JPH104500A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To independently execute various kinds of color adjustment, that is lightness adjustment, saturation adjustment, hue adjustment and density adjustment by permitting a coefficient setting means to set the coefficient of a specified matrix and a correcting coefficient in accordance with color adjustment to be processed. SOLUTION: When lightness adjustment, saturation adjustment, hue adjustment and gray balance adjustment or density adjustment as against an input image is required, a color adjustment setting parat 10 outputs color adjustment information to a coefficient arithmetic part 11 by an instruction from a user or CPU. The coefficient arithmetic part 11 calculates a 3×9 matrix arithmetic coefficient and a constant term based on the color adjustment information and calculated information is set in a second color signal converting part 5. The second color signal converting part 5 executes color conversion into an YMC image signal through the use of the set arithmetic coefficient and the constant term. The YMC image signal outputted from the second signal converting part 5 is given to a marking plate generating part 6 and a marking plate is generated from the YMC image signal so as to be converted into an YMCK image signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus capable of independently adjusting brightness, saturation, and hue.

[0002]

2. Description of the Related Art Digital copiers and the like convert an analog signal obtained by reading an original into digital multi-valued data, adjust graininess, gradation, definition, and other image quality, and reproduce and record a dot image. ing. Also, digital copiers use digitally converted multi-valued data to perform data processing for generating high-definition images, and can freely perform various editing using that data in memory. it can.

FIG. 2 is a diagram showing a configuration example of a conventional digital color image forming apparatus. In FIG. 2, an IIT (image input terminal) 100 reads a color original by decomposing the light into primary colors B (blue), G (green), and R (red) using a CCD line sensor, and converts this into digital image data. Is converted to An IOT (image output terminal) 115 performs exposure and development with a laser beam,
It reproduces a color image.

The END conversion (Equivalent Neutral Density) circuit 101 between the IIT 100 and the IOT 115 is connected to the IOT interface 110.
Up to the image data editing system (IPS: image processing system), which converts B, G, and R image data into Y (yellow), M (magenta), C (cyan), and K (Black or black) and outputs a toner signal corresponding to the developed color in each development cycle.

Here, when converting the color separation signals (B, G, R signals) into toner signals (Y, M, C, K signals), how to adjust the color balance,
The problem is how to reproduce the color in accordance with the IT reading characteristics and the IOT output characteristics, how to adjust the balance of density and contrast, and how to adjust edge enhancement, blur, and moire.

In the IIT 100, a CCD sensor is used, and 400 DPI (Do
The original is read at a resolution of (t Per Inch) and data per pixel is output in 24 bits (3 colors x 8 bits: 256 gradations for each color). The CCD sensor has B, G, and R color filters on the upper surface of the light receiving section.
It has a length of 300 mm at a density of 0 DPI. In the IIT 100, the analog data of the B, G, and R pixels are log-converted to convert the reflectance information into density information, and then to digital data.

The IPS receives color separation signals of B, G, and R from the IIT 100 and performs various data processing to improve color reproduction, gradation reproducibility, definition reproducibility, and the like. The color toner signal is turned on / off and output to the IOT 115.

That is, the IPS is an END conversion circuit 101 for adjusting (converting) to a gray-balanced color signal.
By performing a matrix operation on the B, G, and R signals, Y,
A color masking circuit 102 for converting to a signal corresponding to the M and C toner amounts; a document size detection circuit 103 for performing document size detection during prescanning and platen color erasing (frame erasing) processing during document scanning; A color conversion circuit 104 that performs conversion of a specified color in a specific area according to an area signal input from the image control circuit 111, generates an appropriate amount of K so that color turbidity does not occur, and generates Y, M and C are reduced by the same amount, and K according to each signal of mono color mode and 4 full color mode.
UCR (Under Color Removal: under color removal) & black plate generation circuit 105 which outputs signals after undercolor removal of signals Y, M and C, and has a function of recovering blur and a function of removing moiré A spatial filter 106 is provided.

Further, the IPS uses a TRC (Tone Reproduction Co.) for performing density adjustment, contrast adjustment, negative / positive reversal, color balance adjustment, etc. to improve reproducibility.
ntrol: gradation correction control) circuit 107, a main scanning direction enlargement / reduction processing circuit 108, a screen generator 109 for converting and outputting a process color gradation toner signal into an on / off binary toner signal, and an IOT interface circuit 11.
0, area image control circuit 111 having area generator and switch matrix, area command memory 112
And an editing control circuit having a color palette video switch circuit 113, a font buffer 114, and the like.

