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THE AFFECT OF TEMPERATURE ON FILMThe film most often used in photo-enforcement is an ISO400 color print film consisting of a base layer of acetate and three dye layers made of gelatin with a protective overcoat. (See the KODAK Pro 400 images above.) According to I. J. Marvoka, a technical representative of Fuji, Inc. (Marvoka), film is frequent subjected to extreme temperatures by consumers who leave cameras and film in their vehicles in the summer. Since temperature in a closed vehicle may reach 200° F. considerable empirical evidence exists which demonstrates the effect of temperature on the Fuji product. This is in addition to the standard tests performed by manufacturers. Michael Davignon (Davignon), a technical representative of KODAK, reports that film is damaged by prolong exposure to extreme heat. Typically heat causes the base density of the film to increase which results in what is frequently called "heat fog." The problem of heat fog is temperature dependent and additive. That is, the problem worsens as the temperature increases and the longer the film is exposed to extreme temperatures. Heat fog primarily affects the color tones of the film. This is of more concern to consumers than to those in photo-enforcement since film is used for identification purposes only. However, even when heat fog bias occurs, some of the bias is correctable in processing. According to Mr. Marvoka, "Film used in 120°F environments for one or two days is only marginally affected. (Marvoka)" Since heat damage is temperature dependent and cumulative, jurisdictions should take the following measures in situations where heat may be a problem, i.e. where the ambient temperature may rise above 100 F°:
Based on the comments of the Fuji and KODAK representatives and actual field practice by Gatsometer, the manufacture of the camera who has installed and operated cameras in Australia, Kuwait, Jordan, Egypt, Morocco, and the United Arab Emirates; ambient temperatures of up to 120° should not impact the use, readability, and admissibility of the film used. FILM HANDLING AND STORAGEAs noted above, film is sensitive to light and heat. It is also sensitive to X-rays and other environmental factors. Fuji, a leading manufacturer of film recommends the following for film handling and storage: Film Handling
Film StorageUnprocessed Film StorageWhether exposed or not, at higher temperatures and humidities, films display greater photographic property variations (e.g., speed, color balance, and minimum density), and are more susceptible to adverse physical effects . Formalin vapors and other harmful gases can also adversely affect photographic properties. It is recommend, therefore, that care be exercised as suggested below.
Processed Film StorageProcessed films are subject to color fading and discoloration from light (especially ultraviolet), high temperature and humidity. To avoid the adverse affects of light, heat, and moisture, it is recommended that processed film should be kept in sleeves, envelopes or mounts and stored in dry, cool and dark locations where there is good ventilation.
LIGHTINGLight is usually defined as, " radiation that is capable of affecting the retina of the human eye (Shortley and Williams, 469). It is also the radiation that causes a chemical change in silver halide compounds (photographic film). Adequate lighting is essential in any photograph. It especially important for photographs taken for law enforcement use. Primary lighting is usually provided by a single high power -- 100 to 300 ws-- strobe (pulsed) flash. If conditions warrant, a secondary flash - often called a slave flash - is sometimes used. It is of particular use in red-light and rail crossing enforcement where the intersection is unusually wide. Lighting a red-light violation involves balancing the amount of light reflected to the camera from a vehicle, a driver (if driver recognition is required), and a vehicle's license plate. LIGHT INTENSITYThe placement of the primary light source is very important especially if night and/or driver recognition is required. It has been known for some time that "The intensity of the light varies inversely as the square of the distance from the luminous (Norton, P. 243). Simply stated, doubling the distance results in one fourth the light intensity, not one half. This power function of light means that the observed and recorded effect of light on an object changes dramatically as the distance between an object and the source of light illuminating it increases. Table 2 shows the effect of locating the light source at different distances from a vehicle photo point. Known as the Inverse Square Law, The intensity of light diminishes rapidly as the distance from it increases. If a flash is measured at 10 feet from its source using a flash meter and the meter indicates that an f-stop of 16 should be used, the effect of moving another 10 feet is shown by a value of f8 - twice the aperture opening. By 60 feet an aperture of f2.7 must be used to record the same image. In this example, at any distance greater than 60 feet, the flash has virtually no effect. It would be much the same as the spectator at a sporting event using a standard flash to try capture his or her favorite athlete on the stadium floor many feet below - one can snap the shutter, the flash unit can fire, but the photos come back unviewable - unless enough ambient light is available. There are three basic ways to handle this effect. The first is rather simple: increase the flash output. The second is equally simple: move the camera closer to the vehicle (or wait until the vehicle is closer to the camera). The third way is more difficult but is very effective: add a slave flash. If both flashes are in sync with the shutter- and they should be- then there effects will be additive. That is two, 200 ws strobes will have the same intensity (assuming that they are the same distance from the subject) as one 400 ws flash. Of course there are many possible arrangements of flash units. And flash units are usually duel power. That is, they may have different output levels on the first and second flashes. Since flash intensity is directly related to the amount of energy stored in the units' capacitors at time of discharge, and capacitors take time to charge, it is usually best to have the brightest shot first. It should also be noted that in red-light and rail crossing enforcement the use of enhanced ambient light from overhead luminaires should be considered. Overhead lighting may allow the use of lower wattage primary strobes which may have an added benefit in that they may reduce the effects of glare from some plates. FLASH ANGLEA flash unit is composed of:
As discussed, the flash tube and capacitor play an important role in flash intensity. Another factor also involved is the reflector. The reflector is usually a silvered bowl surrounding the flash tube. The bowl is designed to focus the output of the flash unit. The resulting spread of light is known as the light cone. The light cone is the cone of light emanating from the strobe. It is common to have a light cone with a angle of 30°- 40°. The angle should match the camera angle if recognition of the driver is required to insure that the interior of the vehicle is sufficiently illuminated. Flash cones can be controlled by changing the shape of the reflector. Like lenses, flash units can be obtained with wide, medium, or narrow focused beams. When driver recognition is not required, most emphasis regarding the flash is centered of reducing the glare from license plates. Polarizing filters can be of significant help in reducing glare, but a standard windshield blocks a considerable amount of light from reaching the drivers face. Empirical testing has shown that the light reaching a driver's face may be as little as 1/5 as much as hits the front of a vehicle. There are several techniques which can improve overall lighting of a vehicle. Since the reflectivity difference between a vehicle and a licensee plate may be 100%, bouncing the flash from the pavement to the plate by directing the flash in front of the vehicle and by increasing the distance between the camera and the flash unit may also improve the readability of plates. LENSESAccording to Rossi (p. 83), "A piece of glass or other transparent material bounded by two spherical surfaces (or one plane and one spherical surface) forms an optical system called a simple lens." Professional high quality lenses are used by most makers of photo-enforcement equipment. These usually range from 45-150 mm depending on the distance from the camera to the vehicle to be photographed. Lens quality is very important in photo-enforcement since it is the lens which determines to a great degree the clarity of a photograph. FOCAL LENGTHThe selection of lenses include consideration of its focal length. There are three main categories of lenses: wide angle (<45mm), normal (45-75mm), and telephoto (>75mm). Generally, normal and telephoto lenses are used in photo-enforcement. FIELD-OF-VIEWThe field-of-view is how much the camera "sees" or records on film. For example, a camera with a 45mm lens at a distance of 20 feet will produce a field-of-view of 15'x11'. That is, the camera "sees" an area twenty feet wide by eleven feet high. At the same distance, on the other hand, a 150mm lens "sees" only 4' x 3'. Field of view must be taken into account when selecting a lens. One may use different lens depending on the distance the photopoint is from the camera and how wide the frame must be. FILTERSPhotographic filters are glass or plastic media placed between the lens of a camera and an object to be photographed that change the light entering a camera. The most common filter is a skylight filter that reduces the amount of UV light reaching the film or CCD. Filters are usually placed in front of the lens but can also be placed on the light source to change the color of the flash. This is often used to reduce the effect on the drive's vision. Some filters commonly in use in photo-enforcement are shown below:
CCD TECHNOLOGYCCD technology, like that of film, is also based on a principle of physics. Instead of silver, however, charged coupled devices (CCDs), as they are called, use silicone. Photons of light pass through a lens and strike a cell of the CCD. The amount of light (intensity) is electrically converted to digital information and stored. Merrill and Lichty describe this as: A brief review of how a CCD camera imagine is recorded will help in understanding imagining system optimization. [For more details, see Laser Focus World, Dec. 1994, p. 53 -- Ed.] The LCD imaging array itself has no inherent gain. Every incoming photon generates a single free electron in the pixel it impacts, with a probability ranging from 0% to 70%. This probability is known as the quantum efficiency and is wave-length-dependent, loosely following the absorption curve of silicon. The number of electrons is determined by the light level in the image and the exposure (integration) time. There will also be a few "rogue" background electrons bound in each pixel, known as dark electrons. The number of' these dark electrons is strongly dependent on the CCD operating temperature. The correspondence between object "pixels" and CCD pixels is determined by the magnification of the optical system being used. The array of' active pixels is referred to as the parallel register. Prior to readout, the inherent signal-to-noise ratio (S/N) of the image stored in these pixels is determined by the shot noise -- the natural statistical variation in the number of photons arriving at each pixel. Shot noise is the statistical variation in the light-absorption process. Each exposure results in an array of captured charges in the form of a two-dimensional matrix. This n x m matrix is averaged, row by row, into the serial register. The individual pixels in the serial register are then transferred in serial fashion into an output node. Camera electronics measure the charge in this node, digitize the chordate, and clear the node electrons, leaving it ready for the. next serial transfer. This readout process introduces statistical variations known as read noise. The readout speed is usually limited by the speed of the camera analog-to-digital (A/D) converter, with a maxim of several megahertz (millions of pixels/second). A process known as binning allows the charge from several pixels to be combined before readout. This reduces the number of individual readout events and thus decreases the total readout time, allowing the user to set the camera to a faster frame rate. Binning is possible in both the x and y directions either by combining multiple rows into the serial register before undergoing serial transfer or by reading multiple serial pixels into the output mode between individual readouts. Because it increases the S/N, binning is also used for low light applications. The trade off for higher frame rate and increased S/N is reduced spatial resolution. (Merrill and Lichty 121) As discussed, the resolution of CCDs is measured in pixels. Although similar to CCDs used in video cameras, CCDs used in law enforcement are typically high-resolution using an array of 1,000 x 1,000 pixels (1,000,000) or more. Although not as high as film, digital camera resolution has progressed rapidly in the last five years and is now sufficient for most enforcement purposes. An excellent explanation appeared in Scientific American in June, 1998. DIGITAL CAMERASby Michael D. McCreary
A CCD is an array of light-sensitive picture elements, or pixels, each measuring five to 25 microns across. The camera's lens focuses the scene onto this pixel array. Just as the resolution of conventional photographic film is related to the size of the grain, the resolution of a CCD chip is measured by the number of pixels in the array. A digital still camera intended mainly for nonprofessional use has an array of, typically, 640 by 480 pixels; a top-of-the-line professional camera would have an array of millions of pixels. CCD chips are fabricated in a process that requires hundreds of steps and several weeks. Although CCDs are the dominant light-sensitive semiconductor, companies such as Eastman Kodak, Motorola, Intel, Rockwell and Toshiba have invested heavily in a competing technology, the CMOS image sensor, which is expected to be used in products such as digital cameras, especially lower-end models intended for nonprofessionals. Illustrations by: Jared Schneidman Design WHY IS THE USE OF CCD CAMERAS GROWING?
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| The system shoots and stores 30 pictures at a time and is reusable up to 100,000 times. | |
| Connects to your PC for instant viewing, electronic storage, immediate e-mail transmission and artistic manipulation. | |
| Enables custom and standard photos with your printer. | |
| One EFS-1 Electronic Film system saves you the expenses of 100,000 rolls of film and processing. | |
| Compatible with all standard digital printing methods. | |
| Provides creative freedom with your existing lenses and attachments. | |
| Allows flexibility to choose between standard 35mm film or EFS format at will. |
Imagek CCD Adapter for 35mm Cameras |
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While CCD cameras are analogous to film cameras and both produce images, digital cameras present some issues which must be addressed. KODAK Motion Analysis Systems Division located in San Diego, CA suggests the following as camera/system requirements:
| Data management: facilitate the ability to easily capture, transmit, process, store and recover captured data for both image and text formats. | |
| Resolution: sufficient to meet all the intended uses for the image-reading of the licensee, clear detail of the vehicle and if required, allowing identification of the operator. | |
| Anti-blooming: prevention of spreading of overexposed portions of the image (i.e., vehicle headlights or sunlight from highly reflective surfaces.) | |
| Contrast latitude: adequate differentiation of light-to-dark areas within an image to add detail recognition. | |
| Stopping power: Blur-free images of moving vehicles. | |
| Sensitivity: ability to detect at low-light levels as well as into near-IR special region. | |
| Image enhancement circuitry: camera electronics to eliminate major sensor defects such as bright or dark columns, which detract from the visible presentation of the image. | |
| Frame rate: continuous read out of images to support monitoring along with single frame capture capability for recognizing several successive vehicles committing a violation. | |
| Installation flexibility: ability to mount into permanent or mobile settings. | |
| Environmentally friendly: minimize the impact of any by-products of system. (Erickson 2.) |
CCD Systems
The Redflex System
Redflex Traffic Systems Pty Ltd expects its new digital SMARTCAMred red-light enforcement system will supercede the 'twin-shot' operation of conventional red-light cameras. SMARTCAMred combines advanced high resolution digital imaging with computer vision and communication technologies and has been developed specifically for road safety.
The system has just concluded trial under the Technology Review being conducted by the ICBC in British Columbia, Canada. A separate three month trial starts this month in Howard County, Maryland, USA, where the system's multiple imaging will suit the County's requirement that a vehicle be imaged prior to reaching the intersection stop-bar in addition to conventional shots.
Redflex says SMARTCAMred operates more efficiently than conventional red-light cameras and generates superior sets of image information (that record the whole violation episode). And it allows violation data to be communicated direct to the processing back-office using communications channels (POTS, ISDN, cable modem or fiber optic) for rapid citation issue. Or data can be transferred on a removable disc. The digital image sets and violation data are encrypted to provide absolute security.
Film-handling and printing are, of course, non-issues.
Digital SMARTCAMred cameras image vehicles continuously as they move towards and over the 'stop-bar', cross and exit the intersection. The systems hold up to ten (10) separate images of the entire violation event. These 'overlap' with the actual violation detection that is recorded on a special, high resolution violation image of the license plate (shot at a position to optimize later plate recognition and processing).
The violation image is imprinted with a 256-character datablock.
Because this dataline is fully software configurable, it is completely flexible to client
requirements. This allows full description and records of the intersection details, type
of violation, violation data, time of violation, time elapsed into 'red' cycle', frame
number, direction and speed of the vehicle, date etc. as required.
The systems 200 MMX industrial Pentium Computer Control Unit allows it to be flexibly configured to manage variable enforcement requirements including known variations in traffic flow or altered policy objectives. With the communications systems, the Unit also allows remote status monitoring and direct modem communication of deployment data, status reports, or alarm warnings to enforcement authorities.
SMARTCAMred systems monitor up to four lanes of traffic simultaneously, and are capable of sustainable imaging at two violations per second or better, giving effective enforcement of multiple offences in busy intersections. System housing is environmentally controlled to allow operation in extreme weather conditions on a 24 hour basis.
Alternatively, Redflex' film-based SMARTCAMred camera system may be used if specific jurisdiction rules require film images. The two systems are interchangeable. Redflex high performance technologies take both well beyond conventional cameras.
By far one of the most confusing aspects of photo-enforcement is the meaning and comparison of resolution. We speak of the resolution of cameras -both film and digital-, of monitors, and of printers. And we use different terms or the same term in a different way: lpi, dpi, pixels, etc.
In general, the resolution of an instrument (including the human eye) is the ability to differentiate or resolve objects individually. Devices are said to have high resolution if they are able to provide many unique pieces of information and have low resolution if they present few.
Erickson, identifies five classes of resolution associated with CCD photography which he calls the NTSC-type camera which have resolutions up to 760 x 480 pixels:
| Low Resolution | |
| High Resolution | |
| Ultra Resolution | |
| Very High Resolution |
He further identifies a new class: Mega-resolution with 1,000 x 1,000 Pixels and above. (Erickson 3)
Image Type Bytes per pixel B&W 0.125 Indexed 16-color 0.500 Indexed 256-color 1.000 Grayscale 1.000 RGB true color 3.000 CMYK true color 4.000
The Photographic and Imaging Manufacturers Association (PIMA), which is accredited by the American National Standards Institute (ANSI). , has sponsored a standard for measuring resolution of digital cameras. It is known as The Electronic Still Picture Imaging DRAFT INTERNATIONAL STANDARD ISO 12233.
In part, the draft states:
Forward
The ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard ISO 12233 was prepared by Technical Committee ISO/TC 42, Photography.
Purpose
The spatial resolution capability is an important attribute of an electronic still picture camera. Resolution measurement standards allow users to compare and verify spatial resolution measurements. This standard defines terminology, test charts, and test methods for performing resolution measurements for analog and digital electronic still picture cameras.
Technical background
One of the most important characteristics of an electronic still picture camera is the ability of the camera to capture fine detail found in the original scene. This ability to resolve detail is determined by a number of factors, including the performance of the camera lens, the number of addressable photo-elements in the optical imaging device, and the electrical circuits in the camera, which may include image compression and gamma correction functions. Different measurement methods can provide different metrics to quantify the resolution of an imaging system, or a component of an imaging system, such as a lens. Resolution measurement metrics include resolving power, limiting resolution (at some specified contrast), spatial frequency response, MTF, and OTF.
A method for measuring resolution is to capture an image of a suitable test chart with the camera under test. The test chart must include patterns with sufficiently fine detail, such as edges, lines, square waves, or sine wave patterns. The test chart defined in this standard has been designed specifically to evaluate electronic still picture cameras. It has not been designed to evaluate other electronic imaging equipment such as input scanners, CRT displays, hard copy printers, or electrophotographic copiers, nor individual components of an electronic still picture camera, such as the lens.
The resolution measurements described in this standard are performed in the digital domain, using digital analysis techniques. For electronic still picture cameras that include only analog outputs, the analog signal must be digitized, so that the digital measurement can be performed. The digitizing equipment is characterized, so that the effects of the digitization process can be removed from the measurement results. When this is not possible, the type of digitizing equipment used shall be reported along with the measurement results.
The spatial frequency response (SFR) measurement method described in this standard uses a computer algorithm to analyze digital image data from the electronic still picture camera. Digitized image values near slanted vertical and horizontal black to white edges are digitized and used to compute the SFR values. The use of a slanted edge allows the edge gradient to be measured at many phases relative to the image sensor photo-elements, in order to eliminate the effects of aliasing. This technique is mathematically equivalent to performing a moving knife edge measurement.
Whether a CCD captured image is in analog or digital format, it still must be stored. Analogue images are usually stored on magnetic tape while digital images may be stored in random access memory (RAM), magnetic media such as diskettes, hard disk drives, or on magneto-optical (MO). These devices may be local or the a signal (analog or digital) may be transmitted by wire or radio. Generally, if the data are not to be stored locally, analog signals are much quicker to transmit.
Since images require much storage space, the decision on the method of storage is often made by the size of the file storing the image. To calculate the raw storage required use the following formula:
When the number of images is great or the size of each image file is large, some thought must be give to storing the images in compressed form.
- Where: FS=file size
- H=height of the image in pixels
- W=width of the image in pixels
- R=resolution in pixels
- B=bytes per pixel
One cannot discuss digital technology without discussing compression. Since digital images are usually quite large and storage costs relatively high, some method must be used to reduce the size of images for storage. Two types of compression are generally available: lossy and lossless. As the names imply, the difference is in whether or not information is lost during the compression process. While there are many different compression algorithms used for compressing images, the most popular is probably JPEG.
The Joint Photographic Expert Group (JPEG) created a compression scheme that includes both lossy and lossless algorithms. The actual name of the standard is "Digital Compression and Coding of Continuous-Tone Still Images." It is also known as ISO standard 10918. "JPEG is not one standard but a suite of standards - 29 distinct coding processes in all (Brown and Shepherd 382)."
Brown and Shepherd's book on graphic file formats (Brown and Shepherd) define in detail the specification:
JPEG's baseline sequential scheme is a combination of the Discrete Cosine Transform(DCT), reduced precision of the DCT coefficients (quantization), run-length encoding, and Huffman or arithmetic encoding.
To compress an image, the image data is divided into blocks, where each block is an 8 x 8 array of values. Each block of data is put through three processes: a Forward Discrete Cosine Transform (FDCT), a quantizer, and a coder. To decompress an image, these processes are reversed: an un-coder, a de-quantizer, and an Inverse Discrete Cosine Transform (IDCT) (Brown and Shepherd 221).
Common Compression Encoding Methods
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IMAGE PROCESSING
Once an image of a violation has been captured either on photographic film or in digital format it must be processed so that information about the violator can be obtained. This process depends on the media on which the image was stored.
FILM
The basic processes involved with the use of photographic film involves film development, scanning, and storage. Exposed film must be developed to expose the latent image. It then must be transferred into a computer for viewing. The device at left is a film scanner manufactured by ROBOT FOTO UND ELECTRONIC GmbH and used to scan 33mm film. The scanned images must also be stored if later retrieval is required. If desired by the jurisdiction digitized images of the violation may be included as part of the citation mailed to the violator. This image should provide a good picture of the vehicle, surroundings and data block. If frontal photography is used, the driver's face may be included, but faces of other occupants should be blocked. This increases the response-by-mail rate without infringing on the violator's privacy. According to KODAK:
- You can easily scan Pro Film negatives with a variety of linear-array-CCD, area-array-CCD, and PMT film scanners. You can scan negatives on desk-top scanners as well as high-end drum scanners.
- Because no standards exist to define the colored filter sets that film scanners use to capture the red, green, and blue information of the film image, each manufacturer's scanner has its own characteristic output. The output depends on the scanner's sensitivity to the dyes in the film. This sensitivity is determined by the spectral distribution of the colored filter sets and/or the spectral sensitivity of the charge-coupled-device (CCD). In addition to these spectral specifications, scanner output depends on the look-up tables or matrices that the scanner uses to output information for CRT monitors, transmission, etc. These tables or matrices are part of either "plug-in" programs used with specific software packages designed for image manipulation, updateable ROMs included with the equipment, or fixed algorithms for calibrating and balancing, similar to those used in photographic color printing equipment.
- The generic "color negative film" channel designation available with scanner software is only a starting point. You can adjust the final color balance and the scene-dependent contrast and brightness of an image by using the scanner's controls during pre-scan, or by using an image-manipulation software program or workstation after acquisition.
- Some scanners allow you to use "plug-in" programs to make calibrations based on D-min film stock. Because different types of color negative films have different colored-coupler masks, the optimum D-min balance is different for each type of film. Therefore, for optimum results, set up a specific channel for each type of film you are scanning.
- Note: For more information, visit the KODAK World Wide Web site at http://www.KODAK.com/.
FILM DEVELOPMENT
Most film today is developed using automated film developers frequently seen in fast film processing labs throughout the world. Many professional labs also offer custom development which allows for correction of over or under exposures. Custom labs can also vary the contrast of film during development. However, this level of development is rarely necessary if appropriate film is used and the camera is adjusted properly.
IMAGE STORAGE
Because images contain so much information, they usually require a significant amount of space for storage. There are several ways to store the information contained in images. If film is the media used to record the image, the film itself may be used as an information storage system. Images may also be stored electronically. If digital recordings are used to capture the violation or if the images from film are captured in digital form, some form of magnetic or optical media must be used to store the information.
FILM
As a storage media, photographic film is cheap and dense. If the original violation was captured on film about 6 million bits of information are recorded. With the exception of Hollywood type equipment, the information on film can not be completely captured in digital form.
MAGNETIC MEDIA
Magnetic media include the ubiquitous hard drive, zip drives, and magnetic tape. Hard drive have an advantage when rapid access is desired or copies of the image need to be transmitted over great distances in a short amount of time. Access times are quick and the cost per unit of storage is falling. Frequently violations recorded on film are captured and stored on hard drive for processing then discarded. The original film serves as the long-term storage media.
OPTICAL MEDIA
Optical and magneto- optical storage systems provide a large amount of storage capacity and may be made available on-line if placed in juke boxes. The unit cost is lower that magnetic media but access time is longer. Optical storage (CDs) (Shown Below) can be permanent or re-writable. The KODAK PIW 6600 Film Scanner (Shown here)
can produce high quality scanned images on CD. Permanent CDs offer the added protection that the images remain unchangeable once recorded. This may satisfy some courts as a long-term storage method. On the other hand, re-writeable CDs are more cost effective since they can be reused after the images are no longer needed.
The storage media is often dictated by the type of citation issued by a jurisdiction. If images are to be printed on the citation, they must be stored at least temporarily on magnetic or optical media.
License Plate Recognition
For a full disdussion of automatic license plate recognition technologies, please see click here.
Forensic Photography
The traditional techniques of forensic photography may also be of interest. Many related topics and links can be found Steven Staggs book on Forensic photography titled Crime Scene and Evidence Photographer's Guide. A description of the book and other interesting links can be found at: http://www.pe.net/~staggs/index.html
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