JPH0797828B2 - Image processing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image processing apparatus that performs image processing on an input image to obtain an output image.

[Prior Art] In this type of device, a digital image signal is converted into an analog signal in order to obtain halftone gradation when an image is formed by a laser beam printer or the like based on the input digitized image signal. The applicant of the present application has previously proposed a method of generating a pulse width modulated signal by converting the signal and comparing the converted signal with a pattern signal such as a triangular wave.

However, according to this method, when converting to an image signal having a fine density change such as 64 gradations, an image in which the density change from white to black, such as characters or symbols, or from black to white is rapid. There was a problem that the density change from white to black or black to white became gradual when inputting, and the boundary became unclear and the contrast deteriorated.

In order to solve this problem, a method of emphasizing the edge portion of the image information has been conventionally used. For example, it is a method of subtracting the second derivative of the input image signal from the source signal. As a result, the density change from white to black or black to white becomes sharp,
Character sharpness and contrast are improved.

[Problems to be Solved by the Invention] However, when the image processing is performed only by the method of emphasizing the edge portion as described above, for example, an image such as a point of a laser spot diameter which originally has a sharp density change and is isolated. When there is a signal or a nozzle, there is a problem that the density change is emphasized by emphasizing the edge of the signal or the nozzle, which is undesirably noticeable.

The present invention has been made in view of the above problems, it is possible to accurately detect an isolated point in an image in which it is not preferable to perform edge enhancement, and do not perform edge enhancement processing for the isolated point, which is good. The present invention is intended to provide an image processing device that makes it possible to obtain various image information.

[Means for Solving the Problem] In order to solve this problem, the image processing apparatus of the present invention has the following configuration. That is, in the image processing apparatus including the edge portion enhancing means for enhancing the edge portion of the input image information, the densities of the target pixel in the input image information and a plurality of peripheral pixels within a predetermined distance range from the target pixel are detected. Density detecting means for calculating the density difference values of the plurality of peripheral pixels with respect to the detected density of the target pixel, and the maximum density difference value and the minimum density difference value among the calculated density difference values. When the difference from the density difference value is within a predetermined range and the maximum density difference value is equal to or larger than a predetermined value, the edge portion emphasizing means is deactivated.

[Operation] In the configuration of the present invention, the densities of the target pixel and a plurality of peripheral pixels within a predetermined distance range from the target pixel are detected, and the difference between the densities of the plurality of peripheral pixels and the density of the target pixel is calculated. . When the difference between the maximum value and the minimum value of the density difference is within the predetermined range and the maximum density difference value is equal to or more than the predetermined value, the edge enhancement is not performed.

Embodiments Embodiments according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram of the image information processing apparatus of this embodiment.

In the figure, reference numeral 1 denotes an original serving as an input image, 2 denotes a lens, and 3
Is a CCD which is an image sensor. Reference numeral 4 is an amplifier for amplifying the signal output from the CCD 3, and 5 is an A / D converter for converting the analog electric quantity into digital. 6
Is a shading correction circuit, and 7a is an edge emphasis discrimination circuit. This edge discriminating circuit 7a determines whether or not to emphasize the edge portion with respect to the input image.When the edge portion is emphasized, the input image signal is passed to the next edge emphasizing circuit 7B. When the edge portion is not emphasized, the edge image is input. The image signal is passed to the image processing circuit 8. The criterion for this determination is to pass the input image signal to the image processing circuit 8 without passing through the edge emphasizing circuit 7b, only when the condition for determination described later is satisfied.
In the image processing circuit 8, for example, a 6-bit digital signal is γ-converted. A D / A converter 9 converts a digital signal into an analog signal. Reference numeral 10 is a triangular wave generator for generating a triangular wave in synchronization with the beam detection signal, and 11 is a comparator for comparing the triangular wave generated by the triangular wave generator 10 with the output image level signal of the D / A converter 9. 12
Is a laser driver that causes a laser diode to emit light based on the pulse width output from the comparator 11.
Reference numeral 14 is a scanner composed of a polygon mirror or the like for scanning a laser beam, and 15 is an optical system such as a torque lens for exposing an optical signal from the scanner 14 to the photosensitive drum 17. In addition, 16 is a primary charger, 18 is a developing device,
19 is a resist roller, 20 is a sheet, 21 is a transfer charger, 22 is a separation charger, 23 is a cleaner, 24 is a transport unit for the sheet 20, 25 is a fixing unit, and 26 is a uniform potential on the surface of the photosensitive drum. It is a pre-exposure light emitting element.

