digital image capture — filmless camera technology and techniques

Digital image capture - Filmless technology and techniques

camera

A Kazhuciunas

Department of Colour and Polymer Chemist ,ry, University of Leeds, Leeds> LS2 9]T, United Kingdom

Keywords Cr!a!ge-CoL~p!ec! sen,icunducbl de'riLL, L.orr!p!c!rT!entary metal oxide somicondiidol, Jdotosensm; a'ra- iog'e to digital converte ~. rroi!e fdrgi'rg, onotodJo6e.

l lazlauciunas

Department o f. CoJour and Poi},mer Chemist!-} UniversiT}, of Leeds, leeds, iS? 9Jh United Kirigdom

Tel: +44 (0) ! I 3 243 175! EmaJi: aig)q<[email protected] Fax: 4 4 (0} 113 233 2947

Copyright OCCA 2006

Summaries Digital image capture - Filmless camera te@noaogy and techniques l he cAoJtai imaging re,,olutionn conti-lues apace, aPecting thL whole spectl uF~ of thL photograp"li~: ~ndus- t! ~' in mawr7 pats el tale warld dJgiial camq as row ou!sei! cor ~'entional tJlm cameras and man,/or t~e dis.. advantages assocJaied ~#i!l-- digital image capture in the very recent past ~,~ have bee', nullified

As tne dJgitai i'rdustr}/grows, the va~ Jous tech'roiogies in~'ol,.ed continue to be evm i'rnovaHve gii~I respect to digJta! cameras, the i-age sensor perbrmance criteria have imp~ eyed immeasuraksi) since the iai-nch of !ne rirst soil,u-state camela in the ea~ i b' 1980s l.re cnarge-coupJed semJconcuctor ~se,;ice (CCD), for so long !he unrivalled image capture compor-ent in digital cameras, is 'row being challenged t.,}, compbren!arj rne!ai oxioe seqconductor ',OMOS) tecr-no!ogy and !i-~e Jr-'rova!iveiy re designee F-jJfilm Supra COD In addition, !ne recent introduc!ion of t~e Foveon full co!our imaging sensor ,,as added a 'rew dime'rsion to digital image capture.

This paper reviews current image capture sensors and the wa.ythat t~ie val Jous cjigJtaJ imaging camera desig'rs are able to record ar-o reproouce colour images.

Techniques et technologie de I'appareil sans pellicule et a ~apteur d'image numer i que La r@vohJtlon provoqu~;e pa rirnagerie numerique devie,rt de plus en plus importante eta Line infiuer-ce sLir le specire e,'-tier de i'induSrie p'stographJque. Ii y a beaucoup d'erdroits dar!s le monde o8 !'on vend plus d'appareils photo num~'riques que d'appareils photo de traditior, et beaucoup des inconvenients quJ e!aient reiaiifs s !a calature d'irJage nume~ ique da'rs le passe recent ont eta" supp~ lines.

Au fur e~ 8 lresure que i'Jndustrie pholographlque s'accrst, les piusieurs technologies relatives coniin uent d e e de plus er plus innovatrJces Quant aux appareiis p!--ore num6riques, les critbres de ia per formance du capteur d'Jrnage ont an4iior@ infinJment depuis le laneement du premier appareii photo 8 serrli-conducteurs tO! darts ies annces 80. l e disposJti[ a tlansfm! de crarges (CCD), depi-is si longtemps ie composan! sans pareii en ce qui concer're ia capture d'image, eat rernis en queslion par la bchnoiogie dis r"~al-oxyde-semi-co'rducieul complemen!aire (CMOS) el pa! ie Fidifilrn Super CDD qui a ca@ repens~ d'une manibre !r@s ir-novatrice En plus. l'i,ntroductlon r@cente du capieur Foveon pour image couieur a a~oui@ une nouveiie dlrne,rsion 8 ia capture d'i ~qage num@rique

Ce[ a! !icle exalt Jne ies caAeul s d'il]]age coul a'r[s aussi bien qLie ia fa6ou dent lea plusJeul s conceptions d'appm eils photo a imag8 ie nL4m el ique sent capables d'e,r! egisirer et de I epl oduire des images en couieul

Digitale Fotografie - Technolegie und Technik tier film-lesen Kamera Die digitale Revolution geht welter vora'r und hat dan ganze S:,ektrum der fotografischen indL~strie ergriff en in vieien -mien tier Welt we,rden heute m eir digJtale Kameras dis kort/e'rtioneiie Flimkamerasverkauft, und viele der a,'raengiichen @cr-teiie der digJiaien Bilderfassung besteher- heuie nic~it mehr.