In the digital color image forming apparatus having such a configuration, the IIT 100 outputs 8-bit data (2 bits) for each of the B, G, and R color separation signals.
56 gradations) is input to the END conversion circuit 101, and Y, M,
After the conversion into the C and K toner signals, the process color toner signal is selected, binarized, and output from the IOT interface circuit 110 to the IOT 115 as ON / OFF data of the process color toner signal.

In the case of full color (four colors), after the original size is detected in the pre-scan, the edit area is detected, and other original information is detected, for example, the toner signal of the developed color is first set to Y (yellow). A copy cycle, a copy cycle in which the toner signal of the developed color is M (magenta), a copy cycle in which the toner signal of the developed color is C (cyan), and finally, a K (black or black) toner signal of the developed color Each time a copy cycle is executed,
Signal processing corresponding to four document reading scans is performed.

[0012]

As described above, in the conventional digital color image forming apparatus, B, G,
Y, which is the primary color of subtractive color mixture (such as a printer) from the R signal,
Color adjustment is performed by generating M and C and changing the tone curve. For color adjustment, the brightness (Value
), Saturation (Chroma), and hue (Hue) are intended to be adjusted independently, but if you try to adjust the color simply by modifying the Y, M, and C tone curves, the brightness, saturation, The degree and the hue change.

That is, the brightness, saturation, and hue cannot be adjusted independently, and there is a problem that it is difficult to perform intended color adjustment by correcting the Y, M, and C tone curves.

[0014]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus made to solve such a problem. That is, the present invention is an image forming apparatus that performs color adjustment and color space conversion of input image data, and uses a numerical value based on image data as a parameter to convert 3 × N (N = (4,5,6,7,8,9), a matrix operation means for calculating the determinant, and a sum of a calculation result calculated by the matrix calculation means and a correction coefficient based on color adjustment to be processed, A calculating means for outputting the converted image data which has been subjected to a predetermined color space conversion together with the color adjustment; a matrix coefficient used by the matrix calculating means and a correction coefficient used by the calculating means, the color adjustment and the color to be processed; Setting means for setting according to the space.

In such an image forming apparatus, 3 × N (N = 4, 5, 6, 7, 8, 9) according to the color adjustment to be processed.
Since the coefficient of the matrix and the correction coefficient are set by the coefficient setting means, this 3 × N (N = 4, 5, 6, 7,
The various color adjustments of lightness adjustment, saturation adjustment, hue adjustment, gray balance adjustment, and density adjustment are performed independently by the determinant operation and the correction coefficient addition by the operation means using the coefficients and correction coefficients of the matrices of 8, 9). And the conversion to a predetermined color space can be performed by the determinant.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the image forming apparatus of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating an image forming apparatus according to the present embodiment. The image forming apparatus 1 includes an image input unit 2 having a CCD line sensor and the like, an input tone correction unit 3, a first color signal conversion unit 4 using a matrix operation and a lookup table, and a second color signal conversion unit 5. A black plate generation unit 6, a spatial filter unit 7, an output gradation correction unit 8, an image output unit 9 for outputting an image, a color adjustment setting unit 10 for setting parameters for performing predetermined color adjustment, Coefficient calculation unit 1 that calculates a matrix coefficient or the like corresponding to color adjustment using parameters
1 is comprised.

In the image forming apparatus 1, color image information of a document is read for each color by a CCD line sensor of the image input unit 2, and converted into an electric digital image signal. An image signal (for example,
For the B, G, and R colors, 8 bits are subjected to gradation correction by the input gradation correction unit 3, and the BGR image subjected to gradation correction by the first color signal conversion unit 4 is converted to another color signal (for example, , L ^* a ^*
b ^* ).

The first color signal converter 4 generally converts a BGR image signal into an L ^* a ^* b ^* image signal by using a matrix operation (matrix operation) or a look-up table. Performs color conversion by 3 × 9 matrix operation and addition of constant terms.

