JP2001138608A - Method for evaluating continuity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for evaluating continuity in which continuity of gray scale characteristics of an image output apparatus can be evaluated even if locality is present in the image output apparatus. SOLUTION: The method for evaluating continuity comprises an output step for inputting chart image data indicative of a chart image where each color patch constituting a series of color patches corresponding to a series of values of parameter, e.g. mesh %, is arranged such that two arbitrary color patches, consecutive in the order of parameter value, are contiguous to each other to an image output apparatus and outputting the chart image therefrom, and a step for evaluating the continuity of parameter values representing the color of color patch constituting the chart image outputted in the output step with the predetermined parameters.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image output apparatus which receives an image data and outputs an image, and which receives and outputs image data representing an image including a continuous color change on the image. The present invention relates to a continuity evaluation method for evaluating continuity of expected color change in an image.

[0002]

2. Description of the Related Art An image output apparatus, such as a printing machine or a printer, which receives an input of image data and outputs an image, includes:
The color of the image represented by the image data is not always faithfully reproduced, and an image having a color corresponding to the color of the image represented by the image data is output. The colors referred to here include not only chromatic colors but also achromatic colors. The correspondence between the color of the image represented by the image data input to the image output device and the color of the image output from the image output device is called a gradation characteristic.

[0003] Such a gradation characteristic, if viewed from a different point of view,
It is also considered that when image data representing a gradation image in which lightness or the like of a color continuously changes on the image is input to the image output device, the image data represents a color change expected on the output image. If a discontinuous portion exists in the gradation characteristics, a phenomenon called a tone jump in which the color tone or the brightness jumps on the gradation image occurs. Such a tone jump is conspicuous on an image and causes image quality deterioration.

Therefore, a continuity evaluation method for accurately evaluating the continuity of gradation characteristics is desired, and tone jump can be prevented by correcting image data or the like based on the evaluation result by the continuity evaluation method. Is desired. However, a continuity evaluation method for accurately evaluating the continuity of gradation characteristics has not yet been realized.

[0005] By the way, the color can be quantitatively expressed by various parameters such as halftone%, pigment density, lightness and chromaticity. When a certain parameter is used to express the color, the image output device requires a parameter value. Receiving the input of
It can be thought that a parameter value corresponding to the parameter value is output. Therefore, the gradation characteristic can be expressed as a curve on a graph representing the correspondence between the input parameter value and the output parameter value, and the continuity of the gradation characteristic is evaluated by evaluating the continuity of the curve. It is thought that it is possible.

FIG. 1 is a graph showing an example of a gradation characteristic, and shows a graph (A) of a continuous curve over the entirety and a graph (B) of a curve having a small step.

Here, halftone% is adopted as a parameter for expressing a color, and the horizontal axis in FIGS. 1A and 1B is the color of the image represented by the image data input to the image output device. , And the vertical axis indicates the dot% corresponding to the color of the image output from the image output device.

[0008] Curve 1 shown in the graph of FIG.
Is a continuous curve that is bent as a whole but has no steps. A tone jump does not occur in an image output device having the gradation characteristic represented by such a curve 1.

On the other hand, the curve 2 shown in the graph of FIG. 1B has a small step 2a in the middle, and an image output having a gradation characteristic represented by such a curve 2 is obtained. In the apparatus, a tone jump occurs at a place corresponding to the step 2a on the gradation image. Such a step 2a
It is considered that the continuity of the gradation characteristic can be evaluated by evaluating the presence / absence of the gradation, and the tone jump can be prevented by the correction that cancels the step 2a.

As a continuity evaluation method for evaluating the continuity of the gradation characteristic by evaluating the presence or absence of such a step 2a, a chart image composed of a series of color patches corresponding to the continuous change of the parameter values described above is used. Is input to an image output device, the chart image is output from the image output device, the color of each color patch constituting the output chart image is converted into a parameter value, and a curve representing a gradation characteristic To evaluate the continuity of the curve.

[0011]

However, in general, an image output device has a so-called locality, and even if the input image data represents a solid image of a single color, the image to be output is generally output. Is slightly different depending on the position on the image. The color change on the image due to this locality is a gradual change, not a change that causes a tone jump, but a curve representing the gradation characteristic was obtained based on the chart image output by the image output device. In such a case, it is considered that the influence of locality accumulates, so to speak, so that a step similar to the step causing a tone jump is generated on the curve. For this reason, it is expected that the step which causes the tone jump cannot be found, and the continuity cannot be evaluated.

