JPH10200772A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the color image forming device whose hardware scale and cost are reduced with respect to the color image forming device having a color conversion system employing a direct lookup table. SOLUTION: A 1st direct lookup table color conversion section 32 conducts color conversion processing with high color conversion accuracy and provides an output of a color conversion result S1 in the case that an input picture element is a photograph in the picture character mixture mode requiring high color conversion accuracy. A 2nd direct lookup table color conversion section 32 has a direct lookup table storing three kinds of low color conversion accuracy corresponding to the character mode, the map mode and the three-color mode that have provision for data sufficiently with low color conversion accuracy and any mode is selected by a TAG' signal from a TAG' generating section 31 and the conversion section 33 conducts color conversion processing corresponding to the selected mode and provides an output of an output signal S2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides image processing,
The present invention relates to a digital full-color copying machine for reproducing an original image on a recording medium, a color printer, a color facsimile, a file server having an image processing mechanism, an image processing apparatus used in a computer equipped with image processing, and the like.

[0002]

2. Description of the Related Art Conventionally, a masking matrix method is often used as a color conversion method in image processing such as printing and a color copying machine. In particular, although the linear masking method has a problem in conversion accuracy, the conversion process is simple, so that it is widely used for color conversion and color correction.

It is known that a nonlinear masking method is effective for improving the accuracy of color correction. For example, there is one known as a Clapper quadratic equation, which is used for performing color conversion with higher precision than the linear masking method. Although it is easy to simply combine multipliers and adders to form a circuit according to the formula,
There is a disadvantage that the hardware scale becomes large. In order to reduce the scale of hardware, for example,
No. 5, JP-B-63-32313, etc., a technique for obtaining the operation result of each item from a memory table is disclosed.

Further, as disclosed in JP-A-48-80208 and JP-A-49-106714,
A color conversion method using a multidimensional direct lookup table as a conversion table is known. In particular, a technique that stores only data corresponding to grid points in a small-capacity memory and uses it in combination with an interpolation method to accurately correct nonlinear differences in input / output color correspondence during color conversion. There is. While the above-described nonlinear masking method approximates the correspondence by a higher-order equation, the color conversion method using a direct look-up table is, for example, a technique of approximating with a polygonal line.

The color conversion method using the direct look-up table has a feature that, when mapping from the input color space to the output color space, the more the number of grid points corresponding to the polygonal line, the more accurately the nonlinear characteristic can be followed. In addition, there is an advantage that color reproduction can be controlled near a lattice point outside the color gamut without significantly affecting the inside of the color gamut. Also,
Regarding conversion accuracy, generally, in color conversion using a direct look-up table, the greater the number of grid points holding output values, the higher the color conversion accuracy. This is, for example, the annual meeting of the Society of Electrophotography (73 times in total),
"Japan Hard Copy '94 Transactions",
p. The relationship between the number of divisions and the accuracy is described on page 180. According to this document, the CM is calculated from the L ^* a ^* b ^* color space.
In the color conversion to the YK color space, the number of divisions of each axis is 8 (9
It can be seen from the comparison between (grid points) and 16 (17 grid points) that the division number 16 can obtain higher color conversion accuracy. This result is a natural result even if it is considered theoretically.

However, in order to construct a multidimensional table, it is necessary to hold table values stored at grid points. Therefore, there is a disadvantage that the larger the number of grid points, the larger the hardware scale and the scale of processing associated therewith. Consider the data amount of a multi-dimensional table by taking color conversion from the L ^* a ^* b ^* color space to the CMYK color space as an example. Now, each color of C, M, Y, K, one per color
Considering the case where data of 9 grid points are held for each of the byte and the input color space of the L ^* axis, a ^* axis, and b ^* axis, 9 (L ^* axis grid points) × 9 (a ^* axis grid points) ) × 9 (a
^* Number of axis lattice points) × 4 (CMYK color number) = 2916 bytes. Furthermore, each axis of L ^* axis, a ^* axis, and b ^* axis is 1
Assuming 7 grid points, 17 (L ^* number of axis grid points) × 17 (a ^* number of grid points) × 1
7 (a ^* number of grid points) x 4 (number of CMYK colors) = 1956
It is 2 bytes. Furthermore, if the number of grid points for each axis is increased, the amount of data to be stored will increase exponentially, and in particular, if color conversion is implemented using hardware using a direct lookup table, the memory capacity will increase and the cost will increase. This increases the hardware scale.

On the other hand, a color conversion circuit using a direct look-up table is generally composed of a memory that discretely holds output values and an interpolator.
If the capacity of the memory is small, it can be realized as a one-chip LSI, and there is an advantage that the hardware scale can be reduced. However, to give priority to conversion accuracy,
If a configuration requiring a large amount of this memory is adopted, the memory and the interpolator must be configured as separate LSIs, and wiring such as data lines, address lines, and control lines are required. Has the disadvantage of becoming larger.

