JPH02158275A - Image input device - Google Patents

Abstract

PURPOSE:To miniaturize the size of a circuit by storing black reference output data and a correction coefficient in one ROM and carrying out arithmetic processing such as subtraction by a subtractor or multiplication by a multiplier in synchronism with a clock signal and an image read start signal which are inputted from outside. CONSTITUTION:An analog image signal is inputted to an A/DC 10 and is converted into a digital signal, which is inputted to a data selector 15 and when a correction is made successively, data is selected by the subtractor 16, which subtracts the black reference data 13 already stored in the ROM 30. The data on the subtraction result is latched by a latch 17, an address counter 22 outputs the address where the correction coefficient is stored at the timing of a next clock pulse, and the correction coefficient 11 stored in the ROM 30 is latched by a latch 23. Then the multiplier 18 performs the multiplication by the correction coefficient 11. Thus, the black reference data 13 and correction coefficient 11 are written in one ROM 30, so the circuit constitution is miniaturized.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an image input device that automatically performs image correction on data read by a contact type image sensor widely used in office automation equipment and the like.

[Conventional technology]

Conventionally, there has been a contact type image sensor (also known as a line sensor) of this type as shown in FIG. 3. The figure is a cross-sectional view of a contact type image sensor. In the figure, 1 is a feed roller, 2 is a document fed by the feed roller 1, 3 is a housing molded by aluminum die-casting, etc., and 4 is a front surface of the housing 3. 5 is an LED (light emitting diode) array that illuminates the document 2 in a line through the glass plate 4; 6 is a prismatic Rondo lens array provided in the longitudinal direction; and 7 is a photosensitive element. A plurality of sensors are provided in the longitudinal direction, and 8 is a sensor IC. Next, the operation will be explained with reference to FIGS. 4(a) and 4(b). First, light emitted from the LED array 5 as a light source is reflected by the document 2, passes through the Rondo lens array 6, and enters the sensor 7. This reflected light is shown in Figure 4(a).
As shown in (b), it is converted into an electrical signal and sent to the sensor IC.
When a driving clock signal (CLK) and a start signal (Sr) are applied to 8, the image signal (SIG) is outputted to the outside in synchronization with the clock signal (CLK). Next, a method for correcting image signals will be explained. FIG. 5(a) shows a typical image output when an all-white document 2 with a reflectance of - brightness is read.The reason why this output voltage waveform is not constant is that the sensitivity of the sensor 7 is This is because each element is slightly different, the light source of the LED array 5 has an illuminance distribution, and the Rondo lens array 6 has variations. If the output signals are different for the same input signal in this way, it can be used for simple binary reading, but it is difficult to differentiate the brightness by level! It is difficult to read Pi. Therefore, each bit (element) of the sensor 7 is multiplied by a correction coefficient (each pixel variation information), as shown in FIG.
As shown in b), it is necessary to perform correction to output a constant image signal for the document 2 having a negative density. Next, a specific circuit example of the correction method is shown in FIG. FIG. 6 is a block diagram of a conventional sensor LSI. When the analog data output from the sensor 7 is input to this LSI, the A/D converter (A/DC) 10
The data is converted into a 6-bit digital value, multiplied by a correction coefficient written in advance in the ROMII, and finally the corrected data is output as a 5-bit digital value 13 via the multiplier 12. The calculation in the correction calculation unit composed of the multiplier 12 and its control circuit is performed as shown in the following equation. DBO to DB4: Correction output data (0 to 31..) D,
: Correction coefficient (θ~63..) (63.. indicates 63 in lO base) 7w:
White reference plane signal (0 to 5V) D,; Original image signal data (0 to 63.6) VP Dp = [nt (x64 +Q, 5) ・
・(2) VP: Original image signal voltage (0 to 5 V)

[Problem to be solved by the invention]

Since the correction calculation unit in the conventional image processing apparatus is configured as described above, the output of the sensor 7 may not be zero even when the document 2 is black, but has a certain value, and that output value is determined by the sensor. There are individual variations. Therefore, it is necessary to consider not only the white reference plane of the original 2 that conventional image input devices handle, but also the black reference plane, and then perform correction on the value obtained by subtracting the output value. The brightness of the screen is not the same, but the density (gradation) is between white and black.
There was a problem in that only the data with the variation when reading the black reference plane was always obtained for the original 2 having the same color. In addition, since the sensor 7 and the LED array 5 are temperature dependent, if the temperature of the entire image input device differs from the initial state due to continuous use for a long time, or if the LED array 5
Depending on the lifespan of the D array 5, there may be cases where the output differs even for the same density, and in that case, the correction will fail. As a countermeasure for such cases, ALC (Auto Level C) is set before inputting the image signal to the correction circuit.
Ant, ) circuits can be used to control the image signal within a certain range, and methods to change the reference voltage of A/DCIO when converting an analog image signal to a digital signal are possible, but conventional correction LSIs However, this point has not been taken into consideration, and when an image signal processing circuit including a correction circuit is provided with this function, there are 11 problems in that the configuration of the entire circuit inevitably becomes large. This invention was made in order to solve the above-mentioned problems, and it performs corrections that take into account the white and black image reference planes, and takes into account the aforementioned temperature dependence and output changes due to lifespan, etc.
To provide an image adult device which is compact and easy to use, in which an ALC circuit and a circuit capable of changing an A/DC reference voltage can be easily installed, and an interface is made as simple as possible.

[Means to solve the problem]

The image input device according to the present invention stores correction coefficients and dark data internally in order to correct the output signal in consideration of the white and black image reference planes using data stored in one ROM, and By fixing specific bits (elements) to white and black, the circuit configuration is such that an ALC circuit or the like can be easily added, and the interface is limited to an image reading start signal and a clock signal.

[For use]

The image input device according to the present invention can be easily combined with an ALC circuit by using it in combination with a sensor whose output of a certain bit is fixed to a white reference and a black reference, and can also be used for correction with black reference data. coefficient of one R
By writing to OM, the overall circuit configuration can be made smaller.

【Example】

Hereinafter, a method for correcting a sensor output signal when using an image input device according to the present invention as an embodiment of the present invention will be explained. In Figure 1, the same parts as in Figure 6 are designated by the same reference numerals. , 30a is the black reference output voltage D
ROM that stores d. 16 is a subtracter, and 18 is a multiplier. Next, in FIG. 1(a), if the black reference output is Ov and the white reference output is +5V, and each data is expressed in 8 bits, the correction coefficient Dki of the i-th sensor number which is the i-th element is is expressed as follows. The correction coefficient Dk and the black reference output voltage Dd are written in advance as data in the ROMs 30a and 30b. How to obtain the correction coefficient and how to create the corrected data is shown in FIG. The subtracter 16 subtracts the black reference output voltage Dd written in the subtracter 16, and the multiplier 18 multiplies the black reference output voltage Dd written in the address B of the ROM 30b to obtain the corrected image signal Dw. Here, the mutual relationship between addresses A and B is (1), B-A+N (N is a constant) (2),
It is convenient to use A-2i B-2t+1 (t is the sensor number). Next, in FIG. 2 which shows a block diagram of the image input device according to the present invention, 14a and 14b are reference voltages of A/DCIO, 15 is a data selector, and 17, 19
．． 23 is the 'p notch 2o is the image reading start signal SI!
21 is a delay and pulse generation circuit, 22 is an address counter, and 30 is a ROM storing correction coefficients 11 and dark data (black reference data) 13. Next, the operation will be explained. First, the interface signals necessary to drive the image reading start signal SII and the clock signal CL in FIG.
Only KO, both signals and power supply (+5V, GND)
When given, a signal for driving the sensor 7 is generated by the delay and pulse generation circuit 21. Here, when the analog image signal is input to the A/DCIO, it is converted into a digital signal and input to the data selector 15, which then selects whether or not to perform subsequent correction. If no correction is to be performed, the digital value output by the A/DCIO is output as is and the process ends. When performing correction, the data is selected by the subtracter 16 and stored in advance in the ROM 30.
The dark data (black reference data) 13 stored in is subtracted by the subtracter 16. The data of the subtraction result is latch 1
7, and at the timing of the next clock pulse, the address counter 22 outputs the address where the correction coefficient is stored, and the correction coefficient 11 stored in the ROM 30 is latched.
is latched by latch 23. Subsequently, the multiplier 18 multiplies the data by the correction coefficient 11, and the corrected data is latched into the latch 19 at the next timing. In addition, 14a and 14b are reference voltages for A/DCIO, which are used as constant voltages when an ALC (Out. Level Cont.) circuit is used in the front stage of the correction circuit, and are variable when ALC is not used. shall be. Whichever method you choose, the reference signal is
The output of the sensor 7 fixed to the white reference output and the black reference output is used. This is the sensor 7 of the document 2 reading section.
This can be achieved by attaching the original 2 for white reference output and black reference output to a part of the screen in advance. With this procedure,
For example, some bits of the sensor 7 will not be able to read the document 2, but this is due to the length of several millimeters (
(approximately 2 mm), and there is no practical problem. In the above embodiment, an example has been described in which the white reference signal is extracted and outputted to the ALC circuit, but this white reference signal can also be used as a failure signal. As an example, if the time when the LED array is on is ``Old gh'' and the time when the LED array is off is ``Lo-'', it can be determined that the LED array is not lit or the like is a failure. In this case, it is possible to take measures to set the dot OVF (overflow signal) to the old GH and output all white.

【Effect of the invention】

As described above, according to the present invention, the black reference output data and the correction coefficient are stored in one ROM in advance, and the subtracter outputs the data in synchronization with the externally input clock signal and image reading start signal. Since the circuit is configured to perform arithmetic processing such as subtraction or multiplication using a multiplier, the circuit can be made small and inexpensive, and since the interface signals are limited to the above two types, the circuit is easy to handle. There is an effect that can be obtained.

[Brief explanation of the drawing]

1(a) and 1(b) are explanatory diagrams of a correction procedure according to an embodiment of the present invention, FIG. 2 is a block diagram of an image input device according to an embodiment of the present invention, and FIG. 3 is a general image. Cross-sectional view of the sensor, FIG. 4(a). (b) is a block configuration diagram and time chart of the image sensor in Figure 1, Figures 5 (a) and (b) are explanatory diagrams of signals before and after correction when the image sensor reads the white reference, and Figure 6. The figure is a block diagram of a conventional correction LSI. In the figure, 10 is A/DC, 11 is correction coefficient, 13 is dark data, 16 is subtracter, 18 is multiplier, 30 is ROM
It is. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] An A/DC that converts analog signals output from the sensor into digital signals, and a ROM that stores information on variations in each pixel to correct variations in each element of the sensor.
and a correction calculation section, the variation information of each pixel is stored as black reference output data as data when reading a black reference original, and a correction coefficient indicating the output ratio when reading a white reference original. a subtracter that subtracts the black reference data in the ROM when correction is required for the sensor output, and a correction coefficient in the ROM that is multiplied by the subtraction result data processed by the subtracter. 1. An image input device comprising: a multiplier for controlling the ROM, a clock signal and an image reading start signal as two external control inputs for controlling various circuits such as the ROM and a correction calculation section.