L ^* a output from the first color signal converter 4
^{The *} b ^* image signal is supplied to the second color signal converter 5, where it is converted to another color signal (for example, Y, M, C). The second color signal conversion unit 5 converts the L ^* a ^* b ^* image signal into a YMC image signal by using a general matrix operation (matrix operation) or a look-up table as in the first color signal conversion unit 4. Color conversion. In the present embodiment, similarly to the first color signal conversion unit 4, the second color signal conversion unit 5 performs color conversion by 3 × 9 matrix operation and addition of constant terms.

The YMC output from the second color signal converter 5
The image signal is passed to the black plate generation unit 6, where the black plate is generated from the YMC image signal and converted into a YMCK image signal. The YMCK image signal output from the black plate generation unit 6 is supplied to a spatial filter unit 7, and the YMCK image processing device signal subjected to the spatial filtering process for each color is supplied to an output gradation correction unit 8. Output gradation correction is performed so as to match the image output gradation characteristics.

Then, the YMC in which the output gradation is corrected
The K image signal is supplied to the image output unit 9 to output an image.

In such an image forming apparatus 1, when it is necessary to adjust brightness, saturation, hue, gray balance, or density of an input image,
Color adjustment information is output from the color adjustment setting unit 10 to the coefficient calculation unit 11 according to an instruction from a user or an instruction from a CPU (not shown).

The coefficient calculation unit 11 calculates a 3 × 9 matrix calculation coefficient and a constant term based on the color adjustment information.
It is set in the color signal converter 5. The second color signal converter 5 uses the set operation coefficient and constant term to calculate L ^* a
^* b ^* Performs color conversion from image signal to YMC image signal.
By using the set operation coefficient and constant term,
Along with the conversion of the color space, a predetermined color adjustment based on the color adjustment information is also performed.

In particular, in the image forming apparatus 1 of the present embodiment,
Since color conversion and color adjustment are performed by 3 × 9 matrix operation and addition of constant terms, errors in the color signal to be converted can be suppressed, and various color adjustments can be performed by a simple operation. is there.

Hereinafter, the 3 × 9 matrix used will be described. The linear operation of the 3 × 9 matrix operation and the addition of constant terms in the present embodiment is as shown in Expression 23.

(Equation 23)

Here, L, A and B are each L^*,
a^*, B^*, LA, AB, and BL are L^*
And a^*, A^*And b^*, B^*And L^*Multiplied by the signal value of
Value, L ^Two, A^Two, B^TwoIs L^*, A^*, B^*No faith
Signal value squared (the same applies in the following description).
Mr). In addition, L input to the second color signal conversion unit 5^*, A
^*, B^*Image signals are 8 bits (0-255)
It is assumed that quantization has been performed.

Here, it is considered to adjust brightness, saturation, hue, gray balance, and density. Due to its characteristics, it is desirable to adjust the lightness, chroma, hue, and gray balance in a lightness / color difference space such as an L ^* a ^* b ^* color space that matches human senses. Therefore, in the present embodiment, L
^A case where color adjustment is performed in the ^* a ^* b ^* color space will be described.

Since L ^* , a ^* , and b ^* are each quantized to 8 bits (0 to 255), when performing the above-described operation for adjustment, the quantized L ^* , a ^{* are used.} , B
^* Needs to be converted (dequantized) to a value in the normal (standard) L ^* a ^* b ^* color space. Where the standard L ^* ,
a ^*, a range taken by the _{^{b * L *: l min ~l}} max,
_{^{a *: a mi n ~a max}} , b *: When b _min ~b _max inverse quantization is as few 24.

(Equation 24)

Further, a standard L ^*, a ^*, b ^* from a quantized to 8 bits (0 to 255) in each signal L ^*,
The quantization for converting into a ^* and b ^* is as shown in Equation 25.

(Equation 25)

The brightness adjustment in the standard L ^* a ^* b ^* image signal is as shown in Equation 26.

(Equation 26) In Equation 26, v and j are values indicating the brightness adjustment amount.

Further, the saturation adjustment in the standard L ^* a ^* b ^* image signal is as shown in Expression 27.

[Equation 27] In Equation 27, u is a value indicating the saturation adjustment amount.

The hue adjustment with the standard L ^* a ^* b ^* image signal is as shown in Expression 28.

[Equation 28] In Expression 28, θ is an angle indicating a hue adjustment amount.

The gray balance adjustment for a standard L ^* a ^* b ^* image signal is as shown in Equation 29.

