JP2634939B2 - Image processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus capable of suitably removing noise from a color image.

[Prior Art] In the field of printing and plate making, when a continuous tone image is converted into an electric signal using a solid-state imaging device such as a CCD and then reproduced on a film or the like, the influence of the solid-state imaging device or film graininess and the like is required. , Noise is mixed in the reproduced image. In order to reduce this noise, for example, in the technique disclosed in Japanese Patent Publication No. Sho 63-36189, after the density information corresponding to each pixel is once stored in a recording device, a plurality of pixels stored in the storage device are stored. A density distribution is obtained by arranging these pixels in the order of density using the density information of, and the densities of the pixels located at both ends of the density distribution are defined as a white level and a black level. A predetermined ratio of the number of pixels to the number of pixels is counted, and among the counted pixels, the level of the pixel located closest to the black level is set as the threshold level.

Further, the technology disclosed in Japanese Patent Application Laid-Open No. 63-156475 discloses a characteristic that human vision is close to logarithmic with respect to brightness (that is,
The darker the area, the more sensitive it is to changes in brightness).
If the same amount of noise is mixed in the highlight and shadow areas of the image, the noise will be much more noticeable in the shadow area than in the highlight area, and the accurate reproduction of the gradation will be hindered. However, since human vision can only have a low spatial resolution in shadows, the fact that even if the resolution is slightly reduced in shadows does not make it appear to the human eye that the quality of the obtained image has deteriorated. Paying attention, only in the shadow part of the image, for example, by creating and outputting an unsharp signal by averaging adjacent pixels, etc.,
One reading is intended to reduce noise for human eyes without lowering the resolution. Further, regarding the noise removal in the color image processing, the magnitude relationship between the density of the central pixel and the average density of the neighboring pixels is determined by outputting the density of the central pixel with reference to a look-up table (LUT) or by determining the average density of the neighboring pixels. Techniques for determining whether to output a value are known.

[Problems to be Solved by the Invention] However, in the case of a color signal, film granularity, CCD
There is a problem that good results cannot be obtained if noise is removed with a black-and-white signal because the magnitude of noise differs depending on the color due to the photoelectric conversion characteristics and the like.

The present invention has been made in order to solve the above-mentioned problems, and has been made in consideration of a color signal (Y (yellow), M (magenta), C (cyan) or R (red), G (green), B (color).
(Blue)) It is an object of the present invention to provide an image processing apparatus capable of performing optimal noise removal by independently installing a look-up table in which a conversion threshold level is changed for each (blue)).

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a pixel average value generation circuit for generating an average value of pixel signals in pixels near a pixel of interest, and a color forming image signal. A look-up table that is set every time and holds a coefficient corresponding to the average value, and a calculation unit that obtains a desired image signal from the image signal from the pixel of interest, the average value, and the coefficient. Features.

[Operation] The image processing apparatus according to the present invention changes the threshold level for each color using a look-up table because the magnitude of noise varies depending on the color.
Removes noise from color images.

Embodiment Next, a preferred embodiment of an image processing apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 denotes a noise removing circuit incorporated in the image processing apparatus according to the present embodiment.

For example, color signals S _Y , S _M , and S _C from a photoelectric conversion element (not shown) using a CCD are input to the noise removal circuit 10 as input signals. Here, S _Y , S _M , and S _C are yellow, magenta, and cyan color signals, respectively.
Each signal is input to noise removal circuits 12, 14, and 16 for each color. F _Y , F _M , and F _C are output signals of the respective noise elimination circuits 12, 14, and 16, and represent outputs after noise elimination.

Figure 2 is a diagram showing a configuration of a noise elimination circuit 12 according to the color signal S _Y of Figure 1. Note that other noise removal circuits
The configurations of 14 and 16 are the same as those of the noise elimination circuit 12, and a description thereof will be omitted.

The color signal S _Y is converted to an average value U _Y by a neighboring pixel average value generation circuit 18. This neighborhood pixel average value generation circuit 18
It is, for example, by adding the input signal of the neighboring pixels of a pixel according to the color signal S _Y, a circuit for obtaining the mean.

A look-up table (LUT) 20 is a table to vary the threshold level for the address image processing said average value U _Y.

Subtraction circuit 24 from the average value U _Y and the color signal S _Y (U _Y -
S _Y ).

The multiplication circuit 22 obtains the product of the conversion value Q (U _Y ) output from the lookup table 20 and (U _Y −S _Y ).

The addition circuit 26 adds the outputs of the multiplication circuit 22 and the subtraction circuit 24.

Next, the operation of the embodiment of the present invention configured as described above will be described.

When the color signal S _Y is input, the neighborhood average pixel value generation circuit 18 calculates the color signal S _Y, an average value U _Y. Next, this average value U _Y is used as an address in the lookup table 20.
Output a conversion value Q (U _Y ) corresponding to the threshold level of each color.

On the other hand, the average value U _Y is obtained by the subtraction circuit 24 as (U _Y −S _Y ).

The obtained (U _Y -S _Y ) is multiplied by the conversion value Q (U _Y ) output from the look-up table 20 by the multiplying circuit 22 to obtain a product.

This product, that is, Q (U _Y ) × (U _Y −S _Y ) is further added to the color signal S _Y by the addition circuit 26 to obtain the output signal F _Y of the addition circuit 26.

F _Y = S _Y + Q (U _Y ) × (U _Y −S _Y ) Here, the conversion value Q (U _Y ) takes a value of 0 to 1, and when this value is 0, the output of the noise removal circuit is The input signal is output as it is, and if it is 1, the average value _UY is output. The above processing is performed for each color.

As described above, the noise removal circuit 12 uses the look-up table 20 for each color to output the color signals S _Y , S _M , and S _C for each color.
, The noise of the image is appropriately removed, and the feeling of roughness is reduced.

[Effect of the Invention] The image processing apparatus according to the present invention focuses on the fact that the magnitude of noise differs depending on the color, and independently sets a look-up table for each color, thereby changing the threshold level and changing the color signal. Remove noise. As a result, a good image without roughness can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a noise removal circuit in the image processing apparatus according to the present invention, and FIG. 2 is a configuration diagram of each color of the noise removal circuit. 10: Noise removal circuit 18: Neighboring pixel average value generation circuit 20: Look-up table 22: Multiplication circuit 24: Subtraction circuit 26: Addition circuit

Claims (1)

(57) [Claims] 1. A neighborhood pixel average value generation circuit for generating an average value of an image signal in a pixel in the vicinity of a pixel of interest, and a look which is set for each color constituting the image signal and holds a coefficient corresponding to the average value An image processing apparatus comprising: an up-table; and an arithmetic unit that obtains a desired image signal from an image signal from the pixel of interest, the average value, and the coefficient.