JPH06225130A - Picture processor and method therefor - Google Patents

Abstract

PURPOSE:To prevent picture quality deterioration due to color space compression in a visual sense by not converting a hue and a lightness but converting only the saturation in the picture data conversion between picture processing devices with a different color reproduction range. CONSTITUTION:A color space is expressed by the L, a, b coordinate system and a closed curve including a point F is an outer ridge of a full color space reproduced and displayed by a CRT. Up to a distance DM of M% of a DI of a color reproduction area, it is reproduced as it is, and the data over it are compressed linearly. Let a distance from chromaticity points (a), (b) of colors on the CRT to an origin be DS, a distance from the origin to the outer ridge of the color reproduction area be DI, a distance up to the coordinates (a), (b) before color space compression be DD, and the color coordinate after color space compression be DN. Furthermore, the distances DN, DI, DD, DS, DM are set on the same line. Then the color space compression by a prescribed equation is executed. Thus, the hue is preserved by making the color space compression L constant on a line extended from the origin to compress the saturation thereby preventing picture quality deterioration in a visual sense.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an image processing method and apparatus,
In particular, the present invention relates to an image processing method and apparatus capable of converting image data between image processing devices having different color reproduction areas.

[0002]

2. Description of the Related Art Conventionally, when an image interface is performed between devices having different image color reproduction areas, such as when outputting color image data such as a CRT to a color hard copy device, color space conversion or hardware is performed. Masking processing and the like for correcting unnecessary absorption of ink in the copying apparatus have been performed. However, in each device, the dynamic range of the number of bits of the image data of the device (2 bits for 8 bits) with respect to the color space reproduction area that the device can handle.
55) is set so that it can be fully used.

[0003]

Therefore, in the past, if each device had a completely different color reproduction area, it was impossible to interface the image, or the bit number (for example, 8 bits) of the image of the device itself was forced. , I had to replace it and output it. Even if the replacement is performed by force, for example, if the masking result does not fit within 8 bits due to the difference in the color reproduction area, the data is cut and “25 or more is 25
Only the matching such as "5", "0 or less to 0" is performed, and it is impossible to know or control how the data is converted in the color space.

The present invention has been made in view of the above problems, and an object thereof is to provide an image processing method and apparatus capable of performing a good conversion suitable for an image reproduction range.

[0005]

In order to achieve the above-mentioned object, the first invention of the present application is a method of converting image data between image processing devices having different color reproduction ranges.
The lightness is characterized in that the conversion related to the saturation is performed without substantially performing the conversion.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of implementing the image processing method according to the present invention will be described. Since the color reproduction range of ink used for color hard copy is narrower than the color data captured by the scanner or the color data expression area created by computer graphics (shown in FIG. 12), data outside the color reproduction range of the printer is used. Must be compressed (mapped) to a reproducible color. Here in FIG. 12 is a uniform color space CIE1976L ^* a ^* b ^* space L ^* = 50a
^* b ^* Chromaticity diagram It is a diagram showing the color reproduction range (solid line) of the CRT and the color reproduction range (dotted line) of the printer.

In order to perform mapping, it is necessary to obtain the color reproduction range of an output device such as a printer and the color reproduction range of color data such as CRT. First, a method of obtaining the color reproduction range of the printer will be described. Printer is Cyan, Magen
ta, Yellow, Black (hereinafter C, M, Y, B
All colors are expressed using four color inks (denoted as k), but here, a case where gradation expression is performed by the density pattern method will be described as an example. The density pattern method is a method of expressing gradation by configuring one pixel by a pixel matrix composed of a plurality of elements.
The data of M and Y are compared, and the element of the pixel matrix exceeding the threshold value is set to 1 (that is, ink is placed). The pixel matrix is (1) an element that is a subtractive color mixture (Bk ') of all C, M, and Y. (2) a subtractive color mixture (R, G, B) that is a combination of two colors of C, M, and Y. It is a combination of four types of elements: element (3) element having one color of C, M, and Y (4) element having no ink (White). By replacing Bk ′ in (1) with Bk of black ink, the undercolor is gradually removed,
Assuming that the threshold matrix is the same for C, M and Y, the elements of (1) to (4) above are: Bk = min (C, M, Y) Mix = min (C1, C2) P = max (C, M, Y) -Bk-Mix W = S-Bk-Mix-P.