In this configuration, the original 1 is projected onto the CCD 3 via the lens 2. The analog image signal output from the CCD 3 is amplified by the amplifier 4 and converted into, for example, a 6-bit digital image signal by the A / D converter 5. After that, the shading correction circuit 6 performs the shading correction of the image. Next, the edge emphasis determination circuit 7a determines whether or not edge enhancement is to be performed. When edge enhancement is to be performed, the edge enhancement circuit 7b performs edge enhancement. Otherwise, a signal is passed to the image processing circuit 8. Hereinafter, the processing content will be described.

FIG. 4 is a diagram showing the principle of edge enhancement, in which a signal a is an original signal, signal b is a signal obtained by first-order differentiation of signal a, and signal c is signal c.
Is the second derivative of signal a (first derivative of signal b). The signal d indicates [signal a-signal c], and it can be seen that the change from white to black is steep and the edge portion is emphasized finally. In this process, the process is digitally performed as shown below.

In the 3 × 3 pixel matrix shown in FIG. 2, the density difference between the target pixel density x and the adjacent pixel densities y _{1 to} y ₄ is determined by the main scanning,
It is defined as Laplacian Δ for each sub-scan.

Δ main scan = (y ₁ -x) + (y ₂ -x) Δ sub scan = (y ₃ -x) + (y ₄ -x) α is the emphasis amount in the main scanning direction, and α is the emphasis amount in the sub scanning direction. Letting β be the pixel density X of interest, the pixel density X is edge-enhanced density X ', and x'can be expressed by the following equation.

x '= x- (α · Δ main scanning + beta · delta sub-scanning) = x + 2 (αx + βx) -α (y 1 + y 2) -β (y 3 + y 4) Supporting connexion, when α = β = 1, x '= 5x- becomes _{(y 1 + y 2 + y} 3 + y 4).

When A / D converted to 64 gradations by the A / D converter 5,
The white level is (00) _H ( _H represents a hexadecimal number), and the black level is (3F) _H.

For example, when α = β = 1, the target pixel density x = (21) _H , y ₁ = (1E) _H , y ₂ = (1E) _H , y ₃ = (20) _H , y ₄ = (1F) _H In that case, x ′ = (2A) _H , and the density is emphasized.

However, for example, if there are isolated gray spots with a very small area on the white background of fog, or if there are isolated white spots of a fog with very small area on the gray background, The edges are edge-emphasized, and the former becomes black, and the latter becomes white, and the density change with respect to the background becomes large, which is very noticeable.

In order to prevent such a problem from occurring, an edge emphasis discrimination circuit 7a for deciding whether or not to process the edge emphasis is provided before the edge emphasis circuit 7b. This criterion is
For example, the determination is made by executing the processing shown in FIG.

That is, there is little variation in the pixel density x of interest from the adjacent pixel densities y _{1 to} y ₄ . That is, the following first condition is provided as a condition that the background has a uniform density. (However, Δα is the absolute value of the maximum and minimum density difference among the adjacent pixel densities y _{1 to} y _4. ) Δα ≦ A ... First condition Here, A is (00) _H to (05) _H. Set to a small value. Next, the pixel of interest density x is compared with the maximum density or minimum density among the neighboring pixel density y ₁ ~y _4, as a condition indicating that density difference is large, providing the following second condition.

Larger value compared to α ₁ and α ₂ ≧ B ... Second condition where α ₁ is the absolute density difference between the target pixel density x and the maximum pixel density among the adjacent pixel densities y _{1 to} y _4. The value α ₂ is the absolute value of the density difference between the target pixel density x and the minimum pixel density among the adjacent pixel densities y _{1 to} y ₄ .

Here, the value of B is empirically set as a density difference in which the density of isolated points is conspicuous when edge enhancement is performed.

As shown in FIG. 3A, when the pixel density x of interest is near the black level, α ₁ ≦ α ₂ . Further, when the target pixel density x is close to the white level, that is, in the case of FIG. 3B, α ₁ ≧ α ₂ .

Therefore, it suffices to compare α ₁ and α ₂ and compare the larger value with the value of B.

In this embodiment, only when the first condition and the second condition are satisfied at the same time, it is judged that an isolated image signal (singular point) with a sharp change in density exists, and edge enhancement is not performed. Especially.

The image signal processed by the edge emphasizing circuit 7b is further converted by the image processing circuit 8 into a digital image signal by γ-converting a 6-bit digital image signal. This image signal is again converted into an analog image level signal by the D / A converter 9.

On the other hand, the triangular wave generator 8 generates a triangular wave in synchronization with the beam detection signal.

