JPH06334847A - Picture processor and its method - Google Patents

Abstract

PURPOSE:To improve the picture quality of an error spread picture by improving a wrong intermediate tone expression of an error spread processing start part. CONSTITUTION:Error spread processing is applied to a line [512] from several preceding lines in the order of a line [509] [510] -[511] and the processing result is not written in an output frame buffer 33. Then the write of the processing result to the output frame buffer 33 is executed started from the line [512] sequentially to lines [513], [514],... and the picture processing for several lines at the output start of the processing result is executed in advance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and method for a halftone image displayed on a display having a small number of binary values or gradations.

[0002]

2. Description of the Related Art Conventionally, as a matrix panel display, plasma, electroluminescence (E
L), liquid crystal and the like. Among these, liquid crystal displays are used for a wide range of purposes because of their advantages such as ease of viewing and low power consumption. Further, among the liquid crystals, a ferroelectric liquid crystal (hereinafter referred to as FLC) has a characteristic of "memory property" unlike other liquid crystals. This is because the liquid crystal retains the display state changed by the application of an electric field. In the display device using FLC, the memory property of the display device allows the number of scanning lines for display to be
Therefore, the contrast does not decrease, and a large-screen and high-definition display is possible even with a simple matrix structure.

While the FLC has the above-mentioned characteristics, it is basically a binary (2Gray) device.
It is not possible to represent halftones within a pixel. Therefore,
In order to display an image including many halftones such as a photograph, it is necessary to perform image processing represented by the error diffusion method.

[0004]

However, when the error diffusion method is used to display an image containing halftones, there is a problem that the halftone expression at the start portion of the processing is poor. This is shown in FIG. That is, FIG. 15 is an enlarged view of a part of the processing result when the image processing is performed one line at a time from the upper line in the left to right direction. In the case of such processing, the halftone expression in the area of several lines from the upper end in the vertical direction and in the area of several pixels from the left end in the horizontal direction is poor, resulting in a so-called "solid" display. This is because the error diffused in this area is not sufficient.

Further, FIG. 16 shows the processing results when the conventional error diffusion method is executed, with numerical values of 0 and 1 (0 = black, 1 = white respectively). For example, all the same halftone data [30] (dark gray) is stored in the video memory, and the order of error diffusion processing proceeds from the left end of the first line to the right, and the same applies to the second and subsequent lines. It is assumed that processing is performed from left to right.

As is apparent from FIG. 16, in the conventional error diffusion method, the process starts, that is, several lines (two lines in the figure) from the upper end and several bits (2 bits) from the left end. The area becomes all 0 (black), and a desirable dark gray display cannot be obtained in this area. Furthermore, when the conventional error diffusion processing is performed,
In FIG. 7, the halftone expression becomes worse at the portion indicated by the thick line. For example, in the case of a display device in which processing is started in the middle of the screen, this poor halftone area appears in the middle of the image. This is noticeable, and there is a problem that the quality of the entire image is significantly reduced.

An object of the present invention is to improve the image quality in the error diffusion method by overcoming the above-mentioned drawbacks of the error diffusion method. An object of the present invention is to provide an image processing device capable of improving the image quality of an error diffusion image by improving the badness.

[0008]

In order to achieve the above-mentioned object, the present invention provides a halftone processing of image data by applying error diffusion processing to image data including halftone. In the image processing device for performing the above, means for specifying m × λ (m and λ are integers) image data from the image data, and M × L (M ≧ 1) including the m × 1 image data.
m, L ≧ λ, and M and L are integers) corresponding to image processing means for performing error diffusion processing on image data, and m × λ image data of the image data processed by the image processing means. Means for outputting only the processing result of the area to be processed.

According to a third aspect of the present invention, in the image processing apparatus, the image data including the halftone is sequentially read line by line, error diffusion processing is performed, and the halftone processing of the image data is performed. Means for identifying a line other than the first edge line and the second edge line that configures, and starting error diffusion processing from the identified line,
Between the first edge line and the second edge line, a means for performing the error diffusion process up to the second edge line by reversing the processing direction when the first edge line is reached. And an output unit that outputs only the error diffusion processing result.

[0010]

With the above arrangement, the "solid" display at the start of the error diffusion processing is avoided, and the function of improving the halftone expression is improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the configuration of an information processing system which is an image processing apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 11 is a CPU that controls the entire information processing system, and reference numeral 12 is a C.
A main memory used by the PU 11 to store a processing program or used as a work area when executing a program, 13 is an input / output control device (I / O controller) having an interface such as RS-232C, and 14 is
A keyboard for inputting character information and control information from the user, and a mouse 15 as a pointing device.

Reference numeral 16 is a hard disk device 16a and a floppy disk device 16 as external storage devices.
A disk interface for controlling b, 17 is
In order to make a signal connection between the above devices, a data bus,
It is a bus system consisting of a control bus and an address bus. Reference numeral 19 denotes a ferroelectric liquid crystal display interface (hereinafter,
Reference numeral 18 denotes a ferroelectric liquid crystal display (hereinafter referred to as FLCD).

In the FLCD 18, the FLC display panel 21 is one in which electrodes are arranged in a matrix and the ferroelectric liquid crystal is enclosed in two glass plates which have been subjected to an alignment treatment.
The information electrodes and the scan electrodes (not shown) are respectively connected to the driver I.
It is connected to C22 and C23. Further, reference numeral 24 is a panel drive control controller for controlling panel drive. The FLCD used in this embodiment has a panel size of 15
Inch and resolution are monochrome (2Gray) display with 1024 vertical and 1280 horizontal.

FIG. 2 is a block diagram showing the internal structure of the FLCD interface 19 shown in FIG. In the figure, the display control controller 30 includes a video memory 31.
The image data (multi-valued data including the halftone) is read from the image data, and the read image data is input to the image processing unit 32 and subjected to predetermined image processing. Then, the display data (black and white 2 obtained by the processing in the image processing unit 32
The value) is stored in the output frame buffer 33. The output frame buffer 33 is a buffer that stores data corresponding to white / black (ON / OFF) on the FLCD 18.

The output I / F 34 reads the display data of a certain line from the output frame buffer 33, and combines the data with the scanning line address information indicating the scanning line to display (Data, Line No. in the figure). .), And transfers it to the panel drive controller 24. Then, the panel drive controller 24 displays the sent display data on the scanning line corresponding to the scanning line address information.

The image processing unit 32 performs image processing on the multivalued data from the video memory 31, and the FLCD 18
Output the display data according to the panel specifications of. In this embodiment, the input data from the video memory 31 is 8 bits (256 Gray), and the display data output to the output frame buffer 33 is 1 bit (2 Gray). The display controller 30 can also prohibit writing of display data output from the image processing unit 32 in the output frame buffer.

In the present embodiment, the device for further speeding up the error diffusion process is also devised. That is, in the information processing system according to the present embodiment, the image processing unit has two systems,
The processing capacity is doubled by independently processing the upper half area on the video memory and the lower half area on the other side. FIG. 3 shows the “error diffusion method” used in this embodiment to explain the image processing in the image processing unit 32 in this embodiment. Here, one decision value (white or black, whichever has a closer luminance) is selected with respect to an input value (luminance data) of an input pixel.
Then, the error generated between the input value and the determined value is diffused while weighting the neighboring pixels that have not been processed yet.

Incidentally, as shown in FIG. 3, in the error diffusion method, it is general to diffuse the error not only in the horizontal direction but also in the vertical (down) direction. Therefore, the image processing unit has a line buffer for at least one line. The image processing unit 32 reads data for one line and performs error diffusion processing. At this time, the generated horizontal error is immediately diffused, but the downward error is held in the line buffer. The error is diffused to the next line by adding this when the data of the next line is read.

Therefore, a method for improving the image quality of the error diffusion image in this embodiment will be described below. 4 to 8 are diagrams for explaining a method for improving the image quality near the error diffusion start line in the present embodiment.
FIG. 4 shows a case where the error diffusion processing result from a certain line (line 512 in the figure) is output to the display frame buffer. In this embodiment, the error diffusion processing is performed from several lines above. That is, the line [509] shown in FIG.
The process is performed in the order of [510] and [511].

However, the processing result at this time is not written to the output frame buffer 33. The processing result is written to the output frame buffer 33 by using the line [51
2] starting from line [513], then [51]
4], ... FIG. 5 is a diagram showing a case where the error diffusion processing result from a certain line (line 1) is output to the display frame buffer. Here, the error diffusion processing is performed in the reverse direction from the line [3] to [2]. At this time, the output result frame buffer 3
Writing to 3 is not performed. When the error diffusion process reaches the line [1], the process returns to the line [1] to write the processing result in the output frame buffer 33 from the lines [1] to [2], [3].

As shown in FIG. 6, the lines [1], [2], and [3] are copied into a work area physically or virtually provided outside the upper end of the image, and this work is performed. The same effect can be obtained by performing the same processing from the upper end of the image data including the area as in the case shown in FIG. In the case shown in FIG. 7, the image processing of the line [1] is first repeated twice, but at this time, the processing result is not written, and then the processing of [1], [2], [3] ... While performing, the processing result is written in the output frame buffer 33.

Further, as shown in FIG. 8, a plurality of lines [1] are copied to a work area physically or virtually provided outside the upper end of the image, and the upper end of the image data including this work area is copied. Therefore, the same effect can be obtained by performing the same processing as that shown in FIG. Next, a method of improving the image quality near the left end of each image will be described.

9 to 13 are views for explaining a method for improving the image quality near the left end of the image in this embodiment. FIG. 9 is a diagram illustrating a case where the error diffusion processing result from a certain pixel (indicated by coordinates 10 and 10 in the drawing) is output to the display frame buffer. here,
The error diffusion process is performed from a few pixels before (on the left in the figure). That is, processing is performed from pixels (8, 10) to (9, 10), ... However, the processing result at this time is not written to the output frame buffer 33.

The writing of the processing result to the output frame buffer 33 starts from the pixel (10, 10) and then (11, 10), (12, 10) ,. FIG. 10 shows a case where the error diffusion processing result from a certain pixel (coordinates 1, 10) is output to the display frame buffer, but here, the direction from pixel (3, 10) to (2, 10) Error diffusion processing is performed. However, at this time, the processing result is not written. Then, the process is looped back to the pixel (1, 10), and the output frame buffer 33
Writing the processing result to the pixel (1, 10), (2,
10), (3, 10) ...

As shown in FIG. 11, a work area is physically or virtually provided outside the left end of the image, and pixels (1, 10), (2, 10), (3, 10) are provided in this area. The same effect can be obtained by copying the above, and performing the same processing from the left end of the image data including the work area as in the case shown in FIG. In the process shown in FIG.
First, the image processing of the pixel (1, 10) is repeated twice,
At this time, the processing result is not written, and then the processing result is written to the pixels (1, 10), (2, 10), (3, 10) ... And the output frame buffer 33.

Further, as shown in FIG. 13, a work area is provided physically or virtually outside the left end of the image, and a plurality of pixels (1, 10) are copied to this area to include this work area. The same effect can be obtained by performing the process from the left end of the image data as in the case shown in FIG.
In any of the cases described above, the error diffusion becomes insufficient because the image processing for a few pixels or a few lines at the start of outputting the processing result has already been performed (preprocessing error diffusion). Can be avoided. As shown in FIG. 14, as is clear from the comparison with the image processing result by the conventional error diffusion method shown in FIG. 15, in the image processing according to the present embodiment, the vicinity of the error diffusion start line and the vicinity of the left end are detected. "Solid"
It can be seen that the display and the deterioration of the halftone expression can be improved.

In order to improve image quality and halftone expression, it is important to perform "preprocessing error diffusion" near the output start line as in this embodiment. As described above, according to the present embodiment, the error processing becomes insufficient by performing the image processing for a few pixels or a few lines at the start of the output of the processing result of the image as the preprocessing error diffusion. Therefore, it is possible to avoid the "solid" display near the error diffusion start line and the left end, and to improve the deterioration of halftone expression.

The display system shown in the above embodiment is a monochrome 2Gray display, but the present invention is not limited to this.
GBW (4bit / pixel) and RRGGBB (6b
The same effect can be obtained even in a system using an it / pixel) color panel. Further, in the above embodiment, the error diffusion processing is started from the upper left of the image, but the starting point and direction of the processing are not limited to these.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0030]

As described above, according to the present invention,
By performing image processing of several pixels or several lines already at the start of outputting the processing result, it is possible to improve the image quality by the error diffusion processing, and it is possible to realize good halftone expression even on a display with binary or small gradation.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of an information processing system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an internal configuration of a FLC interface according to an embodiment.

FIG. 3 is a diagram for explaining an error diffusion method according to an embodiment.

FIG. 4 is a diagram for explaining an error diffusion method according to an embodiment.

FIG. 5 is a diagram for explaining an error diffusion method according to an embodiment.

FIG. 6 is a diagram for explaining an error diffusion method according to an embodiment.

FIG. 7 is a diagram for explaining an error diffusion method according to an embodiment.

FIG. 8 is a diagram for explaining the error diffusion method according to the embodiment.

FIG. 9 is a diagram for explaining the error diffusion method according to the embodiment.

FIG. 10 is a diagram for explaining the error diffusion method according to the embodiment.

FIG. 11 is a diagram for explaining the error diffusion method according to the embodiment.

FIG. 12 is a diagram for explaining the error diffusion method according to the embodiment.

FIG. 13 is a diagram for explaining the error diffusion method according to the embodiment.

FIG. 14 is a diagram showing an image processing result by the error diffusion method according to the embodiment.

FIG. 15 is a diagram showing a result of image processing by a conventional error diffusion method.

FIG. 16 is a diagram showing an image processing result by a conventional error diffusion method.

FIG. 17 is a diagram showing an image processing result by a conventional error diffusion method.

[Explanation of symbols]

 11 CPU 12 Main Memory 13 I / O Controller 14 Keyboard 15 Mouse 16 Disk Interface 17 Bus System 18 FLC Display 19 FLCD Interface 21 Ferroelectric Liquid Crystal Display Device 22, 23 Driver IC 24 Panel Drive Control Controller 30 Display Control Controller 31 Video Memory 32 image processing unit 33 output frame buffer

Claims (14)

[Claims] 1. An image processing apparatus that performs error diffusion processing on image data including halftones to perform halftone processing of the image data, wherein m × λ (m and λ are integers) images from the image data. Means for specifying data, and M × L (M ≧ m, L ≧ λ including the m × λ image data
Where M and L are integers, and m × of image processing means for performing error diffusion processing on image data and image data processed by the image processing means.
An image processing apparatus comprising means for outputting only a processing result of a region corresponding to image data of λ. 2. A means for providing a data area for a plurality of lines outside at least one of the edge lines forming the image data, wherein the image processing means stores the image data in the data area. The image processing apparatus according to claim 1, wherein an error diffusion process is performed on M × L image data including the data area as image data of the edge line or image data of a neighboring line. 3. An image processing apparatus for sequentially reading line-by-line image data including halftones, performing error diffusion processing, and performing halftone processing of the image data. Means for identifying a line other than the second edge line, starting error diffusion processing from the identified line, and reversing the processing direction when reaching the first edge line,
It is characterized by further comprising means for performing the error diffusion processing up to the second edge line, and output means for outputting only the error diffusion processing result between the first edge line and the second edge line. Image processing device. 4. The apparatus further comprises means for repeating the error diffusion processing for the first edge line a predetermined number of times, and the output means from the last processing result of the first edge line to the second edge line. The image processing apparatus according to claim 3, wherein only the processing result during the period is output. 5. An image processing method for performing error diffusion processing on image data including halftones to perform halftone processing of the image data, wherein an image of m × λ (m and λ are integers) from the image data. A step of specifying data, and M × L (M ≧ m, L ≧ λ including the m × λ image data.
Where M and L are integers), a step of performing error diffusion processing on the image data, and a step of outputting only the processing result of the area corresponding to the m × λ image data among the error diffusion processed image data. An image processing method comprising: 6. An image processing method in which image data including a halftone is sequentially read line by line, error diffusion processing is performed, and halftone processing of the image data is performed. Specifying a line other than the second edge line, starting error diffusion processing from the specified line, and reversing the processing direction when reaching the first edge line,
An image including: a step of performing the error diffusion processing up to the second edge line; and a step of outputting only an error diffusion processing result between the first edge line and the second edge line. Processing method. 7. An image processing method for performing error diffusion processing on image data including halftone and outputting the processing result, wherein the error diffusion processing is performed in a region near the output start point before the output of the processing result is started. An image processing method comprising: 8. The image processing method according to claim 7, wherein the area near the output start point is set to a predetermined number of pixels in a direction opposite to the error diffusion processing proceeding direction from the start point. 9. The image processing method according to claim 7, wherein the area near the output start point is a predetermined number of pixels in the same direction from the start point with respect to the error diffusion processing progress direction. 10. The image processing method according to claim 7, wherein the area near the output start point is the start point itself. 11. An image processing method for performing error diffusion processing on image data including halftones and outputting the processing result, comprising: An image processing method characterized by performing error diffusion processing. 12. The image processing method according to claim 11, wherein the neighboring lines are a predetermined number of lines in a direction opposite to the error diffusion processing proceeding direction from the output start line. 13. The image processing method according to claim 11, wherein the neighboring lines are a predetermined number of lines in the same direction with respect to the error diffusion processing proceeding direction from the output start line. 14. The image processing method according to claim 11, wherein the neighboring line is used as the output start line itself.