Viele lrnovalio,re,r tleiben die Digitaiindugl ie reran. Bei Digi!alkainsas Plat sich die Biidse'rso! ieigung yon den erster- Modeiien in clef fruehen 80er Jahren enorm entwicicelt Die Charge coupled Device (CCD), so iange der unangefochtene KOnig der digitalen Bilderfassung, laek.ormrt heute yon kompiime~:aren Met alloxidhalbleitern (CMOS) und yon der innovativ reu eg:wJckeiten FL~ifi!m Super CCD Konkurrerz Dazu "ia[ die Fir%'hung des Form on Voiifarbbiidsensors dm Digita!fotoglarJe eine neue Dime,rsion veriiehen.

Diese Arbeit vergleicht die gegenw;Jrtigen Biider'~..ssungssensoren, und wie verschiede,re Digitalkam era Varianien Farbbiider aurr-ei-lmen und wiedergeben

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I n t r o d u c t i o n Although electronic imaging is perceived to be an invention of the modern age, its origins date back to the 1930s, when allegedly the very first colour photo graph to be electronically transmitted was a studio portrait of the legenda U silent movie star of that age, Rudolph Valentino2 The image was taken on the set of the film Monsteux gess and three separations of the image (ie red, yellow and blue) were sent from Chica- go to New York using the telephone lines of the Bell Telephone Company, Once transmitted, a three-colour reproduction was generated,

The general notion of utilising a charge coupled semiconductor device (CCD) as the image capture component lbr a solid state camera was the brainchild of William Boyle and George Smith in 1972, who were employed by Bell Sys terns in the USA, 4 As recognition for the invention and development of the CCD, a contribution that has had a major impact on image creation and utilisa- tion, Boyle and Smith were awarded the Edwdn H Land Medal by the Societ 7 of Imaging Science and Technology in 2001 .s

Filmless canera technology took the best part of a decade to emerge, "when Sony introduced their MA\qCA still cam era to the world at Plhotokina in Ger many in 1981. ~ Although this camera utilised the CCD device as the image sensor, it was not a digital camera, and used the same techno[o~' being utiiised for non-digital motion picture video cameras. The first professional digital single lens reflex camera (DSLR) was ulti- mately launched by Kodak in 1991, namely the DCS IOOF

S e n s o r t e c h n o l o g y

C h a r g e c o u p l e d s e m i c o n d u c t o r (CCD)

The charge coupled semiconductor device has bee:n the dorninant imaging sensor since the introduction of solid- state still cameras in the 1980s, Vvhen image quality is measured with respect to quanttan effidency and noise levels alone, the CCD could not be surpassed, These sensor ~-pes tend to be utilised within areas where image capture of the highest quality is demanded (eg medical, scientific and industrial).

The CCD consists of a molecular layer of dielectric silicon dioxide deposited onto a p b'pe silicon substrate. When light enters the silicon substrate at individual photosites, it provides sufficient ener~,

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Figure 1: The basic working principle of photosites on a CCD sensor

Table 1: Peffom|ance comparison between CCD arid CMOS image sensor technologies

Performance Oharqe c o u p l e d Oomplementary metal oxide ~emiconductor device (OCD) semiconductor (CMOS)

Respor~sivity Moderate Oyna~~ic ~ange High Uni%mii}, High Speed Moderate "o high Biasing Muiripie U!]JLOl-lrl shuttering Fast, commor-

to release negatively charged electrons from the silicon atoms in the substrate. By applying a positive electrical field, the negative charges can be drained to the substrate. Each photosite has an electri col contact, referred to as a gate, ~ d when a voltage is applied to this gate, an area of silicon becomes receptive to the freed electrons, These negatively charged electrons are then stored in pro- portion to the intensity of light encoun- tered. The charge on the photosite is then moved onto a shift register and read. Finally, the variable analogue si@tal is sampled and quantised as a discrete series of steps in the form of a grey scale via an analogue to digital (A,�9 convert er. Figure 1 illustrates, in simple temps, the basic ,a.orking principle of photosites on a CCD sensor.

