JPH11339032A - Image processing method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform detailed control especially of highlight partial density of an image by expanding bits of input image data and processing. SOLUTION: Input pixel data which is inputted to an input pixel value conversion table 2 is 8-bit multivalued image data. In the table 2, the data is expanded to 16 bits which correspond to the value of 8-bit input pixel data and is outputted. An adder 1 adds up input image data which is converted into 16 bits, an rounding off error of the adder 1 which is outputted from a latch 5, an error from the preceding line which is read from an error buffer 11 and an error from a left or right side pixel which is outputted from a latch 10 and outputs them. An error distribution table 3 performs bit expansion of error data, performs weighting, distributes error data that undergoes bit expansion to expanded image data, then binarizes it and outputs it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and an image processing apparatus, and more particularly, to a method of quantizing input data into binary or multi-valued data while storing a difference between an input image density and an output image density by an error diffusion method or the like. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and an apparatus for performing image processing.

[0002]

2. Description of the Related Art Conventionally, an error diffusion method has been known as a pseudo halftone process for expressing input multi-valued data with binary or multi-valued levels smaller than the level of input multi-valued data. The error diffusion method is described in "An Adaptive Algorit
hm for Spatial Gray Scale "insociety for Informati
on Display 1975 Symposium Digest of Technical Pape
rs, 1975, 36.

An example of binarization in this error diffusion method is as follows. The pixel of interest is P, the density of the pixel is v, and the densities of the non-binarized pixels P0, P1, P2, and P3 around the point P are respectively Assuming that V0, V1, V2, V3, and the threshold value for binarization are T, the binarization error E at the point of interest P is expressed by the surrounding pixels P
0, P1, P2, and P3 are empirically determined weighting factors W0,
The output image is weighted by W1, W2, and W3, and the average density of the output image is made equal to the density of the input image macroscopically.

At this time, assuming that the output binary data is Out, errors E0, E1, E2, and E3 with respect to the peripheral pixels P0, P1, P2, and P3 can be obtained by the following equations.

If V ≧ T, Out = 1, E = V−Vmax; If V <T, Out = 0, E = V−Vmin; (where Vmax: maximum density, Vmin: minimum density) E0 = E × E1 = E × W1; E2 = E × W2; E3 = E × W3; (Examples of weighting factors: W0 = 7/16, W1 = 1/16, W2 = 5/1)
However, if this method is realized by a logic circuit as it is, as understood from the above example, the circuit scale becomes large because a multiplier and a divider for each weight coefficient are required. There were drawbacks.

As a method for solving this problem, Japanese Patent Laid-Open No.
JP-A-215169, JP-A-61-52073, JP-A-61-52073
No. 1-293068 describes that the weighting factor is 1 / power of 2.
Thus, a method of reducing the circuit scale by using a shift register instead of the multiplier and the divider is disclosed.

Japanese Patent Application Laid-Open No. Hei 7-212593 discloses a method in which a weighting coefficient is multiplied by a denominator to make an integer and error diffusion processing is performed, thereby enabling high-speed processing without a divider. I have. FIG.
An example of a circuit disclosed in Japanese Patent No. 93 is shown. For the detailed configuration and operation, refer to the description of this embodiment.

[0008]

However, in the former method using the shift register, the decimal point operation is changed to an integer operation by simply shifting the input data to the left to perform the processing. For example, when the input data is 8 bits and the value of the denominator of the distribution coefficient is 256, the input 8 bit data is shifted to the left by 8 bits to produce 16-bit data and processed. In this case, the lower 8 bits of the 16-bit data created by the 8-bit shift are all 0, and there is a disadvantage that the accuracy is still 8 bits despite being 16-bit data. Similarly, in the latter case, as shown in FIG. 6, 8-bit input image pixel data is input to the upper 8 bits of the adder 1, but there is no input image pixel data for the lower 8 bits.

On the other hand, if linear quantization is performed on the input pixel value, the density of the data output from the printer in the highlight portion becomes extremely large, and it is necessary to control the density in detail. There is a problem that the density cannot be controlled, and more detailed control of the density is required.

The present invention eliminates the above-mentioned drawbacks of the prior art, and expands the bits of input image data to perform processing, thereby making the control of the density of a highlight portion of an image particularly detailed. To provide an image processing method and an apparatus therefor.

[0011]

In order to achieve the above-mentioned object, an image processing apparatus according to the present invention comprises an input means for inputting image data of a predetermined bit, and a bit for expanding the image data from the input means. Expansion means, processing means for performing quantization processing on the bit-extended image data, and bit expansion and weighting of error data generated during the quantization processing, and bit expansion into a plurality of bit-extended image data And a dispersing means for dispersing the obtained error data.

Here, the bit extension is performed on a decimal part. Further, the number of bits to be subjected to the bit extension is the maximum number of bits corresponding to the denominator of the weight value. Further, the bit extension is performed by a look-up table. The image processing apparatus further includes an output unit that outputs the quantized image data. The output means includes a printer and a display.

The image processing method according to the present invention is an image processing method including an error diffusion process. In the error diffusion process, input image data is bit-extended and the bit-extended image data is quantized. At the time of processing, the generated error data is bit-extended and weighted, and the bit-expanded error data is distributed to a plurality of bit-extended image data. Here, the bit extension is performed on the decimal part. Further, the number of bits to be subjected to the bit extension is the maximum number of bits corresponding to the denominator of the weight value.

A storage medium according to the present invention is a storage medium for storing a control program for controlling image processing including error diffusion processing in a computer-readable manner, and includes table data for bit-extending input image data. When,
When quantizing the bit-extended image data, table data for bit-extending the generated error data and weighting the input image data, and bit-extending the input image data and quantizing the bit-extended image data. And a control program for controlling the error diffusion process so that the error data to be generated is bit-extended and weighted, and the bit-expanded error data is dispersed into a plurality of bit-extended image data. It is characterized by including.

According to this configuration, instead of simply shifting the input data to the left in accordance with the value of the denominator of the distribution coefficient and performing the processing, table data in which bits are extended from the input pixel value is created in advance. The quantization is performed using the data obtained by bit-expanding the table with reference to the input pixel value, thereby making it possible to particularly control the density of the highlight portion of the image.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

<Configuration Example of Error Diffusion Processing Unit> FIG. 1 is a block diagram illustrating a configuration example of the error diffusion processing unit in the image processing apparatus according to the present embodiment. FIG. 1 shows an example of outputting binary data.

In FIG. 1, reference numeral 2 denotes an input pixel value conversion table. In the conversion table 2 for input pixel values, the input 8
Data Dk obtained by expanding bit data k to 16 bits is stored. This conversion table 2 has a fixed RO
It may be realized by an M table, or may be realized by a RAM table in which values are loaded from an external storage medium described later so as to be changeable according to the characteristics of the input / output device.

Reference numeral 1 denotes an adder.
Error data from a pixel that has already been binarized is added to the data Dk expanded to 6 bits.

Reference numerals 4 and 5 denote latches.
This is for delaying the lower 8-bit data of the output data of 7 bits (including the sign bit at the highest order) one pixel at a time. That is, the 8-bit data of the latch 5 is added by the adder 1 to the input data input two pixels later. This is because the lower 8 bits from the adder 1 are not used for error distribution, and are directly added to the input data to preserve the density.

Reference numeral 3 denotes an error distribution table. The upper 9 bits of the 17-bit data from the adder 1 (sign bit + 8)
For each value of (bit), error data and binary data to be distributed to the pixel positions shown in FIG. 2 are stored in advance. The error distribution table 3 may be realized by a fixed ROM table, or may be realized by a RAM table in which values are loaded from an external storage medium described later according to the characteristics of an input image. In this example, the error distribution table 3 stores an integer value obtained by multiplying the error distribution coefficient of FIG. 3 by 256, and a circuit is realized only by an adder (without using a divider). You.

The 1-bit binary data Out from the error distribution table 3 is sent to a printer unit, which will be described later, including an ink jet printer and a laser beam printer, and an image is formed by turning on / off dots.

Reference numerals 6, 8, and 10 denote latches for storing data as 1
This is for delaying pixels. Reference numerals 7 and 9 denote adders, which are used for adding error data. Also, 11
Is an error buffer capable of storing one line of data, and is for delaying one line of error data.

The circuit of FIG. 1 switches between processing in the left-to-right direction and processing in the right-to-left direction for each input data line. As shown in FIG. 1, the storage position of the error data from the adder 9 in the error buffer 11 is changed between processing in the direction of → and processing in the direction of ←. This control is executed by a CPU circuit unit described later.

For each line, the processing direction is set to the direction
By executing the zigzag processing for changing the direction, it is possible to prevent the occurrence of a unique stripe pattern which has been a problem when the error diffusion method is executed.

Although FIG. 1 shows an example in which binary data is output, it is obvious to those skilled in the art that multivalue data can be output by changing the error distribution table 3.
In order to apply the circuit of FIG. 1 to color output, for example, Y
A plurality of circuits corresponding to MCK may be provided.

<Example of Operation of Error Diffusion Processing Unit> Next, the flow of processing in the error diffusion processing unit will be described.

The input pixel pixel data input to the input pixel value conversion table 2 is 8-bit multi-valued image data. In the input pixel value conversion table 2, 16-bit data corresponding to the value of 8-bit input pixel pixel data is output. The bit-extended data stored in the input pixel value conversion table 2 need not be 16 bits. For example, if the data is 12 bits, the 12-bit data is input to the upper 12 bits of the adder 1.

The adder 1 converts the input image data converted into 16 bits by the input pixel value conversion table 2, the rounding error of the adder 1 output from the latch 5, and the error buffer 11
And the error from the previous line read from the left side (in the case of → processing) or right side (←
In the case of the direction processing), an error from the pixel is added up and output. The lower 8 bits of the 17-bit data output from the adder 1 result in a rounding error less than 1 and the latch 4
Is input to The lower 8-bit data of the 17-bit data output from the adder 1 is
After the delay corresponding to the pixel is given, it is input to the adder 1 again.

The error distribution table 3 refers to the upper 9 bits of the 17-bit data output from the adder 1. Error distribution table 3 is RAM (random access memory)
Alternatively, it is a lookup table constituted by a ROM (Read Only Memory), and stores an integer value obtained by multiplying a predetermined weighting factor by a denominator for each binarization error value. The error distribution table 3 stores values corresponding to the error distribution window as shown in FIG. 2, and each value is multiplied by the denominator of the error distribution coefficient according to the value of the binarization error. Each is represented by a 16-bit number.

In this embodiment, two symmetrical error distribution windows as shown in FIG. 2 are switched for each line in accordance with the processing direction, but the error distribution windows are symmetrical. One distribution table 3 is sufficient. The error distribution table 3 also registers binary data Out, which becomes binary data and is sent to an ink jet printer or a laser beam printer to turn on / off dots.
An image is formed by turning off. When Out is multi-value data, a dot corresponding to the multi-value data is formed.

From the error distribution table 3, the binarization error k
Ek0, ek1, ek2, and ek3 are output in accordance with the values of the error distribution windows e shown in FIG.
It corresponds to the values 0, e1, e2, e3. Therefore,
The output ek0 is input to the latch 10, and is input to the adder 1 again after being delayed by one pixel. Also, output ek
1 is input to the latch 6 and after a delay of one pixel, is input to the adder 7 and added to the output ek2. The output of the adder 7 is input to the latch 8 and, after a delay of one pixel, is input to the adder 9 and the output ek3
Is added. Then, the output of the adder 9 is written to the error buffer 11.

In this embodiment, the place where the error is written is a place two pixels to the left or right of the pixel of interest depending on the direction of the binarization processing, and the direction of the binarization processing is every line. Is switched to.

Since the binarization processing for one input data is completed by the above processing, the above processing is performed in the processing direction by one.
By repeating the process by shifting each pixel, binarization processing can be performed on the entire image.

As described above, according to the present embodiment, instead of multiplying the input 8-bit data by the value of the denominator of the distribution coefficient,
By preparing a conversion table storing conversion data for bit-extending the input 8-bit data, the precision of the input data can be increased from 8 bits to a maximum of 16 bits in this example, thereby increasing the density in the highlighted portion. Control can be performed in detail.

Hereinafter, an example of density control in a highlight portion will be described. In general, when the number of dots per unit area is linearly increased with respect to input image data, the change in density with respect to the change in input image data is very small in a portion where input image data is small (highlight portion). In the high-density portion, there is almost no density change even if the input image data changes. Therefore, as shown in the left diagram of FIG. 7, dot control is performed on the input image data so that the increase amount of the number of dots per unit area is reduced in the highlight portion and the increase amount of the dot number is increased in the high density portion. By doing so, it is possible to obtain an image whose density is linear with respect to the input image data as shown in the right diagram of FIG.

When such a data conversion is performed using a conversion table, for example, when an 8-bit output conversion table is used for an 8-bit input as shown in the upper diagram of FIG.
A gradual change in the output data is not obtained in the highlight portion, and a step is generated in the output data as shown in the lower diagram of FIG. For example, when the input data changes from 4 to 5, the output data of the conversion table changes from 1 to 2. This is 64
When applied to an area of x64 = 4096 pixels, if the input data is 4, the output data of the conversion table is 1, so that 1/255 of the whole (4096 pixels)
Six dots are hit. If the input data is 5, the output data of the conversion table is 2, so that 2/255 of the total
32 dots are printed.

On the other hand, according to the present embodiment, for example, as shown in FIG.
When the conversion is performed using the it conversion table, it is possible to set the output data of the conversion table to change from 5 to 8, for example, when the input data changes from 4 to 5. When this is applied to a 64 × 64 pixel area in the same manner as in the conventional example, when the input data is 4, the output data of the conversion table is 5, and therefore, 5 dots of 5/4080 of the whole are printed, and when the input data is 5, Since the output data of the conversion table is 8, eight dots of 8/4080 of the whole are printed.

In the case where processing is performed with 8 bits as it is, the density control can be performed only in units of 1/255.
By expanding to bits, density control can be performed in units of 1/4080, and when expanding to 16 more, 65280
Concentration control can be performed in a unit of 1 /. As described above, according to the present embodiment, it is possible to perform the density control in the highlighted portion in detail by expanding the bit. <Example of Configuration of Image Processing Apparatus According to this Embodiment> FIG. 4 is a block diagram schematically showing the overall configuration of the image processing apparatus according to this embodiment.

The image reading unit 109 includes the CCD sensor 1
02, an image of the original 100 formed by the analog signal processing unit 103 and the like and formed on the CCD sensor 102 via the lens 101 is R (Red),
The signals are converted into G (Green) and B (Blue) analog electric signals. The converted image information is supplied to the analog signal processing unit 103
After performing sample-and-hold, dark level correction, and the like for each of R, G, and B colors, analog-to-digital conversion (A / D conversion) is performed. The digitized full-color signal is input to the image processing unit 104.

The image processing unit 104 performs correction processing necessary for a reading system such as shading correction, color correction, and γ correction, smoothing processing, edge enhancement, other processing, processing, and the like. Printer unit 10
5 is output.

The printer unit 105 includes, for example, an exposure control unit (not shown) made of a laser or the like, an image forming unit (not shown), a transfer paper transfer control unit (not shown), and the like. The image is recorded on the transfer paper by the image signal.

The CPU circuit section 110 includes a CPU 106 for arithmetic control and an R for storing fixed data and programs.
The OM 107 includes a RAM 108 used for temporarily storing data and loading a program. The RAM 108 controls the image reading unit 109, the image processing unit 104, the printer unit 105, and the like, and totally controls the sequence of the apparatus.

The external storage device 111 is a medium such as a disk for storing parameters and programs used by the present device. Data and programs in the RAM 108 and data in the memory unit 303 described later are stored in the external storage device 111.
It may be configured to be loaded from.

(Image processing unit 104) Next, the image processing unit 10
4 will be described. FIG. 5 is a diagram illustrating an example of a configuration block of the image processing unit 104.

The digital image signal output from the analog signal processing unit 103 shown in FIG.
1 is input. The shading correction unit 201 corrects the variation of the sensor that reads the original and the light distribution characteristics of the original illumination lamp. The corrected image signal is input to the tone correction unit 202 for converting the luminance signal RGB into density data YMC, and the density image data Y
Create MC. The image signal converted to the density data is
The data is input to the color / monochrome conversion unit 203 and output as monochrome data W / B. Then, the monochrome data W / B output from the color / monochrome conversion unit 203
Is input to the above-described error diffusion processing unit 204, and error diffusion processing for performing pseudo halftone expression is performed.

The configuration of the image processing apparatus is an example to which the error diffusion processing of the present invention is applied, and is applied to a printer capable of multi-value printing, a color printer, or a CRT.
Similar effects can be obtained in application to image display devices such as LCDs and LCDs.

Although the input image pixel data in the embodiment described above is 8-bit multi-valued image data, it may be represented by a bit number such as 4 bits, 12 bits, 16 bits, or the like. As described above, the present invention is also applicable to the case where 8-bit input data is quantized into bit data such as 2 bits or 3 bits. Also,
In this embodiment, the error distribution window is composed of four pixels. However, it goes without saying that a larger window or a smaller window can be similarly configured.

The distribution coefficient of the error is not limited to the one shown in FIG. 3, but other values can be used. As described above, the present invention can be used for a color image by providing the circuits of the present embodiment as many as the number of input colors.

The present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), and can be applied to a single device (for example, a copier, a facsimile). Device).

Further, an object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and to provide a computer (or CPU) of the system or the apparatus.
And MPU) read and execute the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the program code is read based on the instruction of the program code. It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0055]

As described above, according to the present invention, by performing processing by expanding the bits of input image data, it is possible to particularly control the density of a highlight portion of an image in detail. A method and apparatus can be provided.

That is, by referring to the table data from the input data conversion table with the input data, the precision of the input data is extended from only the integer part to the decimal part, thereby performing particularly the processing of the highlight part of the image in detail. be able to.

[0057]

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an error diffusion processing unit in an image processing apparatus according to an embodiment.

FIG. 2 is a schematic diagram showing an error distribution window.

FIG. 3 is a schematic diagram showing an error distribution coefficient.

FIG. 4 is a block diagram illustrating a configuration of an error diffusion processing unit in a conventional image processing apparatus.

FIG. 5 is a block diagram illustrating an overall configuration example of an image processing apparatus according to the present embodiment.

FIG. 6 is a block diagram illustrating a configuration example of an image processing unit according to the present embodiment.

FIG. 7 is a diagram showing a relationship between input image data and output density.

FIG. 8 is a diagram illustrating a conversion example using a conventional conversion table.

FIG. 9 is a diagram illustrating a conversion example using the conversion table according to the present embodiment.

Claims (10)

[Claims] An input unit for inputting image data of a predetermined bit; a bit expansion unit for bit-extending the image data from the input unit; a processing unit for quantizing the bit-extended image data; An image processing apparatus, comprising: bit expansion of error data generated at the time of conversion processing, weighting, and dispersing the bit-expanded error data into a plurality of bit-extended image data. 2. The image processing apparatus according to claim 1, wherein the bit extension is performed on a decimal part. 3. The image processing apparatus according to claim 1, wherein the number of bits to be subjected to the bit extension is a maximum number of bits corresponding to a denominator of the weight value. 4. The image processing apparatus according to claim 1, wherein the bit extension is performed by a look-up table. 5. The image processing apparatus according to claim 1, further comprising an output unit that outputs the quantized image data. 6. An image processing apparatus according to claim 4, wherein said output means includes a printer and a display. 7. An image processing method including an error diffusion process, wherein in the error diffusion process, input image data is bit-extended and an error generated when the bit-extended image data is quantized. An image processing method characterized in that data is bit-extended and weighted, and bit-extended error data is dispersed into a plurality of bit-extended image data. 8. The image processing method according to claim 7, wherein the bit extension is performed on a decimal part. 9. The image processing method according to claim 7, wherein the number of bits to be subjected to the bit extension is a maximum number of bits corresponding to a denominator of the weight value. 10. A storage medium for storing a control program for controlling image processing including error diffusion processing in a computer-readable manner, comprising: table data for bit-extending input image data; When performing quantization processing on data, table data for performing bit expansion and weighting of generated error data, and performing bit expansion on input image data and performing quantization processing on the bit-extended image data. And a control program for controlling the error diffusion process so as to perform bit expansion and weighting on the generated error data and distribute the bit expanded error data into a plurality of bit expanded image data. Storage medium.