JPH05276379A - Electronic picture reader - Google Patents

Abstract

PURPOSE:To provide the electronic picture reader utilizing effectively a dynamic range of an A/D converter without saturation by adjusting the gain of an amplifier so as to obtain an optimum luminous quantity even when a luminous quantity distribution of a lamp is changed due to a change with lapse of time. CONSTITUTION:The reader is provided with an optical system collecting a reflected light from an edge white reflecting board 12 of an original read window 11 with illumination from a light source, an image sensor 14 converting the incident light into an electric signal for each picture element, an amplifier 15 amplifying the signal, and an A/D converter 21 converting the signal into a digital signal. Prior to reading of a document, when a reference white level board is read, a means controlling an amplifier gain adjustment circuit 25 to adjust a gain of the amplifier 15 so as to use effectively the dynamic range of the A/D converter 21 while taking the luminous quantity distribution attended with deterioration in a lamp for original radiation into account is built in the CPU 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an electronic image reading device,
In particular, the present invention relates to an electronic image reading device that adjusts the gain of an amplifier so that the amount of light is optimum.

[0002]

2. Description of the Related Art An electronic image reading apparatus optically reads document information and the like with an image sensor and converts it into a digital signal, and records this digital signal or transmits it to a host computer. As described above, since image data such as a document read by the electronic image reading device is processed as an electric signal, it is possible to easily perform storage, retrieval, copying, transmission, etc. at high speed and in large quantities.

In such an electronic image reading apparatus, white reflection is provided at the end of the original reading window in order to obtain a constant reading density without being affected by the change in the light amount due to the deterioration of the original illumination lamp over time. A board is provided.

That is, the image sensor receives the reflected light from the white reflector at the end of the document reading window, and the gain of the amplifier is controlled by the CPU or the like so as to keep this level constant.

As a result, when the light amount is generally reduced as shown in FIG. 3 (FIG. 3 (b)), an image can be read well by adjusting the amplifier to increase the light amount as a whole. ..

[0006]

However, when the light amount distribution of the lamp changes, for example, when the end portion of the lamp is darker than the central portion of the lamp as shown in FIG. 4 (FIG. 4 (b)). )), The amount of light reflected from the white reflector at the end of the document reading window is significantly lower than the amount of light at the white level of the central pixel. Therefore, if the amount of light reflected from the white reflector is corrected by increasing the gain of the amplifier so that the amount of light is a predetermined amount, as shown in FIG. Since the maximum input level is exceeded, there is a problem in that the white of the image in the central portion is crushed, that is, the image is saturated.

Therefore, although the problem of the occurrence of saturation is solved by empirically adjusting the gain of the amplifier to a low level, it is possible to effectively use the dynamic range of A / D as shown in FIG. Since this is not possible, there is a problem that the image becomes noisy.

The present invention has been made in view of the above problems, and an object thereof is to adjust the gain of the amplifier so that the optimum light amount can be obtained even if the light amount distribution of the lamp changes with the passage of time. An object of the present invention is to provide an electronic image reading device which can effectively use the dynamic range of A / D without any need.

[0009]

In order to achieve the above-mentioned objects, the electronic image reading apparatus of the present invention comprises:
An image sensor configured by arranging a plurality of photoelectric conversion elements for converting document information into an electric signal for each pixel, an amplifier for amplifying an output from the image sensor, and an A for converting an output from the amplifier into digital data. / D converter,
Of the data from the A / D converter, a white level memory for storing reference white level information for each pixel when a reference white level light amount of the image sensor is given, and a white reflector provided at the end of the document reading window. End white reflector reflected light level detection circuit that detects the reflected light level of the A / D converter from the output of the A / D converter, and each pixel signal from the A / D converter is linear based on the values of the white level memory and the black level memory. A non-uniformity correction circuit for correcting to a value, a light amount distribution maximum value detecting means for obtaining a light amount distribution from the reference white level information for each pixel of the white level memory, and detecting a maximum value of the light amount distribution; The gain of the amplifier is adjusted so that the reflected light level of the end white reflective plate detected by the reflective plate reflected light level detection circuit becomes a predetermined target value, and the light amount distribution maximum value is set. Amplifier gain adjustment for changing the gain of the amplifier using the target value based on the maximum value of the light amount distribution detected by the output means and the predetermined A / D maximum input level that can be processed by the A / D converter. And means.

[0010]

In the electronic image reading apparatus according to the present invention having the above-mentioned structure, the non-uniformity correction is performed when the light quantity distribution of the lamp is obtained before correcting each pixel signal from the image sensor to a linear value. Turn off the circuit operation and adjust the amplifier gain so that the light amount is optimal in the amplifier gain adjustment circuit, and then calibrate the white level, so even if the light amount distribution of the lamp changes over time, it will not be enough. Therefore, the dynamic range of A / D can be effectively used.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the following drawings.

FIG. 1 is a block diagram showing an embodiment of an electronic image reading apparatus according to the present invention. In FIG. 1, the electronic image reading apparatus includes an optical system 1 including a lens, an optical filter, and the like that condense the reflected light from the end white reflector 12 of the document reading window 11 by irradiation from a light source.
3, an image sensor 14 that converts incident light into an electric signal for each pixel, an amplifier 15 that amplifies this signal, and an A / D converter 21 that converts this signal into a digital signal.
Have and.

Prior to reading a document, the output of the image sensor 14 in the state where the light source is turned off (the state where the level is zero) is amplified as the reference black level light amount, and then converted into a digital signal, and this digital black is output. The average value of the level signal is obtained for each pixel and stored in the black level memory 23.

Similarly, in the white level memory 22, an average value for each pixel of a digital white level signal obtained by reading a reference white paper and converting the reflected light of the reference white paper into a digital signal is stored. ..

Further, in order to keep the reading of the white level constant without being affected by the light quantity of the lamp, the end white reflector 12 of the original reading window 11 is controlled by the end white reflector reflected light level detection circuit 24. Read the reflected light level from
An amplifier gain adjusting circuit 25 that adjusts the gain of the amplifier 15 is provided so that the value becomes a predetermined light amount.

A feature of the present invention is that the A / D converter 2 is considered in consideration of the light quantity distribution due to deterioration of a lamp for illuminating a document or a fluorescent lamp prior to reading a reference blank sheet.
The gain of the amplifier is adjusted so that the dynamic range of 1 can be effectively used.

That is, the CPU 27 turns off the non-uniformity correction circuit 26, directly reads the reflected light of the reference blank sheet, and then removes the noise of the reflected light (hereinafter, this is referred to as averaging of the reflected light). After calculating the maximum value of the light amount distribution and comparing the maximum value with the A / D maximum output level, the gain of the amplifier 15 is adjusted and the reflected light level of the end white reflector is obtained by a predetermined calculation formula. A means for calibrating the light quantity value is provided.

Therefore, the amplifier 15 is adjusted so that the optimum light amount is obtained.
Since the reference blank sheet can be read after adjusting the gain of, the apparatus of the present invention can read an image with clear black and white tones.

The amplifier adjusting means in consideration of the characteristic light amount distribution of the present invention will be described in detail below with reference to the flow chart shown in FIG.

The operation of the non-uniformity correction circuit is turned off.
FF is set (S31), the light source is irradiated, the reflected light from the white reflection plate at the end of the document reading window is read, and the level of this reflected light is adjusted to a predetermined light quantity value, for example, 128 (S32). .. Then, the reference blank paper is scanned (S3
3) Read the light amount distribution of a lamp or the like for direct document irradiation. At that time, the light amount is read for each unit of a certain number of pixels (for example, 32 pixels) in the light amount distribution of the lamp or the like, and the average for each unit is calculated (S34). This is to prevent erroneous recognition of the maximum value due to noise. After that, the maximum value is obtained from these average values, and this is set as the maximum value of the reflected light quantity distribution (S35).

Next, the maximum value of the reflected light amount distribution is the A / D maximum output level (for example, the light amount is 256 when the light source is deteriorated).
Since the value is lower than the value), the optimum set value of the reflected light from the end white reflector is calculated by the following formula (S36).

Optimal set value of reflected light from the end white reflector = (predetermined light amount value × A
/ D maximum output level) / (maximum value of reflected light quantity distribution) = 1
28 × 256 / (maximum value of reflected light quantity distribution) In order to set the light quantity level to the optimum setting value of the reflected light from the end white reflectors obtained by this calculation, the gain of the amplifier is adjusted (S37), Calibrate the white level (S3
8), turn on the non-uniformity correction circuit (S
39).

Actually, as shown in FIG. 7, the maximum value of the reflected light quantity distribution is set slightly lower than the A / D maximum output level.

[0024]

As described above, the electronic image reading apparatus of the present invention can be used even if the light quantity distribution of the lamp changes with time.
By adjusting the gain of the amplifier so that the amount of light is optimum, the dynamic range of A / D can be effectively used without being overwhelmed.

Therefore, it is possible to use a lamp whose end portion is blackened.

[Brief description of drawings]

FIG. 1 is a block configuration diagram showing an embodiment of an electronic image reading apparatus according to the present invention.

FIG. 2 is a flowchart showing an amplifier adjusting means in consideration of a light amount distribution in this electronic image reading apparatus.

FIG. 3 is a light amount distribution chart in which a light amount change of a lamp is only an illuminance change.

FIG. 4 is a light amount distribution chart in the case where the end portion of the lamp is darker than the central portion of the lamp when the light amount of the lamp changes.

FIG. 5: When correction is performed by increasing the gain of the amplifier, the light amount of the white level of the pixel in the central portion exceeds the A / D maximum input level, and the white of the image in the central portion is crushed. It is a light amount distribution map at this time.

FIG. 6 is a light amount distribution diagram when the gain of the amplifier is empirically set low and the gain of the amplifier is corrected.

FIG. 7 is a light amount distribution chart in one example of the correction of the gain of the amplifier according to the present invention.

[Explanation of symbols]

 11 Original Reading Window 12 Edge White Reflector 13 Optical System 14 Image Sensor 15 Amplifier 21 A / D Converter 22 White Level Memory 23 Black Level Memory 24 Edge White Reflector Reflection Level Detection Circuit 25 Amplifier Gain Adjustment Circuit 26 Non-Uniformity Correction circuit 27 CPU

Claims (1)

[Claims] 1. An image sensor configured by arranging a plurality of photoelectric conversion elements for converting document information into an electric signal for each pixel, an amplifier for amplifying an output from the image sensor, and a digital output for the amplifier. A / D to convert to data
Among the data from the converter, the A / D converter, the white level memory for storing the reference white level information for each pixel when the reference white level light amount of the image sensor is applied, and the document reading window end portion are provided. An end white reflector reflection light level detection circuit for detecting the reflection light level of the white reflector from the output of the A / D converter, and each pixel signal from the A / D converter based on the values of the white level memory and the black level memory. A non-uniformity correction circuit that corrects to a linear value, a light amount distribution maximum value detection unit that obtains a light amount distribution from the reference white level information for each pixel of the white level memory, and detects a maximum value of the light amount distribution, The edge white reflector reflection light level detected by the edge white reflector reflection light level detection circuit, while adjusting the gain of the amplifier so as to be a predetermined target value, Serial quantity and intensity distribution maximum value detected by the distribution maximum value detecting means, a predetermined A / D converter can be processed A /
An electronic image reading apparatus comprising: an amplifier gain adjusting unit that changes the gain of the amplifier using the target value based on the D maximum input level.