JPH09233353A - Image color tone correcting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily execute color tone correction by distributing each picture element value in a color space at an equal interval in the direction of lightness and moving each division area in the color space so as to correct the color tone. SOLUTION: A position in an image desired to be corrected is pointed out and, a correction area extract section 24 generates mask data. The generated mask data are outputted to an image data conversion section 30. On the other hand, a correction instruction section 18 enters a color tone correction instruction word and when a data storage section 22 selects a corresponding distribution displacement vector, it is given to a characteristic curve arithmetic section 28, in which a change amount characteristic curve corresponding to L, C, H is obtained through an interpolation arithmetic operation based on the distribution change vector. When the change amount characteristic curve is obtained, it is inputted to an image data conversion section 30. Then mask data are applied to image data received separately from an image storage memory 12 and picture element value conversion is executed only for picture elements in the image whose mask is released and the result is outputted to the memory 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image color tone correcting apparatus suitable for applying when correcting the color tone of a color image.

[0002]

2. Description of the Related Art Conventionally, for example, in a process of preparing an original plate for color printing, after inputting an original image with an input device such as a color scanner, the color tone of the input image is corrected. When correcting an image with a color tone correction device attached to such a color scanner, the operator appropriately controls device parameters such as (highlight / shadow) points, gradation curves, and color correction. By doing so, the color tone of the color image is corrected.

[0003]

However, since a high degree of judgment is required to correct the color tone of a color image, it is necessary to be skilled in controlling the parameters of the apparatus as intended to perform an appropriate color tone correction. There is a problem that skills are required.

The present invention has been made to solve the above-mentioned conventional problems, and provides an image color tone correcting apparatus capable of easily correcting the color tone of a color image without special skill. Is an issue.

[0005]

SUMMARY OF THE INVENTION The present invention, in an image color tone correction device for correcting the color tone of a color image, obtains a distribution in the color space of each pixel value of pixels existing in a target area on the color image. By dividing the distribution into a plurality of areas along the lightness axis of the color space, moving each of the divided areas on the color space, and providing a means for correcting the color tone of the target area, This is a solution to the above problem.

That is, in general, an image is photographed by illuminating an object having a three-dimensional spread and passing the reflected light through an appropriate lens system and mapping it on a two-dimensional plane. At that time, one object has the same spectral reflectance,
That is, they have the same color, and various gradations occur in that color depending on the relationship between the angle of the illumination light, the surface of the object, and the position of the viewpoint.

Therefore, when attention is paid to one object in a color image, it is known that the distribution of pixel values belonging to the image area corresponding to the object in the color space has a certain characteristic tendency. That is, even if the object is the same, the shadowed area where the illumination light does not reach becomes black, and the area of the object surface where the line of sight is close to the exit angle determined by the incident angle when the illumination light enters the surface of the object Because the state is close to reflection,
It becomes the same white as the illumination light, and in the middle part the object surface is diffusely reflected and the reflectance has a distribution with respect to the line-of-sight angle,
Pixels in the same area (same object) have a color space of L * a * b *
In the case of space, as shown in FIG. 1, there is a tendency to be distributed in an arc-shaped gradation along a curve from black (shadow) to a color (object color) specific to an object to white (highlight). Here, L * represents lightness, the distance from the L * axis in the a * b * plane represents saturation, and the rotation angle represents hue.

In the present invention, such a characteristic of the distribution of pixel values representing the same object in the color space is utilized, and the distribution is divided into a plurality of regions along the lightness direction, for example, at equal intervals, and each region is divided into a plurality of regions. By moving the divided areas in the color space, the color tone of the object can be corrected, and the color tone of the color image can be easily corrected.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram showing a schematic configuration of a color tone correcting apparatus according to an embodiment of the present invention. This color tone correction device is comprised of an image input device 10 such as a scanner for inputting a color image from an original image such as a color photograph, an image holding memory 12 for holding image data input by the image input device 10, the input color An image display device 14 such as a display for displaying an image and an image output device 16 for outputting a finally corrected color image are provided.

Further, the arithmetic unit 20 and the arithmetic unit 2 for reading out the image data stored in the image storage memory 12 and executing the tone correction for the color image described in detail below.
A correction designation unit (user interface) 18 including a pointing device such as a mouse for inputting a color-correction directive to 0 and designating a correction target area, a directive to be described later, and a distribution change The data holding unit 22 stores a correspondence table that associates the relationship with the vector (change amount).