In view of the above circumstances, an object of the present invention is to provide a continuity evaluation method capable of evaluating the continuity of gradation characteristics of an image output device even if locality exists in the image output device. And

[0013]

A continuity evaluation method according to the present invention, which achieves the above object, comprises an image output device which receives an input of image data and outputs an image, including a continuous color change on the image. In a continuity evaluation method for evaluating the continuity of characteristics of an image output device that represents an expected color change on an output image when image data representing an image is received, parameters for quantitatively expressing colors are used. One or more color patches constituting a series of color patches associated with each of a series of parameter values corresponding to a continuous value change of the predetermined parameter are one or more for each color patch. For any two parameter values that follow one another in the order of the value change, two color patches associated with the two parameter values are adjacent to each other. An output process of inputting chart image data representing a chart image arranged so that a positional relationship always exists to an image output device, and outputting the chart image by the image output device, and a chart image output in the output process Of the two color patches adjacent to each other and associated with the two values that are adjacent to each other in the order of the above-mentioned value change. And an evaluation step of evaluating continuity.

Here, the term "color" includes not only chromatic colors but also achromatic colors. The evaluation of the continuity in the evaluation process may be an evaluation based on a numerical analysis of the parameter value based on a predetermined algorithm, or may be a visual evaluation based on a graph of the parameter value.

The chart image used in the continuity evaluation method of the present invention includes, for any two parameter values that follow one another in the order of the above-described value change, two colors corresponding to the two parameter values, respectively. There is always a positional relationship in which the patches are adjacent to each other, and the effect of the locality of the image output apparatus can be ignored between two adjacent color patches. As a result, the continuity at each point on the curve representing the gradation characteristic can be evaluated without being affected by locality.

According to the continuity evaluation method of the present invention, the output step is such that each color patch constituting the series of color patches is set to one for each color patch as chart image data.
Each time, a chart image in which two color patches associated with two arbitrary parameter values that are successive to each other in the order of the above value change in the above series of parameter values are arranged so as to be always adjacent to each other. The chart image data to be input may be input to an image output device, and the chart image may be output by the image output device, or
In the output process, as the chart image data, each of the color patches forming the series of color patches is divided into a plurality of parameter value strings each including one of the series of parameter values. In the column, two color patches associated with each of two arbitrary parameter values that come and go in the order of the value change are arranged so as to be always adjacent to each other. In addition, the color patches associated with one of the two parameter values that straddle the two divided parameter value columns are arranged so as to overlap and be adjacent to the arranged color patch associated with the other corresponding to one of the two. The chart image data representing the chart image is input to an image output device, and the chart image is output by the image output device. It may be.

Further, in the continuity evaluation method according to the present invention, the output process may include a series of color patches corresponding to a series of parameter values corresponding to a value change of at least 25 gradations of the predetermined parameter as the series of color patches. It is preferable that chart image data representing a chart image using the color patch is input to an image output device, and the chart image is output by the image output device.

According to such a desirable continuity evaluation method, a series of color patches associated with each of a series of parameter values corresponding to fine value changes over 25 gradations of a predetermined parameter are used. A tone jump, which is a small discontinuity of change, can be easily found.

Further, in the continuity evaluation method according to the present invention, the output step is a chart image representing a chart image in which each color patch constituting the series of color patches is two-dimensionally arranged as the chart image data. It is preferable that data is input to an image output device and the chart image is output by the image output device.

In the chart image used in such a preferable continuity evaluation method, a sufficiently large number of color patches are arranged in a sufficiently small area because the color patches are arranged two-dimensionally. As a result, in such a suitable continuity evaluation method, the effect of the locality of the image output device can be sufficiently suppressed, and highly accurate evaluation can be performed.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, in describing embodiments of the present invention, first, a comparative example will be described, and then embodiments will be described. In the following description, in outputting an image as an image output device,
An image composed of pixels is formed by sequentially arranging pixels in a predetermined main scanning direction to form a pixel row, and sequentially arranging the pixel rows in a sub-scanning direction orthogonal to the main scanning direction. Is assumed to be an image output device that outputs the image data. Further, in the following description, it is assumed that halftone% is adopted as an example of a parameter expressing a color.

FIG. 2 is a diagram showing a chart image used in the comparative example.

The chart image 3 is composed of a plurality of patch rows 5 each consisting of 20 color patches 4, and the number given to each color patch 4 is a dot% value corresponding to each color patch 4. Is represented. However, the numbers themselves are not output. The plurality of patch rows 5 constituting the chart image 3 are arranged in parallel to the above-described main scanning direction. In each patch row 5, the value of the dot% increases toward the right in FIG. Color patches 4 are arranged as described above.

The chart image data representing the chart image 3 on which the color patches 4 are arranged is input to the image output device, and the chart image 3 is output by the image output device.
The dye density of each color patch 4 constituting the output chart image 3 is measured, and the dye density is converted into a value of dot%.

If the image output device is an image output device having an ideal gradation characteristic, the halftone value obtained by converting the pigment density of each color patch 4 is added to each color patch 4 shown in FIG. However, in general, the value of the converted dot% is different from the value of the numeral. Then, by graphing the correspondence between the converted halftone% value and the numeric value, a curve representing the gradation characteristics of the image output apparatus when focusing on halftone% is obtained.

FIG. 3 is a graph showing an example of the gradation characteristics obtained in the comparative example.

As in the graphs of FIGS. 1A and 1B, the horizontal axis of the graph of FIG. 3 indicates the halftone dot corresponding to the color of the image represented by the image data input to the image output device. The vertical axis indicates the dot% corresponding to the color of the image output from the image output device.

FIG. 3 shows, as an example, a graph obtained for an image output apparatus which does not cause a tone jump. A curve 6 in the graph of FIG. 3 shows a plurality of patches shown in FIG. A minute step 6a exists at each position corresponding to each end of the row 5. These steps 6a are steps caused by the locality described above. Since such steps 6a are present on the curve 6 of the graph, there is a slight step in the gradation characteristic that causes a tone jump. Even if it is, it cannot be discovered that it exists near the step due to locality. In other words, the presence of a step due to locality makes it impossible to accurately evaluate the continuity of the gradation characteristics of the image output device.

Such a step 6a corresponds to the color patch at the end of the patch row 5 and the color patch because the continuity of the dot% value is discontinued at the end of the patch row 5 shown in FIG. It is considered that locality is accumulated and generated between the halftone value and the color patches having the halftone value before and after the halftone value.

Therefore, in the present invention, the arrangement of the color patches on the chart image is devised, and for any two parameter values having successive values, the color patches corresponding to the two parameter values are adjacent to each other. Is used in which the color patches are arranged so that the image always occurs somewhere on the chart image. Hereinafter, an embodiment of the present invention using the chart image in which the color patches are arranged in such a manner will be described.

FIG. 4 is a diagram showing a chart image used in the first embodiment of the present invention.

In FIG. 4, in order to make the arrangement of the color patches 11 easy to understand, the boundary between the color patches 11 is partially omitted.

In the chart image 10 shown in FIG. 4, a series of color patches 11 are arranged in series in the order of the dot% so as to reciprocate in the sub-scanning direction. That is, each color patch 1 from the dot% “1” to the dot% “20”
1 are arranged in a row so that the value of the dot% increases as going downward in FIG. 4, the color patch of the dot% "21" is arranged next to the color patch of the dot% "20", and the dot% " 21 "
The color patches 11 from to the dot% “40” are arranged in a row such that the value of the dot% increases toward the top of FIG. Then, the color patch 1 after the dot% “41”
1 is similarly arranged.

As in the description of FIG. 2 described above, image data representing the chart image 10 shown in FIG. 4 is input to the image output device, and the chart image 10 is output by the image output device. Is converted into a value of halftone% to obtain a gradation characteristic curve. Since the arrangement of the color patches 11 is an arrangement devised as described above, the curves obtained here are the same as the curves 1 and 2 shown in FIGS. 1A and 1B. Therefore, by evaluating the continuity of the curve obtained by using the chart image 10, the continuity of the gradation characteristics of the image output device is correctly evaluated.

