JPH01259464A - Sharpness improving circuit - Google Patents

Abstract

PURPOSE:To simplify hard constitution and to improve recording picture quality by utilizing a difference signal, which is common to a chrominance signal, and adjusting the emphasis degree of sharpness on the basis of a signal to correspond to the intensity of the input chrominance signal. CONSTITUTION:A sharp signal S-U is a signal, for which luminance information S of an attention picture element, namely, respective color information are synthesized. Then, for an unsharp signal U, the average value of a luminance signal in a prescribed area, which includes the attention picture element, is used. Accordingly, the both sharp signal S-U and unsharp signal U are commonly used to the respective color information. Thus, the hard constitution is simplified. Since a correcting signal, for which the respective chrominance signals are divided by the luminance signal S, is also utilized as a sharpness improving signal to be added to a primary color signal, the change of color in an edge part due to emphasis can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a sharpness improvement circuit suitable for application to image processing devices such as digital color copying machines and color printers.

[Background of the Invention] Image processing apparatuses such as digital color copying machines and color printers are usually provided with a sharpness improvement circuit in order to improve the sharpness of recorded images.

In this sharpness improvement circuit, a correction signal (sharp signal) for improving sharpness is formed based on input image information, and this is added to the original input image information to record an image. This is to improve sharpness.

The following signals are used as signals for improving sharpness.

Ro=Ri+k (Ri-Rt) Go=Gi+k (Gi-Gt).

Bo=Bi+k (Bi-Bt) Here, RLGi, Bi are input color information of the pixel of interest (before correction) Ro, Go, Bo are output color information of the pixel of interest (after correction) Rt, Gt, and Bt are: Surrounding color information R including the pixel of interest
, G, and B are correction coefficients.

This sharpness improving means is configured to form an average value signal for each color information.

In addition, the following signals may be used as sharpness improvement signals.

Ro=Ri+k (S-3us) Go=Gi+k (S5us) Bo=Bi+k (S-Sus) Here, S is 4 formed based on the color information of the pixel of interest.
No. 8 and is expressed as follows.

S=αRi+βGi+γBi Here, α+β+7=1 Sus... Average value of the surrounding area for S This sharpness improvement means forms a correction signal S common to each color information, and attempts to improve the sharpness of the image based on this. It is something to do.

[Problems to be Solved by the Invention] By the way, when configuring a signal for improving sharpness based on the above-mentioned formula, the following discrepancy occurs.

First, when forming a sharpness improvement signal based on the former formula, it is necessary to form Rt, Gt, and Bt multiplied signals for each color information, which makes the hardware configuration complicated. Become.

In addition, depending on the input image information, color shift may occur after sharpness improvement.

For example, when edge correction is performed on a contour portion having edges that are not very strong as input image information, as shown in FIG. 10A, the edge correction is performed as shown in FIG. 10B.

Therefore, especially in the rising edge part A, the input R
, G, and B change. Changes in ratio appear as color shifts, leading to deterioration in image quality.

In the case of strong edges, for example, in the case of input image information with edges as shown in FIG. 11A, the image becomes as shown in FIG. 11B,
Since the ratios of R1G and B change in the A and mouth portions, respectively, this has the same drawback as the case shown in FIG.

In addition, when forming a sharpness improvement signal based on the latter formula, although the signal S can be used in common, the first
R as shown in Figure 0C and Figure 11C as 2.
, G, and B are all edge-emphasized by the same amount.

Therefore, in this part, R, G.

The ratio of B is different from that of the input, which causes the color to change. This is because edge enhancement is performed based on the common signal S.

Therefore, the present invention proposes a sharpness improvement circuit that solves these conventional problems with a simple structure and can realize recording without color shift while reducing the circuit scale. .

[Means for Solving the Problems] In order to solve the above-mentioned problems, in the present invention, a luminance signal formed from image information of a pixel of interest and an unsharp signal formed from surrounding luminance signals including the pixel of interest. A sharp signal is formed from the luminance No. 48 and the unsharp signal, and a sharp signal or an unsharp signal is formed from each of the plurality of color signals obtained by color-separating the image information of the pixel of interest. Each correction signal is formed from the sharp signal, and a signal obtained by multiplying the sharp signal by this correction signal is used as a sharpness improvement signal for each color signal.

