JPH0253375A - Reading part dirt detecting circuit - Google Patents

Abstract

PURPOSE:To prevent the degradation of picture quality by extracting the ununiformity of a picture signal in an original set part, which is defined as reference white, and judging the presence and absence of dirt in correspondence to a compared result with a reference value. CONSTITUTION:A prescribed range is set by a peak value detecting range setting circuit 7 to the size of the dirt and a peak value, which is obtained by inputting these information to a peak value detecting circuit 6, is set to the reference peak value register of a peak value comparing circuit 8. White data for one line are read again from the original set part, which is defined as the reference white, by an image sensor 1 and amplified to a prescribed level by an amplifier 3. Further, <= 1/3 range of the dirt size is set to the left terminal of an extending window 15 by the peak value detecting range setting circuit 7 and the peak value, which is obtained by inputting these information to the peak value detecting circuit 6, is set to the compared value register of the peak value comparing circuit 8. Then, comparison processing is executed with a value which is set to a comparing value register. Thus, the degradation of the picture quality is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reading section dirt detection circuit in an image reading device using a solid-state image sensor.

[Conventional technology]

Conventionally, in an image reading device, the original to be read is illuminated by illumination means such as a fluorescent lamp, and the original to be read is scanned by a line-shaped solid-state image sensor to obtain an image signal. And shading occurs due to the characteristics of the lens. Therefore, as shown in FIG. 3, before reading the original 28, the original setting section 24, which is set as a reference white, is illuminated with a fluorescent lamp 25, and the lens 26
The image signal (shading waveform 29) of the document setting unit 24 is projected to the image sensor 27 as a reference white as shown in FIG. 4, and this shading waveform 2
A slice level 30 is generated based on 9, and shading correction is performed simultaneously with A/D conversion of the original image signal 31.

[Problem to be solved by the invention]

However, if dirt adheres to the original document set portion 24, which is set as the reference white, the dirt-attached portion of the shading waveform 32 moves toward the black side, as shown in FIG. 5, and the slice level 33 changes in the same way. Therefore, for example slice level 3
3, when the original image signal 31 is binarized, the slice level 33 moves toward the black side due to dirt, and the portion that should originally be extracted as black is treated as white, resulting in deterioration of image quality. There was a problem.

Further, when an image signal is multi-valued using a plurality of slice levels, there is a similar problem in that the density value of a dirty part is lower than that of other parts, leading to deterioration of image quality.

[Means to solve the problem]

In order to prevent the above-mentioned deterioration of image quality, the present invention adds a reading section dirt detection circuit to the conventional shading correction circuit, and detects the reference white of the document set section obtained by the above-mentioned solid-state image sensor. It is an object of the present invention to provide a means for determining the peak values of an image signal at predetermined intervals and determining the presence or absence of dirt on a document set portion, which is used as a reference white, based on changes in the magnitude of these peak values.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an image signal digitization circuit including a white reflector stain detection circuit according to an embodiment of the present invention.

The image sensor 1 includes a photoelectric conversion section and a shift register for charge transfer. Reference numeral 2 denotes a clock pulse generation circuit that supplies a clock pulse signal of a predetermined frequency to the shift register of the image sensor 1. The signal charges of the shift register of the image sensor 1 are sequentially outputted by the clock pulses. 3 is an amplifier that outputs a signal from the shift register of image sensor 1;
That is, a current proportional to a signal charge representing image information corresponding to each pixel of one scanning line is amplified to a predetermined level and output. 4 is a shading correction circuit, which records the image signal obtained from the document setting section, which is set as the standard white, to the image memo! J (R
AM), and the image signal of the document is corrected for each scanning line based on the stored data. Reference numeral 5 denotes an A/D conversion circuit, which is connected to the output terminal of the amplifier 3 and converts the output signal of the amplifier 3 into a digital signal. Reference numeral 6 denotes a peak value detection circuit, into which the image signal of one scanning line received from the output of the amplifier 3 is input, and detects the white side peak value (hereinafter simply referred to as peak value) in a predetermined dynamic range from the black level in an arbitrary range. ) is detected. For example, if detected with 8-bit precision, the peak value will be 256.

The output terminal of this peak value detection circuit 6 is configured to be input to a peak value comparison circuit 8, which will be described later. Note that the peak value increases toward the white side. Reference numeral 7 denotes a peak value detection range setting circuit, which sets the range in which the peak value detection circuit 6 detects the peak value of the image signal. That is, by setting the range for determining the peak value in the image signal of one scanning line using this circuit 8 and inputting this information to the peak value detection circuit 6, the peak value can be obtained. 8 is a peak value comparison circuit, which has four registers. That is, they are a reference peak value register, a compared value register, a comparison value register, and a dirt threshold register. The reference peak value register is set with a peak value obtained using an enlarged window 15, which will be described later, and the compared value register is set with a peak value obtained using a local window 16. Further, the maximum value of the number of quantization bits of the peak value is set as an initial value in the comparison value register, for example, 255 when the peak value is quantized with 8 bits.