(Equation 29) In Equation 29, e and f are values indicating the gray balance adjustment amount.

Since the density adjustment is performed using the YMC image signal, Equation 30 is obtained.

[Equation 30] In Equation 30, p, q, r and g, h, k are values indicating the density adjustment amount.

Using these Equations 24 to 30, Equation 23 is obtained.
By changing each coefficient and constant term of the 3 × 9 matrix operation shown in the following Expressions 31 to 34,
Adjustment of brightness, saturation, hue, gray balance, and density in the second color signal conversion unit 5 can be performed only by changing the coefficient of the 3 × 9 matrix and changing the constant term according to the adjustment amount of various color adjustments. It becomes possible.

(Equation 31)

(Equation 32)

[Equation 33]

(Equation 34)

X = v l _min -l _min + j Y = u (sa _min -t b _min ) -a _min + e Z = u (ta _min + sb _min ) -b _min + f Δl = l _max -l _min Δa = a _max− a _min Δb = b _max −b _min s = cos θ t = sin θ (the same applies to the following formula).

For example, in the second color signal converter 5, L ^* a ^* b
^* When converting a signal to a YMC signal, consider the case of performing color adjustment and color space conversion in the order of inverse quantization, brightness adjustment, saturation adjustment, hue adjustment, gray balance adjustment, quantization, and density adjustment. First, the brightness adjustment, the saturation adjustment, the hue adjustment, and the gray balance adjustment are performed as shown in Expression 35 by combining Expressions 26 to 29.

(Equation 35)

Next, when this is combined with the inverse quantization of Expression 24, Expression 36 is obtained.

[Equation 36]

Further, when this is combined with the quantization of Expression 25, Expression 37 is obtained.

(37)

That is, when various color adjustments such as lightness adjustment, saturation adjustment, hue adjustment, gray balance adjustment, and density adjustment are designated by the color adjustment setting unit 10, the following equation 37 is obtained based on the various color adjustment amounts. Color adjustment is performed using a simple conversion formula.

Further, in order to perform the color space conversion from L ^* a ^* b ^* to YMC together with the color adjustment, the conversion formula shown in Expression 38 may be used.

(38)

Therefore, the conversion from the color-adjusted system value (quantized L ^* a ^* b ^* ) to the YMC signal is as shown in Expression 39 by Expressions 23 and 38.

[Equation 39]

Finally, when the density adjustment is performed, Equation 40 is obtained.

(Equation 40)

As a result, Equation 40 becomes 3 × 9 as shown in Equation 41.
Since it can be transformed into a matrix operation + constant term type, by adjusting each coefficient of the 3 × 9 matrix operation of the second color signal conversion unit 5 and the constant term, brightness, saturation, hue, gray balance adjustment and density can be adjusted. , And color space conversion can be performed.

[Equation 41]

Next, another embodiment will be described. In this embodiment, brightness, saturation, hue, gray balance adjustment, and density adjustment are mainly performed by performing a 3 × 8 matrix operation and adjusting a constant term.

Here, it is assumed that the color conversion in the second color signal conversion unit 5 is performed by a 3 × 8 matrix operation and a linear operation of addition of constant terms as shown in Expression 42.

(Equation 42)

In the quantization, the inverse quantization, and the various color adjustments, the equations (24) to (30) are used in the same manner as in the above-described embodiment, and the equation (43) can be obtained by combining these. .

[Equation 43]

Further, from Equations 43 and 42, Equation 4
4 and Equation 45 can be obtained.

[Equation 44]

[Equation 45]

As described above, since the type is a 3 × 8 matrix operation + constant term type, by adjusting each coefficient and constant term of the 3 × 8 matrix operation of the second color signal conversion unit 5,
It is possible to perform color space conversion as well as lightness, chroma, hue, gray balance adjustment and density adjustment.

In the above embodiment, the color conversion in the second color signal converter 5 is a linear operation of a 3 × 9 matrix operation and a constant term addition, and a linear operation of a 3 × 8 matrix operation and a constant term addition. Although the description has been given of the case of calculation, a 3 × 7 matrix operation and a linear operation of addition of constant terms as shown in Expression 46, and a 3 × 6 as shown in Expression 47 or Expression 48
In the case of a matrix operation and a linear operation of addition of a constant term, a linear operation of a 3 × 5 matrix operation and a addition of a constant term as shown in Expression 49, and a linear operation of a 3 × 4 matrix operation and addition of a constant item as shown in Expression 50 However, by adjusting each coefficient and constant term of each matrix operation, adjustment of brightness, saturation, hue, gray balance, adjustment of density, and conversion of color space can be performed.