Here, an example of mounting a color conversion device used in a color copying machine or the like will be considered. Natural images such as photos,
By holding a plurality of optimal color conversion coefficients for the type of input image such as business graphics such as charts, especially image data with a lot of characters, and by appropriately switching and using it, it always responds to the type of input image. It can be configured to obtain a preferable output image. The optimal color conversion corresponding to the type of the input image is called a mode. The purpose of designing a color conversion system corresponding to various modes is to obtain the image quality of an output image according to the type of input image. For example, with respect to input of a natural image such as a photograph, it is required to reproduce a smooth impression with high accuracy and faithful color. On the other hand, for text-based input, there is a requirement that dark and clear reproduction be desirable over faithful color reproduction.

An example of a specific design guideline taking conversion of the L ^* a ^* b ^* color space to the CMYK color space as an example will be described. In a natural image, a smooth impression is obtained, that is, the graininess is not deteriorated. GCR (Grey Component)
It is desirable to apply a mode in which the number of grid points in the direct lookup table is larger in order to keep the replacement rate at a moderate level and obtain faithful color reproduction. In an image mainly composed of characters, in order to obtain a clear impression particularly in black characters, a darker output value is previously input. In addition, an output value is also provided for a color character so that the saturation becomes vivid. As described above, when characters are reproduced, the color conversion accuracy is not a very important image quality factor. That is, even if a direct look-up table having a relatively small scale (with a small number of grid points) is used, there are few problems in comparison with the image quality.

As described above, since the design guideline of the direct look-up table differs depending on the mode, conventionally, the number of types of color conversion coefficients to be prepared is increased by the type of the mode.

When designing a color conversion system, for example, 1
In some cases, the mode may be switched in units of pixels or in units of designated areas in a page document. For example, in the case of pictographic separation performed by a color copier, a picture or character is determined for each pixel, and based on the result, a color conversion coefficient for a picture and a color conversion coefficient for a character are switched to perform color conversion. May be done. In such a case, the input signal of one pixel,
In synchronization with a designated Tag signal indicating whether the pixel is a picture or a character, a method of switching the color conversion coefficient for a picture or a character to perform color conversion and outputting a color conversion result based on a determination result of the picture / character separation is provided. Can be When a direct look-up table is used as the color conversion method, the grid data of the two types of direct look-up tables need to have the same capacity.

Further, when partial editing is possible and a mode can be specified for each part in a specified area unit, it is necessary to have direct lookup tables of the number of mounting modes or grid point data of the direct lookup tables. Become. In this case, it is necessary to switch the output data for each pixel or to replace the grid point data of the direct look-up table, and a configuration for switching the output table or switching the grid data to be addressed for each pixel is required.

As described above, for example, when a color conversion circuit is to be constituted by one chip, it is necessary to design the number of divisions of each axis, that is, the number of data of grid points, in consideration of capacity and conversion accuracy. For example, if the number of conversion modes is more important than the conversion accuracy, the number of grid point data may be reduced and the number of simultaneously switchable surfaces may be increased. If the conversion accuracy is more important than the number of conversion modes, it is necessary to increase the number of grid point data and reduce the number of simultaneously switchable planes.

For example, Japanese Patent Application Laid-Open No. 1-120965 discloses a configuration in which a direct lookup table is switched and used, but the number of switching surfaces of the table selecting means and the table capacity per one surface are predetermined. ,
The conversion accuracy did not change depending on the mode. Therefore, it is necessary to configure the direct lookup table according to the mode requiring the highest conversion accuracy,
A large amount of memory was required.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and aims at a mode in consideration of a color image forming apparatus equipped with a color conversion system using a direct lookup table. By using a combination of multiple direct lookup tables with the number of grid points corresponding to the required accuracy, the hardware scale and cost can be reduced without impairing the image quality, and the color conversion coefficients can be directly adjusted. It is an object of the present invention to provide a color image forming apparatus that can reduce the time for downloading to a look-up table.

[0016]

According to a first aspect of the present invention, in a color image forming apparatus, a color conversion process is performed on an input image to form a color image. A plurality of table-type color conversion means for performing the color conversion processing using the conversion table of the number of data obtained, and one or more table-type color conversion means having a conversion table having a different number of data. It is assumed that.

According to a second aspect of the present invention, in the color image forming apparatus, a color conversion process is performed on an input image.
In a color image forming apparatus for forming a color image, a plurality of table-type color conversion means for performing the color conversion processing according to a conversion table of the number of data corresponding to the processing type, and a processing capable of specifying the processing type within the same page The table type color conversion means has a conversion table having a different number of data for one or more table type color conversion means, and performs color conversion by the table type color conversion means according to the specification by the processing specification means. It is characterized by the following.

According to a third aspect of the present invention, there is provided the color image forming apparatus according to the first or second aspect, further comprising a matrix type color conversion unit, wherein the color conversion is performed by the matrix type color conversion unit. Thereafter, the table type color conversion means performs color conversion according to the processing type.