Then, the compared value register and the comparison value register are compared, and the smaller value is reset to the comparison value register. This process is repeated a predetermined number of times, the difference between the finally obtained value of the comparison value register and the value of the reference peak value register is determined, and this value is further compared with the value of the dirt threshold register. 9
is a control unit that controls input and output, and the presence/absence of dirt signal 1
1 is output. lO is a digital signal obtained by performing shading correction on the image signal obtained from the image sensor 1 and after A/D conversion.

The operation of the stain detection circuit of the document setting section having the above-described configuration as the reference white will be described below. First, the image sensor 1 reads one line of white data from the original set section, which is to be used as a reference white, and the amplifier 3 amplifies it to a predetermined level, which becomes the shading waveform 14 in FIG. Note that 12 indicates a black level, and 13 indicates a white level.

Here, for example, in a facsimile machine, the main cause of dirt adhering to the original document setting section, which is used as a reference white, is the roller for sending out the original, so the position and size of the dirt can be predicted to some extent. Therefore, a predetermined range (defined as an enlarged window 15) is set for the size of the dirt by the peak value detection range setting circuit 7, and this information is transmitted to the peak value detection circuit 6.
The peak value obtained by inputting the peak value into the reference peak value register of the peak value comparison circuit 8 is set. Again, the image sensor 1 reads one line of white data from the document set section, which is to be used as a reference white, and the amplifier 3 amplifies it to a predetermined level. Furthermore, a range of 1/3 or less of the dirt size (defined as local window 16) is set to the left terminal of enlarged window 15 by peak value detection range setting circuit 7, and this information is input to peak value detection circuit 6. The peak value obtained is set in the compared value register of the peak value comparison circuit 8, and comparison processing with the value set in the comparison value register is performed.

The peak value detection and comparison process using the local window 16 described above is repeatedly performed. However, each time this process is performed, the local window 16 is moved to the right by that size,
Further, when the local window 16 reaches the right end of the enlarged window 15, this process is terminated. When the peak value detection using the local window 16 is completed, the value of the comparison value register and the value of the reference peak value register, that is, the minimum value 23 of the peak values determined in the local window 16 and the peak value 22 determined in the enlarged window 15 are determined. Find the difference. Next, this difference is compared with the value set in the dirt threshold register, and when the difference is larger, the reference white is used as the dirt presence signal 1, which indicates that there is dirt on the document set area, and otherwise indicates that there is no dirt.
1 is output from the control section 9.

〔Effect of the invention〕

As described in detail above, the present invention illuminates the original set area with reference white using the illumination means, reads this using the solid-state image sensor, obtains an image signal, and obtains a peak value when viewed from a broad perspective from this image signal. , find the peak value when viewed locally, compare the difference between those peak values and a predetermined value,
Based on the results, it is possible to determine whether or not there is dirt on the document set section, which is used as the reference white, which causes deterioration in image quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a dirt detection circuit in a document setting section that uses reference white in an embodiment of the present invention, FIG. 2 is a timing chart illustrating setting of an enlargement window and a local window for image signals, and FIG. FIG. 4 is a waveform diagram showing a shading waveform and a slice level, and FIG. 5 is a waveform diagram showing a shading waveform including dirt and a slice level. 1... Image sensor, 2... Pulse generation circuit, 3... Amplifier, 4... Shading correction circuit, 5... A/ D conversion circuit,
6...Peak value detection circuit, 7...Peak value detection range setting circuit, 8...Peak value comparison circuit, 9...Control unit, 10. ...Digital signal, 11...Dirty presence signal, 12...
...Black level, 13...White level, 14...
...Shading waveform, 15... Enlarged window, 16-2.1... Local window 2
2...Peak value found in the enlarged window, 23
... Minimum peak value found in the local window, 24 ... Original set section to be used as reference white, 25.
...Fluorescent lamp, 26...Lens, 27...
...Image sensor, 28...Original L29.
...Shading waveform, 30...Slice level, 31...Original image signal, 32...
...Shading waveform, 33...Slice level. Agent Patent Attorney Shinsho Uchihara Kunidai Tomoe

Claims (1)

[Claims] An original set that provides a reference white signal in an image reading device that has an original setting section that is used as a reference white in the reading area before setting the original, reads a reference white signal in advance, and automatically corrects shading using that signal. a peak value detection circuit that determines the peak value of one line of image signal obtained from the image signal, a peak value detection range setting circuit that determines the range in which the peak value is determined, and a peak value comparison circuit that compares the magnitude of the peak value. and extracting the non-uniformity of the image signal of the original set portion to be used as a reference white by the peak value comparison circuit,
A reading section dirt detection circuit is characterized in that it is able to compare it with a predetermined reference value and determine the presence or absence of dirt attached to a document setting section to be set as a reference white according to the comparison result.