Here, Mix: the number of R, G, B elements C1, C2: C-Bk, M-Bk, Y-Bk that is not 0 P: Number of C, M, Y elements S: Matrix The total number of elements.

All the colors of each pixel are the above-mentioned 4 elements, 8 in total.
Additive color mixture. The XYZ values that are the colorimetric values of these eight colors are Sw, Sc, Sm, Sy, and
If Sr, Sg, Sb, and Sbk are used, it can be calculated by the following equation (1).

[0010]

[Outside 2]

Here, Xcl, Ycl, Zcl (cl =
w, c, m, y, r, g, b, bk) are coordinate values in the XYZ space of each ink color.

In this way, the XYZ colorimetric values of the colors that can be expressed by any combination of C, M, Y, and Bk inks can be obtained. From this result, the uniform color space CIE1976L can be obtained by the equation (2). It can be converted to the ^* a ^* b ^* space, and the color reproduction range of the printer can be calculated.

[0013]

[Outside 3]

Here, X ₀ , Y ₀ , and Z ₀ are the standard light source X,
Y and Z.

Next, a method of calculating the color reproduction range of the CRT will be described. CRT reproduces color by additive color mixture of three colors of R, G and B. If R, G and B at this time are data proportional to the voltage applied to the cathode of the CRT, the XYZ color specification of the pixel. The value can be calculated by the equation (3).

[0016]

[Outside 4]

Here, gma = 2.2 (gamma value of CRT) and XiYiZi (i = r, g, b) are R, G, B.
Are coordinate values in the XYZ space.

As in the case of the printer, the equation (2) is also used to convert into the CIE1976L ^* a ^* b ^* space.
The color reproduction range of the CRT can be calculated.

Since the color reproduction ranges of the printer and CRT can be obtained by the above method, the mapping method will be described below.

FIG. 13 shows DS, DI, DD,
It is the figure which showed DN and S straight line. First, these four types of parameters used for mapping will be described.

[0021] DS: The distance (color difference) between the coordinate point with the highest saturation on the S line and the center DI: The distance between the coordinate point with the highest saturation and the center within the area that can be represented by ink on the S line Distance (color difference) DD: Distance (color difference) between the coordinate point and the center obtained by calculation from input signal RGB data DN: Distance (color difference) between the compressed (mapping) coordinate point and the center

By using these four types of parameters,
Color compression (mapping) according to the present invention can be realized. The five mapping methods will be described below.

1) Colors that can be reproduced by a printer are output as they are, and colors that cannot be reproduced are L ^* a ^{* as} shown in equation (4) ^.
Mapping to a reproducible color that minimizes the color difference in b ^* space. This method is a conventionally used method.

DE = (dL ^{* 2} + da ^{* 2} + db ^{* 2} ) ^1/2 (4)

2) A color that can be reproduced by the printer is output as it is, and a color that cannot be reproduced is compressed as shown in the equation (5) while the brightness and hue of the color data remain unchanged, and only the saturation is compressed.
Map to the outer edge of the reproducible range.

DN = DD (when DD ≦ DI) DN = DI (when DD> DI) (5)

3) Regardless of the color reproducible by the printer and the color not reproducible by the printer, only the saturation of the color data is linearly mapped within the reproducible range as shown in the equation (6).

DN = DD × DI / DS (6) 4) Regardless of colors reproducible and non-reproducible by the printer, as shown in the equation (7), only the saturation of the color data is exponentially expressed. Compress nonlinearly. This method is a mapping method that lowers the compression rate for color data located closer to the center and increases the compression rate for color data located farther from the center.