[0019]

FIG. 1 is a block diagram showing a first embodiment of a color image forming apparatus according to the present invention. In the figure, 1 is an image input unit, 2 is an input gradation correction unit, 3 is a first color signal conversion unit, 4 is a character / photograph / color / black separation unit, 5 is a document mode decoder, and 6 is a second color. Signal converters, 7 and 10 are selectors, 8 and 9 are FIFOs, 11 is a main scanning reduction / enlargement unit, 12 is a spatial filter processing unit, 13 is an output gradation correction unit, 14 is an output screen switching unit, and 15 is an image output Department.

The image input unit 1 decomposes an image on a document into R, G, and B 8-bit color signals at a predetermined pixel density, and sends the signals to the input tone correction unit 2 in pixel order. Input tone correction unit 2
Performs gradation conversion depending on the image input unit 1 and sends it to the first color signal conversion unit 3. In the first color signal converter 3,
The RGB color signals are converted into L ^* , a ^* , b ^* 8-bit color signals, and sent to the character / photograph / color / black separation unit 4 and the second color signal conversion unit 6.

The character / photo / color / black separation section 4 is L ^* a ^* b.
^* Based on the color signal, it is determined whether or not the input pixel is a character, and if it is a character, whether it is an achromatic color or a chromatic color. The determination result is passed to the document mode decoder 5. The document mode decoder 5 converts the document mode signal from the identification result by the character / photograph / color / black separation unit 4 and the document mode designation TAG information set by the user into the second color signal conversion unit 6, the selectors 7, 10, Spatial filter processing unit 12, output gradation correction unit 1
3. Output to the output screen switching unit 14. Each unit receiving the document mode signal processes each unit with parameters according to the document mode.

In the second color signal converter 6, L ^* a ^* b ^*
The signal is subjected to a color conversion process suitable for the original mode.
Here, color conversion processing corresponding to two types of original modes is performed to convert them into two types of YMCK signals S1 and S2, and send them to the selector 7. For example, the YMCK signal S1 is an output value for a photograph that requires high color conversion accuracy, and the YMCK signal S2 is an output value in a character mode, a map mode, a three-color mode, or the like that requires only low color conversion accuracy. YMCK
Color conversion processing corresponding to the document mode is performed on the signal S2. The selector 7 performs YMC according to the original mode signal.
One of the K signals S1 and S2 is selected and output to the FIFO 8. On the other hand, the L ^* signal output from the first color signal converter 3 is input to the FIFO 9 for black characters. One of the outputs of the FIFOs 8 and 9 and the '0' signal is selected by the selector 10 according to the document mode signal, and sent to the main scanning reduction / enlargement unit 5.

The main scanning reduction / enlargement unit 11 performs enlargement or reduction in the main scanning direction according to the set enlargement ratio or reduction ratio. In addition, enlargement / reduction in the sub-scanning direction
This can be performed by changing the scanning speed of the image input device 1 in the sub-scanning direction. Thereafter, the spatial filter processing unit 12 performs processing such as sharpening processing and noise removal, the output correction unit 13 performs gradation conversion according to the image output unit 15, and the output screen switching unit 14 follows the original mode signal. The output screen is selected and used to form an output image, and the image output unit 15 forms an image.

Hereinafter, the operation of the above configuration will be described using a specific example. FIG. 2 is an explanatory diagram of an example of a designated mode. In order to perform optimal reproduction according to the type of original, here, emoji mixed mode, character mode,
It is assumed that four modes of a map mode and a three-color mode are provided. In the document shown in FIG. 2, reference numeral 21 denotes a pictographic mixed mode area, 22 denotes a character mode area, 23 denotes a map mode area, and 24 denotes a three-color mode area. These areas and modes can be designated by, for example, editing designation means (not shown) (such as an instruction from an editor pad or a host computer). When the mode is not intentionally selected, the pictographic mixed mode set as the base is applied. Therefore, in the document shown in FIG. 2, the pictogram mixed mode is applied to an area where no mode selection is made. In the example shown in FIG. 2, each mode is selected for a rectangular area. However, the selection is not limited to the rectangular area and may be a circle or an arbitrary shape.

The character mode is a mode suitable for recording characters, business graphics, and the like, and is a mode for performing deeper and clearer reproduction than faithful color reproduction as described above.

The map mode is a mode effective for a map or the like in which a part or all of the map is often printed with a special color. The special color is the normal printing is the overprinting (process color) of four inks of CMYK, while red,
The color to be reproduced, such as green, gray, light pink, etc., is directly determined by the type and content of the color material or the mixture of the color materials.
This is a printing method that creates as color inks and overlaps by the number of special colors used. A characteristic of such an ink is that the color reproduction range (color gamut) is wider than the process color. Therefore, color gamut compression is more important than color reproduction accuracy. For example, if the colors to be reproduced are red-based colors, it is more likely that less unnecessary colors such as cyan will be favored than the conventional color gamut compression that preserves the hue while preserving the hue of bright and highly saturated colors. . In other words, even in the map mode, if there is a certain degree of color reproduction accuracy, a color reproduction that gives a vivid impression for colors outside the color gamut, or the color discrimination property deteriorates when the colors are separately painted with similar colors No importance is placed on high readability of characters, and absolute color reproduction accuracy is not as important as natural images.

