JP2003209687A - Image processing device - Google Patents

Abstract

(57) [Summary] [Problem] To check a pixel having a missing gradation and perform gradation correction on a pixel having a missing gradation. An image processing apparatus reads an amount of light reflected from a document by a CCD, converts analog data of the read amount of light by an A / DC, corrects the converted digital data in pixel units, and generates image data. Means 819 for generating a multiplier for shading correction;
Means 82 for multiplying the number of tones of the pixel by the multiplier generated by the means and the number of tones one level higher than that of the pixel 82
1,823, and the difference between the number of tones of the pixel obtained by multiplying by the means and the number of tones one rank higher is detected. A gradation correction processing unit 9 that determines a pixel to be corrected and performs gradation correction is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image for correcting a data omission during scaling processing of digital data in image reading in which an original image signal photoelectrically converted by an image sensor such as a CCD is converted into digital data for processing. The present invention relates to a processing apparatus and an image forming apparatus such as a digital copying machine or a stationary image scanner including the image processing apparatus.

[0002]

2. Description of the Related Art A CCD is used as an image pickup device in a digital copying machine, a scanner device or the like. This CC
The output (analog data) of D is converted into digital data, further multiplied by a multiplier (gain) associated with shading correction and the like, and treated as image data. At this time, if the multiplication process is performed with a gain of 1 or more, there is a problem that gradation (data) is lost in the image data obtained as a result. That is, since there is a quantization error in the A / D conversion and a rounding error due to a digital operation, it can be obtained by performing a multiplication process with a gain of 1 or more on digital data including such an error. The data may have missing gradation numbers. FIG. 8 is a diagram showing a state in which the number of gradations is missing,
The horizontal axis represents the pixel position, and the vertical axis represents the output value (gradation number) after A / D conversion. A is the CCD image reading output
A value obtained by the / D conversion, B indicates a value obtained by multiplying the value by a multiplier, and indicates a state in which the gradation number 6 is omitted at the pixel position 4 by the multiplication process. Similarly, a state in which the number of gradations is omitted at pixel positions 7 and 9 is also shown. Conventionally, in order to avoid such a problem of gradation loss and to secure the gradation of digital data after A / D conversion, the amplification factor of the amplifier circuit is changed with respect to the analog signal in the preceding stage of A / D conversion. A technique has been developed in which multiplication processing is performed to secure gradation after A / D conversion (Japanese Patent Laid-Open No. 2000-1.
3598, Japanese Patent Laid-Open No. 10-262152). In addition, as a measure against the loss of gradation, gradation correction has been performed for all pixels.

[0003]

However, in the case where the amplification factor of the amplifier circuit is changed with respect to the analog signal in the preceding stage of such A / D conversion, an analog amplifier capable of controlling the amplification factor and a control method for controlling the same. There is a problem that a mechanism is required, the complexity of the circuit increases and the cost increases. Further, in the method of performing gradation correction on all pixels, gradation deviation occurs because even pixels without gradation omission are subject to gradation correction, and proper correction values cannot be acquired as gradation correction values. That was the problem. The present invention has been made in view of the above circumstances, and an object thereof is to read an original image as analog data in pixel units, convert the read analog data into digital data, and convert the converted digital data in pixel units. In an image processing device that corrects and generates image data,
By omitting the analog amplifier etc. that can control the amplification factor and simplifying the peripheral circuits and control mechanism, the pixels with missing gradation are checked, and the gradation is corrected for the pixels with missing gradation. This is to minimize gradation dropouts and eliminate gradation deviations, and to improve problems such as pseudo contours and streaks that occur on an image due to gradation dropouts. Another object of the present invention is to provide an image forming apparatus equipped with an image processing apparatus that solves the above problems.

[0004]

According to a first aspect of the present invention, an original image is read as analog data in pixel units, the read analog data is converted into digital data, and the converted digital data is corrected in pixel units to form an image. In an image processing device for generating data, at least a means for generating a multiplier relating to shading correction, a means for multiplying the gradation number of each pixel by the multiplier, and a gradation number of the pixel multiplied by the means. A unit for detecting a difference between the pixel and a gradation number of a gradation higher by one gradation; a unit for fixing the pixel as a gradation correction target pixel when the difference exceeds a predetermined number; The image processing apparatus is provided with means for correcting the gradation number of the pixel.

According to a second aspect of the invention, in the image processing apparatus according to the first aspect, the means for correcting the determined gradation number of the pixel is a pixel adjacent to the gradation number of the pixel and the pixel before and after the pixel. The total number of gradations obtained by multiplying the number of gradations of the pixel and the number of gradations one gradation higher than the pixel by the weighting coefficient related to the multiplier, and the number of pixels of the pixel and the pixels before and after the pixel and the weight. The image processing device is characterized by dividing by an addition value with a coefficient and averaging.

According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect, the means for correcting the number of gradations of the determined pixel has the weighting coefficient proportional to the magnitude of the multiplier. An image processing device characterized by changing.

A fourth aspect of the present invention is an image forming apparatus including the image processing apparatus according to any one of the first to third aspects.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 shows a schematic electrical configuration of an image processing apparatus according to an embodiment of the present invention. In FIG. 1, a document (not shown) to be read has image information on its surface read by the CCD 1. The CCD 1 is a one-dimensional image sensor in which a plurality of light receiving parts are arranged on a straight line in the main scanning line direction. It should be noted that the image from the original is CCD
Optical lens (not shown) to form an image on the light receiving part of No. 1
The original document, the CCD 1 and the optical lens are moved relatively in the sub-scanning line direction perpendicular to the main scanning line direction by a moving mechanism (not shown) to read image information from the surface of the original document. .

The CCD 1 reads image information in the main scanning direction at a fixed cycle and sequentially outputs it as an analog image signal for each pixel. Since the analog signal output from the CCD 1 is weak as it is, it is amplified by the fixed gain amplifier 2 that amplifies the signal power by a fixed factor. The analog signal amplified by the fixed gain amplifier 2 is signal-converted by the A / DC 3 based on preset reference signals VRB (fixed value) 4 and VRT (fixed value) 5 for determining the dynamic range, and digital image data is obtained. : Data_ad (l,
n) is output. This digital image data is input to the black subtraction unit 7 of the digital signal correction unit 6.

FIG. 2 shows, as an example of the CCD 1, a color image is read using a line CCD consisting of 32 pixels, and the output value a1 obtained when the analog output of, for example, the R channel is amplified by a fixed gain amplifier is shown in FIG. The axis represents the pixel position and the vertical axis represents the output value (number of gradations). Further, the A / D converted value of the output value a1 is represented by b1. The output value A
1, B1 will be described later.

The black level used in the black subtraction unit 7 is a value D_opb generated from the data in the OPB unit (Optical Black unit) existing outside the effective pixel area in one line of the image signal (not shown) of the image reading apparatus. . For black subtraction, this D_opb is converted from the A / D converted data: Data_ad to Data (l, n) =
This is performed by processing as Data_ad (l, n) -D_opb.

Next, with respect to the data Data (l, n) thus subjected to the black subtraction processing, the gain adjustment processing section 8
Then, gain adjustment processing including shading processing and background removal processing (details will be described later with reference to FIG. 3) is performed to generate a gain for each pixel. The obtained gain is used for gradation correction in the gradation correction processing unit 9 (details will be described later with reference to FIG. 5). The tone-corrected image data is once stored in the image memory 10 or directly output as digital image data to an image processing unit (not shown) in the subsequent stage.

FIG. 3 is a block diagram of the gain adjustment processing section. To describe the generation of gain with reference to FIG. 3, the shading data generation unit 811 first
Shading data is generated before the reading of the original by the scanning operation of the CCD 1. Although various methods have been proposed for generating shading data, in the present invention,
By performing the multi-averaging process in the sub-scanning direction for each pixel, SH_Data (n) = (3 × Data (l−1, n) + Data
(L, n)) / 4 where, shading data is generated with n: pixel position and l: number of sub-scanning lines. FIG. 4 is a diagram showing a method of generating this shading data,
SH_Data (k-1) is generated by the above-mentioned multiple addition averaging for the pixel position k-1 of the l line. The pixel k and the pixel k + 1 are similarly generated, and this is performed for all the pixels in other lines. This shading data is generated for each pixel by the signal of the gate signal generation unit 813 that generates a gate signal (clock signal) at a timing matched with the pixel period, and is stored in the shading data holding memory 812, and the gain generation unit 819 at the subsequent stage is generated. Used in.

Simultaneously with the generation of the shading data, the line peak detection unit 814 detects the peak value of each line and stores it in the whiteboard data peak value holding memory 816 as the whiteboard data peak value: P_wh.

Further, in order to perform the background removal processing, the line peak value detection unit 814 is at the time of reading the original data.
The background peak value P_ae is detected for each line in the background level detection area (not shown), and the background peak value holding memory 817 is detected.
Save to. The detection of these peak values and the storage in the memory are performed by the bus switching 815 for each line by the gate signal (clock signal) of the timing matched with the pixel cycle of the gate signal generation unit 813, similarly to the detection of the shading data and the memory. Be seen.

In order to correct the white level at the time of reading the original, the white reference original is read in advance and the white reference original level: Wh
_kijn detected, whiteboard data peak value holding memory 8
Hold at 16.

The shading data and each data thus obtained are input to the gain generator 819,
A gain is generated for each pixel. That is, the gain when the background removal process is not performed is generated by the following equation as the gain: G_nae (n). G_nae (n) = (white level target value / SH_Data (n)) ×
(P_wh / Wh_kijn) White level target value: Value set from the external device 6a SH_Data (n): Shading data for the nth pixel stored in the memory P_wh: Peak level of the white plate stored in the memory Wh_kijn: White reference original level stored in memory

The gain in the case of performing the background removal process is generated by the following equation as a gain: G_ae (n). G_ae (n) = (target value for reading when removing background / P_ae) x (target value for white level / SH_Data (n)) x (P_wh / Wh_kijn) target value for reading when removing background: value P_ae set from the external device 6b : Background peak level detected in the background detection area White level target value: Value set from the external device 6a SH_Data (n): Shading data of the nth pixel stored in the memory P_wh: Saved in the memory White plate peak level Wh_kijn: White reference document level stored in memory

The gains thus generated are input to the gain multiplication processing units 821 and 823 for multiplication processing, and further input to the gradation correction processing unit 9 for gradation processing.

The gain multiplication processing unit 821 performs gain multiplication processing on the data after black subtraction: Data (l, n) using the gain generated by the gain generation unit 819. That is, when the background removal process is not performed, Data_G (l, n) = Data (l, n) × G_nae (n) When the background removal is performed, Data_G (l, n) = Data (l, n) × G_ae Gain multiplication is performed as (n).

In FIG. 2 again, A1 represents an output value when the output value a1 amplified by the fixed gain amplifier is multiplied by the gain, and B1 represents the A / D conversion data. AD conversion data obtained by multiplying the gain:
Data_G (l, n) has 13 pixels as shown in FIG.
In 16 and so on, gradation loss occurs. However, gradation dropouts do not occur in all data, and if gradation correction is performed on data in which no gradation dropouts occur, there is a possibility that gradation shifts will occur. Therefore, the present invention is characterized in that it is determined whether or not a pixel is missing a gradation before performing the gradation correction process, and the gradation correction process is performed on a pixel having a possibility of the gradation drop.

The correction process will be described below. The addition processing unit 822 of the gain adjustment processing unit 8 adds the data after the black subtraction: Data (l, n) plus 1, that is, Data_1 (l, n) = Data (l, n) +1. To generate. This data represents the number of gradations one gradation higher (larger number of gradations).

The gain multiplication processing unit 823 and the data generated by the addition processing unit 822 and the gain generation unit 819.
The multiplication process is performed on the gain generated in step. That is, Data
When the background removal processing is not performed for _1 (l, n) = Data (l, n) +1, Data_G1 (l, n) = Data_1 (l, n) × G_nae (n) When the background removal processing is performed , Data_G1 (l, n) = Data_1 (l, n) × G_ae (n), and the multiplication process is performed. These multiplied data are
It is input to the gradation correction processing unit 9 and used for gradation correction processing.

FIG. 5 is a block diagram for explaining the function of the gradation correction processing section. In FIG. 5, Data_G (l,
n) and Data_G1 (l, n), and gain G_nae (n)
And G_ae (n) are input to the gradation correction processing unit 9. At this time, the delay element 911 adjusts the reading order of the data for each pixel and each line. From the data input in this way, first, the data Data_G1 (l, n) and Data_G
The difference processing with (l, n) is performed as Δ = Data_G1 (l, n) -Data_G (l, n). If the result Δ of the difference is 1, there is no gradation omission, and if it is 2 or more, gradation omission due to increase in quantization error due to gain multiplication, error caused by rounding in arithmetic processing, etc. There is a possibility that the gradation loss due to Gradation correction is performed on pixels for which the difference value is 2 or more.

This gradation correction is performed by averaging the pixel data of the target pixel and the pixel data of the surrounding pixels. As the averaging method, a known method using a median value filter or an average value filter can be used. Here, the pixel data of the surrounding pixels may also have missing gradation. Therefore, if the averaging is simply performed only with the data after the black subtraction, there is a case where the gradation shift occurs like the gradation number 30 in the pixels 15, 16 and 17 illustrated in FIG. In order to reduce this, the data used in the averaging process, that is, the surrounding pixel data of the pixel of interest and the preceding and following pixel data, is subjected to the averaging process using the data Data_G1 (l, n) used in the determination of the missing gradation. By doing so, even when the averaged result of the surrounding pixels and the preceding and succeeding pixels is lower than the original level, it is possible to bring it closer to the original gradation level.

Further, the degree of gradation loss differs depending on the gain value. For example, when the quantization error δ in the A / D conversion is δ = 1 and the gains when the multiplication is performed are 2 and the gain is 4, the error after the multiplication is 1 ×
2 = 2, 1 × 4 = 4, and it can be seen that the larger the gain, the larger the error. Therefore, it is preferable to adaptively change the averaging process for correcting this as well. Therefore, the number of gradations of pixels to be corrected is Data_h (l, n−1) = {Data_G (l, n−2) + Data_G
(L, n−1) + Data_G (l, n) + α × Data_G1
It is calculated as (l, n−1)} / (3 + α). However, Data_G (l, n): l line after gain multiplication, data of the nth pixel, Data_G1 (l, n)
= Data_G (l, n) +1, α∝G_nae (n), G_ae
It is a weighting factor for Data_G1 (l, n-1) which is (n).

As described above, α is a weighting coefficient that changes in proportion to the gain value. Therefore, for example, α = k × G_nae
(N-1), (k is a constant determined according to the system) and the like.

According to this embodiment, k = 1.2 and gain = 2.0.
In that case, as shown in FIG. 7, gradation loss in multiplication by digital data is reduced as compared with the case where no correction is made (FIGS. 5 and 6). By sending the data that has been subjected to the gradation correction processing to the image processing unit (not shown) in the subsequent stage in this way, pseudo contours caused by gradation loss caused by the gain multiplication processing and streaks that occur in the image are reduced. You can do it.

The image processing apparatus having the above configuration is mounted on an image forming apparatus such as a digital copying machine or a stationary image scanner. According to such a digital copying machine or a stationary image scanner, it is possible to obtain high-quality image data with a simple configuration.

[0030]

The effect corresponding to the first aspect of the present invention: Since gradation loss correction processing is performed after A / D conversion, circuit elements such as a variable gain amplifier in an analog circuit and related mechanisms which have been conventionally required are provided. It can be eliminated and the circuit configuration can be simplified. Further, by obtaining the difference between the number of gradations of the pixel of interest and the number of gradations higher by one gradation, it is possible to easily determine a pixel with a missing gradation, and only for that pixel, there is a gradation missing. Is corrected, it is possible to minimize gradation loss and eliminate gradation deviation. Therefore, it is possible to reduce the occurrence of pseudo contours and the occurrence of streaks due to missing gradation. Effect corresponding to claim 2: Since gradation correction is performed with a more appropriate number of gradations, gradation dropouts and gradation shifts can be corrected more accurately. Therefore, it is possible to output image data with a smooth gradation change. Effect corresponding to claim 3: As the multiplier increases, a quantization error and a rounding error that occur during AD conversion are promoted and gradation loss occurs, but by changing the weighting coefficient in proportion to the multiplier, the quantum is changed. It is possible to perform correction while suppressing the digitization error and the rounding error, and it is possible to minimize the loss of gradation. Effect corresponding to claim 4: It is possible to provide a high-quality image processing device with no missing gradation.

[Brief description of drawings]

FIG. 1 is a schematic electrical configuration diagram of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a photoelectric output value of a CCD, an AD conversion value thereof, a multiplication value thereof, and occurrence of gradation loss.

FIG. 3 is a block configuration diagram of a gain adjustment processing unit in FIG.

FIG. 4 is a diagram showing a method of generating shading data.

5 is a block diagram of a gradation correction processing unit in FIG.

FIG. 6 is a diagram showing the occurrence of a gradation shift in a multiplied AD conversion value.

FIG. 7 is a diagram showing correction of gradation dropouts and gradation shifts in a multiplied AD conversion value.

FIG. 8 is a diagram illustrating gradation loss in a multiplied AD conversion value.

[Explanation of symbols]

1 ... CCD, 2 ... Fixed gain amplifier, 3 ... A / D converter, 6 ... Digital signal correction unit, 7 ... Black subtraction unit, 8 ... Gain adjustment processing unit, 9 ... Tone correction Processing unit, 10 ...

Claims (4)

[Claims] 1. An image processing apparatus for reading an original image as analog data in pixel units, converting the read analog data into digital data, and correcting the converted digital data in pixel units to generate image data, at least shading. A unit for generating a multiplier for correction, a unit for multiplying the gradation number of each pixel by the multiplier, a gradation number of the pixel multiplied by the unit, and a gradation higher by one gradation of the pixel. Means for detecting the difference in the number of gradations, means for determining the pixel as a gradation correction target pixel when the difference exceeds a predetermined number, and means for correcting the number of gradations in the determined pixel. An image processing apparatus comprising: 2. The image processing apparatus according to claim 1,
The means for correcting the determined number of gradations of the pixel is the multiplier of the number of gradations of the pixel, the number of gradations of pixels adjacent before and after the pixel, and the number of gradations one gradation higher than the pixel. An image processing device, wherein the total number of gradations of the number of gradations multiplied by the weighting coefficient according to the above is divided by the sum of the number of pixels of the pixel and the pixels before and after the pixel and the weighting coefficient, and the averaged. . 3. The image processing apparatus according to claim 1, wherein the means for correcting the determined gradation number of the pixel changes the weighting coefficient in proportion to the magnitude of the multiplier. Image processing device. 4. An image forming apparatus comprising the image processing apparatus according to claim 1.