JP2670060B2 - Image processing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image processing apparatus applicable to a digital copying machine or the like. [Prior Art] In conventional digital image processing, smoothing means is defined by the interaction between the dot density of the original and the segment density of the solid-state image sensor (CCD) and the matrix size density of the halftone processing of the image processing. It is a means for removing moire (unevenness of periodic light and shade that does not exist in the original image). By the way, from the viewpoint of the latent image electric field, the electric field intensity is higher when there is unevenness in the latent image, and accordingly, the density after development is higher when moire occurs. In particular, in the highlight area where the electric field strength is low,
This difference is large, and after smoothing, the electric field becomes flat and the concentration decreases. As a rule of thumb, smoothing increases γ,
The highlights are easy to fly. [Purpose] In view of the above-mentioned conventional technique, the present invention has an object to correct the density fluctuation due to smoothing. [Structure] In order to achieve the above object, the present invention provides an image processing apparatus that performs image processing on input digital image data and outputs the digital image data by selecting one from a plurality of types of smoothing processing. Smoothing processing means for performing smoothing processing, gamma correction processing means for selecting one of a plurality of types of gamma correction processing and performing gamma correction processing on the digital image data, and the smoothing processing means. Control means for controlling the gamma correction processing means to select the type of gamma correction processing in accordance with the type of smoothing processing. Hereinafter, a specific description will be given based on an embodiment of the present invention. FIG. 1 is a front view showing an outline of a digital copying mechanism to which the present invention can be applied, and FIG. 2 is a block diagram showing a main body control system,
FIG. 3 is a block diagram showing the image processing unit, FIG. 4 is a diagram showing the relationship between the dispersion value of unevenness and image density, FIG. 5 is a diagram showing the correction .gamma. Characteristic of the combination filter of the present invention, and FIG.
The figure shows a circuit diagram of a 3 × 3 filter. In FIG. 1, a scanner S of the copying mechanism scans an original by appropriately deflecting a laser beam 1 emitted from a semiconductor laser (not shown) by a polygon mirror 2, and an fθ lens 3 and a mirror 4 The document information is formed as a latent image on the plurality of photosensitive drums 5a, 5b, 5c and 5d by the scanning light via the scanning light. The structure of the printer section mainly including the photoconductor drums 5a, 5b, 5c and 5d is well known, and each developing section 6 for black, red, green and blue, the charging section 7, the cleaning section 8 and the P sensor are provided. 9 and the like are provided. Each photoconductor drum 5a, 5b, 5c, 5d
The transfer belt 10 is installed so as to face the transfer belt 10.
The transfer unit 11 is provided via the. Further, reference numeral 12 is a belt charge eliminating portion, and 13 is a fixing roller. As shown in FIG. 2, the control system of the main body controls the system controller 14 with respect to the scanner S and the image processor.
15, the printer 16 and the operation panel 17 are configured to input and output data. The system controller 14 controls each module of the scanner S, the image processor 15, and the printer 16. Specifically, the system controller 14 controls the display of the operation panel 17, the key input processing, and the operation panel 17. It sends commands to each module according to the mode, accepts status signals from each module, and controls the entire system. The scanner S scans a document at a scanning speed that matches a specified scaling ratio in response to a start signal from the system controller 14, and reads the document image with a reading element such as a CCD, for example, an image of 8 bits each for RGB. Data
It is sent to the image processor 15 in synchronization with the horizontal synchronizing signal from the image processor 15 and the image clock. The image processor 15 performs image processing such as γ correction, UCR, and color correction on the RGB 8-bit image data sent from the scanner S to obtain Y-, M-, C-, and Bk 3-bit image data. It is converted and sent to the printer 16 at a predetermined timing. Also, in response to a command from the system controller 14, scaling processing,
Edit processing such as masking, trimming, color conversion, and mirroring. Further, the printer 16 receives Y, M, and Y signals sent from the image processor 15 in synchronization with the horizontal synchronizing signal and the image clock.
According to the image data of 3 bits each of C and Bk, a semiconductor laser is modulated to form a copy image on a transfer sheet by an electrophotographic process using the photosensitive drums 5a to 5d, the transfer belt 10 and the like. A specific example of the image processor 15 is shown in FIG. In the figure, S is a scanner unit, 14 is a system controller, 16 is a printer unit, and 18 is a synchronization control circuit.
Further, 19 is an MTF correction circuit, 20 is a γ correction circuit, 21 is a masking processing circuit, 22 is a UCR processing circuit, 23 is a density pattern circuit, and 24 is a multi-value processing circuit. In the image processor 15, CC of Sukiana S
The image data read by the D light receiving unit or the like is corrected by the MTF correction circuit 19 for optical irradiation unevenness for each of yellow (Y), magenta (M), and cyan (C). The tonality of each color data is corrected by the γ correction circuit 20, the masking correction circuit 21 calculates the optimum amount of Y, M, C at the time of printing, and the UCR processing circuit 22 calculates the appropriate black Bk for creating black. Calculate the amount from Y, M, C. Next, the density pattern processing circuit 23 outputs a pattern distribution corresponding to each gradation of 64 gradations, and the multi-value quantization processing circuit 24 outputs 1 of the patterns.
The pulse width modulation is performed according to 4 values. The synchronization control circuit 18 controls the synchronization of the processing circuits. Incidentally, the MTF correction circuit 19 and the γ correction circuit 20 have conventionally been set with independent processing coefficients, but in the present embodiment, between the MTF correction circuit 19 and the γ correction circuit 20, experimentally, The coefficient of the obtained combination is used. The optimum coefficient value of this combination includes the characteristics of the process processing from development to fixing, which is related to the matrix size of the intermediate image forming process and its development characteristics. FIG. 4 shows the relationship between the standard deviation (dispersion value) of the unevenness of the dot data of the highlight portion and the image density obtained at that time. The data are arranged so that the average values are the same for all image forming conditions. As can be seen from the figure, the image density decreases as the variance value of the unevenness of the data decreases. This means that in the highlight part, if the halftone dots are removed by the smoothing process, the density of the highlight part will decrease, and
Is high (development of so-called highlights). This tendency is directly proportional to the degree of smoothing. Therefore, it is necessary to combine the smoothing filter and the γ correction for processing. Here, the smoothing process is one of the MTF processes, and the MTF process is roughly divided into an edge enhancement process and a smoothing process. Specifically, this is a process of performing convolution integration of a 3 × 3 or 5 × 5 matrix digital filter with image data. For example, with a 3x3 filter Then, if you write with the formula, Becomes However, * represents a convolution integral. Here, the correction γ of the combination filter in this embodiment is
The characteristics are shown in FIG. The γ correction value is stored in a table in the memory provided in the γ correction circuit 20. The smoothing process by each correction shown in FIG. 5 is specifically as follows. That is, the smoothing process for the correction of The smoothing process for correction of The smoothing process for correction of It becomes like. The processing is selected by the system controller 14, and the data is transmitted to the image processor 15 via the system controller 14 by the key input data of the operation panel 17 in FIG. 2 and the MTF correction filter is selected. In addition, the γ correction table is referred to. A concrete circuit diagram of the 3 × 3 filter is illustrated in FIG. In the figure, 25 is a line buffer, 26 is a latch,
27 is an adder and 28 is a multiplier. This circuit has a line buffer 25 for two lines and 3 × 3 = 9 latches 26 for performing a 3 × 3 matrix operation. The latched 9-pixel data is subjected to a predetermined processing operation by an adder 27 and a multiplier 28. Further, by using a ROM instead of the adder 27 and the multiplier 28, it is possible to configure so that matrix calculation of an arbitrary coefficient can be easily performed. [Effect] As described above, according to the present invention, it is possible to correct the density fluctuation due to the smoothing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of the present invention, FIG. 1 is a front view showing the outline of a digital copying mechanism, FIG. 2 is a block diagram showing a main body control system, and FIG. 3 is image processing. Block diagram showing parts, No. 4
FIG. 5 is a diagram showing the relationship between the unevenness dispersion value and image density, FIG. 5 is a diagram showing the correction .gamma. Characteristic of the combination filter of the present invention, and FIG. 6 is a circuit diagram of a 3.times.3 filter. 14 System controller, 15 Image processor, 19 Smoothing filter (MTF correction circuit), 20 γ
Correction circuit.

Claims (1)

(57) [Claims] In an image processing device for performing image processing on input digital image data and outputting the same, smoothing processing means for selecting one from a plurality of types of smoothing processing and performing a smoothing process on the digital image data; Gamma correction processing means for selecting one of the gamma correction processing of the gamma correction processing and performing gamma correction processing on the digital image data; and gamma correction processing means according to the type of the smoothing processing selected by the smoothing processing means. An image processing apparatus comprising: a control unit that controls to select the type of gamma correction processing.