Complementary metal oxide s e m i c o n d u c t o r (CMOS)

Cornplementa U metal oxide semicon ductor circuits were invented by Dank Wanlass of Fairchild Semiconductor, ~ v~ith the first CMOS integrated circuits being introduced by RCA, Not tmlike the CCD, the CMOS imaging sensor also converts light :into an electrical charge

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and then processes it into electronic Big :rials. However; mflike the CCD sensog each pixel is independent of its neigh bouL resulting in random access to each individual pixel by means of an XY address. There is also present an ampli tier at each of the pixel positions consist ing of three transistors utilising C_,MOS technology, This amplification at the pixel level results in a ntm~ber of key advantages over conventional CCD technology, namely lower power con- sumption at the chip level and built-in analogue-to-digital conversion, Table 1 Ibatures a performance comparison between conventional CCD and CMOS image sensors.

kk[)ifilm s u p e r C C D

The initial version of the Fujifilm Super CCD was introduced in 19997 with the present-day fourth generation version now being incorporated into cun'ent ~ujifilm cameras, including their flagslhip digital single lens reflex (DSLR) model, the $3 Pro Fujifilm, having overcome the limitations associated with the convert tional CCD rectangular array by re designing both the shape and the layout of the photo@odes in their proprieta U

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Figure 2: A comparison of the octagonal geometry of the Super CCD and the rectangular geometry of the conventional CCD design

Figure 3: Diagram illustrating the similarity between the working principle oF the Super CCD and modern-day film

Super CCD. A compmison between the octagonal geometry of the Super CCD and the conventional CCD design is illustrated in Figure 2,

A key advantage of the octagonal geometry is that it enables microscopic electronic contact areas to be greatly reduced, and as a consequence, results in individual photosensors being greater in size than would be possible in a con ventional CCD rectangular geometry design. The key benefit of the Super CCD design is a marked reduction in the level of noise.

A major hindrance associated with the octagonal geometry, however, is that images are required to be generated in standard fom~ats such as JPEC (joint photographic expert group) and TIFF

(tagged image file forma0, and these require the intage to be formed of pixels within a rectangular geomet G, The proprietary design of the Super CCD cir- cumnavigates this requirement by using interpolation to achieve a rectangular geomet U double the size of the octagonal geometry of the sensor, This results in the Super CCD having a resolution that is twice that of the actual nmnber of photosensors present on the imaging chip. The general consensus of opinion from within the imaging cornmuni%, is that the octagonal geomet U design has only improved resolution on vertical and horizontal lines and not on diagonal lines.

The design of the current fourth-generation Super CCD lends itself to working

along the lines of modem-day photographic film, The photosensitive component of film (ie silver halide emulsion) contains large surface area grains specifically sensitive to low light levels, togeth er ~ith small surface area grains that are specifically sensitive to high light levels. The current Super CCD mimics film by :mixing low sensiHvib, pixeh, referred to as R pixels, together with high sensitivity pixels, referred to as S pixels. When an :image is being recorded, the high sensitivity pixels are rapidly saturated by the incoming light, whereas the low sensitiv- it? pixels achieve saturation at a much reduced rate, Thus, whereas the S-pixels become quickly saturated in the highlight area of an image, the R-pixels continue to gather light ~ithout achieving over saturation. B~, means of combining both sets of image detail, the principal gain is a wider dynamic range, which leads to highlight and shadow detail, :more natural sMn tones, richer tonality, and better texture rendering in both black emd white fabrics. Figure 3 demon strates the similarity between the work ing principle of the Super CCD and modem-day photographic film,

Foveon X3 CMOS full-colour ~mag ing s e n s o r

This proprietary device, ~ which is a lay- ered silicon sensor fabricated on a standard CMOS processing line, is the first full-colour imaging sensor to be incorporated into commercially-available DSLRs (Sigma SD9 and Sigma SD10), although other research groups are ago working towards this end. !~ ~4

The essential working principle of the sensor relies upon the fact that different wavelengths of light penetrate to differ ent depths ~adthin the silicon surface, However, although the sensor is por- trayed as absorbing only blue light at the upper surface, green light within the central region and red light within the lower region, this is an over simplifica- tion, Figure 4 illustrates the basic working principle of the sensor, whereby three separate PN (positive negative) junctions are incorporated at specific depths within @e silicon surface and u@ised to separate the electron hole pairs that are generated by the silicon. [n reality, a mixture of colours is detected by each sensor layer and algorithms are applied during the processing to corn pensate for the overlap of the spectral sensitivity bands,

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Figure 4: Diagram [[lustratirlg the working principle of the Foveon tull colour imaging sol /sot

the analogue-to-digital (A/D) converter. It should be stated at this juncture that for CMOS sensors, the process is achieved within the architecture of the sensor itself.

The maximurn number of grey levels supported by most image handling applications on a computer workstation is 256, and eight binary digits (bits) are required to enumerate 256 grey levels. floweret, the majority of digital camera analogue-to-digital converters tend to convert into I0, 12 or 14 grey levels, This capability; reDrred to as 'supersam- piing', has the desired effect of improv- ing image quality,, Pixels in an RCB image require art eight-bit number for each of the three colour charnels, offer ing a gamut of nearly I 7 million colours ,fie 256 x 256 x 256). The resulting 24 bit file occupies three times the space of

Digital camera classification/colom' capture and reproduction methodology When light is converted into electrical potential during image capture by CCD or CMOS imaging sensors, no recogni tion is extended to the colour of the light. Thus, without modification, all CCD and CMOS sensors, with the exception of the Foveon CMOS type, are essentially monochrome devices.

In essence, there are six distinct design t)ges of image-capture methodology associated ~r the digital caraera?

One-shot single matrix This b,pe of design (see Figure 5), which is commonly found in all point and shoot and high end DSLR cameras, involves a colour filter array being into grated into a monochrome CCD/CMOS chip using photolithographic techniques to pattern the red, green and blue dye mordar~ts. Normally, the Bayer ~ che- quer-board pattern is used, where there are twice as many green elements com- pared with the red and blue elements, This design feature is included so that the sensor can mimic the hmnan visual system, which is more sensitive to high spacial frequencies in luminance, which is composed primarily of green light, than in chrominance. ~r ~t~e Bayer colour filter array, or 'rr~ask', thus enables con trol of the incoming light using the addi tire principle of colour reproduction,

The interesting feature of this pa.rt[cular method of image capture and reproduc-- tion is that it mimics the design features of the many regular patterned screen--

plates invented during the early days of additive colour photography.~r Although almost all one shot single matrix digital cameras use the RCB (red, green, blue} additive principle to achieve co]our imaging, Kodak have utilised the sub tractive method to record digital images (ie using cyan, magenta ax~d yellow (CMY) filtration), Such an example is the professional grade DCS 620X DSLR. Fob lowing initial negative image capture in CM~ the data are then converted to a positive RGB image to maintain compat- ibility with standard digital architecture.

'1o create a digital image, the analogue charge generated by CCD elements m~dergoes quantisation, whereby each step is assigned a unique bina U number, which represents a specific tone or grey level. The process itself is tmdertaken by

@e monochrome image. At 24 bits per pixel, digital files represent images pho torealisticall2/~ and if a file is greater than 24 bits per pixel, a high percentage of software will utflise the extra information by determining which colours in the largest set most frequently appear, and then use the dominant colours when the data are sampled down to 24-bits5 ~'

1'he obvious advantage of the one-shot single matrix type of camera design is that the image is captured at equivalent speeds to standard film cameras. How ever, the principal drawback is that soft ware interpolation is essential due to only one colour being recorded at each individual pixel site. This, of course, means that all missing colours have to be :filled in, which tmfortunately can lead to Moir~ fringing in areas of a~ image which contain detailed colour patterns, ~s

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A further negative aspect associated with this camera design is the fact that there are only a limited number of dyes that can be utilised for the Bayer colour filter array This places a restriction on the extent of the colour gamut range that is achievable,

TDee-shot single matrix This camera design (see Figure 6) does not have a Bayer filter array integrated into the sensor, It therefore works by capturing colour on a fully monochrome

chip using the same principle of photographic colour separation as initially demonstrated by James Clerk MaxwelP r in 1861 and utilised in the reprographics induct U for a good number of years. This involves capturing three mono chrome images of a subject through individual red, green and blue filters incmporated within a spinning filter >/heel, with every pixel of the image sensor providing sequential red, green and blue readings, This, of course means that maximum resolution of the chip is achieved without recourse to

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Figure 7: Schematic diagram of the one shot triple matrix camera design

interpolation, Other notable advantages of such a design over the one-shot single matrix system are more accurate colour capture, a larger colour gamut, less elec-- tronic noise, and a superior dynamic range. The key disadvantage is that the design cannot be used to photograph moving objects, and therelbre in all practical sense is purely a studio based system.

One-shot triple matrix This design (see Figure 7) uses three individual monochrome sensors within the camera, and with the aid of prisms, or semi reflective mirrors, divides the incoming light that enters through the lens, so that the red fikered, green fil tered and blue filtered sensors all record the image simultaneously This image capture methodology has been employed in some of Minoka's digital cameras, including the liD 3000. The design was initially developed for high- quality professional video cameras and demands high-precision engineering to achieve the desired image quality,

�9 a,o digital arrangements have been utilised with respect to the matrix con figuration. The first arrm~gement involves each monochrome matrix registering only one individual RGB component (as in Figure 8). in the second arrangement, two of the three matrix arrays are set to register green, while the third matrix contains an integrated red and blue mosaic filter, As stated previously, the arrangement is used to mimic the human visual response system, ~s In this particular arrangement, the two green registering matrix arrays are offset from one another by as little as half a pixel to enable increased resolution within the green channel. Interpolation is then used to fill in the gaps with respect to the reduced red blue information.

The key advantage of the one shot triple matrix design over the one-shot single matrix equivalent is that there is either no requirement to use adjacent pixel cobur interpolation (for matrix arrangement one), or only a limited requirement (for matrix arrangement two), This, of course, means that the resolution will be superior and Moir4 fringing far less noticeable. There are disadvantages, however, wifl~ this design type. The first is, as mentioned previousls that high precision engineering is required to enable the design to be fully f,anctional. Other disadvantages include the addi tional cost involved in employing three sensors as opposed to a single sensor, together with the logistics of housing such a system within the camera body,

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Scanning trilinear array This bge of image capture design is associated with digital camera backs which are intended to be attached to specific medimn and large {brmat film cameras. The design is essentially an adaptation of well established line scan ning technology, initially developed for flatbed digital scanners2 ~

Three parallel linear array CCD elements are coated individually with RGB filters, Then by means of a stepper motor turn- ing a metal screw, the trflinear array is moved across the image plane, At each individual stage of the move, readings are recorded for the three individual arrays. Although the design generates high resolution image files, it is essential that daylight, or a continuous light source, is used. Typically hydrargyr~n medium arc length iodide (HMI) is rec ommended because @is produces the necessary daylight balanced output and lighting power required, This is because this type of camera design normally requires several seconds, or even min-- utes, to achieve exposure. Thus, the illumination must not change during the duration of the exposure, If it did, the resulting image would contain the b, pe of flaw generally associated with using strobe lighting out of synchronisation on a [bca] plane shutter camera (ie only one section of the image would show the illumination change).

Due to the fact that each of the CCD elements records its own individual colour in creating the RGB file, the end result is more accurate colour quality; allied to a larger eolour gmnut, The use of scanning trilinear array digital backs in tandem with large-- and medium-format film cameras tends to occur in photographic studios associated with very high quality advertising assignments. Additionalls a further user group would be repro houses involved in photograph ing art reproductions, or in the creation of high resolution files for ve U N~e digi tal fiat copy work (eg maps and architec turn] drawing applications), A schematic diagram illustrating the basic working principle of the scanning trilinear array design is show~ in E[gure 8,

Multi-shot single matrix (with whole-element shiR) This camera design is associated with being coupled to large-format film cameras and works either in a single-shot mode or a four-shot mode, Thus, the benefit of such a design is that the camera is essentially multifunctional. If resolution and colour accuracy need to be

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increased, then the four-shot mode can be utilised. Here this is done by shifting the position of the array; or the light beam, after each individual reading, Positioning of the array, or light beam, is carded out by means of piezo motors, which are capable of both x and y shifts to an accuracy of atom@ 1 O0 nanolne tres. This methodology allows RGB ele merits to tmdertake readings if'ore iden tical image positions, thereby avoiding the requirement for colour interpolation, 1b get the best out of such a design, it is essential that high-resolution lenses are

used with this system. It has been recog- nised that piezo motors are prone to non-linearly, which has the effect of creating artefacts within the digital image, ]b some degree, this can be offset by uJadertaking regular calibration of the camera using propose designed soft ware. A schematic diagram of a multi shot single matrix, with whole element shift, canera design, is illustrated in Fig ure 9.

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Figure 8: A schematic diagram of the basic working principle of the scanning trilinear array camera back design

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Figure 9: Schematic diagram of a multi-shot single matrix, with whole-element shift, camera design

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Figure 10: Schematic diagram 0f a multi-shot single design

Multi-shot single matrix 2.

(with sub-e lement shift) This camera design (see Figure 10) is often seen as a direct alternative to the one-shot, triple-matrix system, whereby 3, full-matrix resolution is obtained with a single array. 'I-b achieve this, the array is moved three to four times by the full 4. width of a pixel, which allows the gaps in the RGB information to be filled with- 5. out recourse to software interpolation. When operated in this manner, the cam 6. era can only be used for stationary sub jects, albeit recorded at a high resolu lion. However, if used in a one shot 7. matrix mode, moving subjects can be captured, with the downside being a reduced image resolution and recourse 8. to software interpolation to enable the missing colour information to be filled- in.

9.

Conclusions This paper introduces some of the key historical l~ctors that have enabled the rapid growth of filmless camera technol ogy and techniques. In addition, it gives an overview of image sensor technology' together with digital camera classifica- lion, with parlicular attention to colour image capture and reproduction.

10.

11.

References 12, 1. Kazlauciunas A, 'Digital imaging ver-

sus silver halide - schism or the per- fect marriage?', ~\dvances in Co~o~ 13. Science a~d q2eehuo~o W , 4~ (3)~ 68 75, 2001

maliix, with sub-element shift, camera

MacDonald L W, Colou~ !magtr%: N~gto;t and ~ec?nnologj, (eds) L W MacDonald M R Luo, 195 6~ John Wiley & Sons~ 1999~ ISBN 0 471 98531 7

.Hamber S and P Green~ D~g~t~_1 PhotL%ra.ph~ ~, 33, Pira international and BPIE 1999, ISBN 185802-207X w-a,~v.physorg, corn/news9590, html (site checked 3/5/06) G ax;d ~[ Reporte~_~ lg~ (2)~ 6 7~ April 2001 Coote j fI, q2he ~t~ust~_ated IIistor? d Co!~ou~ Photovapb_~f, 231, Fountain Press, 1993, ISBN 0-863-43380-4

-[arrant J, rDigita~ C~zmera ~ecb:d~ques, 6, Focal Press, 2003, iSBN 0-240--51087-7 VVanlass E 'Low stand by power conrplementaq field effect circuit U', US Patent 3~356~85& 18th June 1963 Kazlauciunas A, <Digital imaging - Theory and application, Part I: Theory', S~a~e CoaOGs lotevna*ion~c Co~2dpGs '12~ an.sactte;c~s, 84, (B1), 1 9, Janua U 2001 Merrill R B, 'Colour separation in an active pixe[ cell imaging array using a triple well structure' US Patent 5,965,875, 12th October 1999 Nozaki H and T Adachi, 'Color sen- sot', US Patent 4,677,289, 30th June 1987 Gray C F and R D Wieting, '\Jertically integrated solid state co[our imager' US Patent 4,581625, 8th April 1986 Chouikha M B, G N Lu, M Sejil and G Sou, 'Photodetector based on

buried junctions and corresponding method of manufacture', US Patent 5,883,421, 16th March 1999

14. Stannowski B, H Stiebig, D Knipp and H Wagner, 'Amorphous silicon based unipolar detector for color recognition', GEE '~ an_.-,~.ct%t~s on ~ect.t-eff~c De:v~ces, 46, (5), 884, 1999

I5. Bayer B, 'Colour imaging array', US Patent 3,971,065, 20th july 1976

I6. Walker P, Handbook of ~'b~tc;gr~ff/~c ~dence ~n4_ Et:~ne.e~tng, (2rid edition)~ 141 3~ (ed) C N ProudfooL Society for Imaging Science and I~ch, 1997~ ISBN 0 471 81880 l

I7. Kazlauciunas A, Colo~ lPo_otogv_apS-j -- ~ast, Pr esem;t and ~ut~e, 1-3, Oil & Colour Chemists Association, 1996, ISBN 0-903-80925--7

18. de Roeck D and M Peeters, Ehe %cm~.-, el Colouv Ma~z~geme~tJ D~gtt.~ Coleus -t~epmss, 5~ 14, Agfa Gevaert N~V , 1997

19. Kasai A and R Sparkman, Essenttgts cff D~g~1 ~%o~o~4aph:y, 5-17, New Riders, 1997, ISBN 1-562-05762-6

20. Evening M, Adobe ~%otoshep CS ~o, ~hotog~phers, 337, Focal Press~ 2004~ISBN 0 240 51942 6

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digital image capture — filmless camera technology and techniques

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