The three-color photographic mode is intended for natural images such as photographs, and particularly when it is desired to improve graininess, Y, M,
This mode reproduces only the three colors C. The target of the three-color photograph mode is a document such as a photograph which is a natural image in many cases ^.
Since it is a color conversion from a ^* b ^* to CMY three colors, G
There is no need for CR, and local C, M, Y near the gray axis
The change of each output value is smaller than that when GCR is performed, and the interpolation error by the direct lookup table does not matter. Therefore, the high number of divisions in this mode is not very important.

The pictogram mixed mode is a mode in which a character / photo / color / black separation unit 4 automatically determines a natural image such as a photograph and a character image. If it is determined to be a photo,
In order to reproduce a natural image, it is necessary to perform high-precision color reproduction. If it is determined to be a character, the same reproduction as in the character mode is performed.

FIG. 3 is an explanatory diagram of an example of a document mode designation TAG signal in the first embodiment of the color image forming apparatus of the present invention. The document mode as described above is output as a document mode designation TAG signal. At this time, the document mode designation TAG signal can be represented as a 2-bit code, for example, as shown in FIG. In this example, the emoticon mixed mode is “00”, and the character mode is “0”.
1 ", the map mode is" 10 ", and the three-color photo mode is" 1 ".
1 ".

The original mode is input to the input tone correction unit 2, the first color signal converter 3, and the original mode decoder 5 as an original mode designation TAG signal. The input tone correction unit 2 and the first color signal conversion unit 3 perform input processing according to the specified original mode.

FIG. 4 is an explanatory diagram of an example of the judgment result output from the character / photograph / color / black separation section in the first embodiment of the color image forming apparatus of the present invention. Text / Photo ・
The color / black separation section 4 determines whether or not the input pixel is a character as described above, and determines whether the input pixel is an achromatic color or a chromatic color if the input pixel is a character. According to this determination result, for each of the case where the input pixel is not a character, the case of a chromatic character, and the case of an achromatic character, for example, “00”, “01”,
A code such as "11" is assigned, and this code is sent to the document mode decoder 5 as a determination result.

As described above, the document mode decoder 5 outputs a document mode signal from the result of identification by the character / photograph / color / black separation unit 4 and document mode designation TAG information. FIG. 5 is an explanatory diagram of an example of a document mode signal output from the document mode decoder 5 in the first embodiment of the color image forming apparatus of the present invention. FIG. 5 particularly shows output signals for controlling the selectors 7 and 10.

As described above, in the second color signal conversion unit 6, based on the L ^* a ^* b ^* signal input from the first color conversion unit 3, the output value for a photograph with high color conversion accuracy is obtained. S1 and low color conversion accuracy character mode or map mode, or 3
The output value S2 of the color mode is output, and one of them is selected by the selector 7. In the original mode decoder 5, when the original mode is the map mode or the three-color photograph mode (the original mode designating TAG signal is "10", "1"
1), an original mode signal is sent to the second color signal converter 6 so as to perform color conversion processing according to the original mode, and the output value S2
Control to select.

When the original mode is the mixed mode of pictograms, the selectors 7 and 10 are controlled in accordance with the judgment result of the character / photograph / color / black separation section 4. When the input pixel is a photograph, that is, when the code of the determination result in the character / photograph / color / black separation unit 4 is “00”, the output value S1 of the high color conversion accuracy output from the second color signal conversion unit 6 is output. Control is performed so as to be selected by the selector 7. When the input pixel is a character, the process is forcibly set to the character mode.

When the original mode is the character mode, if the input pixel is a photograph or a chromatic character, that is, if the code of the determination result by the character / photo / color / black separation unit 4 is "00" or "01", the second Control is performed so that the selector 7 selects the output value S2 of low color conversion accuracy output from the color signal conversion unit 6. When the input pixel is an achromatic character, that is, when the code of the determination result is “11”, the image output unit 15 controls so that only K (black) is recorded. Here, data is converted into K / Y / M / C in order of each color in accordance with the development cycle of each color in the image output unit 15. Only when the image output unit 15 records K (black), the second
When the L ^* output for black characters to be input to the FIFO 9 is selected by bypassing the color signal conversion unit 6 and the C, M, and Y are recorded, 0 (no signal) regardless of the outputs of S1, S2, and L ^* ) Is selected by the selector 10 and output. With such control, black characters can be clearly recorded. Except when converting achromatic characters in this character mode, the selector 10 selects the output of the FIFO 8.

FIG. 6 is a block diagram showing an example of the second color signal converter in the first embodiment of the color image forming apparatus of the present invention. In the figure, 31 is a TAG 'generator, 32 is a first direct look-up table color converter, 33
Are the second direct look-up table color converters, 3
4 is a parameter storage unit.

