JPH02298165A - Picture reader - Google Patents

Abstract

PURPOSE:To allow the user to recognize the period of lamp replacement without need for always taking care of gradation of a picture by always monitoring the S/N over the entire read area so as to apply proper display when the S/N is deteriorated. CONSTITUTION:The read of a CCD 12 is implemented prior to the lighting of a fluorescent light, a dark signal is digitized as an absolute value, recorded in a RAM 214 through a buffer 222 and the picture signal by one line is stored. While a reference white level board 20 is lighted by the fluorescent light 15a, the light is subject to photoelectric conversion and the result is stored in a RAM 214 as one line data. The calculation of dividing a data Dwmin by a data Ddark is implemented from the two data Ddark and Dwmin obtained in this way and the result is compared with a constant K and when the result is smaller, the leading of a light source is awaited when the time does not reach the specified time. When the time reaches the specified time, a warning is raised.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides a CCD (charge-coupled
It relates to an image reading device that uses a photoelectric conversion element such as a device to scan a document, generates an image signal, and supplies it to an external device, and particularly relates to a reading device that uses a fluorescent lamp or the like as a light source for illuminating the document. It is.

[Conventional technology]

As the processing power of personal computers has improved, image reading devices that can transmit the density of each read pixel to the outside as a 256-gradation (=8 bits/pixel) signal, so-called grayscale output, have become inexpensive and generally available. It has come to be used by being connected to a computer, etc.

Conventionally, fluorescent lamps have been widely used as light sources for illuminating documents used in such high-gradation image reading devices. However, the light intensity of fluorescent lamps changes over time depending on the time of use or the number of times they are turned on. In the long term, the amount of light generally decreases.

Conventionally, so-called black-and-white only binary image reading devices either did not issue a warning at all about a decrease in light intensity after long-term use, or issued a warning if the light intensity did not reach a certain level within a certain amount of time after turning on the device. was. In the case of these conventional examples, a warning was issued regardless of the inherent S-N ratio of the photoelectric conversion element and the dynamic range (ratio of implicit current to saturation current).

Furthermore, in those using fluorescent lamps, lens optical systems, etc., there is a reduction in the amount of light at the peripheral area compared to the central area, so-called shading distortion, etc., and the dynamic range over the entire reading area is not guaranteed.

[Problem to be solved by the invention]

If the above-mentioned conventional method is applied to recent image reading devices with high gradation, it is inconvenient that the user has to pay attention to the gradation of the image every time the user uses the device. There is.

Further, when the timer means measures the time while the light intensity is below a certain value, and the timer means issues a warning when the specified time is reached before the light intensity reaches the specified value,
light? ``Since the light amount detection is performed by focusing on only a portion of the conversion element, as mentioned above, it is not possible to guarantee the image quality over the entire reading area.

The present invention was made under these circumstances, and it is an object of the present invention to provide an image reading device that can ensure a predetermined S-N ratio over the entire reading area.

[Means to solve the problem]

In order to achieve the above object, the present invention configures an image reading device as shown in (1) below.

(1) An image signal reading device that scans a document, generates an image signal, and supplies it to an external device, which includes the following a, b, c,
An image reading device comprising the components d and e.

a. Light source for document illumination.

b. Reference white plate C1 Storage means for storing signals read when the reference white plate is illuminated with the document illumination light source and signals obtained when a reading operation is performed without illuminating the reference white plate.

d. Detection means for detecting that the ratio of the minimum value of the signal read with illumination and the average value of the signal when reading operation is performed without illumination, in the storage means, is below a predetermined value.

e. Display means operated by the output of the detection means.

(Operation) According to the above configuration, when the S-N ratio becomes less than a predetermined value in a part of the reading area, maintenance is requested with an appropriate display.

〔Example〕

The present invention will be explained below with reference to Examples.

FIG. 1 is a block diagram of a document image reading device which is an embodiment of the present invention. In the figure, 1 is a document image reading device R (
(hereinafter referred to as a reader), 2 is a reader main body, in which a document 18 is placed with the document surface facing down on the platen glass 17, and a fluorescent lamp 15a (light source for document illumination) in the document illumination unit 15 is used.
The device is configured to irradiate an original image with a lens 14 via a reflecting mirror 16 and form an image on a CCD (charge-coupled device) 12 for reading. 13 is a CCD driver, and 11 is a control unit which will be described later. 19 is
This is a platen cover for bringing the M-piece 18 into close contact with the platen glass 17. 20 is a reference white plate for obtaining a reference white signal.

Next, the operation of the reader 1 of this embodiment will be explained with reference to FIGS. 1, 2, and 3. Figure 2 shows the control unit 11
FIG. 3 is a sequence flowchart showing a continuation operation.

The original N418 is placed so that the leading edge of the original is at the right end on the platen glass 17 in FIG. Further, the right end of the W/document illumination unit 15 in FIG. 1 is the initial position (home position), and is configured so that the position can be confirmed by a position sensor not shown in the figure. The reader 1 of this embodiment is always connected to the external devices (for example, digital printer, personal computer, etc.) shown in FIG. Image data to the external device 218 is configured to be transmitted through a control signal 221 (see right in FIG. 2).

Prior to the operation of the reader 1, various commands are inputted from the external device 218. For example, set the pixel density to 300,15
Inputs are made for settings such as whether to select 0.75 ppi (pic-cell perinch) and whether to select binary or multivalue mode for the image data format. Upon receiving these commands, the microprocessor 220 makes necessary settings in the timing signal generation circuit 219, FIFO (first-in first-out) circuit 216, etc. in advance. External device 21
When the command to start reading from 8 is given manually, the 3rd
In step S1 in the figure, it is confirmed whether the lighting unit 15 is at the home position, and if it is not at the home position, a stepping motor (not shown) is controlled in step S7 to move it to the home position. The home position referred to here is the position where the lighting unit 15 is moved all at once in the direction opposite to the direction of arrow A in FIG.
The position of the lighting unit 15 is detected by a sensor not shown in the figure. The reference white plate 20 is read at this position. Next, the lamp 15a is turned on (step S2). This step S2, which is the main part of the present invention, will be explained in detail later with reference to FIG. Thereafter, the reader 1 enters a reading operation and starts scanning in the direction of arrow A shown in FIG. Original illumination unit 15
The distance from the initial position to the leading edge of the document on the platen glass 17 is approximately 2 to 3 mm, and the scanning speed of the mirror by the stepping motor is controlled to be stable during this time. When the original illumination unit 15 reaches the leading edge of the manuscript,
The microprocessor 220 has an interface (1/F
) An image signal output permission is output to the circuit 217, and the read image signals are sequentially sent to the external device 218 (
Step 33).

The scanning length of the optical system is uniquely determined by the number of pulses with which the microprocessor 202 drives the stepping motor, so the microprocessor 202 determines that document reading is complete when the required number of pulses are output to the motor. The lamp 15a is turned off, an image output disable signal is output to the interface circuit 217, the stepping motor is stopped, etc., and the external device 2 indicates the end of document reading.
Do this for 18.

Thereafter, the microprocessor 220 reverses the motor in step S4, moves the document illumination unit 15 in the direction opposite to the arrow A in FIG. 1, and returns it to the unillustrated initial position (home position) (step S5). ). When it is confirmed that the motor has returned to the home position, the stepping motor stops (step S6). If the next reading command does not come from the external device 218 while the optical system returns, it stops at the initial position and ends the operation.

To further explain the flow of image signals according to FIG. 2, 12 is a CCD sensor that reads the image of the original 20;
4 is an analog signal amplifier, 205 is a sample and hold circuit necessary for extracting only the image signal from the analog signal of the CCD 12, and timing generation circuit 2
The sampling operation is performed by a timing signal from 19 (indicated by a broken line). 206 is a buffer amplifier, the output of which is supplied to 207 and 208.

207 is an A/D converter for digitizing analog signals. 208 is a peak detection/hold circuit for detecting the highest voltage, that is, the brightest part of the analog signal output from the CCD 12 line by line.

The three switches shown at 210-212 are controlled by microprocessor 220 through timing circuit 219. 209 is a reference voltage circuit that generates a fixed voltage VB.

214 is a RAM (ra) for storing a reference white signal when reading the reference white plate 20 (see FIG.
ndom-access memory (storage means), which, in cooperation with the timing generation circuit 219, transfers all pixel information from the CCD 12 to the A/D converter 2.
It is configured so that it can be stored via 07. Also this R
The output from AM 214 is used to provide white correction data to D/A converter 213 in cooperation with timing circuit 219 during actual document reading operation. Furthermore, this RAM 214 is configured so that the contents of the microprocessor 220 can be read and rewritten through the bus switching circuit 215.

When scanning an actual document, the D/A converter 213 sequentially converts the reference white signal output from the RAM 214 into an analog signal, and feeds it back to the Vref terminal of the A/D converter through the switch 212. FIFO
Reference numeral 216 is for accumulating several lines of image data that are sequentially converted by the A/D converter 207 when scanning the original. The image data temporarily stored in this FIFO 216 is sent to the external device 21 through the interface circuit 217.
8 in sequence.

Based on the above configuration, the main parts of the present invention will be specifically explained with reference to FIG.

Step S21 is a hardware setting that is performed prior to lighting up the fluorescent lamp. Once this setting is done, the CCD
12 read operations are performed, and the analog signal is 20
After passing through the circuits 4, 205, and 206, the signals are digitized by the A/D converter 207 under a constant voltage v8 of the reference voltage circuit 209. That is,
In this state, the dark signal is digitized as an absolute value,
The image signal is recorded in the RAM 214 through the buffer 222, and one line worth of image signal is stored.

Next, the CPU 220 learns after an appropriate time that one line of image signals has been accumulated, and operates to stop recording this one line. After that, in step S22, C
The PU220 operates the bus switching circuit 215 and the RAM21
4 to 1 line's worth of pixel data is manually input, and the average value Ddark is obtained. This average value data Ddark is CC
This is the average value of one line of data including dark voltage etc. present in D12 and subsequent circuits, and is a work RA not shown.
stored in M.

In step 323, the fluorescent lamp is preheated for 3 seconds. Thereafter, in step S24, the fluorescent lamp 15a is turned on. In step S25, a timer T1 is used to count the timeout value when generating a warning.
After setting it to 0, it is set to count at regular intervals.

Next, in step S26, the reference white plate 20 is illuminated with the fluorescent lamp 15a, and the light is photoelectrically converted, as described above! It is stored in the RAM 214 as line data. Next, the CPU 220 uses the RAM 214 as described above.
Data corresponding to the darkest portion is selected from the reference white data stored in the reference white data and stored in a work RAM (not shown).

In the next step S27, the two data Ddark obtained in the step 522 and step S26 are
and by Dwmin.

The calculation of Dwmin divided by Ddark is performed.

The result of this calculation is compared with a constant (detection means).In the case of this embodiment, K is 64 to guarantee output of 64 gradations.
It is determined that As a result of this comparison, if the supplementary calculation result is smaller than K, the process advances to the next step 328. This step 828. In step S25, the counter value started is verified, and if the specified time has not been reached, step 526 is performed to wait for the light source to rise.
The above sequence from . When the predetermined time has been reached, a warning is generated in step S29 (display means). If it is determined in step SZ7 that it is larger than the constant, the normal end occurs without issuing a warning.

In addition, in the embodiment, the calculation was performed using the darkest pixel among all pixels as Dwmin in step 326 in FIG. The darkest one may be selected from among them and set as Dwmin, and the "minimum value" of d in the claims includes this Dwmin.

Also,! The notification may be provided by any appropriate method such as flashing lights or instructions for maintenance using LEDs.

〔Effect of the invention〕

As explained above, according to the present invention, the S-N ratio over the entire reading area is constantly monitored, and when the S-N ratio deteriorates, an appropriate display is performed, so that the user can always monitor the image. There is no need to pay attention to gradation, image quality can be guaranteed over the entire scanned area, and it is possible to know when to replace the lamp.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of the control unit 11, FIG. 3 is a flowchart showing the operation of the embodiment, and FIG. 4 is a detail of step S2 in FIG. 3. It is a flowchart which shows. f5a...R light source 20...Reference white plate

Claims (1)

[Claims] (1) An image signal reading device that scans a document, generates an image signal, and supplies it to an external device, the device comprising: a document illumination light source; a reference white plate; and the document illumination light source that illuminates the reference white plate. a storage means for storing the signal read with the illumination and the signal when the reading operation is performed without illumination; An image reading device comprising: a detection means for detecting that a ratio to an average value has become equal to or less than a predetermined value; and a display means operated by an output of the detection means.