DN = DD {1- (1-DI / DS) ^{DS / DD} } (7)

5) Output up to a specific ratio of the color reproducible range of the printer, for example, up to a distance of 80% from the center, and output color data (including unreproducible colors) at a distance longer than that (( As shown in the formula 8), only the saturation of the color data is 80% to 100% from the center within the linearly reproducible range.
Map to the distance.

DN = DD (when DD ≦ D8) DN = {(DD-D8) × (DI-D8) / (DS-D8)} + D8 (when DD> D8) (8) where D8 = It is 0.8 × DI.

FIG. 14 shows a graph of four types 2) to 5) out of the five types of mapping methods described above. Here, the horizontal axis plots DD normalized by DS, and the vertical axis plots DN normalized by DI.

By the mapping method described above, even color data outside the color reproduction range of the printer can be compressed within the color reproduction range.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of an embodiment of the apparatus of the present invention which specifically realizes color space compression according to the above principle will be described below.

FIG. 2 shows the case where the color space is represented by the L ^* a ^* b ^* coordinate system. The closed curve including the point F indicates the outer edge of the entire color space that can be reproduced and displayed by the CRT. The closed curve including the point E indicates the outer edge of the color space within the range in which the hard copy device can reproduce colors. Also, in this figure, L ^* is constant (L =
const. ), And a similar CRT for each value of L ^* ,
There is a diagram showing the color reproduction area of a hard copy device. However, whether to set the value of L ^* in steps of 0.1 or 10 is not particularly limited here. In this embodiment, FIG. 2 shows the L ^* a ^* b ^* color space, but Y, I, Q
Alternatively, a uniform perceptual color space such as L ^* u ^* v ^* does not cause any problem, and the present invention is not limited to the L ^* a ^* b ^* color space.

In this embodiment, within a closed curve including F, that is, C
A detailed description will be given of a portion of the RT color reproduction area within the closed curve including the point E, that is, a portion for color space compression into the color reproduction area of the hard copy device.

In the following, color reproduction is performed as it is up to the distance of M% of DI in FIG. 2 in the color reproduction area of the hard copy device,
(Example M = 80) Above that, linear compression is performed. Also M%
An example is shown in which the distance is DM.

As shown in FIG. 2, DS is the distance from the a ^* b ^* chromaticity point of the color on the CRT to the origin, and DI is the distance from the origin to the outer edge of the color reproduction area of the hard copy device. Let DD be the distance to the previous a ^* b ^* coordinate position, and DN be the color coordinate after color space compression. Also, DN, DI, D
D, DS and DM exist on the same line. Therefore, a ^* b ^*
If the a ^* axis is at an angle of 0 ° from the origin of the coordinates, 0 ° to 3
DNθ, D for all consecutive angles θ up to 60 °
There are combinations of Iθ, DDθ, DSθ, and DMθ, but in practice, θ is discretized into steps of 0.1 ° or 1 ° and processed. Under such a premise, as the first embodiment, the color space compression is performed by the following theoretical formula.

DN = DD (DD <= DM) DN = (DD-DM) × (DI-DM) / (DS-DM) + DM (DD> DM)

[0040]

[Outside 5]

Such color space compression is performed under the condition of L = constant and on a straight line extending from the origin, so that the saturation is compressed while preserving the hue. The surface cut by such a cutting line is shown in FIG.

As shown in FIG. 3, each point on the line segment DF on the cutting line is linearly compressed on DE, and each point on CD is stored as it is without being compressed.

FIG. 4 shows 8 color components of the color reproduction range of the CRT.
The range of bit (0 to 255) is shown in S1, and the range of possible values of each color component when this is color-compressed under the above conditions is shown in S2. S3 shows a state in which the color reproduction range in the printer is normalized to 8 bits, and finally Di is converted into Df and Fi is converted into Ef.