[Equation 46]

[Equation 47]

[Equation 48]

[Equation 49]

[Equation 50]

In the above-described embodiment, an example has been described in which the color adjustment is performed when the L ^* a ^* b ^* signal is converted into the YMC signal by the second color signal conversion unit 5. The same applies to the case where the color adjustment is performed by the first color signal converter 4 instead of 5. In this case, the connection from the coefficient calculator 11 to the second color signal converter 5 in the block diagram shown in FIG. 1 is changed to the connection from the coefficient calculator 11 to the first color signal converter 4. I just need.

[0052]

As described above, the image forming apparatus of the present invention has the following effects. That is, 3 × N (N = 4, 5, 6, 7, 8, 8,
Since the coefficient and correction coefficient of the matrix of 9) are set by the coefficient setting means, this 3 × N (N = 4, 5, 6, 6)
Various color adjustments such as brightness adjustment, saturation adjustment, hue adjustment, gray balance adjustment, and density adjustment are performed by a determinant operation and an addition of a correction coefficient by operation means using the matrix coefficients and correction coefficients of 7, 8, 9). Independently, it is possible to perform conversion to a predetermined color space by the determinant. Also, 3 × N (N = 4, 5, 6, 7, 8,
By the calculation using the matrix of 9), it is possible to perform color adjustment and color space conversion with few errors that match human senses.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an image forming apparatus according to an embodiment.

FIG. 2 is a block diagram illustrating a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image forming apparatus 2 image input unit 3 input gradation correction unit 4 first color signal conversion unit 5 second color signal conversion unit 6 black plate generation unit 7 spatial filter unit 8 output gradation correction unit 9 image output unit 10 color adjustment Setting unit 11 Coefficient operation unit

Claims (10)

