Image Capture: CCD Cameras
General Considerations | Software | Suppliers
CCD stands for
Charge Coupled Device which is an array of image sensors (single pixel) made using silicon
chip technology. Traditionally sold for security applications, the use of CCD cameras has
now broadened considerably. CCD video cameras are particularly useful for capturing
fluorescent images, or images that require UV illumination. They may also be used for
capturing images of small to medium sized standard gels, blots, autoradiograms. Video
imaging is also ideal for capturing chemi- and bioluminescence in non-isotopic detection
of biomolecules. For small objects the CCD video camera systems have the advantage of both
speed and high resolution. However the resolution capabilities become lessened when the
object is larger. Typical applications include UV trans-illuminated nucleic acid gels and
TLC plates and general low light imaging. The important factors to consider are the
resolution of the camera (should be more than 512 x 512 pixels), the sensitivity (normally
expressed in lux units), the degree of "noise" that is acceptable and whether or
not time integration facilities are required. The camera will require linkage to an image
capture board inside the computer which should be able to handle 8 bit images of 512 x 512
pixels or greater.
A number of
companies have put together complete systems for video photography.
In recent years these systems have become quite popular for two main reasons:
They provide an inexpensive alternative to
Polaroid instant photography by making use of video printing technology.
They provide a means of capturing images for
further analysis using programs such as Phoretix 1D
systems include: CCD Video Camera and Power Supply Camera Stand, Lenses and Filters, Video
Printer (Generally Mitsubishi or Sony) ,Time Integration Unit (or Computer with an image
capture card and time integration software), Monitor and Connecting Cables.
Advice on CCD Camera Systems
In recent years there has been a massive expansion in the use of CCD Video Camera systems
and digitising cameras for gel photography. There are two main reasons for this: - They
provide an inexpensive alternative to Polaroid instant photography by making use of video
printing technology. They provide a means of capturing images for further analysis using
gel analysis programs such as Phoretix 1D. It is fast becoming recognised that there are
real benefits to using good quality gel analysis and reporting software.
CCD stands for Charge Coupled Device, which is an array of sensing pixels made using
silicon chip technology. Traditionally CCD Cameras were sold for security applications,
but now that imaging technology has developed their use has broadened considerably. In
fact imaging technology is moving almost as fast as computer technology. In
electrophoresis applications CCD video cameras are particularly useful for capturing
fluorescent images such as UV illuminated nucleic acid gels and TLC plates. The important
factors to consider are the resolution of the camera (should be more than 512 x 512
pixels), the sensitivity (normally expressed in lux units), the degree of
"noise" that is acceptable and whether or not time integration facilities are
required. The camera will require linkage to an image capture board inside the computer,
which should be able to handle 8 bit images of 512 x 512 pixels or greater.
Time integration is a process which mimics the effect of prolonged exposure. With
conventional photography it is possible to let more light onto the film in two ways. The
iris can be opened and the amount of time the iris is open can be controlled. Opening the
iris too much when taking pictures of fluorescent gels can have the effect of allowing too
much light through for brightly fluorescing bands and just enough light for very faint
bands. It is therefore better to keep the iris small and increase exposure time. This will
allow faint bands to be seen without overexposing the bright bands. The same is true with
CCD cameras. However, under normal circumstances, CCD video cameras are processing a
number of frames per second. Time integration effectively allows frame summation, thereby
mimiking the effect of increased exposure time.
At the low cost end of the market there are those relatively insensitive cameras that are
common in the security markets and could be used for capturing images that do not require
sensitivity for very low light levels. Fluorescent applications generally require better
sensitivities and frequently require the use of computer controlled time integration.
Companies such as Sony, Hitachi and COHU produce typical CCD cameras with reasonable
sensitivity and time integration. Without time integration these cameras will pick up most
bands that can easily be seen by the eye. With correct time integration they can be made
to reveal very faint bands without over exposing the bright bands. However the draw back
is that at high integration times (more than 4 seconds) the noise levels and quantity of
"bad" pixels are high. Nevertheless, it is in fact unusual to require
integration times of more than 4 seconds for DNA/Ethidium bromide applications. In
addition good image capture software, which is generally required to control time
integration cameras, can minimise the effects of noise and bad pixels. If much
higher integration times are required for special applications then it might be prudent to
opt for a cooled CCD camera such as those that can be supplied by Photonic Science, Photometrics and AstroScan.
of Purpose Built Systems (A Personal Perspective)
To my knowledge, the first purpose built system for the DNA gel electrophoresis market was
produced by a German company, Cybertech, who mainly sold through UVP.
