GB2398698A - Optical scanner directing light on middle of image sensor - Google Patents

Abstract

In a scanning imaging device, the exposure periods of respective image sensors are controlled to be variable (e.g. see Figure 4) such that different colours or frequency bands may be integrated over variable time periods by corresponding image sensors in an array. By suitable movement of the scanning head 500 and control by a exposure controller 520, scanning is performed such that, at the midpoint of an exposure time period (e.g. point 440 in Figure 4), light from a point 560 in the scene is incident on the centre or midpoint of the respective image detector or photosensor 511, 512, 513. Separation of light into different colours may be by means of beam splitting lens 515 or, as shown in Figure 5B, the beamsplitter may be omitted, requiring colour filters.

Description

EXPOSIJE T1G ALIGNMENT FOR COLOR SPEc IC EXPOS ORE TOES

FIELD OF THE VENTION

The present invention relates generally to optical detection and, more particularly, to optica! scanners used in the creation of color images.

BACKGROUND OF THE INVENTION

Traditionally stepper motors that move in discreet steps have been used with linear image sensors in optical scanners such as are used, for example, in flatbed scanners, film scanners, and copiers, and certain digital cameras to capture images. Recently DC motors have replaced stepper motors in such devices in order to obtain increased positional accuracy in scanning, to increase scanning speed, and to reduce cost. Images are obtained via either reflected light as in the case of photographs and paper documents or transmitted light as in the case of transparencies, film negatives, and photographic slides.

One of the most popular image sensor technologies is that of chargecoupled devices (CCDs). Depending upon the application, accurate color reproduction by image sensors may pose special problems, as the intensity ofthe optical signal detected by color image sensors is dependent upon wavelength Both the output intensity of light sources and the detection efficiency of detectors typically used in such systems are wavelength dependent. in addition, the transmission characteristics of transparent media is in general strongly wavelength dependent.

Pillages Containing creator are usually created by separating and detecting the image signal in three separate color bands which could be, for example, the red, green, and blue color bands. The use of different amplification gains fir each cuff the three color signals :0 detected could be used to compensate for the combined color dependency of the image creation system. l Iowever, as transparent media is strongly absorbing. especially in the blue color band, this solution may not produce an acceptable result due to noise in low signal level cases.

An alternative technique is to detect the optical signal in the green color band for longer than in the red color band and even longer in the blue color band. An acceptable result is obtainable for those cases wherein the scanning movement is stopped during the exposure, as for example when stepper motors are used. However, when movement of the image sensor occurs relative to the object during the scan, as for example with the use of DC motors, a rainbow effect is often observed caused by misalignment of the areas detected. In other words, the center of the area from which a blue signal is received is different from that from which a green signal is received and is different from that from which a red signal is received. In which case, an unacceptable image can result.

SUMMARY OF THE INVENTION

In representative embodiments, an optical scanning system is disclosed which comprises at least one first photosensitive detector that is sensitive to light in a first frequency band, an exposure control circuit that is capable of exposing the first photosensitive detector for a first time period and at least one second photosensitive detector that is sensitive to light in a second frequency band. The second photosensitive detector is fixed at a first location relative to the first photosensitive detector. The exposure control circuit is capable of exposing the second photosensitive detector for a second time period with the second time period being longer than the first time period and the midpoint of the first time period occurring at a time proximate to the time of the midpoint of the second time period.

Other aspects and advantages ofthe present invention will become apparent from ibe following deiai;cd descripiiol, taken in conj unction with the accompanying drawings, iiustrating by way of example the principles of the invention.

BP3F DESCP31PTION OF THE DRAWINGS The accompanying drawings provide visual representations which will be used to more fully describe the invention and can be used by those skilled in the art to better understand it and its inherent advantages. In these drawings, like reference numerals identify corresponding elements Figure I is a graph of idealized frequency detection band vs. frequency.

Figure 2 is a graph of an exposure timing alignment scheme for colorspecific exposure times.

Figure 3 is another graph of an exposure timing alignment scheme for color specific exposure times.

Figure a is a graph of Art embodiment of an exposure tim.i=.g alignment scheme flier color-specific exposure times consistent with the teachings of the invention.

Figure SA is a simplified block diagram of an embodiment of an optical scanning I S system consistent with the teachings of the invention.

Figure SB is another simplified block diagram of the optical scanning system of Figure SA.

Figure 6 is a simplified block drawing of an embodiment of an image sensor consistent with the teachings of the invention.

Figure 7A is a simplified block drawing that includes the image sensor of Figure 6 front a different viewpoint with other components of the optical system.

Figure 7B is another simplified block drawing that includes the image sensor of Figure 6 from a different viewpoint with other components of the optical system.

Figure 7C is yet ar,other simplified block drawing that includes the image sensor of Figure 6 from a different viewpoint with other components of the optical system, Figure 8 is a drawing of a flow chart of an embodiment of a method for exposing the photosensitive detectors consistent with the teachings of the invention.

DETAILED DESCRIPTION OF THE PREFEI(F.I) EMBODIMENTS In Me following detailed description and in the several figures ofthe drawings, like elements are identif ed with like reference numerals.

Color images are captured by flatbed scampers, film scanners, copiers, certain digital cameras and other image detection devices by detecting the intensity of the image signal for selected bands of frequencies. When performing transparency scans, it is desirable to have different exposure times for each color channel as the color absorption characteristics of the transparent media can pose signal-to-noise difficulties in accurately detecting and recreating the image. However, different exposure times for each color channel can result in positional color misalignment in continuous motions systems, as for example those that use DC motors to move the object being scanned relative to the image sensing device. The result can be an image displaying a rainbow effect with the center of the Thee colors lo, my given ixci being displaced dehorn the others.

Figure I is a graph of idealized frequency detection band 105 vs. frequency 110.

In Figure 1, the intensity of the image is detected in a first frequency band 121 which could be, for example, a red frequency bend 121 which is used to detect the red color in the image, a second frequency band 122 which could be, for example, a green frequency band 122 which is useu' to detect the green color in the image, and a third frequency band 123 which could be, for example, a blue frequency band 123 which is used to detect the blue color in the image. One of ordinary skill in the art will recognize that Figure I is an idealized graph. In practical embodiments the red, green, and blue frequency bands |71,177,17] '7!0'J!n lot baas shy- hou=.a!:es as skoX'3 In Fi=!'e I and '. tot!!H In fact overlap each other to some extent.

Figure 2 is a graph of an exposure timing alignment scheme tor colorspecific exposure times. I ne horizontal axis is time 2;v. In this example, the graph indicates the tiring +cr variable epcsure scanning, depending upon the fireuen.cy band for which intensity is detected. In a practical example, the ratio of exposure time periods could be red:green:blue of 1:2:4, meaning that if the red channel is exposed for X milliseconds, the green channel is exposed for 2X nillisectJnds, and tile blue channel is exposed for 4X fFul;iSCCOndi w;iicli Ct-)U;o represeii a si.uatioii -w-hereii. light is trarlsii-litted shroud, a transparency or photographic film negative. Figure 2 is an example of simriltaneously i ended exposure of the three color channels In Figure 2, first frequency band tinting pulses 21S, which could he' for exmnIe, red frequency bend ti.mingpuises 215 start and stop first frequency band image intensify detection 2 i 6, which also could be, for example red frequency band image intensity detection 216; second frequency band timing pulses S 22n which coul ' be, for example, green frequency band timing-, pulses 22u start and stop second frequency band image intensity detection 221, which also could be, for example green frequency band image intensity detection 221; and third frequency band timing pulses 225 which could be, for example, blue frequency band timing pulses 225 start and stop third frequency band image intensity detection 226, which also could be, for example l O blue frequency band image intensity detection 226. Detection in the first frequency band 121 lasts for a first time period 231, in the second frequency band 122 lasts for a second time period 232, and in the third frequency band t23 lasts for a third time period! 233 Figure 3 is another graph of an exposure timing alignment scheme for color specific exposure times. The horizontal axis is time210. In this example, the graph again indicates the timing for variable exposure scanning depending upon the frequency band for which intensity is detected. And again for this example, the ratio of exposure time periods could be red:green:blue of 1:2:4, representing a situation wherein light is transmitted through a transparency or photographic film negative. Figure 3 is an example of simultaneously-started exposure of the three color channels. In Figure 3, first frequency band timing pulses 215, which could be, for example, red frequency band timing pulses Did start and Stop r;rsr frequency band image intensity detection 216, which also could be, for example red frequency band image intensity detection 21 S; second frequency band timing pulses 220 which could be, for example, green frequency band timing pulses 220 start and stop second frequency band image intensity detection 221, which also could 2> be, for example green frequency band image intensity detection 221; and third frequency band timing pulses 225 which could be, for example, blue frequency band timing pulses 225 start and stop third frequency band image intensity detection 226, which also could be, for example blue equencv hand image intensity detection 226 In this example, detection in the first frequency band 121 lasts for the first time period 231, in the second 3f) frequency band 192 lasts for the second time period 232, and in the third frequency band 123 lasts for the third time period 233.

Figure 4 is a graph of an embodiment of an exposure timing alignment scheme for color-specific exposure tirades consistent with the teachings of the invention. The horizontal axis is time 210. In this example, the graph once again indicates the timing for variable exposure scanning depending upon the frequency band for which intensity is detected. And once again for this example, the ratio of exposure time periods could be red:green:blue ot I:2:4, representing a situation wherein light is transmitted through a transparency or photographic film negative. Figure 4 is an example of simultaneously mid-point440 exposure ofthe threecolorchannelswhereinmidpointsoffirst, second, and third time periods 231,232,233 occur at the same time. In Figure 4, first frequency band timing pulses 215, which could be, for examples red frequency band timing pulses 215 start and stop first Dequency'oand image intensity deieciio'21o, which also could be, roof example redfrequency bend image intensitydetection216; second frequency bend timing pulses 220 which could be, for example, green frequencyband timing pulses 220 start and stop second frequency band image intensity detection 221, which also could be, for example green frequency band image intensity detection 221; and third frequency band timing pulses 225 which could be, for example, blue frequency band timing pulses 225 start and stop third frequency band image intensity detection226, which also could be, for example blue frequency band image intensity detection 226 In this embodiment, detection in the first frequency band 12 l lasts for the first time period 231, in the second e-iei.c I- oared,^- inks Isis die ecuiiLi '; iiic yG-iL'L-i Add, aiiLi iii lily LiiliLi 1feq-licicy- ua,lu 123 lasts for the third time period 233.

Figure 5A is a simplified block diagram of an embodiment of an optical scanning system 5;)() consistent with the teachings of the invention. In Figure SA, an image sensor Sin comprises a first photosensiiivcdetccior5ii, a second pliotosensitive ietectoroi2, and a third photoscnsiti ve detector 513, a lens system S I S. and an exposure control circuit 520. For ease of illustration, other components of the optical scanning system 500, as for example a drive mechanism, are not shown. The second photosensitive detector 512 is positioned at a first location 571 relative to the first photosensitive detector 511. The 3() third photosensitive detector 513 is positioned at a second location 572 relative to the first photosensitive detector 511 In Figure SA, light 550 is transmitted through an object 555 at point 560 While shown as transmitted light 550 the light 550 could also be reflected light 5541. The lens system 515 comprises a beam splitter and insures that the center of exposure for the first, second, and third frequency bands 121,122,123 which could be, for example, the red, green, and blue frequencybands 121, 122,123 respectively coincides on the object 555 with the point 560. While only one light path has been shown in Figure 5A, it will be recognized by one of ordinary skill in the art that the lens system focuses Jight550 from the point 560 onto each photosensitive detector511,522,513 from multiple paths. Light 550 from points in the vicinity of the point 560 are focused onto the ID photosensitive detectors 511,522,513 as the components ofthe optical scanning system 500 to the left of and including the lens system 515 are moved relative to the object 555.

I lie expos-ule COil,iO' circui.52" utilizes the eAposule tillling alilllent scheme shown in Figure 4 to obtain color-specific exposure times in order to provide accurate color alignment when using variable exposures and a positional system with continuous motion.

Thus, the exposure control circuit 520 controls the timing of initiation and termination of exposure for the photosensitive detectors 511,522,513 The exposure control circuit 520 also provides a mechanism for obtaining exposure infonnation from the photosensitive detectors 511,522,513 and rearranging this information as needed in order to create a composed image.

Figure 5B is another simplifidl block diagram of the optical scanning system 500 of. date MA, ,AS,..cse tic tile lens system Eli '2fF'wJ!e A, the lens system 1; of Figure 5B does not include a beam splitter, and light 550 from first and second adjacent points 561,562 is focused onto first and third photosensitive detectors 511,513 respectively white light 551) from the point 560 continues to be focused onto the second if. p', otosensi.ivc detector 512. E3ccause a beam splicer is not used for color separation in Figure SB, color filters are used on the photosensitive detectors 511,512,513 to allow each detector to measure light intensity in one ofthe three frequency bands 121,122,123.

for example, the first photosensitive detector 5ii utilizes a color filter that allows only light in the first frequency band i2i to reach the detector. Similarly, second and third 3() photosensitive detectors 512,513 utilize colorfiiters that allow onlyintensityin the second and third frequency bands 122,133 respectively to reach the detector. For clarity of illustration, the various light rays 50 are not labeled in Figure SB The slightly offset color images which are detected by the optical scaruning system 500 of Figure 5B are reconstructed by the electronics of the system 500 to create a color aligned image. Due to the required beam splitter of the lens system 515 of Figure SA, the optical scanning system 500 of Figure 5B is generally less expensive than that of Figure 5A even with the additional electronics required for image reconstruction of Figure 5B.

The optical scanning system 5()() shown in Figures SA and 5B could be, for example, but not limited to one of the following: optical scanner 500, facsimile machine 500 and digital camera 500 Figure 6 is a simplified block drawing of an embodiment of an image sensor 510 consistent with the teachings ofthe invention. one image sensor5iO of F igure 6 has rows of photosensitive detectors 511,512,513 that detect different colors using, for example, either beam splitters as in Figure 5A or color filters on the photosensitive detectors as in Figure 5B or other mechanism HOW know or later developed. The first photosensitive detectors 511 are located in a first row 681; the second photosensitive detectors 512 are located in a second row 682 fixed at the first location 571 relative to and parallel to the first row 681 of first photosensitive detectors 51 1; and the third photosensitive detectors 513 are located in a third row 683 fixed at the second location 572 relative to and parallel to the first row 681 of first photosensitive detectors 511. For the configuration of Figure I.c c-^posule cuil,i-ul Circuit 52, is cafe o. silluliallcous CApUbUI Of all first photosensitive detectors 511 forthe firsttimeperiod 231, separate simultaneous exposure of all second photosensitive detectors 512 for the second time period 232, and separate shTiullaneous exposure ol all third photosensitive detectors 513 for the third time period 233.

Figure 7A is a simplified block drawing that includes the image sensor 510 of Figure 6 from a different viewpoint with other components ofthe optical system 500 The lens system 515 of Figure 7A comprises the beam splitter as in Figure 5A In Figure 7A.

as the components of the optical scanning system 500, including the lens system 515 and irr.age sensor 510, are moved relative to the object 555 in direction 721), light 550 from points in the vicinity of point 56Q is incident upon the first, second, and third photosensitive detectors 511, 512,513. In discussing Figure 7A, reference is made to the exposure timing alignment of Fi,u.re 2. As the image sensor 510, the lens system 515, and other appropriate components of the optical scanning system 5()0 are moved relative to the object S55, during the first time period 231, 1igrht 550 from a first exposure area 711 on the object 555 is incident on the first photosensitive detector 511; during the second time period 232, light 550 from a second exposure area 712 on the object 555 is incident on the second photosensitive detector512; and during the third time period 233, light 550 from a third exposure area 713 on the object 555 is incident on the third photosensitive detector 513. The misaligrunent of the first, second, and third exposure areas 711,712,713 on the object 555 can result in an unacceptable image.

Figure 7B is another simplified block drawing that incindes the image sensor 5iO of Figure 6 from a different viewpoint with other components of the optical system 500.

The lens system 515 of Figure 7B comprises the beam splitter as in Figure 5A. In Figure 7B, as the components of the optical scanning system 500 including the lens system 515 and image sensor 510 are moved relative to the object 555 in direction 72O, light 550 from points in the vicinity of point 560 is incident upon the first, second, and third photosensitive detectors 511, 512,513. In discussing Figure 7B, reference is made to the exposure timing alignment of Figure 3. As the image sensor 510, the lens system 515, and other appropriate components of the optical scanning system 500 are moved relative to the object 550, during UTC first rime period Ha;, iign'Su from the i"irsi exposure area pi on the object 555 is incident or the first photosensitive detector 511; dur ng the second time period 232, light 550 from the second exposure area 712 on the object 555 is incident on the second photosensitive detector 512; and during the third time period 233, light 55(J *om the third exposure area 113 on the object 555 is incident on the third photosensitive detector 513. The misalignment of the first, second, and third exposure areas 711,712,713 on the object 555 can result in an unacceptable image.

Figure 7(: is yet another simplified block drawing that includes the image sensor SIO of Figure 6 from a different viewpoint with other components of the optica! system 500. T he lens system 515 of Figure 7C comprises the beam splitter as in Figure 5.. In Figure 7C, as the components ofthe optical scanning system500 including the lens system51- and image sensor 510 are moved relative to the object 555 in direction 720, light 55Q *om points in the vicinity of point 560 is incident upon the first, second, and third photosensitive detectors 511,512,513. In discussing Figure 7C, reference is made to the exposure timing alignment of Figure 4. As the image sensor 510, the lens system 515, and other appropriate components of the optical scanning system 50Q are moved relative to the object 555, during the first time period 231, light 550 from the first exposure area 711 on the object 555 is incident on the first photosensitive detector 511; during the second time period 232, light 550 from the second exposure area 712 on the I O object 555 is incident on the second photosensitive detector 512; and during the third time period 233, light550 from the third exposure area713 on the object555 isincidenton the third photosensitive detector 513. Note that the first, second, and third exposure areas 711,712,713 on the object 555 are now aligned an a more acceptable image can result.

In alternative embodiments of apparatus similar to that of Figure 5B, the lens systems 515 of Figures 7A-7C do not include the beam splitter. At any given time during exposure, light 550 from adjacent points 561,562 which are not indicated in Figures 7A 7C is focused onto first and thirdphotosensitive detectors 511,513 respectivelywhilelight 550 from the point 560 continues to be focused onto the second photosensitive detector 512. The slightly offset color images which are detected by the optical scanning system 500 in these embodiments are reconstructed by the electronics ofthe system 500 to create 1;101 d1iCti ill,. tJUe to the ream spiiner orthe lens system 515 ot Figures 7A-7C, the optical scanning system 500 of this alternative embodiment is generally less expensive than that of Figures 7A-7C even with the additional electronics for image reconstruction.

Again with the exposure timing alignment scheme of Figure 4, the first, second, and third US exposure areas 711, /12,7 i3 on the object 555 are aligned and a more acceptable image can result.

Appropriate timing, offset adjustments to the midpoints 440 of the first. second, and third time periods 231,232,233 by the exposure control circuit 520 are made knowing, for example, the speed of relative motion between the object and the image sensor 510 such that at midpoint 440 of the first time period 231, light 550 from the point 56Q on the object 555 is incident at prox;anate center 79Q, not specifically shown in the drawings, ofthe first photosensitive detector511, such tlat at midpoint44() ofthe second time period 232,1iabt 550 from the point 560 on the object 555 is incident at proximate center 790 of the second photosensitive detector 5! 2, and such that at midpoint 440 of the third time period 233 light 550 from the point 560 on the object 555 is incident at proximate center 790 of the third photosensitive detector 513.

Figure 8 is a drawing of a flow chart 800 of an embodiment of a method for exposing the photosensitive detectors 511,512,513 consistent with the teachings of the invention.

1Q In block 805, when time 210 is equal to one-half of the first time period 231 subtracted from the time at which it is intended for the midpoint 440 of the exposure of thefirs'photosensilive ueiecior(s) 51; to occur, IJ;OCKOO5 trarsfel-s conti-o; to block81v.

Otherwise, block X05 transfers control to block 815.

In block X10, exposure of the first photosensitive detector(s) 511 is initiated Is Block X10 then transfers control back to block 805.

In block 815, when time 210 is equal to one-half ofthe second time period 232 subtracted from the time at which it is intended for the midpoint 440 of the exposure of the second photosensitive detector(s) 512 to occur, wherein intended midpoints 440 for exposure of first end secondphotosensitive detector(s) 511,512 occur et proximate times, bloekX15transfers control toblock820. Otherwise, block815 transfers control to block bar 0.

In block X20, exposure of the second photosensitive detector(s) 512 is initiated.

Block X20 then transfers control back to block 805.

In block 825, when time 21() is equal to one-hait of the third time period 233 2 subtracted from the time at which it is inrenuied for the midpoint 44u of the exposure of the third photosensitive detector(s) 513 to occur, wherein intended midpoints 440 for exposure of first and third photosensitive detector(s) 511,513 occur at proximate times, block 825 transfers control to block 830. Otherwise, block 825 transfers control to block 835.

3() In block 83O, exposure of the third photosensitive detector(s) 513 is initiated.

Block S,0 then transfers control rack to block 80.

In block835, when tine210 is equal toone-halfofthefirsttimeperiod231 added to the time at which it is intended for the midpoint 440 of the exposure of the first photosensitive detectcris) 5i1 to occur, bloc' 035 t.a..sfe.s contro, to block 80.

Otherwise, block 835 transfers control to block 845.

In block 840, exposure of the first photosensitive detector(s) 511 is terminated Block 840 then transfers control back to block 805.

In block 845, when time 210 is equal to one-half of the second time period 232 10added to the time at which it is intended for the midpoint 440 of the exposure of the second photosensitive detector(s) 512 to occur, wherein intended midpoints 440 for exposure of first end second r,hotosensitive detector(s) 511,512 Occur at proximate tim..es, block X45 transfers control to block 850. Otherwise, block 845 transfers control to block 855.

15In block 850, exposure ofthe second photosensitive detector(s) 512 is terminated.

Block 850 then transfers control back to block 805.

In block 855, when time 210 is equal to one-half of the third time period 233 added to the time at which it is intende<l for the midpoint 440 of the exposure of the third photosensitive detector(s) 513 to occur, wherein intended midpoints 440 for exposure 20of first and third photosensitive detector(s) 511,513 occur at proximate times, block 855 transfers control to block 860. Otherwise, block 855 transfers control back to block 805.

In block X60, exposure of the third photosensitive ietector(s) 513 is terminated.

Block 860 then transfers control back to block 805.

It be understood by one of ordinary skill in that the art that the time referred to 25herein is time as measured by the optical scanning system 500 and that the blocks of Figure 8 are repeated as dictated by the optical scanning system 500. The time referred to is typically one that repeats on a periorlic basis The optical scanning shysters. 500 relay be hrnplemented as a corl.bination of hardware and software components. Moreover, the Functionality required for 30implementation may be stored in a program storage medieval. The term "program storage medium" is broadly defined herein to include any kind of computer related memory such as, but not limited to. floppy disks. conventional hard disks, DVDs, Cl)-ROMs, Flash ROMs, nonvolatile ROM, and RAM which Could be generally readable by a processing circuit.

A primary advantage of embodiments as described in the present patentdocument over prior exposure timing alignment systems for color-specific exposure times is the ability to align the exposure periods to the point exposed on the object thus reducing the incidence of color smearing.

Claims (3)

1. i. Akin splice' s-anmr.^ system '500', composing: 2 at least one first photosensitive detector 1511 j sensitive to light 1550] 2 first frequency band |121}; an exposure control circuit 15201 capable of exposing the first 6 photosensitive detcc.or 1511 Iror a first tithe period {23'J; 8 at least one second photosensitive detector 1512] sensitive to light 1550 in a second frequency band 11221, wherein the second photosensitive detector 1512; is fixed at a first 12 location 15711 relative to the first photosensitive detector 15111, 14 wherein the exposure control circuit 15201 is capable of exposing the second photosensitive detector 1512] for a second time period 1 6 [2321, 18 wherein the second time period 1232] is longer than the first time period 12311, and wherein when first and second photosensitive detectors 1511,512 22 are moved in a predestined manner relative to an object 15551, 24 at midpoint 14401 ofthe first time period 12311, light 15501 from a point 1560J on the object 1555J is incident at 26 proximate center 17901 ofthe first photosensitive detector 15111 and at midpoint!4401 of the second time period!232], light 30!5501 Mom the point 15601 is incident at proximate center r7901 of the second photosensitive detector 1512J.
2. 2. The optical scanning system [5001 as recited in claim 1, wherein the 2 optical scanning system 15001 is a machine selected from the group consisting of an optical scanner 15001, a facsimile machine 15001 and a 4 digital camera [5001.
3. 3. The optical scanning system 15001 as recited in claim 1, further 2 comprising: 4 at least one third photosensitive detector 15131 sensitive to light 15501 in a third fieq,ency band '1231 and fixed at a second location 1572' relative 6 to the first photosensitive detector [5111, 8 wherein the exposure control circuit 15201 is capable of exposing the third photosensitive detector 15121 for a third time period 1 () 12331, 12 wherein the third time period 12331 is longer than the second time period 12321, and wherein when first, second, and third photosensitive detectors 16 1511,512,513J are moved in a predefined manner relative to the object 1555i,

   I Q

   at midpoint 14401 of the third time period 12331, light 2() 15501 from the point 15601 is incident at proximate center 17901 of the third photosensitive detector 15131.

   4 A program storage medium readable by a processing circuit, embodying 2 a so flare proorarn of instr'.!ctions evecatahle by the processing Cil cud. c, perfóurn exposure alignment, the program comprising: logic, for a first time period j231], tor exposing at least one first 6 photosensitive detector 1511J sensitive to light 1550J in a first frequency band!!211;

   X

   logic, for a second time period 12321, for exposing at least one second photosensitive detector 1512J sensitive to light 1550] in a second frequency band 1122], wherein the second photosensitive detector 1512] is fixed at a first i4 location 1571J relative to the first photosensitive detector f5111, 16 wherein the second time period 12321 is longer than the first time period 12311, and wherein when first and secondphotosensitive detectorsl511,512 are moved in a predefined manner relative to an object [555J, 22 at midpoint 1440] cfthe first time period 1231], lift 15503 from a point 15601 on the object 15551 is incident at 24 proxirn.ate center 17903 ofthe first photosensitive detector |5111 and at midpoint 1440J of the second time period 12321, light 28 15501 from the point 15601 is incident at proximate center 17901 of the second photosensitive detector 15121 5. The program. storage medium as recited in claim. 4, wherein the exposure 2 alignment occurs in a machine selected from the group consisting of an optical scanner i50U;, a Eacsimiic machine i5uu; and a digital camera 4 15001 6. The program storage median as recited in claim 4, the method steps 2 further comprising 4 logic, for a third time period 1233], for exposing at least one third photosensitive detector 1513] sensitive to light 1550] in a third frequency 6 band 1123], wherein the third photosensitive detector 1513 I is fixed at a second location 15721 relative to the first photosensitive detector 15111, wherein the third tibiae period;233; is 1oiigei diai1 tile second iirme 12 period 1232!, and 14 wherein when first, second, and third photosensitive detectors i5i i, 5i2,513; are moved in a predefined manner relative to the 16 object 15551, at midpoint 14401 of the third tirr.e period [2331, light 18 15501 *tom the point t560! is incident at proximate center 79()] of the third photosensitive detector 15131.