[Claims] 1. An image forming apparatus for performing color adjustment and color space conversion of input image data, wherein a 3 × N (N = 4,5,6,7,8,
9) a matrix calculating means for calculating the determinant, and a sum of a calculation result calculated by the matrix calculating means and a correction coefficient based on a color adjustment to be processed is calculated, and a predetermined color space conversion is performed together with the color adjustment Calculating means for outputting the converted image data subjected to the above, and a matrix coefficient used by the matrix calculating means and a correction coefficient used by the calculating means are set in accordance with color adjustment and color space conversion to be processed. An image forming apparatus comprising: a setting unit. 2. The method according to claim 1, wherein the conversion of the color space is performed by converting image data given by L ^* a ^* b ^* into YMC signal data, wherein the matrix calculation means calculates a 3 × 9 determinant. The data input to the matrix operation means is represented by L ^* a ^*
b ^* is obtained from the image data given by b ^*. The coefficients of the 3 × 9 matrix for converting the color space are shown in Expression 2, and Assuming that the correction coefficient is shown in Equation 3, When the lightness adjustment is performed as the color adjustment, a coefficient of a 3 × 9 matrix for converting the color space is used as shown in Equation 4. The one shown in Equation 5 is used as the correction coefficient. The image forming apparatus according to claim 1, wherein: 3. The method according to claim 1, wherein the conversion of the color space is performed by converting image data given by L ^* a ^* b ^* into YMC signal data, wherein the matrix calculation means calculates a 3 × 9 determinant. The data input to the matrix operation means is represented by L ^* a ^*
b ^* is obtained from the image data given by b ^* , the coefficient of the 3 × 9 matrix for the color space conversion is shown in Expression 2, and the correction coefficient is shown in Expression 3. In the case where the saturation adjustment is performed as the color adjustment, the coefficient shown in Equation 6 is used as the coefficient of the 3 × 9 matrix of the color space conversion. The one shown in Equation 7 is used as the correction coefficient. The image forming apparatus according to claim 1, wherein: 4. The apparatus according to claim 1, wherein said color space conversion is performed by converting image data given by L ^* a ^* b ^* into YMC signal data, wherein said matrix calculation means calculates a 3 × 9 determinant. The data input to the matrix operation means is represented by L ^* a ^*
b ^* is obtained from the image data given by b ^* , the coefficient of the 3 × 9 matrix for the color space conversion is shown in Expression 2, and the correction coefficient is shown in Expression 3. In the case where the hue adjustment is performed as the color adjustment, the coefficient shown in Expression 8 is used as the coefficient of the 3 × 9 matrix of the color space conversion. The following equation 9 is used as the correction coefficient. The image forming apparatus according to claim 1, wherein: 5. The apparatus according to claim 1, wherein said color space conversion is performed by converting image data given by L ^* a ^* b ^* into YMC signal data, wherein said matrix calculation means calculates a 3 × 9 determinant. The data input to the matrix operation means is represented by L ^* a ^*
b ^* is obtained from the image data given by b ^* , the coefficient of the 3 × 9 matrix for the color space conversion is shown in Expression 2, and the correction coefficient is shown in Expression 3. When performing gray balance adjustment as the color adjustment,
The coefficients shown in Equation 10 are used as the coefficients of the 3 × 9 matrix of the color space conversion. The following equation 11 is used as the correction coefficient. The image forming apparatus according to claim 1, wherein: 6. A color space conversion device for converting image data given by L ^* a ^* b ^* into YMC signal data, wherein said matrix calculation means calculates a 3 × 9 determinant. The data input to the matrix operation means is represented by L ^* a ^*
b ^* is obtained from the image data given by b ^* , the coefficient of the 3 × 9 matrix for the color space conversion is shown in Expression 2, and the correction coefficient is shown in Expression 3. In the case where the density adjustment is performed as the color adjustment, the coefficient shown in Equation 12 is used as the coefficient of the 3 × 9 matrix of the color space conversion. The following equation 13 is used as the correction coefficient. The image forming apparatus according to claim 1, wherein: 7. The color space conversion given by BGR.
Image data to be L ^*a^*b^*Convert to signal data
Therefore, the matrix calculation means calculates a 3 × 9 determinant.
Therefore, the data input to the matrix operation means is converted by the BGR
From the given image data,
Then,Equation 2 shows the coefficients of the 3 × 9 matrix for the color space conversion.
In the case where the correction coefficient is represented by Equation 3, when the brightness adjustment is performed as the color adjustment, the color space
The coefficients shown in Equation 15 are used as the
, AndThe following equation (16) is used as the correction coefficient.The image forming apparatus according to claim 1, wherein: 8. The color space conversion given by BGR
Image data to be L ^*a^*b^*Convert to signal data
Therefore, the matrix calculation means calculates a 3 × 9 determinant.
Therefore, the data input to the matrix operation means is converted by the BGR
From the given image data,
The coefficient of the 3 × 9 matrix for the color space conversion is shown in Equation 2.
In the case where the correction coefficient is represented by Expression 3, when the saturation adjustment is performed as the color adjustment, the color space
The coefficients shown in Equation 17 are used as the
## EQU17 ##The one shown in Equation 18 is used as the correction coefficient.The image forming apparatus according to claim 1, wherein: 9. The color space conversion given by BGR
Image data to be L ^*a^*b^*Convert to signal data
Therefore, the matrix calculation means calculates a 3 × 9 determinant.
Therefore, the data input to the matrix operation means is converted by the BGR
From the given image data,
The coefficient of the 3 × 9 matrix for the color space conversion is shown in Equation 2.
In the case where the correction coefficient is represented by Equation 3, when the hue adjustment is performed as the color adjustment, the color space
The coefficients shown in Equation 19 are used as the
AndAs the correction coefficient, the one shown in Equation 20 is used.The image forming apparatus according to claim 1, wherein: 10. The apparatus according to claim 1, wherein said image data provided by BGR is converted into L ^* a ^* b ^* signal data as said color space conversion, and wherein said matrix calculation means calculates a 3 × 9 determinant. The data input to the matrix calculation means is represented by Expression 14 obtained from the image data given by the BGR, and the coefficients of the 3 × 9 matrix for converting the color space are represented by Expression 2; In the case where the correction coefficient is shown in Expression 3, when performing the gray balance adjustment as the color adjustment,
The coefficients shown in Equation 21 are used as the coefficients of the 3 × 9 matrix of the color space conversion. The one shown in Equation 22 is used as the correction coefficient. The image forming apparatus according to claim 1, wherein: