CCD SENSOR OUTPUT CIRCUIT OF IMAGE READING APPARATUS

Abstract: A CCD sensor output circuit of an image reading apparatus adapted to output a stable reading signal from the CCD sensor even if the light source changes in temperature due to heating. One portion of a region to be read by a CCD sensor is make to serve as a reference region, in accordance with the output of the CCD sensor corresponding to the reference region when the light source has been turned on according to a lighting control signal, the reflected lights from the images are made to read by the CCD sensor at a first timing after the light source has been made stable, and the output of the CCD sensor is adapted to be transferred at a given second timing from the first timing to the outputting of the next lighting control signal, thus providing the CCD sensor output after the light source has been made stable.

Description: The present invention relates to an image reading apparatus for reading images by means of a CCD sensor. Fig. 1 shows a conventional optical system in an image reading apparatus, to which one embodiment of the present invention applies. Referring to Fig. 1, the light from a white colored fluorescent lamp 3 is applied upon a color manuscript 2 with the color manuscript 2 being arranged before a white-colored back plate 1. The light from the white-colored fluorescent lamp 3, reflected by the color manuscript 2, is reflected by a mirror 4, focused and input to a CCD sensor 6. An image reading apparatus using a CCD sensor 6 as shown in Fig. 1 may be used in a facsimile OCR, a color scanner or the like. In such an image reading apparatus, the white-colored fluorescent lamp 3 is disadvantageous in that the radiation level changes due to differences in ambient temperatures or through rises in the guide temperature which is raised by self-heating after large amounts of lighting. As a measure to prevent these problems, methods have been adopted which use an automatic gain control circuit (AGC circuit) or flash the white-colored fluorescent lamp to change its lighting width thereby controlling the radiation amount. However, disadvantageously, a proper circuit is not provided which precisely controls a high-speed analog signal such as an AGC circuit. A method which varies the lighting width of the white-colored fluorescent lamp becomes unstable in lighting when the lighting duty cycle becomes extremely small. From EP-A-0 006 570 a document scanning system with exposure control is known in which the light amount reflected from a reference region is detected by certain cells (exposure control cells) of a CCD sensor while the other cells thereof (document information cells) receive the light reflected from the document. As soon as the exposure control cells has received a certain light amount the scanning operation for one line is terminated. In this known apparatus, both detection of the light amount and the reading of the document are performed in the same time interval. For this event, the exposure control cells of the CCD sensor must be controlled differently from the document information cells. The layout or design of the CCD sensor must be different in its exposure control section from that in the document information section. Therefore, time control and manufacturing of the CCD sensor of the known apparatus is rather complicated. From EP-A-0 071 005 a further system is known in which a linear CCD sensor is used for reading the light of an illuminated area. Since the sensor is limited in its output by saturation of the CCD analog shift register in the sensor, the useable video signal is maximized among other measures by calibrating the sensor relative to its saturation condition. The calibration operation is performed prior to the reading operation with the calibration not being changed during image reading. An adjustment of the output level of the CCD sensor upon variations of luminance of the light source during image reading is not performed in the known apparatus. Accordingly, an essential object of the present invention is to provide an image reading apparatus in which the CCD sensor may output a stable reading signal even if the light source changes in temperature due to heating. In accompolishing the object of the present invention, according to one preferred embodiment of the present invention, there is provided a CCD sensor output adjusting means for adjusting the output level of the CCD sensor upon changes in the output level due to changes in temperature of said light source, in accordance with the CCD sensor output signal corresponding to a reference region read by the CCD sensor, the output adjusting means detecting when said light source has been stabilized. A lighting control means turns on the light source for a time period less than the length of a predetemined scanning time period, in response to a lighting control signal. A timing signal output means outputs first timing signals for a first time period from the beginning of the lighting of said light source until after the output adjusting means has detected stabilization of the light source, and further outputs a second timing signal for a second time period beginning after said light source has been stabilized but prior to the output of the next one of the lighting control signals. Responsive to the timing signal output means a transfer control means transfers the output of the CCD sensor, which was accumulated therein after lapse of the first time period, at the second time period. According to the invention, the output adjusting means adjusts said first time period for the output of the first timing signals or the width of the first timing signals such that the output level of the CCD sensor transferred at the second time period will be controlled to a given level. With this construction, the reflected light from the image is read by the CCD sensor after the first time period after the light source has become stable, in accordance with the output of the CCD sensor corresponding to a reference region, when the light source has been lighted according to a lighting control signal, with one portion of a region, to be read by the CCD sensor, as a referenced region. After the light source has been stabilized the CCD sensor output is provided by transfering the CCD output at a given second time period before the output of the next lighting control signal but after the first time period. This and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which: Fig. 1 is a view showing an optical system in an image reading apparatus, already refered above. Fig. 2 is a view showing a principle for controlling the CCD output, in one embodiment of the present invention, within a constant range; Fig. 3 is a schematic block diagram of an optical systems in one embodiment of the present invention; Fig. 4 is a detailed block diagram of an image reading portion shown in Fig. 3; and Fig. 5 and Fig. 6 are wave-form views of each portion of Fig. 3 and Fig. 4. Referring to Fig. 2, a reference region 11 in front of which the color manuscript 2 does not pass is provided in the white-colored back plate 1. The reference region 11 is provided as a reference for adjusting the output of the CCD sensor 6 shown in Fig. 1. The lights from the white-colored fluorescent lamp 3 which are reflected by the reference region 11 are input into the CCD sensor 6 through a lens 5. The level of a signal corresponding to the reference region 11, from among the output signals of the CCD sensor 6, is detected by the CCD output adjusting circuit 12 shown in Fig. 3 so that the level is controlled within a constant range. Referring to Fig. 3, the white-colored lamp 3 is turned on by a lighting circuit 7 in accordance with a lighting control signal from a control circuit 10. As described hereinabove, the control circuit 10 is adapted to control the level of the CCD output within a constant range in accordance with the output signal of the CCD sensor 6 corresponding to the reference region 11. Also, the control circuit 10 feeds a transfer pulse ø T , clock pulses ø₁, ø₂ and a reset pulse ø R to the image read-in portion 8. The image read-in portion 8 reads the images in accordance with the reflected lights from the color manuscript 2. An image signal VO, which is read out, is fed to a sample hold circuit 9. A sampling pulse SH is fed from the control circuit 10 to the sample hold circuit 9. The sample hold circuit 9 holds in sample the reading signal VO from the image read-in portion 8 in accordance with the sampling pulse SH. The output signal VO which is sample-held is fed to the control circuit 10. The detailed construction of the image read-in portion 8 shown in Fig. 3 will be described hereinafter with reference to Fig. 4. A CCD sensor 81 outputs light electric-charges in accordance with the reflected lights from the images. The light electric-charges are fed to a transfer gate 82. A transfer pulse ø T is fed to the transfer gate 82 and the light electric-charges from the CCD sensor 81 are transferred to an analog shift register 83 in accordance with the transfer pulse ø T . The clock pulses ø₁, ø₂ are fed to the analog shift register 83. The analog shift register 83 sequentially outputs the light electric-charges of the CCD sensor 81, transferred from the transfer gate 82, in accordance with the clock pulses ø₁, ø₂ to feed them to an output buffer 84. The output buffer 84 sequentially outputs the image data shifted from the analog shift register 83 in accordance with the reset pulse ø R . The operation of an image reading apparatus shown in Fig. 3 and Fig. 4 will be described hereinafter with reference to Fig. 5 and Fig. 6, showing the wave form views of each portion of Fig. 3 and Fig. 4. A flashing circuit 7 flashes a white-colored fluorescent lamp 3 in accordance with a lighting control signal FL to be given from the control circuit 10. The lights from the white-colored fluorescent lamp 3 are applied upon the color manuscript 2 and the reference region 11 of the white-colored back plate 1. The reflected lights from the images and the reflected lights from the reference region 11 from the white-colored fluorescent lamp 3 are detected by the CCD sensor 81. Namely, the light electric-charges corresponding to the reflected lights of the images are accumulated upon, e.g. regions S₁ through S N-3 among the respective regions S₁, S₂, S₃ ... S N-1 , S N shown in Fig. 4, on the CCD sensor 81, with the light electric-charges corresponding to the reflected lights from the reference region 11 accordingly being accumulated upon the regions S N-2 through S N . When the transfer pulse ø T is fed to the transfer gate 82, the light electric-charges accumulated in the respective regions S₁, S₂, S₃...S N-1 , S N of the CCD sensor 81 are loaded into the regions SR₁, SR₂, SR₃, ... SR N-1 , SR N of the analog shift register 83. The analog shift register 83 transfers the loaded contents to an output buffer 84 in accordance with the clock pulses ø₁, ø₂. The output buffer 84 photoelectrically converts the light electric-charges transferred from the analog shift register 83 to output them as the CCD output signal VO. It is to be noted that light electric-charges which are sequentially transferred from the analog shift register 83 are reset each time within the output buffer 84 by a reset pulse ø R . Accordingly, the CCD sensor output signals VO₁, VO₂ VO₃, ... VO N corresponding to the light electric-charges accumulated in the respective regions S₁, S₂, S₃, ... S N-1 , S N are output from the CCD sensor 81. They are the normal CCD output signals. The characteristic aspects of the present invention will be described hereinafter with reference to Fig. 6. In one embodiment of the present invention, one scanning period from the initial lighting of the white-colored fluorescent lamp 3 to the next lighting thereof is divided among a T ON period, a T OFF period, and a T READ period as shown in Fig. 6 (a), and one unit of the scanning period is composed of a scanning period S FLON in which the white-colored fluorescent lamp 3 radiates, and a scanning period S READ for output of the CCD sensor 81. Also, assume that the scanning of the CCD sensor 81 is composed of M, M+1, M+2, M+3. And at the radiation timing of each scanning, the white-colored lamp 3 normally lights only during the same time T ON . In the period S M FLON of the radiation timing in the scanning period M, the transfer pulse ø T is "H" for the time interval Tø T . Accordingly, the light electric-charges in the CCD sensor 81 caused by the radiation (Oblique line portion shown in Fig. 6 (b)) in that intervals are transferred to the analog shift register 83 simultaneously with the production of the light electric-charges. Namely, the light electric-charges are transferred to the analog shift register 83 simultaneously with their production, because the analog shift register 83 is lower in electric potential to electrons than the CCD sensor 81 when the transfer pulse ø T is "H". When the transfer pulse ø T changes from "H" to "L", the light electric-charges caused by the subsequent radiation level of the white-colored fluorescent lamp 3 are accumulated on the CCD sensor 81. Also, simultaneously with the change from the "H" to the "L" of the transfer pulse ø T , clock pulses ø₁, ø₂ are fed to the analog shift register 83 and the output VO M of the CCD sensor 81 corresponding to the light electric-charges produced during the transfer pulsed interval Tø T is sequentially output. A transfer pulse ø T of comparatively short width is given to the transfer gate 82 after the lapse of the T OFF time after the radiation time T ON of the white-colored fluorescent lamp 3 has passed. And the transfer gate 82 transfers to the analog shift register 83 the light electric-charges accumulated on the CCD sensor 81 during the time period (T ON - Tø T ) after the white fluorescent lamp 3 turns off, after the lapse of the interval Tø T of the transfer pulse ø T . Also, the light electric-charges transferred to the analog shift register 83 are sequentially shifted by the clock pulses ø₁, ø₂ and sequentially output as the output of the CCD sensor 81. A T READ period, after a pulse of the comparatively short width among the transfer pulse ø T is assumed to be a scanning period . Accordingly, in Fig. 6, assume that no drifts in temperature are provided in the radiation output of the white-colored fluorescent lamp 3, and the output of the CCD sensor 81, VO FLON + VO READ becomes constant. It is apparent from the above-description that the amount of the output VO READ of the CCD sensor 81 to be produced during the T READ period using the output of the CCD sensor 81, can be controlled in accordance with the width of the transfer pulse ø T . The reason why the T OFF period has been determined will be described. As the interval Tø T of the transfer pulse ø T comes closer to the T ON period, the output of the CCD sensor 81 in the radiation timing is output within the period of T off . Although the precise radiation spectrum has to be used generally when the white-colored fluorescent lamp 3 is used as a light source for reading the color manuscript, the radiation spectrum immediately after the white-colored fluorescent lamp 3 has been turned on and the radiation spectrum after the stable lighting has been provided are somewhat different from each other as shown in Fig. 6 (b). Namely, time taken from the output of the lighting signal FLON shown in Fig. 6(a) to the actual lighting of the white-colored fluorescent lamp 3 is dispersed each time, and the time taken before the stable lighting has been provided is also dispersed. The minimum width of the transfer pulse ø T at the radiation timing is restricted to the time T MIN (see the scanning period M+3 in Fig. 6) taken for the white-colored fluorescent lamp 3 to reach its stable lighting. In this way the output VO READ of the CCD sensor 81 that appears at the timing for output of the CCD sensor 81 caused by the radiation will be provided after the white-coloured fluorescent lamp 3 has reached its stable lighting. Thus, the control circuit 10 shown in Fig. 3 determines the falling timing of the transfer pulse ø T , in accordance with a read-in signal corresponding to the regions S N-2 through S N of the CCD sensor 81 corresponding to the reference region 11, so that the CCD output adjusting circuit 12 may vary the width of the transfer pulse ø T from a time T MIN or more to control the CCD output within a constant range. Namely, the control circuit 10 lenghtens the "H" period Tø T of the transfer pulse ø T in the next scanning period if the output signal level of the CCD sensor 81 corresponding to the reference region 11 of the white-colored back plate 1 is higher than a certain reference level, and makes the "H" period Tø T of the transfer pulse ø T shorter if the output signal level is lower than a certain reference level, so as to control the level of the output VO READ , which appears, at the scanning period S M of a timing, using the output of the CCD sensor 81, within a certain range. In the above description, the transfer pulse ø T becomes "H" only during the Tø T period of the radiation timing as shown in Fig. 6 (b), but it is not restricted to the above description. The pulse signal of comparatively short width may be constructed to be output when the white-colored fluorescent lamp 3 has reached its stable condition. The pulse signal is outputted for a period the white-colored fluorescent lamp 3 becomes stable as shown in Fig. 6 (e). Also, in the embodiment of the present invention, explanation has been given about adjustment of the output level degree of the CCD sensor through changes in the temperature of the light source by the white-colored fluorescent lamp 3. Explanation may be given about each ray of light of three primary colors of the color image reading apparatus. Thus, in accordance with the present invention, it is so arranged that one portion of a region to be read by a CCD sensor is made to serve as a reference region, in accordance with the output of the CCD sensor corresponding to the reference region, when the light source has been turned on according to a lighting control signal. The reflected lights from the images are read by the CCD sensor at a first timing after the light source has been made stable, and the output of the CCD sensor is transferred at a given second timing from the first timing prior to the output of the next lighting control signal, thus providing the CCD sensor output after the light source has been made stable.

Claims: Image reading apparatus comprising a light source (3), a CCD sensor (6) for detecting light from said light source (3) reflected by an image (2) to be read, a CCD sensor output adjusting means (12) for adjusting the output level of said CCD sensor (6) upon changes in the output level due to changes in temperature of said light source (3), in accordance with the CCD sensor output signal corresponding to a reference region (11) read by said CCD sensor (6), with said output adjusting means (12) detecting when said light source (3) has been stabilized, a lighting control means (7) for lighting said light source (3) for a time period (t ON ) less than the length of a predetermined scanning time period (T ON ,T OFF ,T READ ), in response to a lighting control signal (FLON,FLOUT), timing signal output means (10) for outputting first timing signals for a first time period (T øT ) from the beginning of the lighting of said light source (3) until after said output adjusting means (12) has detected the stabilization of said light source (3) and for outputting second timing signal for a second time period (T ON - T øT + T OFF ) beginning after said light source (3) has been stabilized but prior to the output of the next one of said lighting control signals (FLON,FLOFF), and transfer control means (82), responsive to said timing signal output means (10) for transfering the output of said CCD sensor (6), which was accumulated in said CCD sensor (6), after said first time period (T øT ) at said second time period (T ON - T øT + T OFF ), said output adjusting means (12) adjusting said first time period (T øT ) for the output of said first timing signals or adjusting the width of said first timing signals, so that the output level of said CCD sensor (6) transferred at said second time period (T ON - T øT + T OFF ) will be controlled at a given level. Apparatus according to claim 1, characterized by sample holding means (9) for supplying the output signal from said CCD sensor (6) corresponding to said reference region (11) to said output adjusting means (12). Apparatus according to claim 1 or 2, characterized in that said first time period (T øT ) or the width of said timing signals is not shortened beyond a minimum time period or width. Apparatus according to any one of claims 1 to 3, characterized in that said reference region (11) is provided in one portion of a region to be read by said CCD sensor (6), said output adjusting means (12) adjusting said first time period (T øT ) for output of said first timing signals or the width of said first timing signals in accordance with the CCD sensor output read out of said reference region (11). Apparatus according to any one or claims 1 to 4, characterized in that said output adjusting means (12) adjusts said first time period (T øT ) in accordance with the CCD sensor output read out from said reference region (11) in an immediately preceding scanning period.

Inventors: NAGANO, FUMIKAZU
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1985
Main classification: H04N1
IPC codes: G06T1, H04N1, H04N5