The parameter storage section 34 is constituted by storage means such as a ROM or a hard disk, and necessary color conversion set in the first direct lookup table color conversion section 32 and the second direct lookup table color conversion section 33. Parameters (grid point data) are stored in advance. As described above, when the power of the digital color copying machine is turned on or at an appropriate timing during the inter-image (color-color transition), the image output unit 15 is turned on.
Are loaded into the first direct look-up table color conversion unit 32 and the second direct look-up table color conversion unit 33.
Note that signal lines necessary for loading grid point data are omitted in the figure.

The TAG 'generating section 31 generates an 8-bit TAG' signal according to the output value of the original mode decoder 5. Of the 8 bits, the lower 2 bits used here are equal to the values shown in the TAG column of FIG.
The value takes one of 1, 10, and 11. In other words, each value is in emoji mixed mode, character mode,
It supports a map mode and a three-color photo mode. Also, compared to the original mode designation TAG signal code shown in FIG.
When the input pixel is determined to be a character in the pictograph mixed mode, the code only changes to “01”. T
The AG ′ signal is sent to the first direct look-up table color converter 32 and the second direct look-up table color converter 33 for each pixel in synchronization with the L ^* a ^* b ^* pixel signal.

In this example, the first direct look-up table color converter 32 and the second direct look-up table color converter 33 have substantially the same amount of memory. The first direct lookup table color conversion unit 32 performs a color conversion process with high color conversion accuracy. This first
The direct look-up table color conversion unit 32 performs a color conversion process on the input color signal L ^* a ^* b ^* and outputs it as an output signal S1. The output signal S1 is a color conversion result when the input pixel is determined to be a photograph in the pictogram mixed mode. The second direct lookup table color conversion unit 33 includes a character mode (01), a map mode (10),
It has three low-color conversion precision direct lookup tables corresponding to the three-color mode (11). These three
One of the direct lookup tables is selected by the TAG 'signal output from the TAG' generator.
The input color signal L ^* a ^* b ^* is subjected to color conversion processing using a direct look-up table corresponding to the selected mode, and is output as an output signal S2.

At this time, when the lower bit of the TAG 'signal for the second direct look-up table color converter 33 is "00", or when the lower bit of the TAG' signal for the first direct look-up table color converter 32 is lower. When the bit is other than "00", the color conversion result is not as expected, but the selector 7 always selects the output signal S1 or the output signal S2 appropriately. Alternatively, it may be configured such that only the direct look-up table color conversion unit that performs appropriate color conversion is operated.

The mode of the second color signal converter 6 is switched on a pixel-by-pixel basis according to the document mode signal from the document mode decoder 5. Thus, for example, as shown in FIG. 2, it is possible to cope with a case where a plurality of modes are selected using the editing function in the same original.

FIG. 7 is a block diagram showing an example of the direct look-up table color converter. 41 is a direct lookup table color conversion LSI. First Direct Lookup Table Color Converter 32 in FIG.
And direct lookup table color converter 33
Can be configured using a direct look-up table color conversion LSI 41 as shown in FIG. Direct lookup table color conversion LSI4
The role of each of the input signal lines 1 is as shown in FIG.

Direct Lookup Table Color Conversion L
SI41 is a direct lookup table color conversion L
It consists of three parts: setting of grid point data (color conversion parameters) in a storage unit inside the SI 41, operation setting at the time of color conversion, and color conversion. The setting of the grid point data (color conversion parameter) in the storage unit inside the direct look-up table color conversion LSI 41 invalidates the register setting by the reset signal, and the storage unit inside the direct lookup table color conversion LSI by the write enable signal. Write grid point data to Next, in accordance with the timing of the clock signal, the grid point data address is sequentially set to the address signal line in the storage section inside the direct look-up table color conversion LSI, and the grid point data corresponding to the address set to the address signal line is set. By giving the data to the grid point data signal line, a desired color conversion parameter can be set. This setting is performed when the image output unit 15
When printing is performed for each color separation (output color), the next output color can be set again in the inter-image (change between colors).

FIG. 8 is an explanatory diagram of an example of the setting of the storage section and the register value in the direct look-up table color conversion LSI. The storage unit in the direct look-up table color conversion LSI 41 can be used in three ways as shown in the column of the number of divided three-dimensional tables in FIG. The value in this column is the number of bits representing the number of divisions of the L ^* axis−
The number of bits representing the number of divisions on the a ^* axis-the number of bits representing the number of divisions on the b ^* axis are shown in order. For example, 4-4-4
^{Indicates that} the number of bits representing the number of divisions on the L ^* axis, a ^* axis, and b ^* axis is 4 bits, and that 17 grid points can be represented. In the example of the direct look-up table color conversion LSI 41 shown here, the number of divisions forming the three-dimensional table serving as the direct look-up table is 4-4-4 bits (17 grid points × 1).
One plane is the case of 7 grid points × 17 grid points, and 3 is the case of 4-3-3 bit division (17 grid points × 9 grid points × 9 grid points).
In the case of plane, 3-3-3 bit division (9 grid points × 9 grid points × 9 grid points), a direct look-up table of 5 planes can be configured.

The switching of these three configurations is performed according to the value set in the register in the direct look-up table color conversion LSI 41. For example, as shown in the register setting value column of FIG. 8, by setting "00" in the register, 4-4-4 bit division, "01"
Is set, 4-3-3 bit division, "1
By setting "0", 3-3-3 bit division can be set.

TAG 'is equivalent to the name of the three-dimensional table, and among the three sides of the 4-3-3 bit division,
This is to indicate which plane among the five planes of the 3-bit division is used at the time of actual color conversion. In the direct look-up table color conversion LSI 41, switching is possible in pixel units.

Here, the relationship between the direct look-up table color conversion LSI 41 and the original mode will be described.
As described above, when the input pixel is determined to be a photograph in the pictogram mixed mode, color conversion is performed with the highest emphasis on color reproduction accuracy in terms of image quality. Therefore, the color conversion in this case is 4-4-
4-bit division (17 grid points x 17 grid points x 17 grid points)
Is used.

In the character mode, as described above, the color reproduction accuracy is not so important. Also, in the map mode, the absolute color reproduction accuracy is not so important as described above. Further, in the three-color photograph mode, the interpolation error by the direct look-up table does not cause any problem as described above, so that low reproduction accuracy is sufficient. Therefore, in the character mode, the map mode, and the three-color photograph mode, the direct look-up table color conversion LSI 41 can be assigned to three faces of 4-3-3 bit division (17 grid points × 9 grid points × 9 grid points). .

In the configuration of the second color signal converter 6 shown in FIG. 6, a first direct look-up table color converter 32 and a second direct look-up table color converter 33 are shown in FIG. This can be realized by the direct look-up table color conversion LSI 41. The first direct look-up table color conversion unit 32 sets “00” in the register and uses it as one surface by 4-4-4 bit division shown in FIG. A direct look-up table color conversion LSI for realizing the first direct look-up table color converter 32
Performs color conversion processing on an input color signal L ^* a ^* b ^* when an input pixel is determined to be a photograph in the pictogram mixed mode, and outputs an output signal S1.

The second direct look-up table color conversion section 33 sets "01" in the register and uses it as three planes by 4-3-3 bit division shown in FIG. These three sides correspond to the character mode (01), the map mode (10), and the three-color mode (11), respectively, and TAG '
Switching is performed by a TAG ′ signal output from the generation unit 31. The input color signal L ^* a ^* b ^* is subjected to color conversion processing by a three-dimensional table in each mode, and becomes an output signal S2. As described above, for the original mode in which low color reproduction accuracy is sufficient,
By constructing a direct look-up table by reducing the grid point data, one LSI can be used here.
One original mode can be realized.

As described above, by realizing the direct look-up table of each document mode at the same time, it is possible to perform the color conversion with the color reproduction accuracy corresponding to each document mode while switching on a pixel-by-pixel basis, and at the same time, it is possible to achieve low reproduction accuracy. By reducing the memory capacity, a color image forming apparatus capable of performing color conversion according to various document modes on a small scale can be configured. This has made it possible to reduce costs while satisfying the required image quality.

In the above example, the image data is treated as 8 bits. However, any number of bits may be used. The present invention is applied to the color conversion from L ^* a ^* b ^* to CMYK. It goes without saying that the present invention can be applied to conversion from a color signal in a space to a signal in another color space. For example, from RGB to L ^*
The present invention may be applied to a color space to a ^* b ^* or a color conversion from RGB to YMCK.

In the above example, the direct look-up table color conversion LSI 41 as shown in FIG. 7 is divided into a maximum of 4-4-4 bits. Absent. If the pixel density of the LSI increases, the configuration may be such that the maximum 5-5-5 bit division can be used as a plurality of planes of 4-4-4 bit division, and further, a plurality of planes of 4-3-3 bit division. In addition, the number of divisions of high reproduction accuracy and the number of divisions of low reproduction accuracy are not limited to 4-4-4 bit division and 4-3-3 bit division, and the precision is further improved or the precision is further reduced. May be divided.

Further, in the above example, a plurality of direct look-up table color conversions with the same division number and a low reproduction accuracy are mounted in the LSI, and another LSI with a high reproduction accuracy with a different number of divisions, a total of 2 Although the description has been made using the example in which one LSI is used, two direct lookup tables having the maximum density (two modes) and one direct lookup table using different densities may be provided. If the mounting density increases, one LSI
It is also possible to put together. In these cases,
It is necessary to appropriately change the selector 7 and its control according to the number of direct lookup tables that operate simultaneously. Needless to say, a plurality of I / Os realizing direct look-up tables having different numbers of grid points corresponding to each mode.
C may be used.