[Operation] In this configuration, the sharp signal is the luminance information of the pixel of interest, that is, a signal obtained by combining information of each color, and the unsharp signal uses the average value of the luminance signals in a predetermined area including the pixel of interest. Therefore, these sharp signals and unsharp signals are commonly used for each color information.

Therefore, the hardware configuration is simplified.

As the sharpness improvement signal added to the primary color signal, this invention also uses a correction (No. 8) obtained by dividing each color signal by the luminance signal, so that it is possible to suppress color changes at the edge portion due to emphasis.

This is because a signal obtained by dividing each color signal by a luminance signal is used as one of the correction coefficients, so edge enhancement is performed taking into consideration the strength of the original image.

[Embodiment] Next, an example of the sharpness improvement circuit according to the present invention will be described in detail with reference to FIG. 1 and subsequent figures.

As described above, the sharpness improvement circuit according to the present invention can be applied to image processing systems such as digital color copying machines and color printers.

In this invention, the following signal is used as a sharpness improvement signal.

Ro=Ri+ (Ri/S)k (S-U)Go=Gi
+ (Gi/S)k (S-U)Bo=Bi+ (Bi
/S)k (S-U) Here, Ro, Go, Bo are 1.
! The color information Ri, G i, B i of the pixel of interest after sharpness improvement is a composite signal of the color information S of the pixel of interest before sharpness improvement is a luminance signal, and the color information R9G, B of the pixel of interest, S=αR+βG+7 B α+β+γ=1 U is an unsharp signal, and the average value of the surrounding luminance signals including the pixel of interest is used.

k is a correction coefficient as a sharpness improvement signal, which is a coefficient (roughly the ratio of the primary color signal and the luminance signal) to the signal obtained by multiplying the difference signal (sharp signal) between the luminance signal S and the unsharp signal U by the coefficient k. The reason for multiplying by the correction coefficient is to suppress the change in color of the edge portion due to emphasis by multiplying by this coefficient.

This is because, although the coefficient that takes the ratio of the primary color signal and the luminance signal is a coefficient that takes into account the sharpness of the original image, it is possible to obtain a sharpness improvement signal that matches the original image.

The above-mentioned color signals Ro, Go, and Bo after sharpness improvement can be configured in a sequential software manner using a microcomputer, or can be configured in a hardware manner.

FIG. 1 is an example of the latter.

A plurality of color signals obtained by color-separating input image information are supplied to terminals IR to IB. In this example, red, green, and blue color signals Ri to Bi separated into primary color signals are used.

The color signals may be complementary color signals.

Further, this color signal is a digitized signal, and is an 8-bit signal in the figure.

A luminance signal S and an unsharp signal U are generated from each color signal Ri=Bi. The unsharp signal U is the second
As shown in the figure, this is the low frequency component of the original image.

Then, as shown in Figure 3, if the pixel of interest is e,
The luminance component of this pixel of interest e is the signal S, and the pixel of interest e
The unsharp signal U is the average value of the luminance components of surrounding pixels including the pixels, in this example, pixels existing in a 3×3 matrix.

First, in the sharpness improvement circuit 10, a brightness signal S is formed. Therefore, the respective color signals Ri to Bi are supplied to the data converters 2R to 2B functioning as coefficient multipliers, and then added together in the digital adder 3.

Since αR is formed in the data converter 2R, βG is formed in the data converter 2G, and γB is formed in the data converter 2B, the luminance signal S can be formed by adding these signals.

The data converters 2R to 2B can be constructed from ROM or RAM, and when RAM is used, the coefficient values to be loaded can be changed depending on the nature of the input image.

For example, if you want to express human skin smoothly and make tree lines clear, reduce the coefficient value α of R and use G
It is sufficient to set the coefficient value β to be thick. In that case,
Corresponding coefficient values α to γ may be loaded in accordance with external specifications.

Further, the degree of sharpness may be changed between bright parts and dark parts.

To perform constant emphasis regardless of density, coefficient values α to γ as shown in Figure 4A are loaded, and when it is desired to emphasize bright areas, a nonlinear conversion table (coefficient value) α as shown in Figure 4B is loaded.
~7 is loaded, and when it is desired to emphasize a dark part, a nonlinear conversion table α~7 as shown in C in the figure is loaded.

It is also possible to set the conversion tables α to 7 to different values.

The luminance signal S is then supplied to an unsharp signal forming means 5, from which an unsharp signal U is formed.

As shown in FIG. 3, the unsharp signal U is the average value of the luminance components of surrounding pixels including the pixel of interest.

Therefore, in this example, the forming means 5 is composed of two line delay lines and nine unit delay lines (none of which are shown) so that pixel information in a 3×3 matrix is obtained.

The unsharp signal U and the luminance signal S obtained via the digital delay line 4 for timing adjustment are supplied to the subtracter 6, and after a difference signal (S-U) which is a sharp signal is formed, a multiplier 8 guided by.

On the other hand, the luminance signal S that has passed through the delay line 4 is roughly supplied to the data converter 7, and in this example, a conversion process of /S (hereinafter this ratio will be referred to as an emphasis control correction coefficient) is executed.

The data converter 7 outputs a positive or negative emphasis control coefficient. If it is positive, it is sharpening, and if it is negative, it is de-sharpening.

Since it is better to unsharpen an input image that contains a lot of noise, unsharpening processing becomes possible by mtRing the polarity of the data to be loaded.

This data converter 7 can use ROM, RAM, etc.

The emphasis control correction coefficient /S is supplied together with the sharp signal (S-U) to a multiplier M8 for multiplication processing, and then supplied to a bit converter 9 having a limiter function in this example for limiter processing.

This means that the level of the sharp signal is ±32 sampling levels (
In the case of an 8-bit image), the structure of the multiplier in the subsequent stage is simplified.

The limited multiplier output is output from multiple multipliers 11R to 11B.
These multipliers 11R to 1
1B is fully supplied with the corresponding input color signals Ri to Bi,
Multiplication processing is performed between these.

This multiplication process forms a sharpness improvement signal. The sharpness improvement signal is as follows.

Red sharpness improvement signal = (R/S)k (S-U) Green sharpness improvement signal = (G/S)k (S-U) Armor sharpness improvement signal = (B/S)k ( S-U) Here, R/
S, G/S, and B/S are all correction signals corresponding to the strength of the input color signal. Therefore, the red to blue sharpness improvement signals are all signals related to the strength of the edges of the input color signal.

Note that the delay lines 12R to 12B provided before the multipliers 11R to 11B are for timing adjustment.

The sharpness improvement signals for red to katakana are supplied to sharpness adjustment means 13R to 13B each consisting of a data converter (limiter), and the sharpness is adjusted appropriately.

As the limiter characteristics, input/output characteristics shown in FIG. 5A or B can be used.

Note that the bit converter 9 can use 16-5 conversion or the like.

Another example of sharpness adjustment is shown in FIG.

In the examples shown in A and B of the same figure, sharpening is not performed beyond a certain amount for edges that are strong on both the upper and lower edges. This is to prevent color shift at the edges, as will be described later.

This results in an enhanced image 4 as shown in FIG. 7A.
No. 3 is obtained.

Figures 6C and 6D are examples in which sharpening above a certain level is stopped for the lower part of the edge.
As shown in , excessive emphasis at the bottom of the edge can be prevented.

Figures 6E and F are examples in which, on the contrary, the sharpening above a certain level is stopped for the upper part of the edge, and in that case, excessive emphasis at the upper part of the edge is avoided as shown in Figure 7C. It can be prevented.

Incidentally, according to the conventional edge enhancement, both the upper and lower edges of the edge are over-corrected as shown in Figure 7.

The sharpness improvement signal whose sharpness has been adjusted is sent to a rough adder 15.
In R to 15B, the signal is added to the input color signal, which is the original signal, to form a color signal with improved sharpness.

That is, Ro-Ri+ (Ri/S)k (S-U)Go=Gi
+(Gi/S)k (S-U)Bo=Bi+ (Bi/
A color signal Ro-Bo expressed as S)k (SU) is output.

Digital delay lines 16R to 16B are for timing adjustment.

The color signal Ro=Bo is roughly expressed by the gradation conversion means 17R to 17.
B is fully supplied, and polarity correction and gradation conversion are performed to suppress negative values in the image signal to O, and to suppress image signals greater than the maximum value to this maximum value.

As mentioned above, the multiplication output /S (S-U) has positive and negative polarities, but since images are generally represented only by positive values, it is necessary to set negative values to O.

At the same time, in this example, gradation conversion can also be performed.

The gradation conversion mentioned here refers to gamma conversion, positive-negative conversion, and the like.

After such gradation conversion processing is completed, the color signal Ro= whose sharpness has been improved is finally sent to each of the output terminals 18R to 18B.
Bo will be output.

When an input image is reproduced using the color signals Ro to Bo whose sharpness has been improved in this way, the following results are obtained.

When the above-mentioned processing is performed on a waveform with not very strong edges as shown in FIG. 8A, the result will be as shown in FIG. 8B when there is no limiter action by the bit converter 9, and when there is a limiter action, The waveform becomes as shown in C in the figure.

As is clear from this, while appropriate edge enhancement is performed, the ratio of the color signals is almost unchanged from that at the time of input, as shown in FIG. This reduces color shift.

FIG. 9A shows a waveform when the edge is quite strong, FIG. 9B shows a waveform without a limiter, and FIG. 9C shows a waveform with a limiter.

According to this, edges are emphasized according to the input as shown in (H) to (N), and color shift does not occur as shown in (G).

The hardware configuration and bit configuration described above are merely examples.

The input color signal may be, for example, a signal after A/D conversion and shading correction of original image information obtained from a CCD or the like, or a digital color signal from a so-called scanner used for printing.

[Effects of the Invention] As described above, according to the configuration of the present invention, since a difference signal common to color signals is used, the hardware configuration is significantly simplified.

In this invention, R/S, G/S, and B/S are all signals corresponding to the strength of the input color signal, and the degree of sharpness emphasis is adjusted based on these signals. , edge enhancement is performed in relation to the edge strength of the input color signal.

Therefore, even if edge correction is performed, there is no fear that color fading will occur. Therefore, the recorded image quality is significantly improved.

Therefore, the sharpness improvement circuit according to the present invention is extremely suitable for application to image processing devices such as the above-mentioned digital color copying machines, color facsimiles, and input processing devices for printing.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an example of the sharpness improvement circuit according to the present invention, Fig. 2 is a waveform diagram showing the relationship between the luminance signal, sharp (U), and unsharp signals, and Fig. 3 is an explanation of the unsharp signal. Figure 4 is a characteristic diagram of the correction coefficient used for the luminance signal, Figures 5 and 6 are limiter characteristic diagrams used to explain sharpness adjustment, and Figure 7 is the result. 8 and 9 are characteristic diagrams illustrating the sharpness improvement effect, and FIGS. 10 and 11 are characteristic diagrams illustrating the sharpness improvement effect, respectively, which will be used for conventional explanation. 10.・Sharpness improvement circuit 3... Adder 5... Anshar buoy No. 8 forming means 6... Subtractor 8... Multipliers 11R to IIB... Multiplier patent applicant Konica Co., Ltd. Differenceヂ84(S-UI 01'-2'Sif"6-j'e' 484 fist (R+G+8) Fig. 2 Fig. 3 A B C
Figure 4 Selling name/ (S-U) Chicken J/(S-U) Figure 5 Figure 6 etc.? f Rikikari (Volume II, Figure 7)

Claims (1)

[Claims] (1) A luminance signal formed from image information of a pixel of interest;
A sharp signal is formed from the luminance signal and the unsharp signal, and the image information of the pixel of interest is color separated. A respective correction signal is formed from each of the plurality of color signals and the luminance signal or the unsharp signal, and a signal obtained by multiplying the sharp signal by this correction signal is used as a sharpness improvement signal for each color signal. A sharpness improvement circuit characterized by: