JPS6087569A - Color original reader - Google Patents

Abstract

PURPOSE:To correct accurately white balance by storing a correction coefficient by color and picture element indipendently after a reading signal of a white reference plate is A/D-converted in a color original reader and arithmetic processing a scanning signal with the correcting coefficient at reading of original. CONSTITUTION:When a scanner section 10 reads and scans the white reference plate 13, a signal where RGB color signals appear in time series is obtained in response to color arrangement of a color separation filter 17, the level is fluctuated by a lamp 11 and a lens 14 or the like, the result is A/D-converted at a converter 21 of a white balance correction section 20, the correction coefficient M is outputted from an ROM22 by using the result as an address and written in an address corresponding to a sensor element of an RAM23. When an original 12 is carried to the reader and the reading scanning is started, a signal inputted from the scanner section 10 is A/D-converted, then the signal is inputted to an arithmetic device 24, where the signal is multiplied with the correcting coefficient from the RAM23. A scanning signal outputted from the arithmetic device is subject to complete white balance.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a color document reading device.

1 Configuration of Conventional Example and Its Problems FIG. 1 is a block diagram of a conventional color original reading device. In this figure, 1 is a document, 2 is a white lamp, 3 is a lens, 4 is a one-dimensional solid-state image sensor, and 6 is an amplifier. A color separation filter array 6 is mounted on wafer on the light receiving surface of the one-dimensional solid-state image sensor 4. This color separation filter array 6 has red (R) associated with each sensor element.

It consists of an array of minute color separation filters for green (G) and blue (B) (see Figure 3).

To explain the operation, an optical image of a document 1 illuminated by a white lamp 2 is formed on the light receiving surface of a one-dimensional solid-state image sensor 4 via a lens 3, and is divided into n, G, and B by a color separation filter array 6. The light is separated into three primary colors, enters the sensor element, and is converted into a color signal. The main scanning of the original 1 is performed by the one-dimensional solid-state image sensor 4, and the time series of RlG and B color signals of each pixel on one line is outputted from the one-dimensional solid-state image sensor 4 as an analog image signal. (See Figure 3). After this analog image signal is amplified by the amplifier 5,
Output to the outside.

Now, each color signal level of the analog image signal output from such a conventional color document reading device depends not only on the spectral reflection characteristics of the document, but also on the multiplicative product of the spectral characteristics of the white lamp, color separation filter, and image sensor. Therefore, even when the white reference plate is read, it is not the same, and there is a problem in that an image signal with no white balance is supplied to an external reproduction system.

To solve this problem, when reading the white reference plate, R, G,
The level of each color signal of B is detected and held by a sample and hold circuit, and the gain of the AGC circuit for each color is set according to the detected and held level. It is also conceivable to handle the analog image signal by passing it through an AGC circuit corresponding to each color. However, in addition to complicating the device configuration, there are also variations in the sensitivity of individual color separation filters and sensor elements, and white ramp +
7) Why I for each pixel due to unevenness in the amount of light: There is a problem in that disturbances in the balance cannot be corrected.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned problems, and provides a color document reading device that can obtain an image signal with precise white balance on a pixel-by-pixel basis and has a relatively simple device configuration. With the goal.

Structure of the Invention The present invention provides an A/D conversion means for converting an analog image signal outputted from the scanner section into a digital image signal, and an A/D conversion means for converting an analog image signal outputted from the scanner section into a digital image signal, and an A/D conversion means for converting an analog image signal outputted from the scanner section into a digital image signal, and an A/D conversion means for converting an analog image signal outputted from the scanner section into a digital image signal. A storage means for storing a correction coefficient; and a calculation means for performing a specific calculation on the digital image signal and the correction coefficient read from the storage means and outputting a digital image signal subjected to white balance correction. By providing a white balance correction section consisting of the following, the above object is achieved.

Description of examples Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram of a color document reading device according to an embodiment of the present invention. In this figure, 1° is a scanner section, and 2o is a white balance correction section.

To explain the scanner unit 1o, 11 is a white lamp for illuminating the original 12 or the white reference plate 13;
16 is a lens, 16 is a one-dimensional solid-state image sensor, and 16 is an amplifier. A color separation filter array 17 is mounted on the light receiving surface of the one-dimensional solid-state image sensor 15 on wafer.

The color separation filter array 17 consists of an array of minute color separation filters for the three primary colors R, G, and B associated with each sensor element (see FIG. 3).

An optical image of the original 12 or the white reference plate 13 illuminated by the white lamp 11 is formed on the light receiving surface of the one-dimensional solid-state image sensor 15 via the lens 14, and is divided into n, G, and B by the color separation filter array 17. The light is separated into three primary colors, enters the sensor element, and is converted into a color signal. The main scanning of the white reference plate 13 that spans the original 12 is performed by the one-dimensional solid-state image sensor 16, and the time series of RlG and B color signals of each pixel on one line is read as an analog image signal.
It is output from the dimensional solid-state image sensor 15 (see FIG. 3). This analog image signal is amplified by an amplifier 16 and then input to a white balance correction section 2°. Sub-scanning is performed by moving the document 12.

The configuration of the white balance correction section 20 will be explained. 21
is an A/D converter, which converts an analog image signal inputted from the scanner section 1° into a digital image signal. 22 is a ROM, 23 is a RAM, and 24 is an arithmetic unit. The digital image signal output from the A/D converter 21 is stored in the ROM2.
2 as an address signal, and is also input to the arithmetic unit 24 as one input data. The output signal (correction coefficient) of the ROM 22 is input to the RAM 23 as write data, and the output signal of the RAM 23 is input to the arithmetic unit 24 as the other input data.

FIG. 3 is an explanatory diagram of the arrangement of color separation filters constituting the color separation filter array 17, and FIG. 4 (, ) is an illustration of the white reference plate 13.
(b) is a waveform diagram of the analog image signal after white balance correction. The operation of the present color document reading device will be explained with reference to FIGS. 3 and 4.

Prior to reading the document, the white reference plate 1 is scanned by the scanner unit 1o.
3 reading scans are performed. The analog image signal (white reference plate scanning signal) obtained at this time is processed by the third color separation filter.
Since they are arranged as shown in the figure, the R, G, and B color signals appear in time series as shown in FIG. The levels of the R, G, and B color signals depend on the multiplicative product of the spectral characteristics of the white lamp 11, lens 14, color separation filter, and one-dimensional solid-state image sensor 15 as described above. It becomes unbalanced as shown in b).

In addition, the light of the white lamp 11 and the lens 14: n, 'unevenness,
The level of each color signal varies depending on the pixel position due to variations in sensitivity of individual color separation filters and sensor elements.

The white reference plate scanning signal is digitized by the A/D conversion 2t21 for each sensor element of the one-dimensional solid-state image sensor 15, that is, for each pixel, and is input to the ROM 22 as an address signal.

A correction coefficient M determined by the 9th order equation (1) is output from the address specified by the address signal of PL OM 22, and the RA
It is written to the address corresponding to the sensor element M23.

V in x M / 2 = C - (1) where,
V in is the value after A/D conversion of the white reference plate scanning signal,
n is the number of quantization bits of the A/D converter 21, and C is a constant. This C corresponds to the lower limit value of the white balance correction range.

In this way, correction coefficients for each sensor element are sequentially determined and stored in the RAM 23.

When the correction coefficients for one line are stored in the RAM 23, R
AM23 switches to read mode, and the correction coefficient is read out from RAM23 in synchronization with the white reference plate scanning signal.
It is input to the computing unit 24. In the arithmetic unit 24, the digitized white reference plate scanning signal is multiplied by the correction coefficient, and the multiplication result is output as a corrected white reference plate scanning signal (digital signal). The corrected white reference plate scanning signal is normalized to Bell C, with RlG and B color signal levels constant over all pixels, as shown in FIG. 4(b).

Thereafter, the original 12 is conveyed to the reading device, and original reading scanning begins. An analog image signal (original scanning signal) input from the scanner unit 10 to the white balance correction unit 20 is digitized by an A/D converter 21 and input to a calculator 24 . Further, the RAM 23 of the white balance correction IE section 2o operates in a read mode and outputs correction coefficients in synchronization with the reading scan of the scanner section 10. The calculation unit 24 multiplies this correction coefficient by the digitized original scanning signal. Output. As mentioned above, the correction coefficients stored in the RAM 23 are for each color and each pixel of the scanner unit 1°! Since the value is determined to cancel out the effects of single-key variations, the document scanning signal output from the calculator 24 has a perfect white balance.

In this embodiment, the white reference plate 13 is read and scanned immediately before reading the original, and the correction coefficients stored in the RAM 23 are used for correction.
23 (or ROM) and the correction coefficients can be used repeatedly. However, according to the configuration of this embodiment, a stable correction effect can be achieved immediately after the white lamp 11 is turned on. The reason for this is the following westward trend.

In general, immediately after the white lamp 11 is turned on, the light amount, its distribution, and spectral characteristics of the white lamp 11 vary considerably over time. In this case, it is not possible to expect the IF to perform a normal correction operation immediately after the white lamp 110 is turned on. In contrast, in this embodiment, the correction coefficients in the RAM 23 are determined based on the white reference plate scanning signal immediately before the start of document reading, as described above, and reflect the characteristics of the scanner unit 10 at that time. Since the image is faithfully reflected, normal white balance correction is performed immediately after the white lamp 11 is turned on.

Further, although the scanner section 1o of this embodiment is of a dot sequential type, it may be replaced with a line sequential type.

Furthermore, the scanner section 1o of this embodiment has R and G colors.

The configuration was such that originals were scanned by adding color 1') to the three primary colors of B, but the configuration is not limited to this; for example, the complementary colors yellow (Y), magenta (M), and cyan (C) It may be configured to be disassembled.

Effects of the Invention As described above, the present invention provides the following advantages: 1. The same cedar is installed after the scanner unit that separates and reads the original document in color. an A/D conversion means for converting an analog image signal outputted from a digital image signal into a digital image signal; and a storage means for storing correction coefficients for each color and each pixel; Since the configuration includes a white balance correction section that includes a calculation means that performs a specific calculation with a correction coefficient and outputs a digital image signal that has undergone white balance correction, it is possible to input the image signal in pixel units. Effects such as accurate white balance correction and a relatively simple device configuration can be obtained.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional color document reading device;
3 is an explanatory diagram of the arrangement of color separation filters, and FIG. 4 is a waveform diagram of a white reference plate scanning signal before and after correction. 10-... Scanner section, 11... White lamp, 12... Document, 13... White reference plate, 14...
... Lens, 15-... One-dimensional solid-state image sensor, 16-... Amplifier, 17-... Color separation filter array, 20-... White balance correction section, 2
1... A/D converter, 22... ROM, 23-...
--- RAM, 24 --- Arithmetic unit.

Claims (1)

[Claims] It has a scanner section that separates and reads the original by color, and a white balance correction section that performs white balance correction on a pixel basis to the analog image signal of each color output from this scanner section. , an A/D conversion means for converting an analog image signal outputted from the scanner section into a digital image signal, a storage means for storing correction coefficients for each color and each pixel, and reading out the digital image signal from the storage means. 1. A color document reading device comprising three means for performing a specific calculation with a correction coefficient and outputting a white balance corrected digital image signal. .