JPH05115000A - Color image processing method and device - Google Patents

Abstract

PURPOSE:To reproduce a color image while the continuity of a color is kept even except the color reproducing range of a color image forming device by reproducing faithfully the color image in most of the color reproducible range and constituting the color image so that a part can be the compressed space of the whole color space. CONSTITUTION:The data of the color component of color image data equivalent to most of the color reproducing range of a color image forming device surrounded by a closed curve 202 are not converted, the color image data to exceed the color reproducing range surrounded by a closed curve 201 and a closed curve 204 are compressed and converted into the space of the color reproducing range (in the closed curve 202) on a line 203 of the same hue in the color space and outputted to the color image forming device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing method and apparatus for converting a color space of color image data according to a color reproduction range of a color image reproducing apparatus.

[0002]

2. Description of the Related Art Conventionally, there is an apparatus for inputting color image data (multi-valued data) from a color scanner and performing color recording by a color printer based on the color image data. In this case, the color characteristics (read color characteristics) of the color scanner and the color reproduction characteristics (color reproduction range) of the printer may not match. Even in this case,
For example, an image conforming to the color space range that the printer can handle by itself without defining which range on the color space the value (0 to 255) that the multi-valued image data (8 bits) from the scanner can take It was interpreted as data and recorded based on the multivalued image data.

[0003]

Therefore, conventionally, when a hard copy or a soft copy of an original image is performed, the original original or the color of the original image data is not faithfully reproduced on the printer side and the original is not reproduced. There was a problem that it was reproduced in a color different from the image.

The present invention has been made in view of the above-mentioned conventional example. In the color reproduction range of a color image forming apparatus, most of the color reproducible range is faithfully reproduced and one part is a compressed space of the entire color space. It is an object of the present invention to provide a color image processing method and apparatus capable of reproducing a color image while maintaining color continuity outside the color reproduction range of the color image forming apparatus by configuring the color image so that And

[0005]

In order to achieve the above object, the color image processing method of the present invention has the following constitution. That is, a color image processing method for converting a color space range of color image data and outputting the color image data to a color image forming apparatus, in which the color component data of the color image data corresponding to most of the color reproduction range of the color image forming apparatus is obtained. The color image data exceeding the color reproduction range without being converted is compressed and converted into the space of the color reproduction range on the line of the same hue in the color space and output to the color image forming apparatus.

In order to achieve the above object, the color image processing apparatus of the present invention has the following configuration. That is, a color image processing apparatus for converting a color space range of color image data and outputting the color image data to a color image forming apparatus, wherein the color image data included in the color reproduction range of the color image forming apparatus among the color image data. Output means for directly outputting to the color image device, storage means for storing a phase difference between a point on the same hue line of the color image data exceeding the color reproduction range and a point on a straight line corresponding to the point. Conversion means for converting the points on the same hue line into points on the straight line based on the phase difference stored in the storage means, and compressing / converting into points of color image data in the reproduction color space; Means for converting the color components of the compressed / converted image data into the color component data on the same hue line based on the phase difference stored in the storage means.

[0007]

In the above structure, among the color image data,
The color image data included in the color reproduction range of the color image forming device is directly output to the color image device,
The phase difference between the point on the same hue line of the color image data that exceeds the color reproduction range and the point on the straight line corresponding to that point is stored. Points on the same hue line are converted into points on a straight line based on the phase difference stored in this way, and are compressed / converted into color image data in the reproduction color space. In this way, the color components of the compressed / converted image data are converted into the color component data on the same hue line based on the stored phase difference and output to the color image forming apparatus.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. <Description of Color Space Conversion Example (FIGS. 2 and 3)> FIG. 2 is a diagram showing a range of the color space.

In FIG. 2, a closed curve 201 including a point F
Indicates the outer edge of the entire color space, and the closed curve 2 including the point E
Reference numeral 02 indicates the outer edge of the color space within the range in which the printer can reproduce colors. In this embodiment, the closed curve 201 including the point F
The color reproducibility of the printer is improved by spatially compressing the color space (closed curve 201) into the color space of the closed curve 202 including the point E.

In this embodiment, FIG. 2A shows L, a,
Although a uniform perceptual color space such as b, Y, I, and Q is shown, another color space may be used. FIG. 2B shows how the color space of the cross section is compressed when the color space in FIG. 2A is cut by the cutting curve 203. In FIG. 2B, F indicates the outer edge of the entire color space, E indicates the outer edge of the range in which color reproduction by the printer is possible, and D
Indicates a reproduction range in which color misregistration by the printer does not occur, and C indicates the center of the color space.

The color information contained in the color space surrounded by the closed curve 204 passing through the point D in the entire color space indicated by the closed curve 201 (corresponding to F in FIG. 2B) is reproduced by the printer as it is. .. Then, when a color in the color space surrounded by the closed curve 204 and the closed curve 201 is reproduced by the printer, it is compressed in the color space surrounded by the closed curve 202 and reproduced by the printer. This is shown in FIG. 2B, in which the line segment DF on the cutting line is compressed into the line segment DE, and each point on the line segment DF is compressed onto the line segment DE at an equal rate. The point C shown in FIG. 2 indicates the center position of the uniform color space of this embodiment, and its color is white.

FIG. 3 is a diagram showing an example of color space conversion, in which each color component of a given color space is represented by 8 bits (25
The case of 5) is shown by S1. The range of possible values of each color component when this is spatially compressed under the same conditions as shown in FIG. 2B is indicated by S2. Further, S3 shows the case where the range capable of color reproduction in the printer is utilized to the maximum of 8 bits, and finally point D _i of the entire color space is changed to D _f in which color reproduction is possible in the printer, Point F
It suffices if _i is converted to E _f .

As shown in FIG. 2C, the cutting line 2
The color on the line cut by 03 indicates the color of the same hue.

However, in FIG. 2B, the cutting line 20
Since the line segment CDEF indicating 3 is actually a curve as shown in FIG. 2 (A), the phase of the position of each point on the cutting line 203 with respect to the horizontal line 205 drawn horizontally to the right from the point C. The angle (this is called hue) is slightly different. Therefore, the angle of the phase shift from the line segment CF is set to the point SS.
Let θ _{A be} the point SE and θ _B be the point SE.
If the color at the position S is compressed to the point SE without changing the phase, the phase angle at this point is (θ _B −θ _A ) in principle.
You can see that it only needs to be increased.

The distance between the straight line segments C and SS is r _SS , the distance between the straight line segments C and SE is r _SE, and the length of the curved line segments C and SS is R.
_{If SS} and the length of C and SE of the curved line are R _SE , then R _SS and R
_There is no practical problem even if the ratio of _SE is approximated to the ratio of r _SS and r _SE . Therefore, in the present embodiment, the coordinates in the color space are determined using the straight line distances r _SS , r _SE from the point C to the points SS and SE.

FIG. 11 is a diagram showing the data structure of the hue correction table (hue correction table 1).
Data corresponding to the above-mentioned phase angles θ _A , θ _B, etc. are written. That is, the angle θ from the horizontal line 205 in FIG.
defined by a linear distance r _n from _n and center point C cutting line 2
When the position angle (r _n , θ _n ) of the point P on 03 is the phase angle difference from the straight line CF to θ (r _n , θ _n ), the distance r _n to each point and the corresponding phase Data (angle) indicating the difference from the angle θ is written as a table. For example, θ (r _1, 0), the angle 0 ° of the horizon 205
And the position (r ₁ , 0) of the point P on the cutting line defined by the straight line distance r ₁ from the center point C and the angle corresponding to this point is 0
It shows the phase angle difference when moving to a point on the straight line.

Although not particularly shown, a table similar to that shown in FIG. 11 (referred to as a hue correction table 2) is provided, and this color correction table 2 has points SE 'on the straight line FC and points on the curved line portion. A value corresponding to the angle θ _B when SE is returned to the in-phase line is written, and the data is θ ′ (r
_n , θ _n ).

Therefore, the color space compression procedure is as shown in FIG.
From the hue correction table 1 shown in FIG. _A Search for and disconnect
Position of point SS 'on straight line CF from point SS on curve 203
Virtualize. Next, the same straight line from the point SS 'on the straight line CF
The upper point SE 'is derived by distance compression. Next, point SE '
In order to obtain the point SE of the curve 203, the hue correction table
Bull 2 θ_B To find the phase angle of the point SE.
As a result, a point obtained by spatially compressing the point SS on the curve segment 203
SE can be requested.

Further, in order to reduce the data capacity of the hue correction tables 1 and 2, it is easy to hold the data in a rough step size and create the interpolated data during processing (search). I can guess. Further, instead of storing the difference between the phase angles as data, a function for obtaining the difference between the phase angles may be prepared. For example, a function indicating the relationship between the distance r and each phase θ as shown in FIG. 12A may be provided for each phase angle.
As shown in (B), one function indicating the relationship between the distance r and the phase angle θ may be provided for all the phase angles, and these values may be calculated. FIG. 12 (B)
Indicates the correction angle (θ) on the vertical axis and r / Fθ on the horizontal axis. Here, since Fθ represents the outermost edge of the color space, the maximum value is always “1” without depending on the phase angle.

In this embodiment, an example using the color correction tables 1 and 2 described above will be described. <Description of Image Conversion Circuit (FIG. 1)> FIG. 1 is a block diagram showing the configuration of the image conversion circuit of this embodiment for realizing the color space compression described above.

Reference numeral 101 denotes a color conversion unit, which sequentially inputs R,
The G and B image data are converted into Y, I and Q color spaces. Here, it is also possible to convert the image data of R, G, and B into the Lab space and treat Y and L, I and a, and Q and b in the same way, but the description thereof is omitted here. Color conversion unit 10
The image data converted into the Y, I, and Q color spaces in 1 is input to the angle calculation unit 102. The angle calculation unit 102 obtains an angle θ indicating how many times the pixel data P of the image data in the I and Q orthogonal coordinate system is rotated from the Q axis as shown in FIG. This is tan ⁻¹ i / q (q ≠ 0), or sin ⁻¹ i / (i ² + q ² ) ^1/2 cos, where the pixel data P (I, Q) coordinates are (i, q). ^The angle θ can be obtained by using any one of ⁻¹ q / (i ² + q ² ) ^1/2 [(i ² + q ² ) ^1/2 ≠ 0].

The output of the color conversion unit 101 is the r calculation unit 1
03 is also input, and in this r calculation unit 103, r
= (I ² + q ² ) ^1/2 is calculated, and the distance from the center position C of the color space is calculated. Thereby, the coordinates (r, θ) of the image data P in the polar coordinate system are obtained.
In the Cartesian coordinate system, (i, q) = (rsin θ, rcos
can also be expressed as θ).

The output θ of the angle calculator 102 is input to the color correction table 1 (121), and the difference in the phase angle from the point on the cutting curve to the straight line CF is obtained. This difference and the angle θ obtained by the angle calculation unit 102 are added by the adder 122, and the position of the point on the cutting line 203 is converted into the position on the straight line CF. This converted phase difference angle is the D table 1
04, integrated coefficient a table 105 and daily integrated coefficient b table 106. The output of the adder 122 is input to the hue correction table 2 (123).
With this correction table 2 (123), the angle for converting the coordinates of the point on the straight line into the point on the cutting curve is obtained,
The adder 124 returns the point on the straight line to the position of the point on the curve. Further, since r3, which is the output of the selector 112 described later, is input to the correction table 2 (123), it is possible to convert the distance-compressed points on a straight line into a curved line.

The values F _i , E in the entire color space in FIG.
_i and D _i are different depending on the angle θ, and the color reproduction ranges E _f and D _{f of the} printer are also different depending on the angle θ. FIG. 5 shows the actual colors in the entire color space range for each angle θ.
, D _i , E _i , and F _i . Where D with respect to the angle θ
_i , E _i , and F _i are respectively denoted by D _i (θ), E _i (θ), F
It is represented by _i (θ).

In FIG. 5, if the maximum value of F (0) to F (359) is 8 bits, it becomes "255". Here, the minimum unit of the angle θ is set to 1 °, but is not limited to this, and it may be smaller or larger than this. Further, the difference between the angles θ need not be uniform.

In this embodiment, the quantized data within the color reproduction range by the printer is obtained corresponding to each angle.
D _f and E _f for each angle θ are obtained by measuring the color reproduction characteristics of the printer. Thus, the b table 106 is written with D _f / D _i with respect to the angle θ, and the a table 105 has (E _f −D _f ) / (F _i −) for each angle θ.
The value of D _i ) is written.

The output r of the r calculator 103 is input to the comparator 108, and r2 = r- in the subtractor 107.
D _i (θ) is calculated. Here, D _i (θ) is data output from the D table 104 and indicates D _i with respect to the angle θ. This calculation result r2 (= r-D _i (θ)
) Is input to the multiplier 109, and the product coefficient a table 10
It is multiplied with the output of 5. Then, the output of the multiplier 109 is added to the output of the multiplier 117 by the adder 111.

The multiplier 117 outputs the data from the D table 104.
Force D_i(θ) and D from the product coefficient b table 106_f(θ) /
D_i(θ) is input, and as a result, D_f(θ) is output
Be done. Thus, the output of the adder 111 is the pixel data P
It becomes P (r ', θ) after the color space compression of (r, θ). However
And r of the pixel data P (r, θ) is F_i(θ) ≧ r ≧ D _i 
Is the case.

On the other hand, the output of the product coefficient b table 106 is given to the multiplier 110, where the image data P (r,
θ) is multiplied by r. As a result, r ″ of the image data P (r ″, θ) after color space compression when D _i (θ) ≧ r is obtained. These r ′ and r ″ are input to the selector 112, one of them is selected and output as r3.

The output r of the r calculator 103 is input to the comparator 108, where it is compared whether D _i (θ) ≧ r or not, and the comparison result is given as a selection signal of the selector 112. Thus, when D _i (θ) ≧ r, r3 = r ″ is selected, and otherwise, r3 = r ′ is selected.

The color space-compressed data r3 thus obtained, the hue correction table 2 (123), and the adder 1
Since the final phase after spatial compression is determined by the phase obtained in 24 and 24, the synthesizing unit 113 forms one data as P (r3, θ). The color calculation unit 114 uses P (r3,
θ), I = r3 · sin θ, Q = r3 · cos θ are obtained, and further Y data from the color conversion unit 101 is received. The Y, I, and Q data arranged in this way is used by the inverse color conversion unit 1
15, the signals Y, I, Q are converted into R, G, B signals.

The conversion between R, G, B, Y, I and Q in the color conversion unit 101 and the inverse color conversion unit 115 is a linear linear conversion.

[0033]

[Equation 1] It can be expressed by the above matrix calculation. Then, this operation can be realized by a product-sum operation using a multiplier and an adder.
Further, a method of substituting the sum of products of the ROM for the ROM is generally known.

As shown by the broken line in FIG. 1, the luminance signal Y
As a result, the I and Q space widths change, so as shown by the broken line in FIG.
05, it is more desirable to change the output value by switching a plurality of tables of the product coefficient b table 106. <Other Embodiments (FIG. 6)> FIG. 6 shows color space compression in another embodiment of the present invention. The closed curve 202 (FIG. 2) including the limit point E of the color reproduction range of the printer is reproduced as it is. However, other color spaces are converted to the closed curve 202 including the limit point E.

FIG. 10 corresponds to FIG. 3 of the first embodiment described above.
What you do, E_iIs represented by the distance from the center point C of the color space.
And this is 8 bits. And this distance is pudding
Center point C to E in the reproduction range_f Should be converted to
It will be good. Thus, E _i ~ E_f The points on the line segment are all
E_f Becomes

FIG. 8 is a block diagram showing the image processing circuit of the second embodiment for realizing this color space compression. The parts common to those of the first embodiment described above are designated by the same reference numerals, and their description will be omitted. ..

In the second embodiment, the E table 402 is used instead of the D table 104. This E table 4
A table 02 stores the data shown in FIG. Then, in the comparator 108, r of P (r, θ) is E
_{If i} (θ) <r, the E table 4 is selected by the selector 112.
The output r5 = E _i (θ) of 02 is selected, and the combining unit 113
Entered in.

As for the output θ of the angle calculation unit 102, the angle of Fθ is obtained by the hue correction table 1 (121) and the adder 122, and this is given to the product coefficient C table 602 and multiplied by Y and θ. The coefficient is output. This product coefficient is output as a value of E _f (θ) / E _i (θ) with respect to θ, and these are stored as a table for each angle θ. Further, another table may be provided according to the luminance signal Y.

Therefore, in the multiplier 110, the pixel data P
Data after color space compression is obtained by performing an operation of r6 = r × E _f (θ) / E _i (θ) on (r, θ). Therefore, when E _i (θ) ≧ r, the result of the comparator 108 controls the selector 112 to change the output r6 of the multiplier 110 to r
Output as 3 = r6.

FIG. 7 shows color space compression in the third embodiment of the present invention, in which compression is performed uniformly within a closed curve including the outermost edge F of the entire color space.

FIG. 9 is a block diagram showing the arrangement of an image processing circuit for realizing this color space compression.

The output from the r calculator 103 is the multiplier 12
It is multiplied by 1 and given to the synthesizing unit 113 as data after color space compression. Therefore, the output of the multiplier 121 is a conversion ratio when converting to 8-bit (0-255) which is the color reproduction space by the printer when the entire color space is 8-bit (0-255). This conversion ratio is supplied from the product coefficient d table 603. With respect to the contents of the product coefficient d table 603, _if E _f (θ) and F _i (θ) shown in FIG. 10 are used,
E _f (θ) / F _i (θ). Also, this product coefficient d
The table 603 may be provided for each luminance signal Y, and one table content is read and determined by Y information and θ information. The maximum value of E _f (θ) and F _i (θ) is “255”, and the value is “255” or less according to the angle information θ and the luminance information Y.

By the way, in the embodiments of the present invention and other embodiments, the parts for color space compression are all provided with multipliers for uniform compression in proportion to the distance from the center position of the color space. The present invention is not limited to this, and for example, the color difference in color space compression may differ depending on the distance r from the center position. Further, the degree of compression may be changed depending on the angle θ. Further, regarding the luminance component Y as well, since the total color space differs depending on Y, the compression degree may be different.

In the figure, the point D is centered on the point C.
In the closed curve including, the ratio between the line segment CE and the line segment CD may be constant, or the line segment CD may be always constant and the closed curve including D may be a perfect circle centered on the point C. You may set it.

As described above, according to the present embodiment, most of the color reproduction range of a printer or the like is faithfully reproduced, and a part of the color reproduction range is compressed into a compression space, so that the printer can be faithfully reproduced. Color reproduction is almost satisfied, and colors outside the color reproduction range can be recorded and reproduced while maintaining continuity.

According to the present embodiment, the color reproduction range of the printer is faithfully reproduced, and the other colors are approximated to the outer edge of the reproduction color range of the printer, or the entire color space is reproduced by the printer. It can be compressed into a range. Moreover, since the color space compression can be performed on the same hue line, the hue space compression does not cause a slight shift in hue.

In the present embodiment, r indicates the saturation direction, and θ indicates the hue. Therefore, in this embodiment, r
And the θ component is not converted, and only the saturation can be converted without changing the hue by the color space compression.

[0048]

As described above, according to the present invention, in the color reproduction range of the color image forming apparatus, most of the color reproducible range is faithfully reproduced and one part is the compression space of the entire color space. By configuring the color image as described above, there is an effect that the color image can be reproduced while maintaining the color continuity even outside the color reproduction range of the color image forming apparatus.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image processing circuit according to a first embodiment of the present invention.

[Fig. 2]

FIG. 4 is a diagram showing a range of a color space.

[Figure 3]

[Figure 6]

[Figure 7]

FIG. 10 is a diagram showing an example of color space conversion.

FIG. 5 is a diagram for explaining data contents of various tables corresponding to respective angles.

FIG. 8 is a block diagram showing a configuration of an image processing circuit according to a second embodiment.

FIG. 9 is a block diagram showing a configuration of an image processing circuit according to a third embodiment.

FIG. 11 is a diagram showing a configuration example of a hue correction table.

FIG. 12 is a diagram showing a function of hue correction data.

[Explanation of symbols]

 101 color conversion unit 102 angle calculation unit 103 r calculation unit 104 D table 105 product coefficient a table 106 product coefficient b table 107 subtraction unit 108 comparator 109, 110 multipliers 111, 122, 123 adder 112 selector 113 combination unit 114 colors Calculation unit 115 Reverse color conversion unit 117 Multiplier 121 Color correction table 1 123 Color correction table 2

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[Procedure amendment]

[Submission date] September 25, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image processing circuit according to a first embodiment of the present invention.

FIG. 2A is a diagram showing a range of a color space.

FIG. 2B is a diagram showing an example of color space conversion.

FIG. 2C is a diagram showing a range of a color space.

FIG. 3 is a diagram showing an example of color space conversion.

FIG. 4 is a diagram showing a range of a color space.

FIG. 5 is a diagram for explaining data contents of various tables corresponding to respective angles.

FIG. 6 is a diagram showing an example of color space conversion.

FIG. 7 is a diagram showing an example of color space conversion.

FIG. 8 is a block diagram showing a configuration of an image processing circuit according to a second embodiment.

FIG. 9 is a block diagram showing a configuration of an image processing circuit according to a third embodiment.

FIG. 10 is a diagram showing an example of color space conversion.

FIG. 11 is a diagram showing a configuration example of a hue correction table.

FIG. 12 is a diagram showing a function of hue correction data.

[Description of Reference Signs] 101 color conversion unit 102 angle calculation unit 103 r calculation unit 104 D table 105 product coefficient a table 106 product coefficient b table 107 subtraction unit 108 comparators 109, 110 multipliers 111, 122, 123 adder 112 selector 113 Compositing Unit 114 Color Calculation Unit 115 Inverse Color Conversion Unit 117 Multiplier 121 Color Correction Table 1 123 Color Correction Table 2

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location G06F 15/68 310 8420-5L H04N 1/46 9068-5C 9/79 H 9185-5C

Claims (2)

[Claims] 1. A color image processing method for converting a color space range of color image data and outputting the color image data to a color image forming apparatus, wherein the color of the color image data corresponds to most of the color reproduction range of the color image forming apparatus. Color image data that does not convert the component data and exceeds the color reproduction range is compressed and converted into the space of the color reproduction range on the line of the same hue in the color space and output to the color image forming apparatus. And a color image processing method. 2. A color image processing apparatus for converting a color space range of color image data and outputting to a color image forming apparatus, wherein the color image data is included in a color reproduction range of the color image forming apparatus. Outputting means for outputting the color image data to the color image device as it is, storage for storing a phase difference between a point on the same hue line of the color image data exceeding the color reproduction range and a point on a straight line corresponding to the point. Means for converting the points on the same hue line into points on the straight line based on the phase difference stored in the storage means, and compressing / converting to color image data in the reproduction color space; Means for converting the color components of the image data compressed / converted by the converting means into the color component data on the same hue line based on the phase difference stored in the storage means. The color image processing apparatus for.