light Applications
Seconds to minutes
CCD or Filter
Microscope imaging is often plagued by uneven and/or low illumination
levels. Some hybrid cameras (Optronics, Sony) provide the easiest-to-use
solution for low light imaging. With high speed image integration and
Peltier cooling, low light level fluorescence images may be produced
in a short time (seconds), with a single exposure, and viewed live before
they are stored. With some models (Optronics) 3-CCD true RGB imaging,
color correction and digital image enhancement allow the user to control
color appearance and image detail in real time.
cameras use color wheels or color matrix CCDs to capture color information
in the image. What are the pros and cons of these image acquisition
CCD Digital Imaging Cameras
(Roper, Apogee, Kodak)
imaging "chip" manufacturers (primarily SONY and Kodak) provide
color versions of their megapixel imagers. All of the lower cost digital
imaging cameras use this form of sensor. Color is provided by segregating
the color information into a mosaic on the chip surface. This is accomplished
by taking a group of four pixels and assigning a color frequency to
each in a specific pattern. There are usually single red, single blue
and two green pixels in the array. This array is replicated over the
chip surface to create a color mosaic on to which the incoming color
image is mapped. The
chip is "read", and the color image is reconstructed using
software or dedicated firmware.
is gained and what is lost in this process? There is an obvious gain
in speed. A color image is possible with a single exposure. Single pass
color imaging has the further advantage of permitting the frame and
focus functions of the camera to be in color as well (often at 12 images/second
or more). What is lost is resolution. The color and image definition
produced by this method will not tolerate the same degree of enlargement
as will an image produced by a multi-pass imaging camera. Color fidelity
and registration will not be as good, since each pixel in the array
is not exposed to each color of the image. What you get is an "averaged"
image, with the resultant compromises.
Wheel and Tunable Filter Digital Imaging Cameras (Optronics, Diagnostic
wheel and "tunable" filter imaging cameras require multiple
subject exposure (at least three; red, green and blue). Often, a fourth
exposure is taken, a "dark" exposure, which may be used to
subtract image noise from the result. The four exposure method, although
longer, generally provides superior image results, with superior color
rendition and minimal noise artifact. The down side is that the additive
exposure and subsequent image transfer and computer color reconstruction
can create a total image acquisition time of a minute or more in cameras
with slow data transfer rates and/or long integration times.
addition, there are distinct differences between color wheel and tunable
filter technologies that are significant to long exposure (fluorescent)
wheels add a mechanical component to the camera design that increases
size and adds an additional service component. The good news is that
you maintain the high sensitivity of the imager. The fact that all
pixels read the RGB component of the image results in better color
fidelity when compared to mosaic imagers.
filters greatly reduce camera sensitivity (by as much as 60% when
compared to color wheel cameras). Reduced sensitivity extends exposure
time (more integration: often to critical exposure levels with highly
light sensitive fluorescent preparations). The good news is that the
camera package can be made smaller and less expensive (there are fewer
mechanical and electronic components).
Application Table III: Ease of Use
to Acquire Image
to Store Image
on scanner speed and resolution, generally minutes.
on storage program used, generally 5-15 seconds.
requiring knowledge of emulsions, developers, and printing papers.
to 1/30 second
on image processing components
to minutes depending on need for color and light level
Seconds to minutes depending on camera model
than film, but similar in nature. Trial and error exposure
to 15 seconds
short , easiest of all to use
summarizing this article, I would recommend the following (assuming
that your choice meets your application requirements):
you want the ultimate in ease of use, excellent image quality, "real-time"
image display and you are not concerned with a large field of view,
I would recommend a hybrid camera.
you want the ultimate in image quality and format size, go with the
multi-pass digital camera.
you want a large format image, with digital image quality and cost
is a factor, go with a mosaic digital imaging camera.
you need real time, and the ability to record strings of images (motion
studies, etc.), go with a high quality hybrid or video camera and
an appropriate video digitizing board.
you have lots of time, and you enjoy darkroom photography, film is
still an option
Copyright, ©1999 Optronics All rights reserved.
WGH 11/11/99 rev.4
Optronics, 175 Cremona Drive, Goleta, CA 93117. Tel: 805-968-3568; Fax: 805-968-0933.