FIG. 1 shows a hardware embodiment for realizing the color space compression described above.

Reference numeral 1 is a color conversion unit for R, G, B in the CRT.
Thus, the colors are once converted into the X, Y, Z color system.

[0046]

[Outside 6] gma: CRT gamma value R, G, B CRT applied voltage value (0 to 1)

Next, after conversion into L ^* , a ^* , and b ^* , 0 to
It is normalized to 255 (8 bits). This is the coordinate value of the point DD. It is also possible to use other uniform color spaces such as L, u, and v here. The data converted into L, a, and b is input to the angle calculation unit 2, and the angle θ indicating how many times the color data is rotated from the a-axis is obtained on the a ^* and b ^* coordinates. If the a ^* b ^* coordinate values are A and B,

[0048]

[Outside 7] It is possible to obtain θ from the above.

In the Lab input to the r calculation unit 3,

[0050]

[Outside 8] Is calculated to obtain the distance r from the origin to DD, and the coordinates (A, B) in the rectangular coordinate system are set in polar coordinates (rs
in θ, r cos θ).

The output θ of the angle calculator 2 is input to the D table 4, the integration coefficient a table 5, and the integration coefficient b table 6.

The value Fi in the reproduction color space of the CRT shown in FIG.
Ei and Di differ depending on the angle θ (hue). It should be noted that D, E, and F are the values of the reproduction range that does not cause color shift, the outer edge of the color reproduction range of the hard copy device, and the outer edge of the CRT color reproduction area. Further, the color reproduction ranges Ef and Df of the color hard copy device also differ from each other in the angle θ. CRT for each angle, D determined from the color reproduction range of the color hard copy device,
The distance r between the points E and F and the origin is shown in D of FIG.
i, Ei, and Fi. Further, this table is prepared differently for each value of L ^* . Among all L, the maximum of F _{0 to} F ₃₅₉ is 8 bit 255. The step width of the angle θ is not limited to 1 °, and may be fine or rough, or may not be a uniform step width.

In this embodiment, the quantized data to be given to the color hard copy device is obtained for each angle.
Df and Ef in FIG. 3 are determined after obtaining the color reproduction characteristics of the color hard copy apparatus as described in principle, and b
Df / Di for each angle θ is written in the table. Also, in the table a, (Ef-D
The value of f) / (Fi / Di) is written.

The output r of the r calculator 3 is input to the comparator 8 and the subtractor 7 subtracts r2 = r-Dθiα. This corresponds to DD-DM in principle

[0055]

[Outside 9]

Dθi is data output from the D table 4. This r2 is multiplied by the multiplier 9 with the output of the product coefficient a table. Further, from FIG. 3, (Eθ of the product coefficient a table
f-Dθf) / (Fθi-Dθi) is the principle (DI-D
M) / (DS-DM) times α (α (DI-D
M) = Eθf−Dθf). The output of the multiplier 9 is the adder 11
Is added to the output of the calculator 17. In the multiplier 17, the output Dθi of the D table 4 and the Dθf / of the product coefficient b table 6 are calculated.
Since Dθi = α is input and Eθf (α times DM of the principle) is obtained as a result, the output of the adder 11 is the color coordinate DD.
It is DN (r ', θ) after the color space compression of (r, θ).
However, the output of the adder 11 is r ′ = α {(DD-DM) × (DI-DM) / (DS-DM) + DM}. However, this is the case where r is (DD is) r> Di (corresponding to DD> DM). On the other hand, the output of the product coefficient b table 6 is given to the calculator 10 where it is multiplied by r (DD), and as a result, the image after color space compression in the case of Dθi ≧ r (DM ≧ DD) The data r is determined. This is αDD
Equivalent to.

