GB2232844A

GB2232844A - Image reading apparatus

Info

Publication number: GB2232844A
Application number: GB9008235A
Authority: GB
Inventors: Noriko Tanaka; Yoshihiro Nagata
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1989-04-26
Filing date: 1990-04-11
Publication date: 1990-12-19
Anticipated expiration: 2010-04-11
Also published as: CA2015426A1; GB2232844B; GB9008235D0; DE4013404A1; CA2015426C; DE4013404C2

Description

a IMAGE READING APPARATUS is

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to automatic gain control of an image reading apparatus using a line image sensor.

2. Description of Prior Art

Fig. 4 is a schematic perspective view showing the conventional image reading apparatus as disclosed, for example, in- Japanese Patent Unexamined Publication No. Sho-63-316567. In the drawing, the reference numeral 11 designates a line image sensor having a multi-row structure for reading a picture signal; 12, a light source; 13, a rod lens array; 14, an original; and 15, a white reference plate attached on the apparatus body at a position adjacent to the original 14.

Here, as the line image sensor ii.. used is one long enough in length to read the original 14 as well as the white reference plate 15 at the same time.

Fig. 5 showsan automatic gain control circuit in the conventional image reading apparatus. In the drawing, the reference numeral 11 designates a line image sensor; 21 and 22, amplifiers; 23 and 24, analog-to-digital converters (hereinafter, referred to as A/D converters); 25 and 26, sample hold circuits; and 27 and 28, amplifiers.

The line image sensor 11 is constituted by an image sensor having a tworow structure in which one row is constituted by white (W) elements and yellow (Ye) elements arranged alternately in this order and the other row is constituted by green (G) elements and cyan (Cy) elements arranged alternately in this order, so that a picture signal is produced from the two rows. One picture element is -constituted by the four adjacent W, Ye, G, and Cy elements.

Next, the operation of the conventional image reading apparatus will be described.

First, an image of the original 14 and the white reference plate 15 irradiated by the light source 12 is focused on the line image sensor 11 through the rod lens array 13 in Fig. 4. In Fig. 5, the picture signal put out f rom the one is row of the line image sensor 11 constituted by the W and Ye elements is applied to the amplifier 21 so.as to be amplified therein and the picture signal put out from the other row of the line image sensor 11 constituted by the G and Cy elements is applied to the amplifier 22 so as to be amplified therein.

The output S(1) of the amplifier 21 is applied to the AID converter 23. As for the picture signal of the white reference plate, the picture signal put out only from the W elements is sample-held by the sample hold circuit 25 so as to be utilized as a reference voltage Ref(l) of the AID converter 23.

1 1 The output S(2) of the amplifier 22 flows similarly to the picture signal S(1). In the case of the picture signal S (2), however, the picture signal put out only f rom the G elements is sample-held by the sample hold circuit 26.

Fig. 6 shows signal waveforms at main portions of Fig 5. In Fig. 6, S(1) represents a one-line picture signal which is applied.to the AID converter 23 when scanning is performed in the direction of line starting from the white reference plate 15 side; S/H represents a pulse signal which is only the sapple-held picture signal put out f rom the W elements corresponding to the white reference plate; and ref (1) represents a reference voltage applied to the AID converter 23. Further, the level of the picture signal S(1) is lower in the vicinity of the opposite ends than the center portion in one is line because of a shading ef f ect of the light source 12 as shown in Fig.6.

The reference voltage ref. (1) to be applied to the AID converter 23 is obtained by amplifying the output of the sample hold circuit 25 by means of the amplifier 27, as shown in Fig.

5, with a suitable amplification factor (for example, with an amplification factor Ai (Ai>l)) to thereby make correction so that a oneline picture signal is within the range of AID conversion.

In the foregoing configuration, even in the case where the intensity of light of the light source 12 so fluctuates in sub-scanning that the picture signal changes, for example, from S(l) shown in Fig. 7 (a) to SI(l) shown in Fig. 7(b), the reference voltage ref (1) applied f or every line to the A/D converter 23 changes at the same rate as that of the picture signal if the white reference is read before reading every line.

That is, the following expression is established.

ref'(1) = ref(l)(Sl(l)/S(l)) Therefore, the output of the A/D converter 23 is even regardless of fluctuations of the intensity of light.

Although description has been made as to the method of automatically controlling the gain of the picture signal S(l) in reference to Fig. 6 and Fig. 7(a), (b), quite the same applies to the output S(2) of the amplifier 22 as for the is operation thereof except that in this case the picture signal from the G elements is sample-held by the sample hold circuit 26 so as to be used. as the reference voltage for the A/D converter 24.

Thus, the reference voltages ref (1) and ref (2) are obtained from the picture signals produced from the W and G elements respectively and the white reference is read by the A/D converters 23 and 24 in accordance with the reference voltages ref (1) and ref (2) respectively. Therefore, reading of the white reference is accurate in comparison with the case of a single system, and each of the outputs of the A/D - 4 1 1 converters 23 and 24 is even regardless of the fluctuations of the intensity of light.

Having such a configuration as described above, the conventional image reading apparatus has a problem in that if a part of the white reference plate 15 becomes dirty or dust sticks on a part of the white reference plate 15, the reading level of the white reference plate 15 falls only in the dirty portion so that the signal level f or one line based on the reduced reading level relatively rises to thereby cause local disturbance, such as transversal stripes having higher luminance than other portions, in an output picture.

1 SUMMARY OF THE INVENTION

The present invention has been accomplished to solve the above problem, and is intended to provide an image reading apparatus in which even if- a part of a white reference plate becomes dirty or dust sticks on a part of the white reference plate, no local disturbance, such as transversal stripes, is caused in an output picture.

The Image reading apparatus according to the present invention comprises a reading unit constituted by an integrally provided optical system formed of a line image sensor, a rod lens array, a light source, and the like, and a white reference plate.attached on one end of the reading unit.

1 t According to the present invention, since the white reference plate moves together with the reading unit in direction of sub-scanning in reading an original, one and the same portion of the white reference plate is read for every line so that no variation due to dirt or dust is caused in reading level. Accordingly, it is possible to prevent deterioration, such as generation of transversal stripes, from -occurring in the output picture.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic perspective view showing an embodiment of the reading unit of the image reading apparatus according to the present invention; Figs. 2 and 3 are schematic perspective views showing examples of arrangement of the same embodiment of the reading is apparatus according to the present invention; Fig. 4 is a schematic perspective view showing the conventional image reading apparatus; Fig. 5 is a block connection diagram showing the automatic gain control circuit in the conventionalimage reading apparatus; and Figs. 6 and 7 are diagrams showing signal waveforms at various portions of the automatic gain control circuit of Fig. 5 for explaining the operation of the circuit.

f 1 1 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An embodiment of the present invention will be described hereunder with reference to the accompanying drawings. Fig. 1 is a schematic perspective view showing an embodiment of the reading unit according to the presen_ invention. In Fig. 1, constituent components the same as or corresponding to those of Fig. 4 are correspondingly referenced, and duplicate explanation is omitted. In Fig. 1, the reference numeral 16 designates a reading unit for scanning (sub-scanning) an original 14 in reading the original. The reading unit 16 has an optical system composed of a line image sensor 11, a light source 12, a rod lens array 13, and the like which are arranged so as to be able to perf orm integral scanning. The reference numeral 17 designates a white reference plate attached on one end of the 'ieading unit 16 so as to be moved together with the reading unit 16 in the sub-scanning direction. The white reference plate 17 is attached on the reading unit 16 in a manner so that the white reference surface is located in the same plane on which the original 14 is mounted as shown in Fig. 2. Alternatively, the white reference plate 17 is attached on the reading unit 16 in a manner so that the white reference surface is located just under a glass plate 18 on which the original 14 is mounted as shown in Fig. 3.

1 5, is 1 1 A circuit for processing a picture signal produced from the line image sensor 11 has the same configuration as that of the conventional image reading apparatus.

Next, the operation will be described.

First, the original 14 and the white reference plate 17 attached on the one end of the reading unit 16 are irradiated -with the light source 12 arranged in the reading -unit 16 so that the respective images of the original 14 and the white reference plate 17 are focused on the line image sensor 11 through the rod lens array 13. A circuit f or processing a picture signal produced from the line image sensor 11 has the same configuration as that of the conventional image reading apparatus.

Being attached on the reading unit 16, the wh.ite reference plate 17 is interlocked with the light source 12, the rod lens array 13, and the line image sensor 11 so that one and the same portion' of the white reference plate 17 is read for every-line.

Even if a part of the white reference plate 17 becomes dirty, therefore, the reading level of the white reference plate"17 referred to when the signal level of the original 14 is determined for every line falls at the same rate for all the lines, so that the white reference does not become different among the lines. Consequently, the signal level in reading the original relative to the reading level of the white reference w 1 is plate never becomes dif f erent among the lines even if the intensity of light of the light source fluctuates, so that an original reading signal having a level which is not different among the lines can be obtained after A/D conversion. Accordingly, deterioration in picture quality, such as local generation of transversal stripes, can be prevented to thereby make it possible to obtain an output which is even in quality over the whole surface of the original 14.

Although description has been made as to the case of reading a color image in the above embodiment, the present invention provides the same effects as those obtained in the above embodiment also in the case of performing reading by means of a monochrome sensor in which no color separation filter is provided on the line image sensor 11.

Further, in the above embodiment,the white reference plate 17 is attached to the reading unit 16 in a manner so that the white reference plate 17 is located on the right of the original 14 in the drawings as show in in Figs. 2 and 3. Thus, it is made possible that the reading unit 16 reads the white reference plate 17 before performing scanning from the right to the left for every line to thereby produce a reference voltage f or every line so that the reading of each line can be performed on the basis of the thus obtained reference voltage. Alternatively, in the case where the fluctuation of the intensity of light of the light source 12 is suf f iciently - 9 1 1 gentle relative to the time required for one-line reading of the line image sensor 11, the configuration may be made changed such that the white reference plate 17 is attached on the reading unit 16 so that the white reference plate 17 comes on the left of the original 14 and the reading unit 16 reads the white reference plate 17 attached on the left of the original 14 so as to generate a reference voltage after reading for every line to thereby make it possible that the next line can be read on the basis of the thus obtained reference voltage.

Moreover, although the white reference plate 17 is attached on the same plane as the original 14 or just under the glass plate 18 in the above embodiment, the white reference plate 17 may be attached at any position of the reading'unit 16 so long as the white reference plate 17 can be irradiated with is the light s ource 12 so that the image.Of the white reference plate 17 can be made on the line image sensor 11 through the rod lens array 13 to thereby make it possible to obtain a reading signal. Also in this case, the same effects as those obtained in the above embodiment can be obtained.

As described above, according to the present invention, the reading unit is constituted by the optical system integrally provided with the line image sensor, the rod lens array, the light source, and the like, and the white reference plate is attached on one end of the reading unit. Therefore, there is an ef f ect in that one and the same portion of the white reference plate is read by the line image sensor every time an original is read line by line to thereby make it possible that the gain control can be made on the basis of the output of the line image sensor. Further, even if a part of the white reference plate becomes dirty, an even output can be obtained throughout the whole surface of the original to thereby make it possible to prevent deterioration, such as generation of transversal stripes, from occurring in the output picture.

1 1 k

Claims

Claims:

An image reading apparatus comprising: integral reading means, integrated with an optical system having a light source for Irradiating an original, a rod lens array for focusing an image of said original. and a line image sensor for reading the image focused by said rod lens array, for scanning said original; an automatic gain control circuit having sample-andhold means for holding an output of said line image sensor upon reading said white reference plate; and a white reference plate having a reference surface to be used as a reference image upon reading of said original, said white referene plate being attached on one end of said reading means so as to move togeter with said reading means.
2. An image reading apparatus as claimed in claim 1, wherein said line image sensor has white, yellow, green and cyan elements in a multi-row structure.
3. An image reading apparatus as claimed in claim 1, wherein said line image sensor has a two-low structure in which one row is constituted by white elements and yellow elements arranged alternately in this order, and the other row is constituted by green elements and cyan elements arranged alternately in this order.
4. An image reading apparatus as claimed in claim 1, wherein said line. Image sensor Is a monochrom sensor.
5. An Image reading apparatus as claimed in claim 1, wherein said reference plate is attached on the reading means in a manner so that the white reference plate surface is lacgted in the same plane on which the orginal is mounted.
6. An image reading apparatus as claimed in claim 1, wherein said reference plate is attached on said reading means in a manner so that the white reference surface is located just under a glass plate on which the orginal is mounted.
7. An image reading apparatus as claimed in claim 1, wherein said automatic gain control circuit further includes analog-to-digital convert means for converting outputs of said line image sensor.

1 13 - Published 1990 at The Patent Office. State House, 66'71 High Holborn, LandonWCIR4TP.F'urther copies maybe obtained from The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187