The arithmetic unit 20 includes a correction area extraction unit 24, a distribution displacement vector selection unit 26, a characteristic curve arithmetic unit 28, and an image data conversion unit 30, whose functions will be described in detail later. There is. Then, in this arithmetic unit 20,
Image tone correction, which will be described in detail below, is executed, and the corrected image data is output to and stored in the memory 12.

In this embodiment, as shown in FIG. 3, for a pixel existing in a target area which is, for example, one object on a color image, as shown in FIG. 3, a banana-shaped distribution A in the same color space as that in FIG. Is obtained, and the distribution is equally divided into a plurality of (here, three) regions along the lightness axis L * of the color space, and the distribution of each divided region is expressed by a vector (hereinafter , Also referred to as a distribution displacement vector), the color tone is corrected by changing the color space. The equal division of the distribution means that the range of maximum and minimum L * values of the pixel values existing in the distribution is equally divided.

Further, when performing the above-mentioned color tone correction, the correction designation unit 18 is only required to input a color tone correction instruction word, which is a color proofing term generally used in printing and platemaking, and the distribution displacement vector selection unit In 26, the distribution displacement vector corresponding to the input directive can be selected with reference to the correspondence table between the color tone correction directive and the distribution displacement vector (movement amount) stored in the data holding unit 22. Therefore, it is possible to easily implement the correction as instructed.

First, the distribution displacement vector will be described. Here, taking into account the correspondence with human color perception,
The LCH color space corresponding to the L * a * b * color space shown in FIG. 1 and FIG. 3 on a one-to-one basis is adopted (L: lightness, C: saturation, H: hue).

For one distribution on the color space, the displacement vector for the representative point (for example, the center of gravity or the center of the distribution) for each divided area is expressed as in the following equation (1).

ΔVi = (ΔVi, ΔCi, ΔHi) (1) i = 0, 1, ... M-1 (M: number of divisions)

FIG. 3 shows a case where the number of divisions M is 3, but the displacement vectors for each representative point for each divided area thus obtained are arranged as in the following equation (2). What is called a distribution displacement vector that describes the distribution change of the whole.

ΔV = (ΔV 0, ..., ΔV _M-1 ) (2)

The correspondence table stored in the data holding unit 22 is prepared by previously determining the correspondence relationship between the color tone correction directives generally used in printing and the like and the distribution displacement vector as shown in FIG. This can be created as versatile data by a statistical method such as principal component analysis. At this time, each displacement vector that defines the distribution displacement vector of the above equation (2) is, for example, an actual value obtained by moving the pixel value existing in each divided area when the color tone correction corresponding to the directive is performed in the actual sample. Can be obtained as an average value of the displacement amount of.

This correspondence table is referred to when the distribution displacement vector selection unit 26 selects the distribution displacement vector as described above, but the correction designation unit 18 selects, for example, "bright" at the top.
When the directive is input, it corresponds to a set of displacement vectors in which the L (brightness) component is increased (ΔV 0, ..., Δ
The distribution displacement vector of V _M-1 ) is automatically selected by the selection unit 26.

Also, as shown in FIG. 4, "vividly",
Entering the directives "contrast enhancement" and "pressing fog" mainly means "increasing the C component", "stretching the whole in the L-axis direction", and "similarly wearing similar lines This is equivalent to selecting a distribution displacement vector having the content of “reducing color components”.

Next, the actual color tone correction processing will be described. First, as conceptually showing the screen of the image display device on the left side of FIG. 5, a location (center portion) to be corrected in the image is designated, and the correction area extraction unit 24 creates mask data. For this purpose, for example, a part of the correction area in the image is designated by a pointing device (correction designation unit) 18 such as a mouse to obtain color data representative of the area, and shown on the right side of FIG. In addition, considering a rectangular parallelepiped area in a color space surrounding the color, the pixels inside the rectangular parallelepiped are masked OFF and the pixels outside thereof are masked ON, so that only the OFF area on the screen is tone-corrected. Create mask data to do this. In this way, the mask data created by the correction area extraction unit 24 is stored in the image data conversion unit 3
Output to 0.

On the other hand, when a color tone correction directive is input in the correction designating section 18 and a corresponding distribution displacement vector is selected from the data holding section 22, it is input to the characteristic curve calculating section 28, where the distribution displacement vector is selected. By interpolation calculation from
A change amount characteristic curve corresponding to each of L, C, and H is obtained.

FIG. 6 conceptually shows an example of linear interpolation when the number of divisions M is 5, and a displacement vector ΔV 0 (ΔL 0, ΔC 0, Δ) with respect to a representative point (center of gravity or center) of each divided area.
H0) to .DELTA.V4 (.DELTA.L4, .DELTA.C4, .DELTA.H4) which correspond to the respective components and which are indicated by thick lines .DELTA.L0 to .DELTA.L4 and .DELTA.C0 to .DELTA.
By performing linear interpolation for each value of C4 and .DELTA.H0 to .DELTA.H4, a displacement vector for points other than the representative point is obtained. Then, using the displacement vector for each representative point and the interpolated values for the other points, the values of the pixels included in the entire distribution A shown in FIG. Move to.

When the characteristic curve calculation unit 28 obtains the change amount characteristic curve in this manner, it is calculated by the image data conversion unit 30.
Is input to Then, here, the mask data is applied to the image data separately input from the image holding memory 12, and only the pixels of the mask OFF in the image are subjected to the pixel value conversion based on the characteristic curve. Is executed, the L, C, and H values of each pixel are changed to the converted L ', C', and H'values as shown in FIG. Is output to and stored in the memory 12 for use.

As described in detail above, according to the present embodiment, the pixel values forming one object in the image are distributed along the curve from black to the object color to white in the color space. By utilizing this feature, the distribution is divided at equal intervals in the lightness direction, and each divided region is moved in the color space,
By enabling color tone correction, it has become possible to easily perform color tone correction.

In addition, a correspondence table of color tone correction directives (color proofing terms) used in printing and plate making and vectors describing distribution changes in the color space is provided, and the directives are handled with reference to this table. Since the correction is realized, it has become possible to easily carry out the color tone correction which has required skill in the past.

The present invention has been specifically described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention.

For example, in the above-described embodiment, the color space coordinate system is L * a * b * and LCH corresponding to the LCH is one-to-one. However, the present invention is not limited to this, and any color such as RGB can be used. It can also be applied to spatial coordinates.

Further, when the displacement vector for each of the divided areas other than the representative point is obtained by linear interpolation from that of the representative point, the value corresponding to the lower end of the divided area having the minimum brightness is set to 0 in FIG. Further, in the divided area with the maximum brightness, the value that hits the upper end of the area is set to 0, but the value is not limited to this, and the value from the representative point to the lower end or the upper end is, for example, the same at the representative point. May be the same value as.

[0032]

As described above, according to the present invention,
The tone of a color image can be easily modified without special skill.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a distribution in a color space of pixel values representing the same object in an image.

FIG. 2 is a block diagram showing a schematic configuration of a color tone correction device according to an embodiment.

FIG. 3 is an explanatory view showing color tone correction by distribution displacement in a color space.

FIG. 4 is a diagram showing a correspondence table of color tone correction directives and distribution displacement vectors.

FIG. 5 is an explanatory diagram conceptually showing creation of mask data.

FIG. 6 is an explanatory diagram showing a method of calculating a variation characteristic curve by interpolation calculation.

FIG. 7 is an explanatory diagram conceptually showing conversion of pixel values.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Image input device 12 ... Image holding memory 14 ... Image display device 16 ... Image output device 18 ... Correction designation part 20 ... Calculation part 22 ... Data holding part 24 ... Correction area extraction part 26 ... Distribution displacement vector selection part 28 ... Characteristic curve calculation unit 30 ... Image data conversion unit

Claims (4)

[Claims] 1. An image color tone correcting device for correcting the color tone of a color image, wherein a distribution of each pixel value in a color space is calculated for pixels existing in a target area on the color image, and the distribution is used as a lightness of the color space. An image color tone correction device, comprising means for dividing a plurality of regions along an axis and moving each of the divided regions in a color space to correct the color tone of the target region. 2. A means for determining the amount of movement of each divided area of the distribution based on a distribution displacement vector that describes the amount of change in the color space corresponding to the amount of tone correction for each representative point. An image color tone correction device characterized by being provided. 3. The color tone correction of an image according to claim 2, further comprising means for obtaining a movement amount other than the representative point of each divided area of the distribution by interpolating a displacement vector of each representative point. apparatus. 4. The correspondence table according to claim 1, further comprising a correspondence table of a color tone correction directive and a distribution displacement vector describing a variation amount in a color space with respect to a representative point of each divided area of the distribution. Image color correction device.