These r'and r "are input to the selector 12, one of them is selected and r3 is output.
The output r of the calculation unit 3 is input to the comparator, where Dθi ≧
It is compared whether or not r (DM ≧ DD), the comparison result is given as a control input of the selector, and r3 = r ″ is selected when Dθi ≧ r (DM ≧ DD), and r3 = r ′ is selected otherwise. The color space-compressed data r3 thus obtained and the output θ of the angle calculation unit 2 are obtained by the synthesizing unit 13.
The polar coordinates (r3, θ) can be obtained with and a ^* = r3 ·
sin θ b ^* = r3 · cos θ and L ^* from the color conversion unit
Receive data. This data is converted to L by the inverse color conversion unit 15.
^* , A ^* , b ^* from C, M, Y, BK of the hard copy device
Is converted to.

The inverse color conversion unit 15 can be realized by the LUT that minimizes the color difference dE as described in the principle.

Since the color reproduction area in the a ^* b ^* space is different from the L ^* value, a plurality of tables 4, 5 and 6 are held for switching.

[0060] Actually, since can not have countless tables for all of the L ^*, performs the table switched L ^* obtained in the process of truncation, such as by setting the step size, L ^* a more some of the table The values in the a table and the b table may be recreated by referring to and interpolating.

[Other Embodiments] FIG. 6 shows the color space compression in another embodiment of the present invention, in which a closed curve including the limit point E of the color reproduction range of the color hard copy apparatus is reproduced as it is, Other color spaces are converted to a closed curve including the limit point E.

This is DN = DD (DD ≦ DI), DN
= DI (DD> DI). It should be noted that this conversion also compresses only the saturation.

FIG. 10 corresponds to FIG. 3 of the first embodiment and is linearly converted to 0 to Ef when the distance r (= DD) from the origin is 0 ≦ r ≦ Ei (where Ef = All colors with r up to Ei <r <Ef can be converted to Ef, which can have values up to 8 bit255 in αDI. FIG. 8 shows a hardware embodiment for realizing this color space compression, and the same numbers as those in the first embodiment have the same functions, so that the description thereof will be omitted. In the second embodiment, E tables 4-2 are used instead of D table 4. That is, the E table 4-2 shows Eθi at each angle.
(= DI) is used and is shown in FIG.

If Eθi <r (DI <DD) in the comparator 8, the output of the E table 4-2 from the selector 12 r5 = Eθ
i (= DI) is selected and an output is given to the synthesizing unit 12. (DN = DI).

The output θ of the angle calculator 2 is given to the product coefficient table C, and the product coefficient is output by L and θ.
The product coefficient has a table for each L ^*, but Eθ for each angle θ
It has a table of f / Eθi. (Eθf / Eθi =
α).

Therefore, in the calculator 10, r6 = r × Eθf / Eθi with respect to r (DD) obtained from the color of the pixel data.
The data DN = αDD after color space compression is obtained by performing an operation of (= DD × α). Therefore, Eθi ≧ r (DI ≧ D
In the case of D), the result of the comparator 8 controls the selector 12 to output the output r6 of the calculator 10 as r3 = r6.

Further, as a result, α = constant α is a multiplication coefficient for effectively utilizing the full dynamic range of 0 to 255 with the number of quantization bits of 8 bits.

FIG. 7 shows color space compression in another embodiment of the present invention. The color space within the closed curve including the outer edge F of the CRT color reproduction area is composed of the outermost edge E of the color reproduction area of the color hard copy apparatus. DN that compresses linearly within a closed curve
= DD * DI / DS is a linear compression of saturation.

FIG. 9 shows a hardware embodiment for realizing this color space compression. The output from the r calculation unit 3 is multiplied by the calculator 21 and the data after color space compression is given to the combining unit. Therefore, the compression ratio multiplied by the multiplier 21 is supplied from the product coefficient d table. As for the contents of the d table, if Eθf and Eθi shown in FIG. 10 are used, Eθf /
Eθi, which is equal to α times DI / DS of the principle.

