JP2672541B2 - Image processing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image processing apparatus, and in particular, image processing is performed on digital image data read by a scanner, and the obtained image data is recorded as a visible image. Image processing apparatus.

[Prior Art] Conventionally, in this type of apparatus, image processing was performed after gamma (γ) correction. FIG. 5 is a schematic block diagram of a conventional digital copying apparatus. In the figure, 1 is a CCD for reading an original image, 2 is an A / D conversion circuit for converting the image signal read by the CCD 1 into digital image data, and 3 is a printer characteristic (sensitivity of photosensitive drum, ink color, toner) of digital image data. Γ correction circuit for performing γ correction for matching with (color etc.), 4 is an image processing circuit for performing data interpolation processing, edge enhancement processing, dither conversion processing, smoothing processing, etc. on the digital image data after γ correction, Reference numeral 5 is a printer.

Generally, in order to faithfully reproduce the image data sampled by the scanner, it is necessary that the image data does not include noise or the like. However, since the γ correction is a correction performed to match the sampled image data with the printer characteristics such as the sensitivity of the photosensitive drum, the ink color, and the toner color, it means that the image data read by the scanner is changed, and the latter stage will be changed. Proper image data cannot be provided to the image processing circuit.
For this reason, the image reproduced from the γ-corrected signal is prominently deteriorated in image quality (such as occurrence of moire) as compared with the original image.

[Problems to be Solved by the Invention] The present invention eliminates the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide an image processing apparatus that causes little visual deterioration. .

[Means for Solving Problems] In order to achieve the above object, the image processing device of the present invention includes a data interpolation circuit that performs data interpolation processing on sampled image data by a data interpolation matrix including a plurality of coefficients, The outline is to include an image processing circuit that performs a predetermined image processing on the image data after the data interpolation processing.

The data interpolation matrix has a center coefficient value of 1, a total sum of remaining coefficient values of 1, and a ratio of the remaining coefficient values substantially equal to a ratio for a sinc function corresponding to the scan pitch of the scanner. It consists of the following.

The outline of the image processing circuit is that it is a gamma correction circuit that performs gamma correction on the image data according to the characteristics of the recording unit.

The outline of the image processing circuit is that of an edge enhancement circuit for enhancing edge of image data.

In order to achieve the above object, the image processing apparatus of the present invention uses a logarithmic conversion circuit that performs logarithmic conversion processing on sampled image data, and a data interpolation matrix that includes a plurality of coefficients for the logarithmically converted image data. The outline is to include a data interpolation circuit that performs interpolation processing.

[Operation] This image processing device is an image processing device that performs image processing on digital image data read by scanning and records the obtained image data as a visible image. Data interpolation processing is performed on the data by a data interpolation matrix composed of a plurality of coefficients. Preferably, the data interpolation matrix has a central coefficient value of 1, a total sum of the remaining coefficient values is 1, and the ratio of the residual coefficient values is approximately the ratio for the sinc function corresponding to the scan pitch of the scanner. Consist of equal coefficients. Then, the image processing circuit performs predetermined image processing on the image data after the data interpolation processing. Preferably, the image processing circuit performs gamma correction on the image data according to the characteristics of the recording unit. Alternatively, the image processing circuit performs edge enhancement processing on the image data.

Further, this image processing device is an image processing device that performs image processing on digital image data read by scanning and records the obtained image data as a visible image, and a logarithmic conversion circuit is provided for the sampled image data. Performs logarithmic conversion processing. Then, the data interpolation circuit performs data interpolation processing on the logarithmically converted image data by using a data interpolation matrix composed of a plurality of coefficients.

[Description of Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a digital copying apparatus according to an embodiment. In the figure, 103 is a CCD, which reads a document image according to main scanning and sub-scanning control. A sample and hold circuit (SH) 201 removes noise components from the image signal read by the CCD 103. 202 is a DC clamp circuit (DC clam
p), which reproduces the black level of the image signal from which the noise component has been removed. An amplifier (AMP) 203 amplifies the level-reproduced image signal to a signal level suitable for A / D conversion. Reference numeral 204 denotes an A / D conversion circuit (A / D), which converts the amplified image signal into digital image data. An offset correction circuit 205 corrects the dark voltage of the input digital image data. 206 is a shading correction circuit,
With respect to the digital image data after dark voltage correction, sensitivity correction such as illuminance unevenness of light source and unevenness of CCD sensitivity is performed. Reference numeral 207 denotes an interpolation processing circuit, which performs data interpolation processing described later on the sensitivity-corrected digital image data. A gamma correction circuit 208 converts gamma data, which is brightness data, into density data suitable for a printer, and performs gamma correction for matching printer characteristics (sensitivity of photosensitive drum, ink color, toner color, etc.). To do. The γ correction circuit 208 is a RAM (not shown)
It is possible to store a conversion table for converting the brightness data into the density data, and the CPU 212 can write a desired conversion curve based on the print density designation by the operator or the density characteristic of the recording unit 210. A buffer memory 209 is provided to match the output speed of the image data when recording in the image recording unit (printer) 210.
For example, it has a storage capacity of image data for two lines. An image recording unit 210 reads out image data from the buffer memory 209 and records it on a recording sheet. Reference numeral 212 denotes a CPU circuit unit, which performs sequence control of each of the above-described configurations of the embodiment apparatus. An operation unit 213 is provided with operation switches for various purposes operated by the operator. A drive signal generation circuit 211 generates various drive signals for the reader unit until the image signal is taken out from the CCD 103 and stored in the buffer memory 209 under the control of the CPU circuit unit 212. Further, the drive signal generating circuit 211 has an address corresponding to each pixel position of the image data for one read line, and each component can perform a corresponding process using this address.

2 (A) and 2 (B) relate to a diagram for explaining the data interpolation matrix of the embodiment, and FIG. 2 (A) is a diagram for explaining the interpolation processing by the sinc function. In FIG. 2 (A),
The function h (x) is a sinc function, the horizontal axis represents the distance x, and the vertical axis represents the weighting coefficient value. P _{0 to} P ₅ is a predetermined interval Δx
Original image data sampled at (cycle T),
I _{0 to} I ₄ are interpolation data for interpolating the middle of the original image data. However, the pixel of interest for which data interpolation is to be performed is now I ₂ . Therefore, the weighted (coefficient) data necessary for data interpolation in the sinc function h (x) is the image data P _i.
It is a value of the sinc function h (x) corresponding to the position of, and is b, a, c, ... In FIG. 2 (A). By the way, for example, when the sinc function for the image reading pitch 16pel is examined, the relationship of center = 1, b = 0.63, and a = -0,21 is obtained. Therefore, the ratio b / a of a and b is -3, and the total of 2 (a + b) of the sum of a and b is 0.84. In general, the sum of the sinc functions is 1 when 2 (a + b + c + d +...) Is performed.

FIG. 2B is a diagram illustrating an example of a one-dimensional data interpolation matrix according to the embodiment. In the figure, 100 is the size (1
× 7) is a data interpolation matrix, each element (coefficient)
Is determined based on the intrinsic properties of the sinc function described above. That is, for example, a '=-0.25 and b' = 0.75, and their ratio b '/ a' satisfies -3. By doing so, data interpolation can be performed almost by the sinc function. In addition, the sum of the sum of the remaining coefficients excluding the center coefficient 1 is 2
(A '+ b') satisfies 1. By doing this
This aims to reduce the effect of truncation error caused by aborting the infinite calculation of the nc function. From the above, the interpolation data I ₂ is I ₂ = a ′ (P ₁ + P ₄ ) + b ′ (P ₂ +
P ₃ ), and the interpolated data P ₃ is P ₃ = 1 × P ₃
Required by

Note that even when the size of the matrix is increased and the coefficients c, d, e,... Are adopted, the condition of the ratio of each coefficient and the condition of the sum of the remaining coefficients are the same.

FIG. 3 is a diagram showing the γ correction characteristic of the embodiment. The γ correction circuit 208 of the embodiment converts the digital image data, which is the brightness data, into the density data suitable for the printer (logarithmic conversion), and also matches the characteristics of the printer (sensitivity of the photosensitive drum, ink color, toner color, etc.). Γ correction for The same applies when the RGB color signal is converted into a CMY (BK) signal and γ correction is performed.

Since the data interpolation processing is performed on the image data sampled in this way, first, data interpolation faithful to the original can be performed. Therefore, after that, γ correction, edge enhancement (MTF correction) processing, and the like can be performed based on appropriate image data.

[Other Embodiments] FIG. 4 is a block diagram showing the image processing unit of another embodiment. The same components as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 4, reference numeral 301 denotes a LOG conversion circuit, which converts digital image data, which is a luminance signal read by a CCD, into density data that can be perceived by human eyes (logarithmic conversion). Comparing with the γ correction circuit 208 of FIG. 1, printer characteristics (sensitivity of the photosensitive drum,
The relationship excludes γ correction for matching with ink color, toner color, etc.). Accordingly, 302 is the γ that performs the original γ correction.
It is a correction circuit. An image processing circuit 303 includes processing such as edge enhancement, smoothing, image moving method (trimming), and masking. Thus, even if the LOG conversion is performed first, since the human eye evaluates the finally output image, there is no difference in the evaluation of the image quality. In addition, this
The LOG conversion may be optically performed before digital image data, for example, an analog signal immediately after being read by a CCD, before being read by a certain CCD, which increases the degree of freedom in the device configuration.

[Effect of the Invention] As described above, according to the present invention, the data interpolation process is performed by γ
Since it is performed before image processing such as correction or edge enhancement, CCD
The image can be reproduced without damaging the frequency component of the read image data.

Moreover, since the data interpolation is performed in a manner similar to the case of using the sinc function, it is possible to remove moire in the output image.

In addition, since data interpolation processing is performed after LOG conversion, the degree of freedom in the device configuration increases without impairing image quality.

[Brief description of the drawings]

FIG. 1 is a block diagram of the digital copying apparatus of the embodiment, FIGS. 2 (A) and 2 (B) are diagrams for explaining the data interpolation matrix of the embodiment, and FIG. 3 is a diagram showing the γ correction characteristic of the embodiment. FIG. 4 is a block configuration diagram showing an image processing unit of another embodiment, and FIG. 5 is a schematic block configuration diagram of a conventional digital copying apparatus. In the figure, 103 …… CCD, 201 …… Sample hold circuit (S
H), 202 ... DC clamp circuit (DC clamp), 203 ... Amplifier (AMP), 204 ... A / D conversion circuit (A / D), 205 ... Offset correction circuit, 206 ... Shading correction circuit, 2
07: interpolation processing circuit, 208: γ correction circuit, 209: buffer memory, 210: image recording section, 211: drive signal generating circuit, 212: CPU circuit section, 213: operating section.

Claims (5)

(57) [Claims] 1. An image processing apparatus for performing image processing on digital image data read by scanning and storing the obtained image data as a visible image, the data interpolation including a plurality of coefficients for the sampled image data. An image processing apparatus comprising: a data interpolation circuit that performs data interpolation processing by a matrix; and an image processing circuit that performs predetermined image processing on the image data after the data interpolation processing. 2. The data interpolation matrix has a center coefficient value of 1, a total sum of remaining coefficient values of 1, and a ratio of the remaining coefficient values for a sinc function corresponding to a scan pitch of the scanner. The image processing apparatus according to claim 1, wherein the image processing apparatus comprises a coefficient substantially equal to the ratio. 3. The image processing apparatus according to claim 1, wherein the image processing circuit is a gamma correction circuit for performing gamma correction on the image data according to the characteristics of the recording section. 4. The image processing circuit is an edge enhancing circuit for enhancing edge of image data.
The image processing device according to the item. 5. An image processing apparatus for performing image processing on digital image data read by scanning and recording the obtained image data as a visible image, logarithmic conversion for performing logarithmic conversion processing on sampled image data. An image processing apparatus comprising: a circuit; and a data interpolation circuit that performs data interpolation processing on the logarithmically converted image data using a data interpolation matrix composed of a plurality of coefficients.