This was a time integration system, but used a low resolution camera. UVP and Vilber
Lourmat found that the higher resolution, low light COHU cameras produced a far better
quality image even without time integration and therefore produced systems based on the
COHU camera. As technology improved a time integration COHU camera formed the basis of the
UVP system, whilst Vilber Lourmat went for the more compact Sony camera. UVP went to great
lengths to educate the market on the benefits of using these systems and soon became
recognised throughout the World as the major supplier. As market awareness of the benefits
expanded, so did the number of competitors. Now there are quite a number of companies have
put together complete systems for CCD video photography,
- Time Integration
CCD Video Camera and Power Supply
- Camera Stand,
Lenses and Filters
- Video Printer
(Generally Mitsubishi, Sony or Fuji)
- Time Integration
Unit (or Computer with an image capture card and image capture software)
- Light exclusion
- Video Monitor
such systems include:
- UVP (Ultra
Violet Products) GelWorks
- Biocom Phoretix
- Photonic Science
Laboratories Molecular Analyst
NB. This list
is not meant to be complete.
In the early
days nearly all systems included the Mitsubishi video printer and the main motivation for
purchase was to reduce the cost of Polaroid instant photography. There was (and still is)
a greater than ten fold saving per print and much lower wastage with regard to badly
exposed pictures. This amounts to a considerable saving in consumable costs for most busy
laboratories. Nowadays, Mitsubishi are currently loosing favour as they are not keeping up
to date with the needs of scientists in this market. Sony video printers are becoming much
more popular, partly because they have had the sense to produce a Windows driver, albeit
not a very good one (Sony please read this! We are waiting for a decent upgrade!).
Pharmacia have opted for the Fuji printer as the prints look nicer since a different
process is employed. However their competitors say that it is not without its problems,
but then they would.
Capture Vs Image Analysis
It is often a good idea to have Image Analysis located on separate computers away from the
image capture for several reasons:
Image Capture is generally performed in a laboratory area whilst good quality Image
Analysis that facilitates proper reporting tends to be an office based function (i.e. On a
computer containing a Word Processor, a Spreadsheet, a Database and a Slide Design package
which is linked to a proper printer.)
Image Capture is not always followed by Image Analysis. Image Capture by CCD video
photography is often a multi-user facility and is often used as a low cost replacement for
Image Capture may only require a low cost computer, whereas good quality Image Analysis
requires a higher specification computer.
The Image Capture board inside the computer may prevent the use of high-resolution screens
(1024 x 768 x 256 colours) that are important during Image Analysis. Hopefully this
situation will change in the future.
A user of Phoretix software may want to link several images together in one experiment for
the purposes of comparison and reporting. When the gels are run at different times,
possibly weeks apart, a combination system offers no advantage and can suffer
disadvantages (particularly if space management on the Hard Drive is a problem).
Good quality Image Analysis packages, such as all Phoretix products, will be able to
import and analyse images from a wide variety of image capture devices. This means that
the analysis computer can be linked to document scanners such as the Epson GT8000 or the
Sharp JX330 which are both excellent for scanning blots, gels and autorads at far higher
resolutions than is possible with CCD cameras. Other devices such as radiation imaging
equipment could also be networked to the same analysis station.
Image Analysis Software
The Video camera systems on the market at the present time have all tended to concentrate
on the quality and flexibility of their image capture systems. Some of these companies
have added some image analysis capabilities. The image analysis software they provide
falls into one of the following categories:
Software that is completely dependent on
the image acquisition card and is therefore restricted to the image size dictated by the
Basic software purchased from outside the
company that offers only basic image analysis solutions.
We therefore recommend that all users of CCD Video based Image Capture systems purchase
Phoretix software for their analysis requirements.
cost, low-sensitivity (security-type) CCD cameras may be suitable for many routine gel or
TLC image capture applications. Fluorescent applications generally require higher
sensitivity and, frequently,the use of computer controlled time integration. When bands
are sufficiently intense, low cost cameras without time integration can be quite
effective. Such cameras can be forced to image faint bands by opening the camera shutter
to maximum. However most gels have both bright and weak bands. When the shutter is open
wide this will tend to let in too much light for sharp imaging of the bright bands. Thus,
because the standard CCD video camera is limited to a set number of frames per second, it
becomes very difficult to acquire images with both high sensitivity and the required
sharpness of image for all bands on the gel.
integration, a good low level light CCD camera (<0.1 lux sensitivity) will pick up most
bands that can easily be seen by the eye in UV illuminated ethidium bromide-stained gels.
With good quality time integration hardware and software such cameras can be made to
reveal very faint bands which can be captured together with fairly bright bands. Generally
only small time integration periods (0 to 3 seconds) are required to get good quality
images. This is useful because much higher integration times can require higher cost
equipment to avoid problems associated with increased background noise and the appearance
of CCD pixel problems.Cooling the CCD device alows longer integration times (up to 30
minutes0 with a linear response, allowing detection of extremely weak signals (see below).
A camera that
may be considered as better suited for very low light level applications that require
longer time integration is the CoolView camera system from Photonic Science Ltd. This
camera is cooled with a Peltier device and is supplied with an image capture card, a
board, operating software, cables and manuals. Because the camera is cooled, the
background levels and the number of "bad" pixels are low which makes the camera
better suited for very low light level situations and applications that require good
densitometry analysis on the captured images. However the price for the CoolView basic
system is over £7000 without accessories, computer or printer. Good cameras may offer binning
Binning combines the charge from adjacent pixels on the CCD chip improving
sensitivity and dynamic range at the expense of spatial resolution.
low light level sensitivities are required for new fluorescence applications, then Astrocam Ltd of Cambridge have some excellent cameras
developed for astronomy applications.
Standard 1D gel
images can be read at 100dpi (i.e. at a resolution of 254 microns per pixel). Indeed some
imaging systems are limited to resolutions of over 400 microns. However, gels with many
close and tight bands, 2D gels and miniature gels do require higher resolutions. Pharmacia
Phast gels (35mm square) captured by standard CCD video cameras have a resolution of 68 gm
(35mm/512 pixels) which is very good. However a 20cm gel will only have a resolution of
390ptm which is OK for some applications. Desktop scanners such as the Epson GT9000 and
the Sharp JX330 can scan better than 600dpi (42gm per pixel).
Capture vs Image Analysis
It is often not
advisable to have Image Capture and Image Analysis located on the same computer for
Image capture is generally performed in a
laboratory area whilst good quality Image Analysis that facilitates proper reporting tends
to be an office based function (i.e. On a computer containing a Word Processor, a
Spreadsheet, a Database and a slide design package which is linked to a proper printer.)
Image capture is not always followed by image
analysis. Image capture by CCD video photography is often a multi-user facility and is
often used as a low cost replacement for instant photography.
Image capture only requires a low cost computer,
whereas good quality Image Analysis requires a higher specification computer.4. The image
capture board inside the computer may prevent the use of high resolution screens (1024 x
768 x 256 colours) that are important during image analysis. Hopefully this situation will
change in the future.
A user of Phoretix software may want to link
several images together in one experiment for the purposes of comparison and reporting.
When the gels are run at different times, possibly weeks apart, a combination system
offers no advantage and can suffer disadvantages (particularly if space management on the
hard drive is a problem).
Good quality image analysis packages, such as
all Phoretix products, will be able to import and analyse images from a wide variety of
image capture devices. This means that the analysis computer can be linked to document
scanners such as the Epson GT9000 or the Sharp JX330 which are both excellent for scanning
blots, gels and autoradiographs at far higher resolutions than is possible with CCD
cameras. Other devices such as radiation imaging equipment could also be networked to the
same analysis station.
available video camera systems tend to concentrate on the quality and reliability of their
image capture hardware. Some products include image analysis capabilities:
Software that is completely dependent on the
image acquisition card and is therefore restricted to the image size dictated by the card.
Basic software, often purchased from third party
suppliers, that offers only basic image analysis solutions for electrophoresis
Higher quality software, often supplied by
Phoretix or one of its distributors.
software systems it is important to consider your present and also future analytical needs
and insist on high quality, supported software. Some companies offer sofware from more
than one supplier. Check the options available and choose the system which is best suited
to your present and likely future needs
Amersham Pharmacia Biotech
software from two different sources. For 1D applications ImageMaster Prime or ImageMaster
Elite is available:
These are fully
integrated units which offer simple sample location with a built-in transilluminator,
video monitor and thermal printer. The system has a high sensitivity for ethidium bromide
stained gels and an optional PC interface for image transfer as a tiff files.
Tel: +44 (0)
Fax: +44 (0) 1727 814001
Photometrics Gmbh products
Sollner Strasse 61, D-81479 Munich, Germany
Tel: +49 89 79 95 80
Fax:+49 89 79 97 15
Gel Documentation (AGD)
Photometrics offer package consisting of a "back thinned" 512x512 CCD
from SITe with up to 85% quantum efficiency (as against a more common 40%). and a dynamic
range of 16bits (65,535 counts). Phoretix Windows gel analysis software (1D and/or 2D) and
a tabletop darkroom (Dark Top®) designed for long exposures of bio-luminescence and
This is a modular table dark room for long-term exposures of chemiluminescence
and bioluminescence probes without the need for darkroom operating. This has an open base
to accept most transilluminators, UV interlocks and filter holder
air-cooled camera system
Thermoelectric cooled CCD, 768x512 - 1536-1024 pixel area, PC 486/Pentium ISA
Interface/Mac OS SCSI interface;Imaging software
Camera control & Image acquisition software
software from Photometrics has been designed to operate with Phoretix gel analysis
software.This is native 32-bit software operating under Windows 95 (or Windows 3.x)
supporting Photometrics CCD cameras.
bit image arithmetic with constant or images
plot, X and Y line plot and X, Y area plot
display for image min. max, stnd and sigma
16-bit PMIS files
FITS image files
8-,16- and 32-bit gray scale TIFF files
zoom, squeeze & panning
time cursor X, Y coordinate & Intensity display
time min/max intensity display
false colour log & inverted image display
fast focus region readout
time dark current correction
support for the AT200 Controller TTL I/O port
- supply Phoretix software with their CCD Camera Systems.
See also radiation and phosphoimaging section
A number of
companies with a long background in image acquisition offer much useful information on
conventional camera systems (film, use of filters, image capture and analysis and so on).
A number of these manufacturers have significant sales in the bioscience market and so
offer information specific to biochemists: