JPS62291256A - Color original reader - Google Patents

Abstract

PURPOSE:To uniformize the dispersion of output signals among color sensors having the output signals of different voltages, by controlling an AGC circuit by using a chrominance signal having the maximum output out of sample-held chrominance signals. CONSTITUTION:A signal from a CCD21 is added on an AGC circuit 133 through a buffer circuit 131, and furthermore, it is added on a multiplexer 132 which performs color separation. At such a time, a color output signal (for example, Ye) having the maximum output at the time of radiating a white color plate at the preceding stage of the scan of a document, out of color outputs outputted from the multiplexer 132, is supplied to an AGC circuit 138, and an AGC circuit 133 is controlled by using the signal. Each color output from the multiplexer 132 is sent to a color conversion circuit 139, and furthermore, it is stored on a memory 137 through an A/D converter 13b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a color document reading device that photoelectrically reads a color document.

[Prior art]

Various image reading devices that photoelectrically read original images have been proposed.

Furthermore, a line sensor is known in which a plurality of light receiving elements made of amorphous silicon or the like are arranged in a line across the width of the document to be read in order to photoelectrically read the density of the document image.

Now, the short hair direction (approximately 210 mm) of an A4 size document is 1
When reading at the same size with a resolution of 6 pixels/mm, approximately 3
1 with about 3,500 light-receiving elements on a 00mm substrate
Requires a book line sensor. However, it is difficult to form such a large number of light-receiving elements on the same substrate without any defects and with approximately uniform sensitivity, and therefore, it is not practical in terms of cost unless the yield is improved.

Therefore, it is conceivable to arrange a plurality of line sensors each consisting of about 300 light receiving elements in the scanning direction and read the 1-line image by dividing it with each line sensor. In this way, since the number of light receiving elements to be formed on the same substrate is not so large, the yield can be improved and the above-mentioned cost problem can be solved to some extent.

However, currently there is a variation in sensitivity between each line sensor of about 10 to 20%.

Furthermore, when color-separating a color original into the three primary colors and reading it photoelectrically, image signals for the three colors are required for each pixel, resulting in three times the amount of signal compared to a black-and-white image. For high-speed processing, the processing speed is three times that of black-and-white images, and it is difficult to process them at the same high speed as black-and-white images.

〔the purpose〕

The present invention has been made in view of the above points, and it is possible to read and scan a document by dividing it with a plurality of line sensors, solve the above-mentioned problems in this divided reading and scan, and make it possible to read color documents in good quality. It is an object of the present invention to provide a color document reading device that can read color documents.

〔Example〕

Next, embodiments of the invention will be described with reference to the drawings. In this embodiment, a color contact sensor is used to read the original. This color contact sensor is shown in Figure 1(a).
As shown in (b), a sensor unit 11 equipped with a plurality of CCD chips, a focusing rod lens array 12 placed on the sensor unit, and a linear light source provided near the side surface of the focusing rod lens array 12. 13 and the reflective gash 14 form an integral structure. Then, the light from the linear light source 13 is reflected from the document, and the reflected light is not equally reduced (combined as a royal real image on a plurality of CCD chips in a one-to-one relationship through the focusing rod lens array 12). be done.

In addition, the sensor unit 13 focusing rod lens array 1
2. As shown in FIG. 1(b), the light source 13 and the reflective gasket 14 are mounted on a movable body 15 and moved together with a signal processing board 17, a flexible electric wire 18 connecting the sensor unit 11 and the signal processing board 16. A flexible electric wire 19 is used to connect the body 15 and the main body.

The optical image formed on the CCD chip as described above is converted into electric charge by the photoelectric conversion capability of the CCD. This charge is sequentially transferred by the charge transfer ability of the CCD and becomes an image signal.

Each part will be explained in detail. The contact type color CCD sensor (sensor unit) 11 has five CCD chips 21 to 2 arranged in a staggered manner, as shown in FIGS. 2 and 3.
5, a cover 27 covering the ceramic substrate 26, and flexible electric wires 28a to 28f for connection.

The CCD chips 21 to 25 each have a light receiving section consisting of a p-n photodiode, and the size of the light receiving section is 62.5 μm x 15
．． It is 5 μm. Each CCD chip photosensitive pixel is connected to a blank feed pixel DI-D which is not connected to a photosensitive pixel as shown in Figure 4.
Light shield pixel D1 with 12/l shielding
3-D36. Dummy pixels D37~D72° Effective signal pixels S1~53072. It is composed of a total of 3168 bits of light receiving section including rear end dummy pixels D73 to D76.

Further, as described above, the CCD chips 21 to 25 are arranged in two rows in a staggered manner as shown in FIG.

In this case, as shown in FIG. 3, adjacent CCD chips are arranged in parallel with a center distance of 1 (in this embodiment, /=4 pixels) between the centers of the light receiving sections.

Further, these CCD chips 21 to 25 are arranged along the arrangement direction so as to overlap with each other.

As described above, the light receiving portions of the CCD chips 21 to 25 are arranged in the empty feeding areas DI-DI2. Light shield area DI3
~D36. Dummy areas D37 to D72 effective pixel area S1
~53072. It consists of rear end dummy areas D73 to D3072, of which the areas excluding the 3072-bit effective pixel area 5t-33072 are arranged so as to overlap each other, and the effective reading area is the short side of A3 size. width 2
It is 320mm, which is slightly longer than 97mm.

Furthermore, in order to receive color signals in the light receiving portions of the CCD chips 21 to 25, a color filter must be placed above the photodiode 81. This method uses color filters and Si
There are two methods: one method is to bond the elements together with an adhesive, and the other method is to directly laminate the color filter on the Si element. In the former case, the color filter can be manufactured on a glass substrate, but an extra step of adhesion is required when combining it with the Si element, and alignment errors are likely to occur. It is quite difficult to suppress the adhesion error to a few mm or less, which may cause deterioration of color reproducibility and shading characteristics. On the other hand, in the latter case, a color element is completed by simply manufacturing color filters in accordance with the pixels of the Si element, so the process is extremely simple and alignment accuracy can be greatly improved.

Therefore, the latter color filter is used for the CCD chip used in this embodiment.

Next, a specific filter array will be explained.

In this example, as shown in FIG. 5, the color is yellow (Ye).

A green (G) and cyan (Cy) filter array,
Three bits constitute one pixel during reading.

The spectral characteristics of these filters are shown in FIG.

As shown in Figure 6, the transmittance of the Ye filter is curve 6.
As shown in 1, it increases rapidly from around 500 nm. c.
The transmittance of the filter in y is 500 as shown by curve 62.
It shows a peak near nm. In this example, the G filter is obtained by superimposing a cy filter and a Ye filter, so the transmittance is 50 as shown by curve 63.
A peak is shown near 0 nm.

An important point in the spectral characteristics of these filters is that the transmittance does not become zero even for wavelengths of about 700 nm, which are outside the human visual sensitivity range.

Here, the color filters and CCD chips 21 to 25 must perform a function similar to that of the human eye.

As shown in FIG. 7, the spectral characteristics of the light receiving parts of the CCD chips 21 to 25 reach a maximum at a wavelength of about 550 nm, and the lo
It has a finite relative sensitivity up to oom or more.

In other words, the light receiving portions of the CCD chips (4a) to (4e) provided with color filters in this embodiment respond even to light having a wavelength of 700 nm or more.

On the other hand, the visibility of the human eye is zero for wavelengths of 700 nm or more. Therefore, it is simply a CCD chip (4a
) to (4e) and the Cy, G, and Ye color filters alone cannot perform the same functions as the human eye. Therefore, in this embodiment, as will be described later, a filter is used to correct the above-mentioned characteristics.

Next, the focusing rod lens array will be explained. The convergent rod lens array 12 in this embodiment has an original surface 81 at the focal length on the light incident side, and two CCD chip rows 82 at the focal length on the exit side.

With this setting, the document surface 81 and the CCD chip array 82 are in an imaging relationship. That is, the image on the original surface 81 is formed on the CCD chip array 82 as a one-to-one erect image. However, the focusing rod lens array 21
Since there is one CCD chip row 8 in this embodiment,
The erect image formed on the document surface 81 becomes an image spaced apart by four lines. To solve this problem, this embodiment uses a dedicated memory as described later.

Next, the light i13 will be explained. In this example, optical 7IA
13 uses a halogen lamp.

The function required of a contact type sensor as a reading device is the ability to read colors, similar to the human eye.

FIG. 9 shows the Thomson-Wright basic curve. This curve shows the visibility characteristics of the human eye according to color, that is, the relationship between brightness sensation for colored light and the wavelength of light. p,, p2. As is clear from the p3 curve, the human eye does not sense light with long wavelengths of 700 nm or more.

On the other hand, as mentioned above, the spectral characteristics of the light receiving parts and color filters of the CCD chips 21 to 25 have a finite sensitivity value even to light with a long wavelength of 700 nm or more. When white light is made incident on the light receiving parts 21' to 25, the light having a long wavelength of 700 nm or more is also perceived.

Therefore, in this embodiment, an infrared cut filter having almost no spectral characteristics in a long wavelength region of 700 nm or more is used together with a halogen lamp. FIG. 10 shows the spectral characteristics of the above-mentioned halogen lamp, and FIG. 11 shows the spectral characteristics of the infrared cut filter.

Now, FIG. 12 is a block diagram of a color image reading device 121 using the above-mentioned contact type color CCD sensor. Reference numeral 14 denotes an original scanning unit which reads the image of the original 123 on the original platen (moves in the direction of arrow A and at the same time lights up the exposure lamp 13 in the original scanning unit 14, so that the light reflected from the original is focused. The light is guided by the rod lens array 12 and condensed on the contact type color CD sensor 11 described above.In addition, 126 is a standard white plate that is read to obtain a reference signal.

As mentioned above, the close-contact color CCD sensor 11 has a diameter of 62.5
1024 with p m (1/16 mm) as one pixel
Five chips for each pixel are arranged in a staggered pattern, and each pixel is divided into three parts of 15.5 p m x 62.5 μm, each with cy.

G and Ye color filters are attached. As a result, a color document is read photoelectrically while being color-separated line by line.

Next, the electrical system will be explained. The electrical system consists of a drive circuit that operates the CCD, an analog processing section that converts the output signal of the COD into a form suitable for image information, and a digital signal processing section that converts the signal from the analog processing section into a signal suitable for the recording format. It is configured.

First, the drive circuit will be explained. However, in the following explanation, CC
This is a drive circuit for the D chip 21. - Other CCD chips are also provided with similar drive circuits. This drive circuit is the 14th
As shown in the figure, two-phase clock φ1. φ2 scanning period signal SH
, reset signal RS, and output signal O8.

An inverter 141 is connected to the input terminal of the clock signal φ1, and a resistor 142 and a speed-up capacitor 143 are connected in parallel to the output of the inverter 141.
Furthermore, it is connected to an input terminal of a MOS clock driver 144. The output terminal of this MOS clock driver 14.1 is connected to the φ terminal of CCD chip 21. The clock signal φ2 is also similar to φ1. In addition, the inverter 141 .
Resistance 142. A capacitor 143 and a MOS clock driver 144 are connected.

The output signal O8 terminal is connected to an emitter follower consisting of an npn transistor 145, a collector resistor 146, and an emitter resistor 147. In addition, the CCD chip 21
The power supply voltage +V is connected to the capacitor 148. C after 149
Connected to the OD terminal of the CD chip.

2-phase clock φ1. φ2 is a signal necessary to transfer the charge generated in each bit of the CCD chip 21.

The scan synchronization signal SH is a signal that distinguishes one scan in the charge transfer of the CCD chip 21, and the reset signal R3 is a signal that erases the bit after the charge has been transferred.

The signal O8 is an output signal from the CCD chip 21, and as shown in FIG. 4, it is a valid signal of 3072 bits, and outputs a dummy signal, a blank feed signal, and a reference black level signal. The bit positions of these signals are accurately defined, and the reference black level signal is a dark signal of the light receiving section, and is used to obtain a true output corresponding to the color.

Next, the analog processing section is shown in FIG. This analog processing section is provided for each CCD chip 21-25. Here, a circuit for the CCD chip 21 will be explained as a representative. The same circuitry is provided for other CCD chips as well.

The signal from C0D21 passes through the buffer circuit 131,
This signal is input to a multiplexer 132 that separates it for each color. Among the output signals of each color from the multiplexer 132, the color output signal (Ye in this embodiment) having the maximum output voltage when irradiating the white plate 126 in the stage before document scanning is provided at the front stage of the multiplexer 132. It is also input to an AGC control circuit 138 that controls an automatic gain control (AGC) circuit 133 that amplifies the output signal from the CCD 21 to a predetermined voltage value.

Then, when irradiating the white plate, the AGC voltage for amplifying the output signal from the CCD 21 to a predetermined voltage value is fixed.

In addition, the output signal of each color is the first one based on the reference black level signal.
The clamp circuit 134 obtains a true output according to the light, and the output of each color (Cy, G, Ye) from the amplifier 135 is further amplified to a voltage to be input to the next stage color conversion section. is input to a color conversion circuit 139 which outputs one primary color word of blue (B), green (G), and red (R). The output signal from the color conversion circuit 139 is converted into a digital signal by the A/D conversion section 136, and the signal from this A/D conversion section is further stored in the memory section 137.

The multiplexer 132 includes first sample-and-hold (S/H) circuits 132a and 132b that separate cy and G from the output signal from the buffer circuit 131, and the sample-and-hold CM and G signals and the output signal from the buffer circuit 131. Second S/H circuit 1 that separates Ye from inside
32c to 132e, and as mentioned above, CCD2
The serial signals of Cy, G, and Ye output from 1 are converted into synchronized parallel signals by sampling and holding twice. By doing so, the actual signal processing time in the next stage of color conversion is three times the signal output period, and a sufficient margin can be created for the performance of the circuit.

In the stage before document scanning, the output signal from the CCD 21 when the light source 13 illuminates the white plate 126 provided at the end of the contact glass 125 is separated into Cy, G, and Ye by the multiplexer 132. The AGC control circuit 138 has a configuration as shown in FIG.
A DC signal smoothed through a low path filter is converted into a digital value by an A/D converter 142, and the data is held in a latch circuit 143 until the next document scan. This held latch data is again converted into an analog DC signal by the D/A converter 144 and input to the differential amplifier 145. A reference voltage Vret is input to the other input terminal of the differential amplifier 145, and the output signal of this D/A converter and the reference voltage Vref
The difference signal is amplified to a voltage necessary to operate the AGC and inputted as an AGC voltage to the AGC circuit 133, which operates so that the output voltage of the C0D21 becomes a constant value.

The color conversion circuit 139 converts Cy, G, Ye to B, G,
It consists of differential amplifiers 139a-139c for converting into R, and outputs color difference signals of primary colors.

The A/D converter 136 converts the B, G, and R output signals output from the color conversion circuit 139 into an A/D converter 1365.
an amplifier 1362 that increases the dynamic range to
After passing through, it is sampled by the S/H circuit 1364 and the A/
It is converted into 8-bit digital data by a D converter 1365. Here, the S/H circuit 1364 is present immediately before the A/D converter 1365 because the A/D converter 1365 is of a serial-parallel type and must temporarily hold the input signal.

Furthermore, the A/D converter 136 feeds back a digital value corresponding to the reference black level out of the A/D converted digital data to the clamp circuit 1361 to control the black level to be constant. 1362 is a feedback circuit.

In this embodiment, the original scanning unit 14 includes an A/D converter 1.
Up to 36 systems are mounted and connected to a main body board 124 including a memory section 140 and a digital signal processing section through flexible electric wires 19.

As described above, the corresponding density data Dy, Dm, and Dc for B, G, and R converted into 8-bit digital signals by the A/D converter 136 are latched by the latch circuit 1366 and sent to the main body board 1 by the flexible electric wire 19.
24 and input into the memory section 140.

The memory section 140 consists of a storage area 140 a = l 40 c provided corresponding to R, G, and B, and a memory control section 140 d.
It has a function of performing connection processing on the corresponding density data Dy, Dm, and Da of B as one line of image data, and outputting it to an output device such as a printer.

〔effect〕

By controlling the AGC circuit using the color signal having the maximum output among the sampled and held color signals as in the above configuration, variations in output signals between color sensors having output signal voltage differences are equalized. Is possible.

In addition, parallel output signals of the same phase can be obtained by sample-holding the serial color signal output of three colors in time series, and then simultaneously sample-holding the sample-hold signal of the previous color output signal when outputting the last color. , it is possible to reduce circuit characteristics in subsequent color conversion and create margin for signal processing.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are configuration diagrams of the sensor unit,
Fig. 2 is a diagram showing the configuration of the color contact sensor, Fig. 3 is a diagram showing the state of adjacent CODs, Fig. 4 is a diagram showing the contents of the photosensitive pixels, Fig. 5 is a diagram showing the filter configuration, and Fig. 6 is a diagram showing the configuration of the color contact sensor. Characteristic diagram of the filter, Figure 7 is a characteristic diagram of the photodiode, Figure 8 is a configuration diagram of the optical system, Figure 9 is a characteristic diagram showing visibility, Figure 1
Figure 0 is a spectral characteristic diagram of a halogen lamp, Figure 11 is a spectral characteristic diagram of an infrared cut filter, Figure 12 is a configuration diagram of a color image reading device, Figure 13 is a block diagram of an image signal processing circuit, and Figure 14. is a block diagram of the COD drive circuit, No. 15
The figure is a configuration diagram of an AGC control circuit. 11 is a sensor unit, 13 is a light source, 21 to 25 are CCs
A D chip, 132 is a multiplexer, 132 is a sample and hold circuit, 133 is an AGC circuit, 138 is an AGC control circuit, and 140 is a memory section.

Claims (1)

[Claims] A light source, a color sensor that has color filters of multiple colors and converts reflected light from a target object irradiated with light from the light source into electrical signals of each color, and corresponds to each color filter output from the color sensor. In an original reading device that has an automatic gain control means for amplifying a color signal to a predetermined voltage value, and a sample hold means for outputting a color signal corresponding to each color filter individually, 1. A color original reading device, characterized in that said automatic gain control means is controlled using a color signal having a maximum output.