Further, in the above-described example, four types of original modes, ie, a pictogram mixed mode, a character mode, a map mode, and a three-color mode, corresponding to the type of the original of the digital color copying machine are described. Or 4
More than three types may be used, or three or less types may be used. In addition, other modes may be used as the above-described document modes. Regardless of the mode prepared, the direct lookup table color can be changed by changing the number of grid points (grid point density) of the direct lookup table color conversion unit according to the color reproduction accuracy required for each mode. The scale of the conversion unit can be reduced.

FIGS. 9 and 10 are block diagrams showing a color image forming apparatus according to a second embodiment of the present invention. In the figure, the same parts as those in FIG. 51 is a FIFO, 52 is an image output processor for K, 5
3 is an image output processing unit for C, 54 is an image output processing unit for M,
55 is an image output processing unit for Y, 56 to 58 are FIFO, 5
9 is a K image output unit, 60 is a C image output unit, 61 is an M image output unit, and 62 is a Y image output unit. The second embodiment is an example of an image forming apparatus in which C, M, Y, and K colors must be simultaneously input. 9 and 10 are shown separately for convenience of illustration. Also, M
Image output processing unit 54 and Y image output processing unit 55
Is the same as the configuration of the C image output processing unit 53,
Illustration of the inside is omitted.

L ^* a converted by the first color signal converter 3
^{The *} b ^* signal is temporarily stored in the FIFO 51 in order to match the timing of signal output from the character / photograph / color / black separation unit 4 and the original mode decoder 5. FI
The L ^* a ^* b ^* signal stored in the FO 51 and the document mode signal output from the document mode decoder 5 are K, C,
It is input to the M and Y image output processing units 52, 53, 54 and 55.

Image output processing units 52, 5 for K, C, M, Y
Reference numerals 3, 54, and 55 denote second color signal conversion units 6,
It has selectors 7 and 10, a main scanning reduction / enlargement unit 11, a spatial filter processing unit 12, an output gradation correction unit 13, and an output screen switching unit 14. The second color signal conversion unit 6
A plurality of direct look-up table color conversion units having different numbers of divisions for performing color conversion in each original mode for each corresponding color. For example, this can be realized by the configuration shown in FIG. 6, but since the grid point data does not need to be replaced, the configuration may be made without the parameter storage unit 34.

The output signals S 1 and S 2 output from the second color signal converter 6 for each color are selected by the selector 7 according to the mode, and input to the selector 10. In the K image output processor 52, the selector 10 selects either the output from the second color signal converter 6 selected by the selector 7 or the L ^* signal for black characters according to the mode. In the C, M, and Y image output processing units 53 to 55, the selector 10 selects either the output from the second color signal conversion unit 6 selected by the selector 7 or “0” according to the mode. I do. As described in the first embodiment,
When it is determined in the character mode that the character is an achromatic character, the selector 10 of the K image output processing unit 52 selects the L ^* signal for black characters, and the selector 10 of the C, M, Y image output processing units 53 to 55 selects the L ^* signal. Selects "0". Thus, image formation is performed only in the K image output unit 59.

The FIFOs 56, 57 and 58 are FIFOs for timing adjustment when outputting each color. Here, the K image output unit 59 starts forming an image first, and thereafter, C,
Since the M and Y image output units 60, 61, and 62 start image formation sequentially, the K image output processing unit 52
Although no FIFO is arranged between the image output units 59,
If an image of another color starts to be formed first, a FIFO may be arranged here as well.

By adopting such a configuration, C,
In a color image forming apparatus for forming M, Y, K images in parallel, K, C, M, Y image output sections 59, 60, 6
The output signals of K, C, M, and Y can be sent in parallel to the signals 1 and 62, respectively.

FIG. 11 is a block diagram showing a color image forming apparatus according to a third embodiment of the present invention. In the figure, FIG.
The same parts as those described above are denoted by the same reference numerals and description thereof will be omitted. 7
Reference numeral 1 denotes a color adjustment matrix unit. In the third embodiment, an example is shown in which a color adjustment matrix unit 71 that performs overall color adjustment is added before the second color signal conversion unit 6. The color adjustment matrix unit 71 adjusts the lightness, the hue, and the like as a whole, and converts the L ^* a ^* b ^* color space into L ^* 'a ^* '.
b ^* 'Convert to color space. Color adjustment using a matrix
For example, as disclosed in JP-A-5-14699, the entire color can be adjusted. Such a circuit for adjusting the entire color space is provided by the second color signal converter 6.
, The overall color adjustment common to various original modes can be easily performed with a matrix circuit having a small parameter capacity. Further, since the color conversion is performed by the second color signal conversion unit 6 according to the document mode, excellent color adjustment capability can be exhibited, and a color image forming apparatus that is significant in hardware scale and control can be realized. become.

