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 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.
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:
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
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.
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
35mm slide reader
Movement of annotaion
Burn-In vs. overlay
Cut and paste multiple images
Multiple images into one
How fine can one cut
Manipulation of clips
Continuous linear segments
Statistical data generation
Image adjustments and analysis
Convert to black and white
Brightness and contrast
Multiple area measurements
User defined macros
Real time video
Ease of viewing
Titling Copying and deletion
Exporting Image compression
File formats supported
Ease of info input
Multiple storage devices
English vs. Boolean logic
Multiple field searches
Various field configurations
Set for required input
Adding and removing fields
Based on search
Copying, arranging and shifting
Built-in User definable
Notes and dbase information
Live within an image
Scrolling and hunting
Comparisons Multiple images
Building block vs. "everything"
Capture and viewing stations
Multiple site and licenses
Installation, training, upgrades
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.