JPS61257069A - Correcting method for quantity of light variation - Google Patents

Abstract

PURPOSE:To correct the read image information according to the quantity of light variation of the light source to be used for reading device and to minimize the read density error by providing an optical sensor a shading correction plate and a sample and hold circuit. CONSTITUTION:Before reading an original, the output of the shading correction plate 12 provided prior to the read start position of outside range of an original mounting area is fetched to a line photoelectric transducer 3, converted into an electrical signal and stored at a memory 6 through an amplifier 4 and an A/D converter 5. At the same time, the quantity of light of fluorescent lamp is measured by an optical sensor 2 and inputted to the sample and hold circuit 8. Next,the reading of the original in a sub-scanning direction is started, and inputted to the sample and hold circuit 7 through the sensor 2. The quantity of light of circuits 7 and 8 are compared by a divider 9 and a factor is obtained. The factor and the value obtained by A/D-conversion of the video signal of the correction plate 12 stored in the memory 6 are multiplied by a multiplier 11, and the correction is performed to the shading waveform. In this way, it is possible to obtain the image information with less read density error due to the variation of the quantity of light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an image reading device, and particularly relates to a light amount change correction method suitable for correcting read information by following changes in light amount after a light source is turned on. .

[Background of the invention]

Conventional image reading devices correct read image information for temporal changes and positional changes in the amount of reflected light from the original, as described in Japanese Patent Application Laid-open No. 153377/1982, from a correction plate immediately before reading the original. This method is performed using only the information received from the line photoelectric conversion elements on the reflected light, and is a correction for a positional change in the amount of reflected light in the direction in which the line photoelectric conversion elements are lined up, that is, in the main scanning direction, that is, a shuding correction. However, no consideration was given to temporal changes in the amount of light from the light source.

[Purpose of the invention]

An object of the present invention is to provide a light amount change correction method that corrects read image information by following temporal changes in light amount of a light source used in a reading device and reduces read density errors.

[Summary of the invention]

To correct fluctuations in read information due to changes in the light intensity of the light source 1
It is necessary to sense temporal changes in light intensity. Figure 2 shows an example of the change in light intensity from when a fluorescent lamp is turned on. There is a significant change in light intensity at the beginning of lighting, and even after two minutes have elapsed after lighting, the light intensity changes by 2 to 3% per minute. In order to achieve high gradation reading, it is necessary to constantly measure changes in the light intensity of the light source and correct the changes in light intensity for each reading.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, an optical sensor 2 for constantly measuring the amount of light after the fluorescent lamp 1 is turned on is placed near the fluorescent lamp, and directly receives light to measure the amount of light. The fixed position of the optical sensor 2 can be placed anywhere as long as it is at a constant distance from the fluorescent screen and can receive direct light from the fluorescent lamp.In this way, the light intensity changes from when the fluorescent lamp is turned on to when reading is completed. By constantly measuring the
It is possible to correct changes in light amount in the sub-scanning direction (the direction in which the yX document moves).

FIG. 3 is a block diagram of a processing circuit according to an embodiment of the present invention that realizes light amount change correction when a photosensor for measuring changes in light amount is placed near a fluorescent lamp.

Immediately before reading the document, the line photoelectric conversion element 3 captures the shooding correction plate 12 provided outside the document placement area and in front of the reading start position, converts the shooing waveform into an electrical signal, and amplifies it with the amplifier 4. , an A/D conversion circuit 5 converts the analog signal into a digital signal, and stores the digital signal in a memory 6. Simultaneously with reading the correction plate 12, the light intensity of the fluorescent lamp is measured by the optical sensor 2, and the sample and hold circuit 8 holds the sample.Next, reading of the document in the sub-scanning direction is started.

The light intensity of the light source at that time is measured by optical sensor 2, and switch 1
4 and sample and hold the sample and hold circuit 7. A divider 9 compares the sample-held correction plate and the amount of light when reading the original to obtain a coefficient, and this coefficient and a value obtained by D/A converting the video signal of the correction plate stored in the memory 6 are used in a multiplier 11. Correct the shooting waveform by multiplying by .

By performing this process every line in the sub-scanning direction or at regular intervals and making corrections that follow changes in light intensity, reading can be started regardless of changes in the light intensity of the light source, and there is no reading error due to changes in light intensity. You can get information about rain sounds.

