The following article, "How to Choose an Imaging System" was written by Richard V. Resh of MIS, Inc.. It originally appeared in the July, 1998 edition of Advanced Materials and Processes magazine and is reproduced here with the kind permission of Margaret Hunt, AM&P Editor.
Imaging systems include many components, and it is helpful to know which
are necessary for your application.
Electronic imaging systems are being purchased at an unprecedented rate.
New forms of these imaging systems are being developed, filling the market
with countless and confusing offerings. Because imaging systems are more
than just software, each component needs to be carefully selected to ensure
the anticipated results.
This article provides an overview of the critical elements in an imaging system, and includes a few tables to aid in the selection process. It will guide the potential user through the key issues surrounding electronic imaging, in an effort to provide a better understanding of the process.
Aim for performance
The first and most critical concept is that a system is only as good as its
weakest component. This may sound elementary, but people frequently install
systems that lack the capability they require because one segment of the
system delivers low performance.
The second concept is that an imaging system starts with the sample and sample-preparation equipment. If the sample is poor or is improperly prepared, even the best system will produce an unsatisfactory image. Above all, be sure that the sample is flat. Due to the size of a computer monitor screen, an uneven sample will be more obvious than it would be through the microscope. An imaging system also includes a micro- or macro-scope, camera, capture board, computer system, hardcopy printer, and imaging software.
Many companies want to utilize the equipment they currently own. For most applications, micro- and macro-scopes that have been properly main- tained may still be utilized, providing the optics are clean, photo-ports are available, sufficient lighting exists, and the required filtering is accessible.
The camera
The camera is a critically important system component. The best medium for
images is still 35 mm film, but electronic imaging is not far behind and
the gap is closing rapidly. Film is still better, but how much better is
relative. The answer lies in the question, "How does it look to you?" The
video and digital cameras on the market today produce outstanding images,
thus eliminating the film issue.
Many people confuse video and digital cameras. Actually, it is difficult to differentiate between a high-quality video image and the image from a digital camera. However, as a rule, a digital camera produces a better image than its video counterpart.
A digital camera captures an image, displays that image, and then repeats the capture and display process again and again. This is called "refresh." Early versions of digital cameras had relatively slow rates of refresh. The sample image could not be quickly moved around the screen, and the cameras produced a "roller-coaster effect" as the images appeared in jerky movements. To overcome this effect, digital camera manufacturers now provide a video preview signal, or have raised their refresh rates such that the "roller-coaster effect" is reduced. New cameras use the video signal to find and focus on the area of interest, and then capture in digital mode. A "super high" resolution digital camera produces an image that is typically 1600 x 1200 pixels and over 5 MB in size.
By contrast, a video camera is a constant stream of video that may be stopped when the appropriate image is displayed. A high-quality video camera displays an image that is typically 800 x 500 pixels and about 1 MB in size.
Within the video camera family, two video formats and three signal types are available. One format, NTSC, is preferred in North America; the other format, PAL, is the European standard. However, formats play a lesser role in image quality and will be ignored in this discussion.
The three signal types are: Composite, S-Video (sometimes called YC), and RGB. Composite cameras are inexpensive and usually selected for ap- plications in which resolution is not critical, such as surveillance and face-to-face video conferencing. S-Video is the next notch up in video quality. The images produced from an S-Video signal are generally acceptable in macro appli- cations. The final signal type is RGB, the highest- quality video signal.
The RGB family is comprised of single-chip and three-chip cameras. Single chips are the usual choice for macro applications, while three-chip cameras are recommended for most microscope applications. A recommendation for camera types versus applications is shown in Table 1 (Note that the NR rating for the high-end cameras in macro applications does not mean that the image would be poor, but refers to the fact that the extra cost is typically not worth the gain).
|
||||||||||||||||||||||||||||||||||||||||||||||||||||
Cost of the cameras is proportional to the image quality. Typically, composite cameras are under $1000; SVideo are under $2000; single-chip RGBs are under $3500; three-chip RGBs are under $6000; and digital cameras are under $10,000. Macro applications generally utilize S-Video or single-chip RGB cameras, while microscopic work is better served with three-chip RGB or digital cameras.
Capture board
The function of capture boards is often misunderstood, and their quality
and cost can vary widely. The interaction between the capture board, computer
hardware, and software is complex, and a high-quality board is very important.
Typically, imaging systems manufacturers develop their software around a
number of high-quality boards, and offer several options in this area. When
reviewing systems and their capture boards, look for the following points:
Computer system
Three key components influence computer performance: processor type, system
clock speed, and RAM. The better the processor, the faster the clock; and
the more RAM, the better the system performance. Before junking your old
computer, check the processor and RAM. Processor upgrade chips will tum a
486 into a faster 586. (A Pentium chip is a 586 with the name trademarked.)
Additional RAM can be purchased, which will greatly increase the performance
of your PC. Many "old technology" processors can be upgraded to 16MB of RAM
for less than $800.
Another important item is storage space. As pointed out in the camera section, a digital image requires 5 MB and a video image needs 1 MB. Capturing video images at the rate of five per day for one year, the amount of space required for the images would be 1.3 GB. But digital camera images captured at the same rate would increase the memory requirements to at least 6.5 GB. Therefore, a large capacity hard drive, an extra hard drive, and/or internal or external storage is recommended. A Zip, Jaz, CDROM burners, or some other device should be considered for long term archiving.
A final element is access to the Internet, either through a company network or a direct link via modem. No computer should be without this capability for sharing images and sending reports. An overview to choosing a computer system is provided in Table 2.
| Table 2 - Tailoring a computer system | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Hardcopy printers
The requirement for printed reports is still a necessity for the foreseeable
future. Video printers that produce 8 1/2 x 11 in. prints are expensive but
produce outstanding results. Laser jets are middle-of-the-road in price and
can produce good results. Ink jet printers are the best bargain on the market
today. Regardless of the printer selection, images should not be printed
at less than 600 dpi resolution.
Imaging software
Before selecting the software, define what you want to accomplish. This should
be the key selection factor. Every software package will have extra bells
and whistles that are both appealing and confusing. If the original requirements
are kept in focus, choosing the proper package will be easier. Select the
product that meets the needs. Then look at all the extras and compare costs.
A list of functions and features to look for in a software package is provided in Table 3. When reviewing products, this list can be turned into a comparison chart. The following considerations will shed some light on the various functions:
| Table 3 - Imaging software function and feature checklist | ||
| (1) Input Video camera Digital camera Scanner 35mm slide reader Import SEM compatible Camera presets Adjustments Storage |
(2) Annotation Notes Voice Pen Text Preconfigured functions Editing Color separation Movement of annotaion Burn-In vs. overlay Cut and paste multiple images Multiple images into one How fine can one cut Manipulation of clips |
(3) Basic measurement Linear Continuous linear segments Rectangles Elliptical Irregular areas Statistical data generation Unit conversions Calibration techniques Verification |
| (4) Image adjustments and analysis Color separation Color inversion Convert to black and white Brightness and contrast Sharpness Image rotation Histograms Edge detection Point isolation Dilation Porosity Volume fraction |
(5) Counting Multiple area measurements Grain sizing Hardness User defined macros Image integrity Communications Real time video Stored images Archiving Ease of viewing Titling Copying and deletion Exporting Image compression File formats supported |
(6) Database searching Ease of info input Quick presets Look-up tables Multiple storage devices English vs. Boolean logic Multiple field searches Various field configurations Set for required input Adding and removing fields Presentation Based on search Copying, arranging and shifting Manual/timer mode |
| (7) Report generation Built-in User definable Measurable reports Notes and dbase information Security Multiple levels Multiple users Windowing Live within an image Scrolling and hunting Comparisons Multiple images |
(8) Other needs Building block vs. "everything" Capture and viewing stations Laptop version Multiple site and licenses Installation, training, upgrades Upgrades Technical support Self diagnostics and repair |
|
For more information: Richard V. Resh is VP of East Coast Operations, Midwest Information Systems, Inc., 100 Alexander Way, Orchard Park, NY 14127; tel: 716/646-1218; fax: 416/352-5148.