In order to accurately evaluate the continuity of the gradation characteristics, it is desirable that the color patches have at least 25 gradations or more corresponding to parameter value changes, as shown in FIG. In the chart image 10, as an example, color patches 11 corresponding to each of 60 or more parameter values are arranged. Also, the arrangement of color patches
A two-dimensional arrangement as shown in FIG.
A dimensional arrangement is preferable because more color patches can be arranged in a range with less locality.

The first embodiment has been described above, and other embodiments will be described below. In the following description, only the chart images used in each embodiment will be described, and those chart images will be described. The procedure for evaluating continuity using the same is the same as in the first embodiment, and a description thereof will be omitted.

FIG. 5 is a diagram showing a chart image used in the second embodiment of the present invention.

In FIG. 5 as well, in order to make the arrangement of the color patches 21 easy to understand, the boundary between the color patches 21 is partially omitted.

In the chart image 20 shown in FIG. 5, the color patches 21 are spirally arranged in the order of the dot%, and the value of the dot% is smaller inside the spiral. Also in this chart image 20, the color patches 21 are arranged in a line in the order of the dot%, so that the continuity of the gradation characteristic can be correctly evaluated using the chart image 20.

FIG. 6 is a diagram showing a chart image used in the third embodiment of the present invention.

In the chart image 30 shown in FIG. 6, the color patches 31 reciprocate in the main scanning direction as described above.
They are arranged consecutively in the order of the values of the dot%.

FIG. 7 is a diagram showing a chart image used in the fourth embodiment of the present invention.

In the chart image 40 shown in FIG. 7, the color patches 41 are spirally arranged in the order of the halftone dot value, and the halftone dot value becomes smaller outside the spiral.

The chart images 10 and 2 shown in FIGS.
At 0, 30, 40, the chart images 10, 20, 30,
The color patches 11, 21, 31, and 41 constituting 40 are halftone%
, But the color patches constituting the chart image according to the present invention need not necessarily be arranged in a series. Hereinafter, a case where the color patches are not arranged in a row will be described.

FIG. 8 is a diagram showing a chart image used in the fifth embodiment of the present invention.

The chart image 50 shown in FIG.
As with the chart image 3 of the comparative example shown in FIG.
The patch array 51 is composed of a plurality of patch arrays 51 composed of three color patches 52 and parallel to the above-described main scanning direction.
Are arranged such that the value of the color patch 52 becomes large.

However, the chart image 50 shown in FIG.
Differs from the chart image 3 of the comparative example shown in FIG.
Three color patches at the end of each patch row 51 are arranged so as to overlap by three. For example, each color patch 52 from halftone "1" to halftone "13" forming the uppermost patch row in FIG.
Among them, the net% “11” which is the last three in the order of the net% value
Of each color patch 52 from the dot% “13” to the dot% “13”, among the color patches from the dot% “11” to the dot% “23” constituting the next patch row, in the order of the dot%. Are arranged so as to overlap with the respective color patches from halftone% “11” to halftone% “13”, which are the three. Here, "1"
Columns of dot% values from “11” to “10” and “11” to “2”
The sequence of the dot% values up to “0” is an example of the divided parameter value sequence according to the present invention.

As described above, since the color patches 52 are arranged in an overlapping manner, for example, from the dot% “11” to the dot%
The continuous arrangement of each color patch up to “13” is also performed in halftone “10”.
The continuous arrangement of each color patch from to
The continuous arrangement of each color patch from "12" to halftone% "14" is also all prepared on the chart image 50. Therefore, as will be described in detail below, by using the chart image 50, even if a discontinuity of the gradation characteristic that causes a tone jump occurs near any value of the dot%, the discontinuity is surely reduced. Can be found.

FIG. 9 is a graph showing an example of a gradation characteristic curve obtained by using the chart image shown in FIG.

Similar to the graph of FIG. 3, the horizontal axis of the graph of FIG. 9 represents the halftone dot corresponding to the color of the image represented by the image data input to the image output device, and the vertical axis represents the image. A dot% corresponding to the color of the image output from the output device is shown. Further, the graph of FIG. 9 shows a tone characteristic curve 53 obtained when there is no step that causes a tone jump. The curve 53 representing the gradation characteristic has a discontinuity 53a in some places.
In the vicinity of a, the curve 53 is a double line. The double line portion is a portion corresponding to the color patches 52 that are overlapped in the chart image 50 shown in FIG. 8, and the interval between the double lines corresponds to the locality of the image output device. Therefore, when a step that causes a tone jump occurs on the curve 53 shown in FIG. 9, the step is surely found, and the continuity of the gradation characteristic can be appropriately evaluated. .

In each of the above-described embodiments, halftone% is used as a parameter for expressing a color. However, the parameter according to the present invention is limited to halftone% as long as it expresses color quantitatively. Instead, it may be a pigment concentration, chromaticity, a coordinate value in a color space, or the like.

[0052]

As described above, according to the continuity evaluation method of the present invention, it is possible to evaluate the continuity of the gradation characteristics of an image output device even if locality exists in the image output device. .

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a gradation characteristic, in which a graph (A) of a continuous curve over the entirety and a graph (B) of a curve having a small step are shown.

FIG. 2 is a diagram showing a chart image used in a comparative example.

FIG. 3 is a graph showing an example of a gradation characteristic curve obtained in a comparative example.

FIG. 4 is a diagram showing a chart image used in the first embodiment of the present invention.

FIG. 5 is a diagram showing a chart image used in a second embodiment of the present invention.

FIG. 6 is a diagram showing a chart image used in a third embodiment of the present invention.

FIG. 7 is a diagram showing a chart image used in a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a chart image used in a fifth embodiment of the present invention.

FIG. 9 is a graph showing an example of a gradation characteristic curve obtained by using the chart image shown in FIG. 8;

[Explanation of symbols]

 10, 20, 30, 40, 50 chart image 11, 21, 31, 41, 52 color patches

Claims (5)

[Claims] 1. An image output apparatus that receives an input of image data and outputs an image when the input of image data representing an image including a continuous color change on the image is expected. A continuity evaluation method for evaluating the continuity of characteristics of the image output device representing a color change, wherein a series of parameters corresponding to a continuous value change of a predetermined parameter among parameters quantitatively expressing color. Each color patch constituting a series of color patches associated with each value is one or more for each color patch, and, for any two parameter values that are successive in the order of the value change in the series of parameter values, The chart image represents a chart image in which two color patches associated with these two parameter values are arranged so that there is always a positional relationship adjacent to each other. Inputting the chart image data to the image output device, outputting the chart image by the image output device, and, among the color patches constituting the chart image output in the output process, adjacent to each other, An evaluation step of evaluating continuity between two values in which colors of two color patches respectively associated with two values that are adjacent to each other in the order of the value change are expressed by the predetermined parameter. Continuity evaluation method. 2. The output step includes, as the chart image data, one set of color patches constituting the series of color patches, one set for each color patch, and one set of parameter values in the order of the parameter change in the set of parameter values. Chart image data representing a chart image in which two color patches associated with each of two arbitrary preceding and following parameter values are always arranged adjacent to each other is input to the image output device, and the chart image is input to the image output device. 2. The continuity evaluation method according to claim 1, wherein the continuity evaluation is output by the image output device. 3. In the output step, as the chart image data, each color patch constituting the series of color patches is divided into one for each color patch, and a parameter value sequence including the series of parameter values is divided into a plurality. In the resulting divided parameter value sequence, two color patches associated with each of two arbitrary parameter values that follow each other in the order of the value change are arranged so as to be always adjacent to each other. The color patches associated with one of the two parameter values that precede and follow in the order of the change and straddle the two divided parameter value sequences overlap each other, and the arranged colors associated with the other correspond to the other. Inputting chart image data representing a chart image arranged adjacent to a patch to the image output device, and outputting the chart image to the image output device 2. The continuity evaluation method according to claim 1, wherein the continuity evaluation is output. 4. The output step includes using, as the series of color patches, a series of color patches respectively associated with a series of parameter values corresponding to a value change of the predetermined parameter over 25 gradations. The continuity evaluation method according to claim 1, wherein chart image data representing a chart image is input to the image output device, and the chart image is output by the image output device. 5. The output step includes inputting, as the chart image data, chart image data representing a chart image in which respective color patches constituting the series of color patches are two-dimensionally arranged to the image output device. 2. The continuity evaluation method according to claim 1, wherein the chart image is output by the image output device.