The use of photography in law enforcement is as old as photography itself. Moenssens, et al, write:

In civil as well as criminal cases, photography provides the most potent tool in conveying facts to a jury. In criminal trials, photography plays an extremely important role for the police and prosecutor and can play the same role for the defense. Invented in 1839 by Daguerre, photography was used as early as 1843 to provide pictures of arrested persons - what we now call mug shots - in Belgium. These early pictures were on metal plates, called daguerreotypes.... The use of mug shots to identify individuals has survived to this day.

At a very early stage, photographs were also used to record scenes of crimes and accidents, of bodies and wounds, of suspect documents and checks and of other items of evidence such as murder weapons. As early as 1860, courts were confronted with photographic enlargements of questioned documents in criminal cases and by 1871 post modern photographs, photo-micrographs and photomicrographs, and X-rays.

As photographic techniques became more sophisticated, still photographs were made through a microscope of hairs, fibers, paint chips, tool marks, and other minute items of trace evidence. The advent of color photography, stereo photography, and infrared and ultraviolet picture taking, sometimes in conjunction with the use of a microscope, also permitted the taking of photographs of small details that the human eye could not distinguish.

Because of the wide uses of photography by the general public, it is probably the one type of evidence that is best understood by all people, including police officers, lawyers and judges. Most anybody (sic) has used a simple camera, and a good many people can operate quite elaborate pieces of photographic equipment. All but the smallest law enforcement agencies possess photographic laboratories as well as a wide array of specialized and general-purpose photographic instruments. (Moenssens, Inbau, and Starrs 601)

 PHOTOGRAPHIC PRINCIPLES

Original photographic technology is based on a simple physics principle: certain compounds of silver - silver halides - change their chemical structure when exposed to light. The silver compounds are mixed with warm liquid gelatin and applied to a flat surface, exposed to light, and processed chemically. Silver compounds were first applied to glass plates in the 1800's and later to plastic sheets and strips. These coated strips are called film and have been used in photo-enforcement for over forty years. Recently, digital cameras have been developed that do not depend on film for storage of an image, but rather the image is stored in electronic form. In the following section, we discuss film, camera orientation and placement, lighting, Lenses, focal length, field of view, and filters.

FILM

History of Kodak Roll Film Numbers

The following information on the history of photographic roll film is taken from W. J.'s  Photo home page http://members.aol.com/thombx19/history.html. This excellent site is focused on IR and UV film and contains many useful links.

Roll Films Starting with 101

It first became necessary to specify which Kodak roll film was required with the introduction of the No. 2 Kodak camera in 1889. As different models and sizes of cameras were introduced, the film boxes were marked with the names of the cameras that the roll would fit.

By 1908, this system had become difficult to use for ordering film. It was now necessary to specify the image size and the camera the film was to be used in as not all films for the same size pictures could be used interchangeably. To simplify this system it was decided that the daylight-loading roll films on flanged spools would be numbered in the order of introduction, starting with the first Kodak film of this type introduced with the No. 2 Bullet camera in 1895 as number 101.

This system was gradually phased in as new film boxes and camera instruction manuals were printed, but the numbers did not appear in Kodak price lists until 1913. By this time, numbers 101 through 129 were used. Numbers 106 through 114 were used for films spooled for Cartridge Roll Holders, which allowed roll film to be used with cameras designed to use glass plates. In 1916 one more number in this series was added: No. 130 for pictures 2-7/8 by 4-7/8 made with No. 2C Kodak cameras.

Some Kodak and Brownie folding cameras made from 1914 to the 1930's have a little door on the back which is marked "use Autographic film A-(number)". A-116 film, for example, was for the same size pictures as 116 film but instead of red and black duplex paper, the film was wound with a sheet of carbon paper and thin red paper. This film used in an Autographic Kodak camera allowed a brief message to be written on the film in the space between the pictures. Pressure of a stylus on the backing paper transferred the carbon to the red paper and light passing through these lines in the carbon paper would photograph the message onto the film.

When 620 and 616 films were designed in 1931, considerable thought was given to the numbering. These films were for the same picture sizes as 120 and 116 but the spool diameters were smaller to allow them into thinner cameras. The "6" was to indicate the number of pictures per roll but by the time this product had reached the market, the decision had been made to increase the number of pictures on this size and on sizes 120 and 116 to eight exposures so the "6" became meaningless.