The comparator 11 compares the analog image level signal with the triangular wave signal. Only when the triangular wave signal is larger than the image level signal, the output signal of the comparator 11 is
Become high. Therefore, as the image level changes from "low (black) to" high "(white), the pulse width of the output signal of the comparator 11 becomes smaller. The laser driver 12 is driven in proportion to this pulse width, and the laser diode 13
Emits light.

The laser beam emitted from the laser diode 13 is scanned
14, the beam spot is scanned on the photosensitive drum 17 by the optical system 15. Thereby, an electrostatic latent image is formed. Next, the toner in the developing device 18 adheres to the portion irradiated with the laser beam, and a visible image is formed on the surface of the photosensitive drum 17 (in the case of an image scan).

On the other hand, the paper 20 is transferred to the transfer charger via the registration roller 19.
Sent to 21. Here, the toner adhering to the surface of the photosensitive drum 17 is transferred to the paper 20 and is separated by the separation charger 22.
Is electrostatically separated from the photosensitive drum 17.

Next, the sheet 20 is conveyed by the conveying unit 24, and the fixing unit 25 fixes the sheet. On the other hand, the toner adhering to the surface of the photosensitive drum 17 is removed by the cleaner 23, and the charges charged on the surface of the photosensitive drum 17 are removed by the pre-exposure light emitting element 26. This completes a series of electrophotographic processes.

In the electrophotographic process, on the photosensitive drum 17,
The longer the light emission time of the laser diode 13, the lower the surface potential due to the light attenuation. In the reversal development, the lower the surface potential, the higher the density of the copied image.

Therefore, the copy image density and the pulse width of the output signal of the comparator 11 are proportional to each other, and a copy image having gradation is obtained.

As described above, according to the present embodiment, a signal obtained by converting a digital image signal into an analog image signal is compared with a pattern signal having a predetermined period, and in the pulse width modulated signal output device, the density change is sharp. If there is a large isolated image signal (singular point), edge enhancement is not performed.
It is possible to prevent the problem that a singular point becomes conspicuous due to edge enhancement.

Further, in this embodiment, the densities of the target pixel density x shown in FIG. 2 and the adjacent pixel densities y _{1 to} y ₄ are compared to check whether the first condition and the second condition are satisfied. However, regarding the pixel densities y _{1 to} y ₄ adjacent to the target pixel density x,
It may be set as shown in FIG. 6 or FIG. 6 to compare the densities to check whether the first condition and the second condition are satisfied.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to detect an isolated point in an image in which it is not preferable to perform edge enhancement processing, and it is preferable to eliminate the edge enhancement processing for an isolated point. It becomes possible to obtain an image.

[Brief description of drawings]

FIG. 1 is a block diagram relating to the image processing apparatus of the present embodiment, FIG. 2 is a diagram showing the positions of the target pixel density and its surrounding pixel density, and FIGS. 3 (a) and 3 (b) are the target pixel density. , FIG. 4 is a diagram showing a peripheral pixel density difference, FIG. 4 is a diagram showing a waveform conversion process serving as a reference for edge enhancement processing, and FIGS. 5 and 6 are the positions of other target pixel densities and their peripheral pixel densities. It is a figure. In the figure, 1 ... manuscript, 2 ... lens, 3 ... CCD, 4 ...
Amplifier, 5 ... A / D converter, 6 ... Shading correction circuit, 7a ... Edge enhancement determination circuit, 7b ... Edge enhancement circuit, 8 ... Image processing circuit, 9 ... D / A converter, 1
0 ... triangular wave generator, 11 ... comparator, 12 ... laser driver, 14 ... scanner, 15 ... optical system, 17 ... drum.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Moto Kato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yukihiro Ozeki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Takahiro Inoue 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroshi Sasame 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. ( 56) References JP-A-58-173974 (JP, A) JP-A-58-80968 (JP, A) JP-A-57-157686 (JP, A)

Claims (1)

[Claims] 1. An image processing apparatus comprising edge enhancement means for enhancing an edge portion of input image information, comprising: a target pixel in the input image information; and a plurality of peripheral pixels within a predetermined distance range from the target pixel. Density detecting means for detecting the density, density difference calculating means for respectively calculating the density difference values of the plurality of peripheral pixels with respect to the detected density of the target pixel, and the maximum density difference among the calculated density difference values And a minimum density difference value is within a predetermined range, and the maximum density difference value is equal to or greater than a predetermined value, the image processing means is provided with a control means for deactivating the edge portion emphasizing means. apparatus.