JPH0832838A - Gradation correction method and gradation correction device - Google Patents

Abstract

PURPOSE:To provide a gradation correction method and a gradation correction device in which gradation is corrected with high accuracy optimum to a scene of images with simple configuration. CONSTITUTION:Scene information of an input image is decided (step 2), the degree of lightness of the input image is decided (step 1), basic density gradation correction information being a basis of a scene depending on the scene information is generated as a basic density gradation table of a density input/density output (step 3), the basic density gradation table is modified (step 4) so as to obtain a gradation correction characteristic suitable for the input image depending on the degree of the lightness of the input image, the modified table is converted into a gradation correction table of the luminance input/luminance output (step 5), and the gradation of the input image is corrected by using the luminance of the input image as an input and the corrected luminance as an output based on the gradation correction table (step 6).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation correcting method and a gradation correcting apparatus for a video equipment for making a hard copy of a video signal.

[0002]

2. Description of the Related Art In recent years, with the development of hard copy technology, especially full-color hard copy technology, it has become possible to reproduce faithful images using a printing technology such as a sublimation type thermal transfer system. In terms of color reproduction, recording materials and image processing have provided a reproduction capability equivalent to that of silver salt photographs, and in terms of resolution, silver salt photographs are approaching by using high-definition video signals such as high definition.

However, the video signal has luminance, color difference and R
(Red), G (green), B (blue), etc. are reproduced with an additive color mixture, while the hard copy is reproduced with a subtractive color mixture of Y (yellow), M (magenta), C (cyan), The dynamic range and reproducibility of each other are very different.

For example, since the skin color seen on a CRT does not have an object to be compared with the surroundings, a relative comparison with other colors on the CRT is made to judge whether it is preferable or not preferable. Since there is a skin color of one's hand and the like nearby, the preferred skin color is absolute. Therefore, it is said that a preferable skin color is about +0.5 on the surface of a hard copy.

As described above, the absolute density is important in hard copy, and the preferable reproducibility is greatly different from that of the video signals of TV and VTR. In addition, hard copy has a visual effect that it is difficult to see the change in extremely dark and bright density areas, so it is said that it is good to compress the gradation of these areas and emphasize the halftone. It is said that it is better to compress the bright density range more gently than the dark density range because the change in the bright density range is easier to understand in the bright density range than in the very dark density range.

However, it is very difficult to realize these characteristics of the density by the brightness, and the information which is linear in the density becomes non-linear in the brightness, and in order to realize the optimum gradation property for hard copy in the brightness information. It requires a very complicated operation. In gradation correction with luminance information, therefore, it is difficult to realize the visual characteristics peculiar to these hard copies by a simple method.

[0007] The gradation correction of a conventional device that handles video signals is as follows.
A method for correcting gamma by preparing a conversion table suitable for the input environment for each RGB (Japanese Patent Laid-Open No. 62-004771),
In order to make the density of the highlight part and the density of the shadow part match the output dynamic range, a method of performing correction when converting RGB into density (Japanese Patent Laid-Open No. 63-061578), etc. The key correction was decided and it was corrected. Therefore, it was very difficult to consider the visual characteristics peculiar to the hard copy as described above.

A method of correcting the luminance so that the density distribution of the image becomes uniform, for example, "means for correcting the density distribution of the image using a non-linear amplifier and its processing result", IEICE Technical Report T
ECNICAL REPORT OF IEICE. I
In E92-112 (1993-01), since the density distribution is corrected so as to be uniform, the optimum correction is not performed according to the scene such as backlight or a human image.

[0009]

However, in the gradation correction device based on the conventional gradation correction method as described above, since gradation correction is performed on the brightness, it is attempted to consider density characteristics in this gradation correction. In that case, there is a problem that it is necessary to perform a complicated calculation such as logarithmic conversion, and gradation correction in consideration of density characteristics cannot be easily realized.

Further, gradation correction has not been performed so as to obtain the optimum gradation according to the scene of the image. For example, for each scene such as a backlight image or a person image, the optimum gradation according to each scene is obtained. There is a problem that gradation correction is not performed.

In view of the above problems, the present invention can easily realize gradation correction in consideration of the brightness characteristic and the density characteristic with a simple structure, and the optimum gradation can be obtained according to the scene of an image. It is an object of the present invention to provide a gradation correction method and a gradation correction device that can realize the obtained accurate gradation correction.

[0012]

In order to solve the above problem, a gradation correction method according to a first aspect of the present invention is a floor correction method for controlling the gradation of luminance according to the scene information and the degree of brightness of an input image. Tone correction method, in which the scene information of the input image is determined, the degree of brightness of the input image is determined, and basic density gradation correction information, which is the basis of the scene according to the scene information, is output to the density input density output. Created as a basic density gradation table,
The basic density gradation table is modified so that the gradation correction characteristics suitable for the input image are obtained according to the degree of brightness of the input image, and this modified table is converted into a gradation correction table for luminance input brightness output. A method of performing the gradation correction of the input image by converting and inputting the brightness of the input image and outputting the corrected brightness based on this gradation correction table.

A gradation correction device according to a second aspect is
In a gradation correction device that controls the gradation of brightness according to the scene information and the brightness of the input image, a scene information determining unit that determines the scene information of the input image, and the brightness of the input image. Level information determining means, basic density gradation table generating means for creating basic density gradation correction information that is the basis of a scene according to the scene information as a basic density gradation table for density input density output, and level information determination Table modification means for modifying the basic density gradation table so as to obtain gradation correction characteristics suitable for the input image in accordance with the degree of brightness of the input image determined by the means, and a table modified by the table modification means. Has a gradation table conversion unit for converting the input image to a gradation correction table for the luminance input luminance output, and the gradation correction table converted by the luminance table conversion unit. The luminance as input, and a gradation correction means for outputting a corrected luminance, and configured to output an output of said tone correction means as a corrected luminance signal.

A gradation correction device according to a third aspect is
In a gradation correction device that controls the gradation of brightness according to the scene information and the brightness of the input image, a scene information determining unit that determines the scene information of the input image, and the brightness of the input image. Level information determining means, a plurality of basic density gradation tables each having basic density input density output gradation information for each of a plurality of scenes of the image, and an input image according to the scene information from the plurality of basic density gradation tables. Selection means for selecting one basic density gradation table having gradation correction information suitable for the scene, and gradation suitable for the input image according to the degree of brightness of the input image determined by the degree information determination means. The table transformation unit that transforms the basic density gradation table selected by the selection unit so that the correction characteristic is obtained, and the table transformed by the table transformation unit is output as the brightness input luminance. A gradation correction table for converting the gradation correction table into a gradation correction table, and a gradation correction table converted by the brightness table conversion means. The gradation correction means outputs the corrected brightness with the brightness of the input image as an input. With and
The output of the gradation correction means is output as a corrected luminance signal.

The gradation correction device according to a fourth aspect is
In a gradation correction device that controls the gradation of brightness according to the scene information and the brightness of the input image, a scene information determining unit that determines the scene information of the input image, and the brightness of the input image. Level information determining means, a plurality of basic luminance gradation tables having basic luminance input luminance output gradation information for each of a plurality of scenes of the image, and a plurality of basic luminance gradation tables, and an input image according to the scene information. Selection means for selecting one basic luminance gradation table having gradation correction information suitable for the scene, and gradation suitable for the input image according to the degree of brightness of the input image determined by the degree information determining means. A table modification unit that modifies the basic luminance gradation table selected by the selection unit so as to obtain a correction characteristic; and a gradation correction table that is modified by the table modification unit, And a gradation correction unit that outputs the corrected brightness, and the basic brightness gradation table is determined based on a combination of straight lines having a plurality of slopes in a density input density output system. The density correction curve thus obtained is converted into a brightness input brightness output table in advance.

The gradation correction device according to a fifth aspect is
In a gradation correction device that controls the gradation property of luminance according to the scene information of the input image and the degree of brightness, scene information determination means for respectively determining the scene information of the input image as the reliability of each of a plurality of scenes, Degree information determining means for determining the degree of brightness of the input image for each of a plurality of scenes, a plurality of basic density gradation tables having basic density input density output gradation information for each of a plurality of scenes of the image, The scene information deciding means decides a plurality of table transforming means for transforming each basic density gradation table for each scene and each table transformed by the table transforming means according to the brightness degree information for each scene. Table synthesizing means for synthesizing according to the reliability of each of the generated scenes, and the table for synthesizing the table synthesized by the table synthesizing means, a gradation correction table And a gradation correction unit that has a gradation correction table that is converted by the brightness table conversion unit, and that inputs the brightness of the input image and outputs the corrected brightness. The output of the gradation correction means is output as a corrected luminance signal.

The tone correction device according to the sixth aspect is
In a gradation correction device that controls the gradation property of luminance according to the scene information of the input image and the degree of brightness, scene information determination means for respectively determining the scene information of the input image as the reliability of each of a plurality of scenes, A degree information determining unit that determines the degree of brightness of the input image for each of a plurality of scenes, and a plurality of basic luminance gradation tables that respectively have basic luminance input luminance output gradation information for each of a plurality of scenes of the image, A table modification unit that modifies the basic luminance gradation table so that the gradation correction characteristics suitable for the input image are obtained according to the brightness level information for each scene determined by the level information determination unit, and a table modification unit. The tables transformed by the above are combined by the table synthesizing means and the table synthesizing means for synthesizing according to the reliability of each scene determined by the scene information determining means. And a gradation correction unit which has a gradation correction table and which receives the brightness of the input image and outputs the corrected brightness. The basic brightness gradation table has a plurality of straight lines in a density input density output system. The density correction curve determined by synthesizing the polygonal line according to (4) and a curve connecting the bent portions of the polygonal line smoothly is converted into a table of luminance input luminance output in advance.

[0018]

According to the method of claim 1, the scene information of the input image is determined, the degree of brightness of the input image is determined, and the basic density gradation correction information, which is the basis of the scene, is added to the density according to the scene information. It was created as a basic density gradation table for input density output, and the basic density gradation table was modified according to the degree of brightness of the input image so that it has gradation correction characteristics suitable for the input image. The table is converted into a gradation correction table for brightness input brightness output, and based on this gradation correction table, the brightness of the input image is input and the corrected brightness is output, thereby correcting the gradation of the input image. To do.

According to the structure of claim 2, the scene information determining means determines the scene information of the input image, the degree information determining means determines the brightness degree of the input image, and the basic density gradation table generating means determines. Basic density gradation correction information, which is the basis of the scene, is created according to the scene information as a basic density gradation table of density input density output, and the brightness of the input image determined by the degree information determination means in the table transformation means. The basic density gradation table is modified so that the gradation correction characteristics suitable for the input image are obtained according to the degree of, and the table modified by the table modification means is used by the brightness table conversion means for the gradation of the brightness input brightness output. In the gradation correction unit having the gradation correction table converted into the correction table and converted by the brightness table conversion unit, And enter the degrees, and outputs the corrected luminance.

According to the structure of claim 3, the scene information determining means determines the scene information of the input image, the degree information determining means determines the degree of brightness of the input image, and the selecting means determines a plurality of scenes of the image. One basic density gradation table having gradation correction information suitable for the scene of the input image is selected from a plurality of basic density gradation tables each having basic density input density output gradation information for each. In the table transforming means, the basic density gradation table selected by the selecting means is set in accordance with the brightness degree of the input image determined by the degree information determining means so as to have the gradation correction characteristic suitable for the input image. In the luminance table conversion means, the table transformed by the table transformation means is transformed into the gradation correction table of the luminance input luminance output, In the gradation correction means having a converted gradation correction table in degrees table conversion means inputs the luminance of the input image, and outputs the corrected luminance.

According to the structure of claim 4, the scene information determining means determines the scene information of the input image, the degree information determining means determines the degree of brightness of the input image, and the selecting means determines a plurality of scenes of the image. One basic luminance gradation table having gradation correction information suitable for the scene of the input image is selected from a plurality of basic luminance gradation tables each having basic luminance input luminance output gradation information for each. In the table transforming means, the basic luminance gradation table selected by the selecting means is set in accordance with the degree of brightness of the input image determined by the degree information determining means so as to obtain the gradation correction characteristic suitable for the input image. In the gradation correction unit having the gradation correction table which is modified and modified by the table modification unit, the brightness of the input image is input and the corrected brightness is input. To output.

According to the structure of claim 5, the scene information determining means determines the scene information of the input image as the reliability for each of a plurality of scenes, and the degree information determining means determines the brightness degree of the input image by a plurality of degrees. For each scene, and a plurality of table transforming means sets a plurality of basic density gradation tables each having basic density input density output gradation information for each of a plurality of scenes of an image, for the brightness of each scene. The tables are transformed according to the degree, and the table synthesizing unit synthesizes the tables transformed by the table transforming unit according to the reliability of each scene determined by the scene information determining unit. The table synthesized by the synthesizing means is converted into the gradation correction table of the luminance input luminance output, and converted by the luminance table converting means. In the gradation correction means having a gradation correction table as input brightness of the input image, and outputs the corrected luminance.

According to the structure of claim 6, the scene information determining means determines the scene information of the input image as the reliability of each of a plurality of scenes, and the degree information determining means determines the brightness degree of the input image by a plurality of degrees. For each scene, and the table transforming means sets a plurality of basic luminance gradation tables each having basic luminance input luminance output gradation information for each of a plurality of scenes of the image to the degree of brightness of each scene. According to the reliability of each scene determined by the scene information determining means, the tables are transformed by the table synthesizing means so as to have gradation correction characteristics suitable for the input image. In the gradation correction unit having the gradation correction table combined by the table combination unit, the brightness of the input image is input and the corrected brightness is input. It performs the output of.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A gradation correction method and a gradation correction apparatus according to embodiments of the present invention will be described below with reference to the drawings.

The gradation correction method of the first embodiment will be described below. FIG. 1 shows a gradation correction method according to the first embodiment. Reference numeral 1 denotes a degree information determining step for determining degree information on the brightness of an input image. Step 2 is a scene information determination step of determining the scene information of the input image. 3 is
A density gradation table generating step for generating gradation correction information optimum for this scene as a scene basic density gradation table for density input density output according to the scene information determined in the scene information determining step 2. 4 corresponds to the degree information determined in the degree information determination step 1,
A table modification step for modifying the scene basic density gradation table, and a brightness table conversion step 5 for converting the density gradation table modified in the table modification step 4 into a gradation correction table for the brightness of the brightness input brightness output. Reference numeral 6 is a brightness gradation correction step for correcting the brightness information of the input image based on the gradation correction table converted in the brightness table conversion step 5 and outputting the corrected brightness information. 7 is the brightness information of the input image. Reference numeral 8 is the output brightness information corrected by the brightness correction step 6.

In this embodiment, these steps are realized by software by a microcomputer. The operation of the above gradation correction method will be described below with reference to FIGS.

FIG. 2, FIG. 3, and FIG. 5 show flowcharts of the processing performed by the microcomputer. First, in step 10, input is performed by determining which scene the input image belongs to. In the present embodiment, a person determines which scene of the portrait image, the backlight image, and the other images the input image belongs to and inputs it as scene information. Then, in step 11, the difference between the basic gradation of the scene selected in step 10 and the gradation of the input image is input as a degree. In the present embodiment, the degree information is input to the image serving as the reference of the scene, with 9 stages of 4 stages for each of the bright side and the dark side. Then, in step 12, based on the scene information input in step 10, a basic density gradation table that is optimal for all images of the scene is created. Then, in step 13,
Step 1 based on the degree input in step 11
In step 2, the basic density gradation table of the scene created by the basic density gradation table generating means and the gradation information when the correction is not performed are internally or externally divided to obtain optimum corrected density gradation information for the input image. Ask for. Then, in step 14, the correction density gradation information obtained in step 13 is converted into luminance information. Then, in step 15, based on the brightness gradation table converted in step 14, the brightness information 7 of the input image is converted into the brightness information 8 of the gradation-corrected output and output.

Next, the basic density gradation table generating step for the scene in step 12 will be described in detail with reference to FIGS. 3 and 4. In step 21, it is determined which scene the input image belongs to according to the scene information input in step 10. Then, if the scene is a portrait, in step 22, the density and straight line of the low density correction for generating the density gradation correction information suitable for the portrait are equal to the unchanged density and the straight line. The slope, the unchanged density and the slope of the straight line at which the input and the output on the intermediate density correction straight line are equal are determined, and in the system of density input density output, the correction straight line of the low density portion expressed by Expression 1 and Expression 2 Two straight lines, that is, the slope and the correction straight line of the intermediate density portion are determined.

[0029]

[Equation 1]

[0030]

[Equation 2]

Here, d _in is the input density, d _out is the output density, k ₁ is the slope of the straight line that determines the low density correction straight line, and d
_const1 is unchanged density inputs and outputs for determining the low density correction straight lines are equal, k ₂ is the slope of the straight line for determining the low density correction line, d _const2 the non inputs and outputs for determining the low density correction straight lines are equal The changed concentration.

If the scene is a backlight image, two straight lines of the density input density output system suitable for the backlight image are determined in step 23. If the scene is neither of these, the step At 24, two straight lines of the system of density input and density output suitable for hard copy in general are determined, and at step 25, as shown in FIG. 4, a straight line 31 of a low density portion and a straight line 32 of a high density portion on the density plane.
A table is created by combining the two straight lines.

Then, in step 26, a maximum density straight line 36 showing a maximum density limiter of the output system dynamic range, a minimum density straight line 34 showing a minimum density of the output system dynamic range, and a minimum density straight line 34 created in step 25. A table is created by combining these straight lines.

Then, in step 27, the portions of these straight line connecting portions 39 are connected to the curves 33, 35 and 3.
Connect smoothly so that there is no discontinuity like 7
Create a basic density gradation table.

In the present embodiment, in order to easily perform this smooth connection, a smoothing of the connection portion is performed by using a method called a moving average in which the average value of the values in the section of a predetermined width is used as the output value for the input. Making a good connection. This can be expressed by equation 3
become that way.

[0036]

(Equation 3)

Here, d _n is the density of the output, n is the density of the input, w is a half of the width of the moving average, and f (k) is the table created up to step 26. However,
For the range in which the values in the table do not exist, the moving average is performed assuming that the boundary values inside and outside the range are continuous.

Next, the method of correcting the scene density gradation in step 13 will be described in detail with reference to FIGS. 4, 5 and 6. In step 41, the degree information input in step 11 is converted into an internal division ratio or external division ratio between the scene density gradation information determined in step 12 and the uncorrected information. Subsequently, in step 42, the inside / outside of the scene density gradation table 51 and the non-correction table 52 determined in step 12 is performed to create a density gradation table 53 modified to be suitable for an input image. To do.

The non-correction table in this embodiment is a table in which the basic density gradation table 53 is created with respect to the table in which the straight line 38 having the same input density and the same output density, the maximum density line 36, and the minimum density line 34 are combined. It was created by performing a similar moving average.

Next, the specific effect of this embodiment will be described. As described in the related art, due to the difference in visual characteristics between the monitor and the hard copy, it is necessary to optimally set the gradation reproducibility by the density in the case of the hard copy. However, setting in density was very difficult and required knowledge about hard copy.

In this embodiment, a basic density gradation table of density input density output suitable for a scene is provided, and the modification of this table is performed based on the degree to create a gradation correction table suitable for an input image, Since the tones are corrected, it is possible to input the scene of the input image, the basic gradation characteristics for each scene, and the difference in brightness between the input image as a degree of a very simple method. It is possible to realize gradation reproducibility suitable for an input image without knowledge of hard copy.

Further, in the present embodiment, by performing internal division or external division of the basic gradation characteristic and the non-correction for each scene, an image having a difference between the basic characteristic of the scene and the input image is obtained. Also, it is possible to deal flexibly.

Further, in this embodiment, the basic density gradation information is combined with a plurality of straight lines having different inclinations, so that the gradation reproducibility can be finely optimized. Further, in the present embodiment, by connecting the connecting portions of the straight lines having a plurality of slopes smoothly, the system of luminance input and luminance output requires a very complicated calculation of continuously changing the value of gamma. The method can be done with very simple arithmetic,
It is possible to maintain the continuity of gradation.

Further, in the present embodiment, the basic density gradation information is divided into a low density correction straight line for determining low density reproducibility and an intermediate density correction straight line for determining intermediate density reproducibility. It is a very simple method of determining by specifying the slope and slope, and in the hard copy, it is particularly important to optimize the gradation reproducibility of halftones and to optimize the gradation reproducibility of the low density range where changes are easy to understand. Can be converted.

The tone correction apparatus of the second embodiment will be described below. FIG. 7 shows the configuration of the tone correction apparatus according to the second embodiment. Reference numeral 61 is a degree information determining means which is composed of a switch which can be changed in 9 steps and which inputs the degree information of the brightness of the input image. Reference numeral 62 is a scene information determination means which is composed of a switch which can be changed in three steps and which inputs scene information of an input image. 63A is a first basic density gradation table having basic density gradation information of density input density output when the scene is a portrait. 63B
Is a second basic density gradation table having basic density gradation information of density input density output when the scene is a backlight image. 63C is a third basic density gradation table having basic density gradation information of density input density output when the scene is an image other than a person and backlight, that is, another image. 64
The selecting means selects one of the gradation correction information suitable for the scene of the input image from the basic density gradation table 63A, 63B, 63C according to the scene information input by the scene information determining means 62. Reference numeral 65 is a table transformation unit that transforms the selected density gradation table selected by the selection unit 64 according to the degree information determined by the degree information determination unit 61. Reference numeral 66 is a brightness table conversion means for converting the density gradation table modified by the table modification means 65 into a brightness gradation table of brightness input brightness output.
Reference numeral 6 denotes a gradation correction unit that has a brightness gradation table converted by the brightness table conversion unit 66, corrects the brightness information 7 of the input image, and outputs the corrected brightness information 8.

The operation of the gradation correction device configured as described above will be described below with reference to FIGS. 7 and 8.
The scene information determining means 62 is composed of a switch, and a person selects one from three scenes of a person, a backlight, and another image, and outputs it as 2-bit data. The degree information determining means 61 is configured to compare the degree of brightness of the input image with that of the basic image of the selected scene, and to specify 9 steps of 4 steps for light and 4 steps for dark. By operating the switch, the degree of brightness is determined and output as 4-bit data. Then, 2b decided by the scene information decision means 62
Based on the information of it, in the selecting means 64 composed of a selector for selecting one from three 8-bit data buses, the table is calculated in advance for each scene in the same manner as in FIG. 3 of the first embodiment. One is selected from the basic density gradation tables 63A, 63B, and 63C for each converted scene. Then, in the table transforming means, based on the degree inputted by the degree information determining means 61, the internal division of the basic density gradation table of the scene selected by the selecting means 64 and the gradation information when the correction is not performed or Do the extra work,
The optimum correction density gradation information for the input image is output. Then, when the density is input, the output of the correction means 65 is given as an address to the brightness table conversion means 66 composed of a table which outputs the corresponding brightness, and the density table is converted into the brightness table. Then, the converted luminance table is stored as table information in the memory forming the gradation correcting unit 6, and after all the gradation information is stored in the memory, the address of the memory forming the brightness correcting unit 5 is input to the input luminance. 7, the data is switched to the output brightness 8. Then, in the brightness correction means 5, the brightness correction means 5
The gradation-corrected brightness information is obtained by giving the gradation-corrected brightness information as an address by applying the brightness information converted to digital 8-bit by AD conversion as an address to the memory constituting the.

Next, the correcting means 65 will be described in detail with reference to FIG. In FIG. 8, 71 is a table memory storing uncorrected information, and 72 is a selection means 64.
A subtracter 73 for taking the difference between the basic density gradation selected in step S1 and the uncorrected information, and a degree conversion means for converting the degree information input by the degree information determination means 61 into an internal division ratio or an external division ratio, 74 is a multiplier that multiplies the output of the difference means and the output of the degree conversion means, and 75 is an adder that adds the output of the multiplier and the output of the uncorrected information.

The operation of the correction means 65 having such a configuration will be described. First, in the subtractor 72,
The difference between the basic density gradation selected by the selection means 64 and the uncorrected information calculated in advance and tabulated is calculated. Then, in the degree converting means, the degree information inputted in the degree information determining means 61 is converted into the form of the internal division ratio or the external division ratio in the degree converting means 73, and in the multiplier 74, the internal division ratio or the external division ratio is obtained. The ratio is multiplied by the output of the difference means. Then, by adding the output of the multiplier and the output of the non-correction information, the internal or external division of the basic density gradation information and the non-correction information according to the degree is performed.

Next, the specific effects of this embodiment will be described. As described in the related art, due to the difference in visual characteristics between the monitor and the hard copy, it is necessary to optimally set the gradation reproducibility by the density in the case of the hard copy. However, setting in density was very difficult and required knowledge about hard copy. In this embodiment, a basic density gradation table of density input density output suitable for a scene is provided, and the modification of this table is performed based on the degree to create a gradation correction table suitable for an input image and correct the gradation. Since the input image scene and the difference in brightness between the input image scene and the basic gradation characteristics for each scene are input as a degree of several steps, hard copy is performed. It is possible to realize gradation reproducibility suitable for an input image without knowledge of the above.

Further, in the present embodiment, by performing the internal division or the external division of the basic gradation characteristic and the non-correction for each scene, an image having a difference between the basic characteristic of the scene and the input image is obtained. It is possible to flexibly deal with it.

Further, in the present embodiment, the basic density gradation information is combined with the straight lines having a plurality of inclinations, so that the gradation reproducibility can be finely optimized. Further, in the present embodiment, by connecting the connecting portions of the straight lines having a plurality of slopes smoothly, the system of luminance input and luminance output requires a very complicated calculation of continuously changing the value of gamma. The method can be done with very simple arithmetic,
It is possible to maintain the continuity of gradation.

Further, in this embodiment, the basic density gradation information is divided into a low density correction straight line for determining low density reproducibility and an intermediate density correction straight line for determining intermediate density reproducibility. It is a very simple method of determining by specifying the slope and inclination, and optimization of halftone gradation reproducibility, which is especially important in hard copy, and optimization of gradation reproducibility in the low density range where changes are easy to understand. It is possible to

Further, in this embodiment, since the basic density gradation information is calculated in advance and made into a table, it is not necessary to calculate the basic density gradation, so that the speed can be increased.

The tone correction apparatus of the third embodiment will be described below. FIG. 9 shows the configuration of the gradation correction apparatus in the third embodiment, and 61 is a degree information determining means for determining the degree information of the brightness of the input image. Reference numeral 62 is a scene information determining means for determining the scene information of the input image. 63
A is a first basic density gradation generation table having basic density gradation information of density input density output when the scene is a portrait. 63B is a second basic density gradation table having basic density gradation information of density input density output when the scene is a backlight image. 63C is a third basic density gradation table having basic density gradation information of density input density output when the scene is an image other than a person and backlight. Reference numeral 81 is a brightness table conversion means for converting the basic density gradation information of the basic density gradation tables 63A, 63B, 63C into basic brightness gradation information of the brightness input brightness output. 64 represents the scene information determined by the scene information determining means 62.
Selection means for selecting one of the basic luminance gradation correction tables of the luminance input luminance output suitable for the scene of the input image from the outputs of the respective luminance table conversion means. 65 indicates the degree information determined by the degree information determining means 61,
Table modification means for modifying the brightness gradation table information selected by the selection means 82. Reference numeral 67 denotes a gradation correction unit that has the brightness gradation table corrected by the correction unit 65, corrects the brightness information 7 of the input image, and outputs the corrected brightness information 8.

The operation of the gradation correction device configured as described above will be described below with reference to FIG. The degree information determining means 61 and the scene information determining means 62 are similar to the operation shown in the second embodiment, and output degree information and scene information, respectively. The basic density gradation tables 63A, 63B and 63C are also output in the same manner as in the second embodiment. Then, the basic density gradation tables 63A, 63B, 6
3C is converted into a basic luminance gradation table of luminance input luminance output by the luminance table conversion means 81. The brightness table conversion means 81 is similar to that of the second embodiment. In the present embodiment, the basic density gradation table and the brightness table conversion means are preliminarily calculated and configured as respective tables 82A, 82B and 82C. Then, the input brightness 7 is corrected by the selection means 64, the correction means 65, and the brightness correction means 6 having the same configuration and operation as those in the second embodiment, and the corrected output brightness 8 is output.

Next, the specific effects of this embodiment will be described. The effect of this embodiment is similar to that of the second embodiment, but in addition to this, the basic density gradation information converted into luminance is calculated in advance and tabulated. Of the basic density gradation generating means table memory and the density / luminance converting means table memory,
In this embodiment, one table memory can be used to simplify the circuit configuration and reduce the cost.

The tone correction apparatus of the fourth embodiment will be described below. FIG. 10 shows the structure of the gradation correction apparatus according to the fourth embodiment. Reference numeral 91 is a switch that can change eight steps for each scene, and inputs scene information for each scene of the input image. Scene information determination means. Reference numeral 92 is a degree information determining means which is composed of a switch that can be changed in 9 steps for each scene, and which inputs the degree information of the brightness of the input image for each scene. 63A is a first basic density gradation table having basic density gradation information of density input density output when the scene is a portrait. Reference numeral 63B is a second basic density gradation generating means having basic density gradation information of density input density output when the scene is a backlight image. Reference numeral 63C denotes a third basic density gradation generating means having basic density gradation information of density input density output when the scene is an image other than a person and backlight. Reference numeral 65 is a table transformation unit that transforms each basic density gradation table according to the degree information for each scene determined by the degree information determination unit 92. Reference numeral 93 is a table synthesizing means for synthesizing the density gradation table transformed for each scene based on each scene information inputted by the scene information determining means 91. Reference numeral 66 is a brightness table conversion means for converting the density gradation table combined by the table combining means 93 into brightness gradation information of brightness input brightness output. Reference numeral 6 has a brightness gradation table converted from the brightness table by the conversion means 66, and has the same configuration as that of the second embodiment, and corrects the brightness information 7 of the input image and outputs the corrected brightness information 8. It is a brightness correction means for

The operation of the gradation correction device configured as described above will be described below with reference to FIGS. 10 and 11. The scene information deciding means 91 is composed of a switch that can be changed in eight steps, judges how much the input image includes two scenes of a person and a backlight, and changes each of the eight steps of the switch. Input the ratio of the scene and output it as 3-bit information.
Then, the degree information determining means 92 compares the brightness of the basic image with the input image for each scene such as person, backlight, and the like, and sets the degree of brightness information of the input image to four levels for the bright side and four levels for the dark side. It is composed of switches that can be changed in 9 steps, and a person operates the switches to determine the degree, and outputs each as 4-bit data. In addition, the basic density gradation table 63
Similarly to the second embodiment, A, 63B, and 63C have the basic density gradation table for each scene. The basic density gradation information of the basic density gradation tables 63A, 63B and 63C is a table for performing the same operation as that of the second embodiment based on the degree information of each scene input by the degree information determining means 92. The transformation unit 65 transforms each scene. Then, the output of each table transforming unit is combined into one combined density gradation table in the table combining unit 93 based on the information for each scene input in the scene information determining unit. Then, after being converted into a table of brightness input brightness output by the brightness table conversion means 66 similar to the second embodiment, the selection means 64, the correction means 65, and the brightness correction which have the same configuration as the second embodiment. The input luminance 7 is corrected by the means 6.

Subsequently, the table synthesizing means 9 will be described with reference to FIG.
3 will be described in detail. Reference numeral 101 denotes an adder that adds the scene information of each of the person and the backlight input by the scene information determining unit 91. Reference numeral 102 is a subtracter that obtains other scene information by subtracting the output of the adder 101 from the sum of the maximum values of both scene information, that is, 16 in this embodiment. A multiplier 103 multiplies the scene information of the person input by the scene information determining means 91 and the corrected basic density gradation information of the person. A multiplier 104 multiplies the backlight scene information input by the scene information determining unit 91 and the corrected basic density gradation information of the backlight. Reference numeral 105 denotes a multiplier that multiplies the other scene information output from the subtractor 102 and the corrected basic density gradation information of the person. An adder 106 adds the multiplication results of the respective scene information and the corrected gradation information. Reference numeral 107 is a divider for matching the output range of the adder 106 with the correction gradation information.

The operation of the table synthesizing means 93 configured as described above will be described. The scene information of the person decided by the scene information deciding means 91 is multiplied as it is by the multiplication ratio with the value of the basic density gradation table of the person transformed by the table transforming means in the multiplier 103 to obtain the synthesized value. Is determined. In addition, the backlit scene information input in the scene information determination means 91 is
As it is, as a synthesis ratio, the multiplier 104 multiplies the value of the basic density gradation table of the backlight, which has been transformed by the table transforming unit, to determine the synthesis value. As for the composition ratio of the other images, the sum of the sum of the scene information of the person output from the adder 101 and the scene information of the backlight is the maximum value of both scene information, that is, in the present embodiment, 16 is subtracted from the subtracter 102.
Is determined by subtracting at. Then, the multiplier 105 multiplies the output of the subtractor 102 and the values of the other basic density gradation tables transformed by the table transforming means 65, and determines the combined value. continue,
All three combined values are added in the adder 106. Then, the output of the adder 106 is a value in a range of up to 16 times the corrected density gradation information. Therefore, in order to match the corrected density gradation range, the divider 1
At 07, division is performed by the sum of the maximum values of both scene information, that is, the value of 16 in this embodiment.

In the present embodiment, in the divider 107,
As a result of combining three scenes, the maximum is 16 times the correction gradation information, so division is performed by performing a 4-bit shift.

Next, the specific effects of this embodiment will be described. The effect of this embodiment is similar to that of the second embodiment, but in addition to this, in this embodiment, the respective scenes are combined to create a combined density gradation table of density input density output. Therefore, it is possible to flexibly correct even an image in which the input image cannot be properly classified into any scene.

The gradation correction apparatus of the fifth embodiment will be described below. FIG. 12 shows the structure of the gradation correction apparatus in the fifth embodiment. Reference numeral 91 is a switch that can be changed in eight steps for each scene, and determines scene information for each scene of the input image. Scene information determination means. Reference numeral 92 is a switch that can be changed in 9 steps for each scene, and a degree information determining means for determining the degree information of the brightness of the input image for each scene, and 63A is a case where the scene is a portrait. A first basic density gradation table having the basic density gradation table of
63B is a second basic density gradation table having a basic density gradation table when the scene is a backlight image. 63C
Is a third basic density gradation table having a basic density gradation table when the scene is an image other than a person and backlight. Reference numeral 81 is a brightness table conversion means for converting each basic density gradation information of the basic density gradation tables 63A, 63B and 63C into a brightness table of brightness input brightness output.
Reference numeral 65 is a table modification unit that modifies the basic density gradation table according to the level information determined by the level information determination unit 92. Reference numeral 93 is a table synthesizing unit for synthesizing the corrected density tables transformed for each scene based on the respective scene information determined by the scene information determining unit 91. Reference numeral 67 is a luminance that corrects the luminance information 7 of the input image and outputs the corrected luminance information 8 based on the luminance gradation table synthesized by the table synthesizing unit 93 and having the same configuration as in the second embodiment. It is a correction means.

The operation of the gradation correction device constructed as above will be described. Degree information determining means 92,
The scene information determining means 93 is similar to the operation shown in the fourth embodiment, and outputs the degree information and the scene information for each scene. Also, the basic density gradation generating means 6
Similar to the second embodiment, 3A, 63B, and 63C also have respective basic density gradation tables. And
The basic density gradation information of the basic density gradation tables 63A, 63B, 63C is converted by the brightness table conversion means 81 into the basic brightness gradation table of the brightness input brightness output. In the present embodiment, the basic density gradation table and the brightness table conversion means are calculated in advance and configured as one table 111A, 111B and 111C, respectively. Then, the table synthesizing means 93, the correcting means 65, and the brightness correcting means 6 having the same configuration and operation as those in the fourth embodiment.
Thus, the input brightness 7 is corrected, and the corrected output brightness 8 is output.

Next, the specific effect of this embodiment will be described. The effect of this embodiment is similar to that of the fourth embodiment, but in addition to this, the basic density gradation information converted into luminance is calculated in advance and tabulated. Since the table memory of the basic density gradation generating means and the table memory of the density / luminance converting means of the example can be configured by one table memory in this embodiment, the circuit configuration can be simplified and the cost can be reduced. .

[0066]

As described above, according to the present invention, the scene information determining means determines the scene information of the input image, and the degree information determining means determines the degree of brightness of the input image. In the generating means, basic density gradation correction information that is the basis of the scene is created as a basic density gradation table of density input density output in accordance with the scene information, and in the table transforming means, the input determined by the degree information determining means. According to the degree of brightness of the image, the basic density gradation table is modified so that the gradation correction characteristic is suitable for the input image, and the brightness table conversion means
The table transformed by the table transforming means is converted into a gradation correction table for luminance input luminance output, and the gradation correction means having the gradation correction table converted by the luminance table conversion means receives the luminance of the input image as an input. The corrected luminance can be output.

Therefore, it is possible to easily realize the gradation correction in consideration of the brightness characteristic and the density characteristic with a simple structure, and to perform the gradation correction with high accuracy so that the optimum gradation can be obtained according to the scene of the image. Can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a gradation correction method according to a first embodiment of the present invention.

FIG. 2 is a flowchart of signal processing of the same embodiment.

FIG. 3 is a flowchart of a basic density gradation table generating means of the embodiment.

FIG. 4 is an explanatory diagram of a basic density gradation table of the same embodiment.

FIG. 5 is a flowchart of a gradation correction unit of the same embodiment.

FIG. 6 is an explanatory diagram of a gradation correction table according to the same embodiment.

FIG. 7 is a configuration diagram of a gradation correction device according to a second embodiment of the present invention.

FIG. 8 is a configuration diagram of a gradation correction unit of the same embodiment.

FIG. 9 is a configuration diagram of a gradation correction device according to a third embodiment of the present invention.

FIG. 10 is a configuration diagram of a gradation correction device according to a fourth embodiment of the present invention.

FIG. 11 is a block diagram of a table synthesizing means of the same embodiment.

FIG. 12 is a configuration diagram of a gradation correction device according to a fifth embodiment of the present invention.

[Explanation of symbols]

 6 gradation correction means 61, 92 degree information determination means 62, 91 scene information determination means 65 table transformation means 66 luminance table conversion means

Claims (14)

[Claims] 1. A gradation correction method for controlling gradation characteristics of luminance according to scene information of an input image and a degree of brightness, wherein scene information of the input image is determined, and brightness of the input image is determined. The basic density gradation correction information that is the basis of the scene according to the scene information is created as a basic density gradation table of density input density output, and according to the brightness level of the input image, The basic density gradation table is modified so as to have a gradation correction characteristic suitable for the input image, and the modified table is converted into a gradation correction table for brightness input brightness output, and the gradation correction table is converted. On the basis of the above, the gradation correction method for correcting the gradation of the input image by inputting the brightness of the input image and outputting the corrected brightness. 2. A gradation correction device for controlling gradation characteristics of luminance according to scene information of an input image and a degree of brightness, scene information determining means for determining scene information of the input image, and the input image. Information determining means for determining the degree of brightness of the image, and basic density gradation correction information, which is the basic of the scene according to the scene information, is created as a basic density gradation table of density input density output. A table for transforming the basic density gradation table so as to have gradation correction characteristics suitable for the input image according to the brightness level of the input image determined by the table generation means and the degree information determination means. Deformation means, luminance table conversion means for converting the table transformed by the table transformation means into a gradation correction table for luminance input luminance output, and the luminance table conversion means. The gradation correction table converted by the conversion means, the gradation correction means for inputting the brightness of the input image and outputting the corrected brightness, and the output of the gradation correction means is corrected. A gradation correction device that outputs as a luminance signal. 3. A tone correction device for controlling tone gradation of luminance according to scene information of an input image and a degree of brightness, scene information determining means for determining scene information of the input image, and the input image. Information determining means for determining the degree of brightness of the image, a plurality of basic density gradation tables respectively having basic density input density output gradation information for each of a plurality of scenes of the image, and the plurality of basic density gradation tables Selection means for selecting one basic density gradation table having gradation correction information suitable for the scene of the input image according to the scene information, and the brightness of the input image determined by the degree information determination means. Table transformation means for transforming the basic density gradation table selected by the selection means so that gradation correction characteristics suitable for the input image are obtained according to the degree of The input image includes the brightness table conversion means for converting the table modified by the table modification means into a gradation correction table for brightness input brightness output, and the gradation correction table converted by the brightness table conversion means. And a gradation correction unit that outputs the corrected brightness, and outputs the output of the gradation correction unit as a corrected brightness signal. 4. A tone correction device for controlling tone gradation of brightness according to scene information of an input image and a degree of brightness, scene information determining means for determining scene information of the input image, and the input image. Information determining means for determining the degree of brightness of the image, a plurality of basic luminance gradation tables each having basic luminance input luminance output gradation information for each of a plurality of scenes of the image, and the plurality of basic luminance gradation tables Selection means for selecting one basic luminance gradation table having gradation correction information suitable for the scene of the input image according to the scene information, and the brightness of the input image determined by the degree information determination means. Table transformation means for transforming the basic luminance gradation table selected by the selection means so that gradation correction characteristics suitable for the input image are obtained according to the degree of The basic brightness gradation table has a gradation correction table modified by the table modification means, and a gradation correction means for inputting the brightness of the input image and outputting the corrected brightness. A gradation correction device in which a density correction curve determined based on a combination of straight lines having a plurality of slopes in a density output system is converted into a brightness input brightness output table in advance. 5. A gradation correction device for controlling gradation of luminance according to scene information of an input image and a degree of brightness, wherein the scene information of the input image is determined as reliability for each of a plurality of scenes. A plurality of scene information determining means; a degree information determining means for determining the degree of brightness of the input image for each of a plurality of scenes; and a plurality of basic density input density output gradation information for each of a plurality of scenes of the image. A plurality of table modification means for respectively modifying the basic density gradation table and each basic density gradation table for each scene according to the brightness degree information for each scene, and each modified by the table modifying means. A table synthesizing unit for synthesizing a table according to the reliability of each scene determined by the scene information determining unit, and a table synthesizing unit for the table synthesizing unit. Table is converted to a gradation correction table of brightness input brightness output, and the gradation correction table converted by the brightness table conversion means is provided, and the brightness of the input image is input and corrected. Gradation correction means for outputting the brightness, and a gradation correction device for outputting the output of the gradation correction means as a corrected brightness signal. 6. A gradation correction device for controlling gradation of luminance according to scene information of an input image and a degree of brightness, wherein the scene information of the input image is determined as reliability for each of a plurality of scenes. A plurality of scene information determining means; a degree information determining means for determining the degree of brightness of the input image for each of a plurality of scenes; and a plurality of basic luminance input luminance output gradation information for each of a plurality of scenes of the image. According to the basic brightness gradation table and the brightness degree information for each scene determined by the degree information determining means,
Table transformation means for transforming the basic luminance gradation table so that the tone correction characteristics are suitable for the input image, and each table transformed by the table transformation means are determined by the scene information determination means. Gradation correction means having a table synthesizing means for synthesizing according to the reliability of each scene, and a gradation correction table synthesized by the table synthesizing means, for inputting the brightness of the input image and outputting the corrected brightness In the system of density input and density output, the basic luminance gradation table has a density correction curve determined by combining a polygonal line formed by a plurality of straight lines and a curve that smoothly connects the bent portions of the polygonal line, A gradation correction device that is converted into a brightness input brightness output table. 7. The basic density gradation table and the uncorrected one are modified when the basic density gradation table is modified so as to have a gradation correction characteristic suitable for the input image according to the brightness of the input image. The gradation correction method according to claim 1, wherein an internal division or an external division with respect to the density value is performed. 8. The table transformation means performs internal division or external division of the basic density gradation table and the non-corrected density information according to the degree of brightness determined by the degree information determination means,
6. The gradation correction device according to claim 2, wherein the basic density gradation table is modified. 9. The table transforming means performs internal division or external division of the basic luminance gradation table and the uncorrected luminance information according to the degree of brightness determined by the degree information determining means,
7. The gradation correction device according to claim 4, wherein the basic luminance gradation table is modified. 10. The gradation correction method according to claim 1, wherein the gradation correction table is determined based on a combination of straight lines having a plurality of slopes in a density input density output system. 11. The gradation correction table is determined on the basis of a combination of straight lines having a plurality of slopes in a density input density output system.
The gradation correction device according to any one of 1. 12. The gradation correction device according to claim 4, wherein the connecting portion of a combination of straight lines having a plurality of inclinations is configured so that the connection of the straight lines is smooth. 13. A combination of straight lines having a plurality of inclinations is constituted by a low density correction straight line for determining reproducibility of a highlight portion and an intermediate density correction straight line for determining reproducibility of intermediate density, and the low density correction straight line is formed. In the concentration input concentration output system,
The intermediate density correction line is determined by the first unchanged density at which the input and the output are equal and the first slope, and the intermediate density correction line is set at the second unchanged density at which the input and the output are equal in the density input density output system. A second slope, and the first unchanged density is made smaller than the second unchanged density, and the intersection of the low density correction straight line and the intermediate density correction straight line is set to the dynamic range of the output system. 12. The gradation correction device according to claim 4, 6 or 11, wherein the density is higher than the minimum density and lower than the maximum density of the dynamic range of the output system. 14. A combination of straight lines having a plurality of inclinations, a low-density correction straight line for determining reproducibility of a highlight portion, an intermediate density correction straight line for determining reproducibility of intermediate density, and a maximum dynamic range of an output system. The maximum density straight line showing the density limiter and the minimum density straight line showing the minimum density limiter of the dynamic range of the output system are constituted, and the low density correction straight line has the same input and output in the density input density output system. Is determined by the first unchanged density and the first slope, and the intermediate density correction straight line is set to the second unchanged density and the second slope in which the input and the output are equal in the density input density output system. The first unchanged density is made smaller than the second unchanged density, and the intersection of the low density correction straight line and the intermediate density correction straight line is set to the minimum of the dynamic range of the output system. 12. The gradation correction device according to claim 4, wherein the density is higher than the density and lower than the maximum density of the dynamic range of the output system.