In 1935, the Kodak Bantam cameras were introduced. The film for these cameras provided for eight exposures 28 x 40 mm, and the number 828 was chosen for this films.

Size 220 was introduced in 1965 and is twice the length of 120 size film although it uses the same spool. This film has only a paper leader and trailer for light protection and no paper behind the film. It is used with professional cameras which advance the film automatically instead of using a window on the back of the camera to position the film.

35mm:

In 1916, a very small box camera named the No. 00 Cartridge Premo camera was introduced using a No.35 roll film. This was numbered differently as it was not the same as the Eastman Non-Curling film supplied in the other roll film sizes but was apparently made from unperforated 35mm motion-picture film. In 1934 when 35mm film in cartridges were introduced with the Kodak Retina camera, number 135 was assigned to this product. This film size could also be used in the Contax and Leica cameras. Daylight-loading spools of film for these two cameras were also offered, and were numbered 235 and 435. In July 1952, a special length of film for 20 pairs of pictures made with 35mm stereo cameras was introduced and designated as 335.

Instamatic

In 1963 the Kodak Instamatic cameras were introduced. These used roll film in cartridges from drop-in film loading. The image size is 28 x 28 mm, but slight masking is required in printing and slide mounting so the useable image is 26.5 x 26.5 mm. The number 126 was used, as the original roll film for this size had been discontinued in 1949.

For the Kodak Pocket Instamatic cameras introduced in 1972, a number lower than 126 was preferred, partly to indicate a smaller image than the 126 film. The number 110 was chosen because it could be said as "one ten" and was easy to remember.

Advantix

Kodak's latest film number 240 for the Advanced Photo System was introduced in 1996. Using the trade name ADVANTIX, it is the first film from Kodak to incorporate traditional silver halide technology and a transparent magnetic recording medium (IX - Information eXchange) allowing the following information to be recorded and exchanged with the photofinisher:

Camera Recorded Data (if enabled)

Customer Recorded Data (if camera enabled)

Advanced Photo System also allows data recording to be read by the Certified Photofinisher:

Resolution

Modern photographic film is still made by applying a coating of light sensitive chemicals to a plastic base. The amount of information that can be stored on film is usually referred to as resolution.

The human eye has the equivalent of 1,893,376 pixels while a common computer screen has a resolution of 620x480 (or about 297,600 pixels) as the table below shows.

The resolution of film is very high. According to Norman Breslow,

"...based on the specifications for KODAK Varicolor film and a Nikon 50mm autofocus lens, show that there would be between 2.5 and 3 million pixels in the negative, depending on the f/stop the lens was used at (Breslow, 1990)."

Others (Larish, p. 19) suggest even more resolution from film depending on film type.

Film used in photo-enforcement includes both black and white (B/W) and color. Color film is more commonly used today in photo-enforcement, especially if driver recognition is required because of the greater amount of visual information contained in color film such as the color of the vehicle. Black and white film on the other hand has a greater dynamic range than color film and provides greater detail for difficult plate recognition.

In addition to sensitivity to color, film is manufactured with varying degrees of sensitivity to light. The ISO standards for film rate film's sensitivity on a linear scale.

Film for general use is marketed in the ISO range of 25 to 1000. Film used in photo-enforcement generally has an ISO rating of 100-400. Other standard include the European DIN and the former Soviet bloc countries GOST system.

SELECTING FILM FOR PHOTO ENFORCEMENT

35mm Print Film

There are many brands and types of film on the market. As noted above a film with an ISO rating of 100-400 is preferred. The distinguishing feature of all film used in photo-enforcement is graininess.

Graininess is the characteristic of film to show the individual grains of silver halide when the negative is enlarged. When a film has a small grain pattern that is not noticeable in a standard enlargement, it is said to be fine grained. The ability to identify the letters and numerals in a license plate or the ability to recognize the driver of a vehicle is determined directly by the inherent graininess of a film.

Graininess is often measured using an ISO Root Mean Square (RMS). This actually measures the granularity of the negative. Whole values (4,5,etc.)only are reported. However effective differences may exist in the same value.

KODAK, however, developed a new index for print film since the relative affect of print film is noticeable more in the actual print than in the negative. The scale is called a Print Grain Index. According to KODAK:

Film of Choice

Since KODAK Pro 400 MC film is the recommended standard for photoenforcement, the following technical information has been extracted from the KODAK web site. Please consult the KODAK web site or your KODAK representative for additional and / or more current information regarding KODAK Pro 400 and other KODAK films:

KODAK Pro 400 MC Film / PMC is a high speed color negative film that features moderate color saturation and contrast, and wide exposure latitude. Its color and flesh-tone reproduction characteristics are similar to those of KODAK Varicolor III Professional Film / VPS.

 

KODAK Pro 400 Film / PPF is a high speed color negative film that features high color saturation and wide exposure latitude. It is designed for situations that have uncontrolled, low-contrast lighting.

NOTICE: The sensitometric curves and data in this publication represent product tested under the conditions of exposure and processing specified. They are representative of production coatings, and therefore do not apply directly to a particular box or roll of photographic material. They do not represent standards or specifications that must be met by Eastman KODAK Company. The company reserves the right to change and improve product characteristics at any time. E-182, February 1997

35mm IR, UV, and Alternative Film

According to WJ's photo homepage, some IR films may be useful for specific applications: Ilford SFX200/SP815/816T and Agfa APX200S

The Photography Center contains information and links a variety of photographic topics.  Two examples include:

THE AFFECT OF TEMPERATURE ON FILM

The 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 STORAGE

As 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 Storage

Unprocessed Film Storage

Whether 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 Storage

Processed 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.

LIGHTING

Light 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 INTENSITY

The 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 ANGLE

A 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.

LENSES

According 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 LENGTH

The 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-VIEW

The 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.

FILTERS

Photographic 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 TECHNOLOGY

CCD 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 CAMERAS

by Michael D. McCreary
Director of Operations, Microelectronics Division
Eastman Kodak

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?

Regardless of the method used to capture a violation, it is still necessary to convert the image of a violation to a form that a computer can use: digital. With film-based systems, film must be exposed, developed, scanned, digitized, and stored on a computer in digital form.

CCD cameras eliminate most of these steps. In addition, a digitized image can be sent electronically from the point of capture to a processing center by way of telephone, cellular phone, FM signal, or satellite eliminating the need (and danger) of manually retrieving film and reducing the time required to issue a citation.

But the growth of digital cameras is also guided by economic reasons as Hedgecoe writes:

"A replacement for silver-based image recording is inevitable. Silver is an increasingly rare and thus increasingly more expensive resource, and the film industry uses millions of ounces a year. Video is an attractive option, especially since more of the technology is already in place because of the popularity of video cameras and recorders. Another feature of digitized images is that they can be transmitted down normal telephone lines, even computer-to-computer with the help of a modem, making them of vital interest to the news gathering industry. On the minus side, at present, no matter how sensitive the CCD within the camera, it cannot compare with the literally millions of 'image grabbing' surfaces of the silver-halide grains that are present in traditional camera film." (Hedgecoe 24)

And 1998 may be the year. In a news story in EE Times, 03/03/98, By Margaret Ryan writes:

Digital Cameras Expect Big Exposure In '98

With more than 100 different digital-camera models offering improved image quality, ease of use, and cheaper prices than older designs, the market for digital cameras is poised for explosive growth in 1998.

Forecasts for worldwide shipments of digital cameras hover between 3.8 million to 5.3 million units for 1998. One long-term prediction from researcher Frost & Sullivan, in Mountain View, Calif., expects the United States market to reach 2,357,800 units and $478.1 million in revenue by 2000.

Jonathan Cassell, senior industry analyst of the semiconductor-applications program at Dataquest, in San Jose, Calif., said he believes 1998 will be the biggest year -- "a barn-burner" -- in terms of unit production of digital cameras. Cassell said he projects 5.377 million digital-camera units will be produced worldwide in 1998, more than double the 2.089 million units produced in 1997.

Surge To Come From Businesses, Not Consumers

The growth will mostly come from business users, rather than consumers, according to market researchers. That's primarily because business users have a compelling reason to buy digital cameras: They need digital images that can be manipulated for inclusion into computer databases, presentations, and Web pages. There's nothing to compel consumers yet. Nevertheless, consumer acceptance of the devices is increasing, analysts said.

What may entice consumers to purchase digital cameras is the introduction of higher-resolution mega-pixel cameras this year. In 1998, digital cameras will move beyond Video Graphics Array (VGA) resolution (which is not adequate for applications, especially photo prints) to devices that produce images closer to photo-print quality.

At the same time, there will be a glut of VGA 640 x 480 basic point-and-shoot cameras on the market, and prices of those cameras are expected to drop to less than $200 by midyear. Prices of these VGA digital cameras are likely to drop once Complementary Metal Oxide Semiconductor (CMOS) sensors replace charge-coupled devices (CCD), which captures the image, in digital cameras this year. CMOS sensors offer the potential for lower power consumption and greater chip integration for digital cameras going forward.

The main manufacturers of digital cameras for the consumer market include Casio, Dycam, Eastman Kodak, Fuji Photo Film USA, Olympus, and Canon.

There are also a host of consumer-electronics company participants including Sony and Samsung. Other competitors making and selling digital cameras include Agfa Division Bayer, Apple, Canon Computer Systems, Chinon America, Epson America, Logitech, Nikon, Olympus America, Ricoh, Ritz Camera Centers (Ritz sells a camera made by Chinon), and Sanyo Fisher.

There are also a host of companies that design and manufacture chips for the cameras, such as Analog Devices, 8x8, LSI Logic, and companies that design and sell photo-editing software. Adding to the long list of players are companies that produce digital desktop cameras including Connectix, Pixera, StarDot Technologies, and Vivitar.

In addition to all those players, Ron Tussy of International Data said a number of Taiwanese companies jumped into the market this year.

Something's got to give this year with more than 45 vendors and more than 100 digital-camera models, price erosion, and product life spans shrinking from one year to six months in 1998. Companies will find it difficult to make a profit (as they have for the past two years) on digital cameras, and some players are likely to exit this year.

A San Jose, Calif.-based hardware-software company called Flashpoint ... believes the intelligence is in the camera in the form of Flashpoint's Digita software. The cameras are complex with LCDs and infrared radiation capability for connections between camera and printer, camera and camera, and camera and computer. Motorola allied with Flashpoint, while camera makers Kodak, Sharp, and Minolta committed to building Digita software into their cameras.

In addition to buying trends, technology trends will drive the market for digital cameras. The introduction of CMOS sensors to replace CCDs will enable lower-cost, lower-power consumption and greater integration of the circuitry of digital cameras.

The use of CMOS sensors will allow more chip makers to expand into the digital cameras and that will drive prices of cameras down even further.

CCD TECHNOLOGY

While current technology limits the use of digital cameras to enforcement of one to two lanes of traffic, rapid development in CCD technology is likely to continue and digital cameras will vie with film based systems for use in law enforcement. Many agencies are already using digital cameras for many forensic activities. For a description of some of the uses, see Digitizing the Law.

There are two types of CCD cameras in use today in automated law enforcement: analog and digital. Most of us are familiar with analog video cameras. These are the NTSC/PAL analog cameras which have been in wide use for many years by consumers and are often referred to as camcorders or videocams. These video cameras record analog signals (usually NTSC or PAL) on moving magnetic tape.

In August 24, 1981 the first still frame camera was introduced by Sony. Called the MAVICA, an acronym for magnetic video camera (Larish 3), it was an analog NTSC/PAL type system which recorded its captured images on 2-inch video floppy disk.

It wasn't until the fall of 1988 that the first digital still camera was released by Fuji. It used an 8-bit/color, 400,000 pixel CCD sensor combined with a fixed focus 16mm lens with a 1/60 to 1/2000 electronic shutter and storing captured images on an S-RAM card. (Larish 44).

In 1998,IMAGEK introduced an adaptor for standard 35mm cameras that converts them to digital. The company claims that:

CCD CAMERA REQUIREMENTS

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:

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 system’s 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.

 Resolution

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:

He further identifies a new class: Mega-resolution with 1,000 x 1,000 Pixels and above. (Erickson 3)

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.

Storage of Digital Images        

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.

File Size

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.

          FS=HW(R2)B

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

Compression

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