FIG. 12 is a system configuration diagram showing a fourth embodiment of the color image forming apparatus of the present invention. In the figure,
81 is a photo CD, 82 is a scanner, 83 is a host computer, and 84 and 85 are color printers. In each of the embodiments described above, the color conversion processing in a digital color copying machine has been described as an example. However, the present invention may be applied to, for example, a color conversion unit of an image processing system via a network. For example, the present invention can be applied to a system in which a photo CD 81, a scanner 82, a host computer 83, color printers 84, 85, and the like shown in FIG. Host computer 83
Has a configuration excluding the image input unit 1 and the image output unit 15 in each of the above-described embodiments. The host computer 83 performs color conversion on an input image from the photo CD 81 or the scanner 82. , Color printer 8
4 or a color printer 85.

Alternatively, the color printer 84 or 85
Has a processing unit that executes color conversion processing according to the original mode (characters, graphics, images, etc.), and can be applied to the case where interpretation and instructions are given in the color printer 84 or 85. The input / output management of the image data and the creation and editing of the image may be performed on the side 83, and the color conversion of the present invention may be performed on the color printer in accordance with the instruction.

[0065]

As is apparent from the above description, according to the present invention, in the color image forming apparatus using the direct look-up table color conversion, the optimal number of grid points according to the type of the original is set, and the color reproduction is so reduced. For document types for which accuracy is not required, reduce the amount of memory by realizing a direct lookup table with a small number of grid points, reduce the scale required for color conversion processing, and thereby reduce the overall scale of the color image forming apparatus. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a color image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an example of a designated mode.

FIG. 3 is an explanatory diagram of an example of a document mode designation TAG signal in the first embodiment of the color image forming apparatus of the present invention.

FIG. 4 is an explanatory diagram illustrating an example of a determination result output from a character / photograph / color / black separation unit according to the first embodiment of the color image forming apparatus of the present invention.

FIG. 5 is an explanatory diagram of an example of a document mode signal output from a document mode decoder 5 in the color image forming apparatus according to the first embodiment of the present invention.

FIG. 6 is a configuration diagram illustrating an example of a second color signal conversion unit in the color image forming apparatus according to the first embodiment of the present invention.

FIG. 7 is a configuration diagram illustrating an example of a direct lookup table color conversion unit.

FIG. 8 Direct Lookup Table Color Conversion LS
FIG. 4 is an explanatory diagram of an example of a setting of a storage unit inside I and a register value.

FIG. 9 is a block diagram illustrating a color image forming apparatus according to a second embodiment of the present invention.

FIG. 10 is a block diagram illustrating a color image forming apparatus according to a second embodiment of the present invention.

FIG. 11 is a block diagram illustrating a color image forming apparatus according to a third embodiment of the present invention.

FIG. 12 is a system configuration diagram illustrating a color image forming apparatus according to a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image input part, 2 ... Input gradation correction part, 3 ... First color signal conversion part, 4 ... Character / photograph / color black separation part, 5 ... Original mode decoder, 6 ... Second color signal conversion part , 7, 10... Selector, 8, 9... FIFO, 11.
2 spatial filter processing unit 13 output gradation correction unit 14
... output screen switching unit, 15 ... image output unit, 21
... Pictogram mixed mode area, 22 ... Character mode area, 23
... map mode area, 24 ... three-color mode area, 31 ... TA
G 'generation unit, 32: first direct lookup table color conversion unit, 33: second direct lookup table color conversion unit, 34: parameter storage unit, 41: direct lookup table color conversion LSI, 51: FI
FO, 52 ... K image output processing unit, 53 ... C image output processing unit, 54 ... M image output processing unit, 55 ... Y image output processing unit, 56-58 ... FIFO, 59 ... K image output unit , 60 ... C image output unit, 61 ... M image output unit, 62 ...
Y image output unit, 71: color adjustment matrix unit, 81: photo CD, 82: scanner, 83: host computer,
84, 85 ... color printer.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04N 1/46 Z (72) Inventor Atsushi Kitagawara 2274 Hongo, Ebina-shi, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. (72) Inventor Yamazaki Toshio 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. A color conversion process is performed on an input image,
In a color image forming apparatus for forming a color image, the color image forming apparatus includes a plurality of table-type color conversion units that perform the color conversion processing according to a conversion table of the number of data corresponding to a processing type,
A color image forming apparatus, wherein at least one of the table type color conversion means has a conversion table of a different number of data. 2. A color conversion process is performed on an input image,
In a color image forming apparatus for forming a color image, a plurality of table-type color conversion means for performing the color conversion processing according to a conversion table of the number of data corresponding to the processing type, and a processing capable of specifying the processing type within the same page The table type color conversion means has a conversion table having a different number of data for one or more table type color conversion means, and performs color conversion by the table type color conversion means according to the specification by the processing specification means. A color image forming apparatus, comprising: 3. The apparatus according to claim 1, further comprising a matrix type color conversion unit, wherein the color conversion is performed by the matrix type color conversion unit, and then the table type color conversion unit performs the color conversion according to the processing type. 3. A method according to claim 1, wherein
3. The color image forming apparatus according to 1.