FIG. 4 shows an application example of the present invention, in which the amount of light is changed not by direct light but by reflected light. The configuration consists of a chuding correction plate 12 placed in front of the document reading position, and a J
It is characterized in that a light amount measuring reflector 13 is arranged in the sub-scanning direction outside the M document placement area, and the light amount of the fluorescent lamp when reading is performed in the sub-scanning direction is measured using reflected light.

FIG. 5 is a block diagram of an application example in which the amount of light from a light source is measured by reflected light and correction of the amount of light is realized. The configuration is almost the same as that shown in FIG. 4, but instead of the optical sensor for measuring the amount of reflected light, it is characterized by the shared use of a line photoelectric conversion element 3 for reading originals, and the number of pixels of the line photoelectric conversion element 3 is , it is sufficient if the number of pixels is one or more more than the number of pixels required for reading the document. The correction method is almost the same as the processing explained in FIG.

The purpose is achieved by using a part of the in-photoelectric conversion element 3. In this way, the number of parts can be reduced by sharing the line photoelectric conversion element for document reading instead of the optical sensor.

FIG. 6 is an example of a light amount change correction processing circuit that measures the amount of light using an optical sensor. This is an attempt to digitally determine the ratio of the amount of light before reading and the amount of light during reading. The configuration is that the optical sensor 2 measures the amount of light just before reading, and
It is A/D converted by the D converter 5, enters the latch 15, measures the amount of light during the primary reading that is input to the upper three addresses of the memory 6, and is A/D converted and enters the driver 16 as before. It is input to the lower address of memory 6. Numerical values are set in advance in the memory 6, and when the rear address is determined, the ratio of light amounts is output as a digital amount. In this way, the ratio of the light amount at the time of capturing the shading waveform to the light amount during reading can be determined as a ratio of the digital amount. Figure 7 shows the relationship between the reading error and the number of gradations.
By measuring and correcting the amount of light in this way, reading errors can be reduced.

〔Effect of the invention〕

According to the present invention, images can be read regardless of the state of the light source, and reading errors due to changes in light amount can be reduced, making high gradation reading possible.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is a light output characteristic diagram of a fluorescent lamp, and FIG. 3 is a block diagram of an application example of the cylinder 54 of the present invention. ■... Fluorescent lamp, 2... Optical sensor for measuring light amount, 3...
- Line photoelectric conversion element for document reading, 12... Shuding correction plate.

Claims (1)

[Scope of Claims] 1. In an image reading device comprising a light source for illuminating a document and a photoelectric conversion element that receives reflected light from the surface of the document and converts it into an electrical signal, from when the light source is turned on to when reading is completed. A light sensor is provided to measure the amount of light from the light source, the shooing waveform is captured immediately before image reading, the light amount of the light source is measured during image reading, and the shooing waveform is corrected according to the measured light amount. Change correction method. 2. The light amount change correction method according to claim 1, wherein the method for measuring the light amount of the light source includes arranging the optical sensor capable of receiving direct light from the light source. 3. The light amount change correction method as set forth in claim 1, wherein the method for measuring the light amount of the light source includes arranging an optical sensor that receives reflected light through a reflecting plate. 4. The light amount change correction method according to claim 3, wherein the optical sensor that measures the light amount of the light source using reflected light and the photoelectric conversion element for reading a document are used in common. 5. The light amount change correction according to claim 3, wherein the reflecting plate of the reading device that measures the light amount of the light source using reflected light is arranged in the sub-scanning direction outside the document placement area. Method. 6. Using a divider, calculate the ratio between the value of the optical sensor output for measuring the light intensity change of the light source at the time of capturing the shooing waveform and the optical sensor output for measuring the light intensity change of the light source during image reading, using a divider. , the light amount change correction method according to claim 1, characterized in that the shading waveform is multiplied by the result. 7. As a circuit for calculating the output ratio of the optical sensor, the value at the time of capturing the shooting waveform and the value during image reading are each digitized, and the respective values are used as addresses, and the values are converted into digital quantities from a memory element in which numerical values are set in advance. Claim 6, characterized in that the value of the ratio of is read out.
The light amount change correction method described in .