By the way, the maximum values of Eθf and Fθi are 8 bit25 through all the similar tables for all L ^* .
Since it is normalized so as to be 5, it is impossible that Eθf and Fθi are always 255 as shown in FIG. The same applies to FIG. d table is have every L ^* L ^* information and of the angle θ information (color information)
Thus, one table content is read and determined.

By the way, in the present embodiment, all parts for color space compression are calculated by using a calculator, and a distance r from the center position (a ^* , b ^* coordinate origin) of the color space (r corresponds to saturation). ) Is linearly converted, but the degree of color space compression may be different (non-linear conversion) depending on the distance r (saturation) from the origin, without being restricted by this method. Further, the degree of compression and the degree of non-linearity may be varied depending on the angle θ (hue).

Furthermore, it can be easily inferred that the compression method and the degree of non-linearity may be different depending on the L ^* component.

An example will be described below in which r (saturation or DD) is non-linearly compressed using an exponential function, and the compression rate increases as the distance r from the center increases.

DN = DD (1- (1-DI / DS) ^{DS / DD} ) Here, DD is r and DI and DS correspond to Eθi and Fθi.

These Fθi and Eθi are the F table and E table shown in FIG. 5, and Fi and Ei at each angle are written as data Fθi and Eθi.
This table is prepared for each value of L ^* .

Under such a premise, FIG. 11 shows an example of hardware implementation for implementing color space compression. Basically, the operation is almost the same as that of the embodiment shown in FIG. In the function calculator 31

[0077]

[Outside 10] Is calculated.

Since Eθi is written in the E table 4-2 and Fθi is written in the F table 4-3, the L ^* angle θ is given to each table, and E ^* i corresponding to L ^* and hue is given.
θi and Fθi are given to the function calculation unit 31. In addition to this, r and α are given to the function calculation unit 31, and the above-described function calculation is performed.

For α, the output of the function calculation unit 31 is L ^* , θ,
The maximum value for all combinations of r is set to 255 of the full dynamic range of 8 bits.

Accordingly, DN = α × DD (1- (1-DI / DS) ^{DS / DD} ) is obtained from the function calculation section 31, and based on this, the synthesizing section 13, color calculating section 14, and inverse color converting section 15 It is converted into C, M, Y, Bk to be given to the color hard copy device.

In the embodiment of the present invention, the data type colors given to the color hard copy device are Y, M, C and Bk (black), but the image data interface formats of the color hard copy device are R, G and B. It goes without saying that it does not matter. Further, it can be easily inferred that the data of the image before compression is not the one in the CRT but the entire color space area may be compressed.

Further, in the present embodiment, the image processing device includes a scanner or a television camera as the image input means and a CRT or a color printer as the image output means, but the present invention is not limited to such an image processing device. Absent. In this embodiment, a means for converting the color information of color image data into a uniform perceptual color space is provided, a color coordinate system consisting of saturation and hue is obtained, and a color group having a constant hue in the color coordinate system is a half range from the origin. By utilizing the property of being on a straight line and the saturation being proportional to the distance from the origin, the saturation is substantially linearly or non-linearly compressed.

Therefore, there is an effect of visually reducing the degree of image quality deterioration due to color space compression, which does not affect the brightness and hue, which humans have a sensitive sensation.

Therefore, according to this embodiment, it is possible to compress and map the color reproduction area of the CRT within the color reproduction range of a color hard copy device or the like.
Further, when compressing the color space, by compressing only the saturation while preserving the lightness, the information L ^* and the hue component θ, it is possible to store information sensitive to the sensitivity of the human eye and the cognitive ability in the brain. By compressing only the saturation that is relatively unnoticeable as image quality deterioration, it has become possible to perform color space compression that is less noticeable to humans.

Further, according to the present embodiment, the saturation is preserved from the low saturation portion to the intermediate saturation, and the saturation change is performed even in the high saturation area without causing the saturation loss. It is possible to maintain natural continuity.

[0086]

As described above, according to the present invention, it is possible to perform a good conversion suitable for an image reproduction range while maintaining a preferable image quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first exemplary embodiment of the present invention.

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

FIG. 3 is a diagram showing a color space conversion method.

FIG. 4 is a diagram showing a color space conversion method.

FIG. 5 is a diagram showing the contents of various tables.

FIG. 6 is a diagram showing a color space conversion method.

FIG. 7 is a diagram showing a color space conversion method.

FIG. 8 is a block diagram showing the configuration of a second embodiment.

FIG. 9 is a block diagram showing a configuration of a third embodiment.

FIG. 10 is a diagram showing a color space conversion method.

FIG. 11 is a block diagram showing a configuration of a fourth embodiment.

FIG. 12 is a diagram showing a color reproduction range of a CRT printer.

FIG. 13 is a diagram showing a color reproduction range of a CRT printer.

FIG. 14 is a diagram showing saturation compression characteristics by mapping.

[Explanation of symbols]

 1 Color Converter 2 Angle Calculator 3 r Calculator 4 D Table 5 Product Coefficient a Table 6 Product Coefficient b Table 7 Subtractor 8 Comparator 9, 10 Calculator 11 Adder 12 Selector 13 Combiner 14 Color Calculator 15 Reverse color conversion unit 17 Calculator 4-2 E table 6-2 Product coefficient C table 6-3 Product coefficient d table 21 Calculator 4-3 F table 31 Function calculation unit

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Osamu Yamada 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (9)

[Claims] 1. A method of converting image data between image processing devices having different color reproduction ranges, characterized in that conversion relating to saturation is performed without substantially converting hue and lightness. Processing method. 2. The image processing method according to claim 1, wherein the conversion of the color reproduction range is performed in a uniform perceptual color space. 3. A device having a small color reproduction range is characterized in that reproducible colors have constant brightness and hue, and are compressed into saturation to be converted into a surface (outermost edge) of a reproducible area. The image processing method according to claim 2. 4. On the device side having a small color reproduction range, the saturation is linearly compressed, and the compression ratio between the outer edge DS of the saturation of the device having a wide color reproduction range and the outer line DI of the saturation of the device having a small color reproduction range. The image processing method according to claim 2, wherein conversion equal to the ratio DI / DS is performed. 5. On the device side having a small color reproduction range, the saturation is nonlinearly compressed using an exponential function, and the center (white point) is obtained.
3. The image processing method according to claim 2, wherein the color reproduction area is converted so that the compression rate increases as the distance from the color space increases. 6. The M of DI at the distance from the outer edge of the reproducible saturation of the color space on the device side having a small color reproduction range.
Reproduce as it is up to the distance of% (O <M <100),
The saturation is linearly compressed for distances longer than that. Assuming that the distance DS to the outer edge of the saturation on the device side with a wide color reproduction range is the saturation DD of the color before conversion and the saturation DN after conversion, [External 1] 3. The image processing method according to claim 2, wherein the color reproduction area is converted. 7. The color reproduction region is converted by obtaining a color reproduction range of each model for each lightness and hue and performing conversion according to the value. Image processing method. 8. A method for converting a color reproduction range between scanners / printers or different models having different color reproduction ranges, wherein a color space reproducible color is reproduced as it is on a device side having a small color reproduction range. Impossible colors are the uniform perceptual color space L ^* ,
Color difference between a ^* and b ^* ΔE = (dL ^{* 2} + da ^{* 2} + d
b ^{* 2} ) An image transfer processing method characterized by converting to a color that minimizes ^1/2 . (DL ^* , da ^* , and db ^* are the differences between L ^* , a ^* , and b ^* before and after color conversion) 9. An image processing apparatus for converting image data for use between image processing devices having different color reproduction ranges, wherein conversion for saturation is performed without substantially performing conversion for hue and lightness. An image processing apparatus comprising means.