JP3306239B2 - Multi-tone image data converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-tone image data converter, and more particularly to a multi-tone image data converter for quantizing a multi-tone image into a low-tone image.

[0002]

2. Description of the Related Art Hitherto, a dither method and an error diffusion method have been proposed as pseudo halftone processing. However, since the dither method performs shading expression within a fixed area (dither matrix size), a dither matrix is used. When it is increased, the gradation is good, but the resolution is low. When it is small, the resolution is good, but the gradation is low. In addition, the error diffusion method has a property that a good gradation property and resolution can be realized by diffusing an error at the time of quantization to peripheral pixels. This error diffusion method is described in R. W. Floyd and L. Steinbe
rg "An Adaptive Algorithm
for Special Gray Scale'SI
G 75 Digest.

However, in the conventional error diffusion method, in an area having a large density level such as a character image, image quality is deteriorated near the edge due to error propagation. Further, the error diffusion method is often applied to static display means such as a printer and a facsimile. The static display means here means that a display image cannot be changed with time by printing on paper. When this error diffusion method is applied to a dynamic display means such as a CRT or an LCD, a constant gradation conversion is performed in the time direction regardless of the vertical synchronization signal of the display means. Is input continuously, there is a problem that the distribution of the error accumulation amount becomes constant between frames, and the accumulation of a large error in the character area does not change in the time direction, and the occurrence of notch noise causes image quality deterioration.

In order to solve this problem, in an error diffusion method for a CRT or an LCD, blurring of edges is reduced by using an inter-frame error diffusion method using vertical synchronization of display means. Japanese Patent Application Laid-Open Nos. 6-118920 and 6-138 disclose methods for preserving the gradation.
No. 858. In a conventional tone conversion unit using an error diffusion unit, a display unit after the tone conversion is mainly used for a still image such as a copier or a facsimile.

[0005]

Problems to be Solved by the Invention
No. 0, JP-A-6-138858 discloses a method of diffusing a quantum error generated in a pixel of interest in an image of a frame to be processed by an error diffusion method, and a method of diffusing a quantum error adjacent to a frame to be processed. A method has been proposed in which an error diffusion method is used for a frame to be diffused to perform good gradation conversion in an edge area and a photographic area. Therefore, one line and a buffer memory for applying the error diffusion method and an error accumulation buffer memory for one screen for applying the error diffusion method between frames are required, which causes an increase in cost and an increase in system size. Become.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and uses a small-capacity line memory.
In contrast to dynamic display means such as LCDs and CRTs, notch noise in the edge area, which is a problem when the tone is converted by the error diffusion means, can be reduced, and a natural tone can be obtained in the photographic area. It is an object of the present invention to provide a multi-tone image data conversion device which can obtain a good quantized image even in a character area without particularly providing an image area separating unit.

[0007]

According to the present invention, there is provided an image input device for inputting a captured image, comprising:
A gradation converting means for converting the multi-gradation image data into low gradation image data by quantizing the image inputted by the image input means; and data before the quantization and after the quantization. Note from data
Error calculating means for calculating a quantization error at the eye pixel,
Error accumulation means for accumulating the calculation result as a quantization error,
The quantization error occurring at the pixel of interest is predetermined
Error diffusion means to absorb by adding the offset value
And a low gradation image from the quantized multi gradation image data.
Display means for displaying image data converted to data ,
From the data before and after quantization by the error calculation means.
The data of the quantization error obtained and stored in the error storage means is obtained.
Data to the image data input by the image input means.
Calculated, and to generate an image by the low tone image data converted by the gradation converting unit when displaying on said display means
That in synchronization with the vertical synchronizing signal of said display means, said error expansion
Image to which the data of the quantization error is added by
Be achieved by multi-tone image data converting device you wherein <br/> Rukoto to generate a fine quantization image by a predetermined offset value is added by switching periodically with respect to the image data You.

[0008]

According to the present invention, the above object is provided for
Image input means for inputting an image, and
A gradation conversion means for converting a multi-tone image data to the low tone image data the image inputted Te by quantizing, quantization
Quantization at target pixel from previous data and quantized data
Error calculating means for calculating an error, and quantizing the calculation result
Error accumulating means for accumulating the error,
Add a predetermined offset value to the generated quantization error.
Error diffusion means that absorbs by calculating
Display means for displaying <br/> image data converted to a low tone image data from the multi-tone image data Te, wherein the error蓄
The product means calculates an error amount calculated by the error calculation means;
If the value is out of the predetermined range, the error outside the range is discarded.
Limiter and offset to add predetermined offset amount
Adding means, and quantizing by the error calculating means.
When the quantization error is calculated from the data before and after, the gradation change is performed.
A predetermined frame which is synchronized with a vertical synchronizing signal of the display means, which is generated when an image is displayed on the display means by the low gradation image data converted by the conversion means.
Frame does not perform limiter processing and other frames
In the system, the limiter process is performed, and the limiter process is performed.
For certain frames that are not distorted,
The error truncated by the limiter is
Is added as an offset by the
You and generates a fine quantization image Rukoto
It is achieved by the multi-gradation image data conversion device.

[0010]

[Action] In the multi-tone image data conversion apparatus, imaging
Captured by the image input means for inputting the captured image
An image is input, and the input image is
Quantization to convert low-gradation image data to multi-gradation image data.
Data before and after quantization.
Calculate the quantization error at the pixel of interest using the error calculation means.
The calculation result is stored in the error storage unit as a quantization error.
And the error diffusion of the quantization error
Means to add a predetermined offset value.
And is quantized to reduce the gradation from the multi-gradation image data.
Display the image data converted to image data on the display
Calculated from the data before and after quantization by the error calculation means.
Quantization error data stored in the error storage means.
Is added to the image data input by the image input means, and the floor
By the low gradation image data converted by the tone conversion means
The vertical orientation of the display that occurs when displaying images on the display
In synchronization with the synchronization signal, the quantization error is
Of the image data to which the data of
The added offset value is periodically switched and added. As a result, even when still image data and moving image data with a small amount of change are continuously input to the gradation conversion means, the error propagation distribution is not constant between frames, and gradation reproducibility and resolution are compatible in visual evaluation. Good tone conversion can be performed.

[0011]

[0012] In this multi-tone image data conversion apparatus,
Input the image taken by the image input means,
By quantizing the input image by the gradation conversion means,
Convert multi-tone image data to low-tone image data and quantize
Quantization at target pixel from previous data and quantized data
The error is calculated by the error calculation means, and the calculation result is
The error is stored in the error storage means as a
The quantization error generated by the error diffusion means
The added offset value is absorbed and quantized.
Is converted from multi-tone image data to low-tone image data.
Error display means for displaying the image data on the display means.
Is within a predetermined range.
If outside, limiter rounds out errors outside the range
Offset adding means for adding a predetermined offset amount
And before and after quantization by the error calculation means.
When the quantization error is calculated from the data of
Therefore, an image is displayed based on the converted low gradation image data.
The same as the vertical synchronization signal of the display means generated when displaying on the column.
In particular, limiters are used for specific predetermined frames.
No processing is performed, and limiter processing is performed for other frames.
Specific, and this limiter process is not performed.
In frames, cut by limiter in other frames
The discarded error is offset by the offset addition means.
The processing of adding as a bit is performed. As a result, notch noise in a character area due to a large accumulation error can be reduced, and excellent gradation conversion can be performed visually even in a photographic area.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a multi-tone image data converter according to the present invention will be described below with reference to the drawings.

First, an image recording / display apparatus to which the present invention is applied will be described.

As shown in FIG. 1, the image recording / display device includes a CCD camera 100 for photographing an image.
The camera 100 has a video RAM for storing image data.
101 is connected. An error diffusion unit 102 for quantizing image data is connected to the video RAM 101, and an LCD unit 103 as display means for displaying an image is connected to the error diffusion unit 102. The error diffusion unit 102 is configured to receive a vertical synchronization signal generated by the LCD unit 103.

Therefore, the image input from the CCD camera 100 is temporarily stored in the video RAM unit 101. Then, after being sent to the error diffusion unit 102 and quantized,
It is displayed on the unit 103.

Next, a first embodiment will be described. In this embodiment, a case where the original image is quantized into binary values will be described in order to particularly explain the principle clearly.

The multi-tone image data converter of the present embodiment
As shown in FIG. 2, an image input unit 200 for inputting an image composed of a CCD camera or the like is provided. The image input unit 200 includes an output of the image input unit 200 and an output of an error calculation unit 206 described later. And an adder 207 for adding. The output of the adder 207 is connected to an offset addition unit 201 as an error diffusion unit for adding a predetermined offset value.
Is connected to a quantization unit 202 as gradation conversion means for quantizing the output of the offset addition unit 201. A display unit 203 for displaying an image is connected to the quantization unit 202, and the vertical synchronization signal of the display unit 203 is input to the offset addition unit 201.
Further, the quantization unit 202 is connected to an error calculation unit 206 that calculates a quantization error at the target pixel from the data before quantization and the data after quantization, and the error calculation unit 206
An error accumulating unit 204 that accumulates a quantization error obtained from data before and after quantization and a one-line delay unit 205 that delays the quantization error by one line are provided.

Next, the operation of this embodiment will be described.

First, when 8-bit digital data (luminance value 0 to 255) is input from the image input unit 200, the output from the error accumulating unit 204 is added to the data by the adder 207. 256-level image to output 0 and 1
When quantifying, the quantization error is in the range of -255 to 255. The quantization error is a difference between an original value and a value after thresholding, which occur when thresholding from a multi-bit digital value to a low-bit digital value. When the quantization difference is large, image quality after conversion such as notch noise in a character area, black point noise in a white area, and white point noise in a black area becomes remarkable. In the error diffusion method, a quantization error generated at a pixel of interest is multiplied by a predetermined weight coefficient and added to the luminance value of a peripheral pixel to absorb the quantization error. As shown in FIG.
Coefficients for multiplying by 1/8, 1/4, and 1/8 in order from the pixel position on the left of the dot are provided, and a coefficient for multiplying the error data of the pixel position on the left of the pixel of interest by 1/2 is provided. I have.

In practice, the operation of multiplying the above coefficient is simplified by bit shifting. That is, if the data is 1
In the case of / 8, the bit string is shifted to the left by 3 bits, and 0 is buried in the empty bits on the right.

An offset adding unit 201 adds a predetermined offset value to the pixel value to which the quantization error has been added. In this embodiment, three values of 0, 16, and -16 are prepared in advance as offset values, and 0, 16, -16, 0, 16, and 16 are used for each frame using the vertical synchronization signal of the display unit 203. The value is changed periodically, such as -16. However, the value is constant within the same frame. As a result, the error propagation analysis does not become constant for each frame, and the continuous display means can obtain a good gradation conversion image with less fixed patterns and moire.

The result is input to the quantization unit 202.
In the quantization unit 202, if the input data is 128 or more, 1
If it is less than 0, a quantization process of outputting 0 is performed. In this embodiment, the offset adding section 20 is provided before the quantizing section 202.
An operation equivalent to changing the threshold fixed at 128 is realized by arranging 1s.

The processing of the quantization unit as in this embodiment can be easily realized by hardware, but a comparator is required to configure a hardware for changing the threshold value, and the scale of the circuit becomes large. By adding the offset in the preceding stage, the same function can be realized by a small-scale adder.

The error calculator 206 calculates the quantization error amount at the target pixel from the data before quantization and the data after quantization. In the present embodiment, since the data after quantization is 1-bit data of 0 or 1, the same data is embedded in all 8 bits, and then subtracted from the data before quantization. This error is input to the error accumulating unit 204 for propagation in the main scanning direction, further input to the one-line delay unit 205 for propagation in the sub-scanning direction, delayed by one line, and sent to the error accumulating unit 204. In the error accumulating unit 204, the accumulated error is multiplied by a coefficient as shown in FIG. 4A and added to the output of the image input unit 200.

Next, a second embodiment of the present invention will be described.

The multi-tone image data converter of the present embodiment is
As shown in FIG. 3, the image input unit 300 includes an image input unit 300 for inputting an image composed of a CCD camera or the like. The image input unit 300 includes an output of the image input unit 300 and an output of an error storage unit 301 described later. Is added. The adder 308 is connected to a quantization unit 302 as a gradation conversion unit for quantizing the output of the adder, and the quantization unit 302 includes a display unit 30 for displaying an image.
5 is connected. Further, the quantization unit 302 includes an error calculation unit 3 that calculates a difference between the original brightness value and the brightness value after quantization.
The error calculation unit 303 is connected to an error accumulation unit 301 that accumulates errors and a one-line delay unit 304 that delays quantization errors by one line. The error accumulating unit 301 outputs the coefficient sets 1/8, 1/4, 1/8, and 1/2 as shown in FIG.
4, a coefficient 2 multiplier 306 that multiplies a coefficient set １ ／, 、, ８, １ ／ as shown in FIG. 4B, and a coefficient 1 multiplier 307. An adder 309 for adding the output and the output of the coefficient 2 multiplier 306 is provided. The vertical synchronizing signal of the display unit 305 is input to the coefficient 1 multiplier 307 and the coefficient 2 multiplier 306.

Next, the operation of the second embodiment will be described.

When 8-bit digital data (luminance value 0 to 255) is input from the image input unit 300, the output from the error storage unit 301 is added to the data, and the quantization error around the target pixel is collected. Will be collected. The result is quantized into two values by the quantization unit 302 with the threshold value 128, and the difference between the original luminance value and the luminance value after quantization is obtained by the error calculation unit 303. Since the luminance value after quantization is 0 or 1, when subtracting from the original luminance value, the 7th to 0th bits are filled with the same quantized data. The difference calculated in this way is called a quantization error. Next, the quantization error is multiplied by a predetermined coefficient by a coefficient 1 multiplier 305 in the main scanning direction, and is delayed by one line by a one-line delay unit 304 in the sub-scanning direction. The error is reflected on the peripheral pixels by multiplying and adding to the luminance value when the peripheral pixels are quantized.

Coefficient 1 in main scanning direction, coefficient 2 in sub-scanning direction
Several sets are prepared in advance. In the second embodiment, the coefficient sets 1/8, 1/1, as shown in FIG.
4, ８, 、 and coefficient sets １ ／, 、, ８, １ ／ as shown in FIG. 4B are prepared. The display unit 3 is displayed on the coefficient 1 multiplier 307 and the coefficient 2 multiplier 306.
The vertical synchronization signal 05 is input, and the coefficient set is switched using the vertical synchronization signal. Note that the coefficient sets are the same in the same frame.

Error calculation section 303 and 1-line delay section 304
The operation of multiplying the data input from by the coefficient is simplified by bit shifting to the left as in the case of the first embodiment described above. Since the coefficient set is switched by the vertical synchronizing signal, the error propagation distribution is not constant between frames, and a visually favorable gradation conversion can be obtained.

Next, a third embodiment of the present invention will be described.

The multi-gradation image data converter of this embodiment is
As shown in FIG. 5, an image input unit 500 for inputting an image composed of a CCD camera or the like is provided. The image input unit 500 includes an output of the image input unit 500 and an output of an error storage unit 501 described later. And an adder 509 for adding. The adder 509 is connected to a quantization unit 502 as a gradation conversion unit that quantizes the output, and the quantization unit 502 is connected to a display unit 508 that displays an image. An error calculation unit 503 that calculates a quantization error from the data after quantization and the data before quantization is connected to the quantization unit 502, and the error calculation unit 503 has an error that accumulates the error. The storage unit 501 is connected. The error accumulation unit 501 includes a one-line delay unit 504 that delays the quantization error by one line, a coefficient multiplier 505 that multiplies the output of the error calculation unit 503 by a predetermined coefficient, and an error amount that is within a predetermined range, for example, −32 to +32. If there is an error accumulation other than, a limiter 506 that cuts off the other errors
And an offset adder 5 for adding a predetermined offset amount
07.

Next, the operation of the third embodiment will be described.

When 8-bit digital data (luminance value 0 to 255) is input from the image input unit 500, the output from the error storage unit 501 is added to the data, and the quantization error around the target pixel is absorbed. Is done. The result is quantized into two values by the quantization unit 502 with the threshold value 128. The error calculator 503 calculates a quantization error from the data after quantization and the data before quantization, and diffuses the error in the main scanning direction and the sub-scanning direction. In order to diffuse the error in the sub-scanning direction, the one-line delay unit 504 delays the error by one line. If the limiter 506 has accumulated errors outside the error range from -32 to +31, the other errors are discarded. That is, when the error accumulation amount is calculated as +50, the error amount is set to +31, and the remaining +19 is discarded. As a result, it is possible to prevent image quality degradation such as notch noise that occurs when the edge region is subjected to error diffusion. On the other hand, when the error is rounded down by the limiter 506,
The average luminance value in one image changes before and after quantization, causing moiré and lowering the resolution.
Therefore, the limiter processing is not performed in a predetermined frame in synchronization with the vertical synchronizing signal of the display unit 508, and the error truncated in other frames is reflected. Is applied. In this embodiment, one in four frames
Limiter processing is not performed at the rate of frames, and processing for adding +32 to the error amount is performed.

[0036]

According to the multi-tone image data conversion device of the present invention, the image input means for inputting the picked-up image is used.
Input the captured image and change the input image
Multi-level image data by quantization
Convert to gradation image data, data before quantization and after quantization
The quantization error at the pixel of interest from the data of
Therefore, calculation is performed, and this calculation result is stored as an error
Accumulates in the product means and generates the quantization error
To the offset value predetermined by the error diffusion means.
Absorbed by addition, quantized and multi-tone image data
Display image data converted from
When displaying in the column, the data before and after quantization is
Quantization error obtained from the data and stored in the error storage means.
The difference data is converted to the image data input by the image input unit.
Low tone image data converted by the
Display that occurs when an image is displayed on a display by data
In synchronization with the vertical synchronization signal of the means, by the error diffusion means
The image data to which the quantization error data has been added
The predetermined offset value is periodically switched and added , so that even when still image data and moving image data with a small amount of change are continuously input to the gradation In this case, the error propagation distribution is not constant, and it is possible to perform good tone conversion in which the tone reproducibility and the resolution are compatible in visual evaluation.

[0037]

According to the multi-tone image data conversion device of the present invention, an image picked up by the image input means is input, and
The input image is quantized by the gradation converting means.
To convert the multi-tone image data into low-tone image data,
The amount at the pixel of interest from the data before quantization and the data after quantization
The child error is calculated by the error calculation means, and the calculation result
Is stored in the error storage means as a quantization error.
The quantization error that occurs in the element is
Absorbed by adding the specified offset value, quantum
And convert from multi-tone image data to low-tone image data
When displaying the displayed image data on the display unit, error accumulation
Means for determining the amount of error calculated by the error calculating means;
If the error is out of the range, the limit is cut off.
And an offset adding means for adding a predetermined offset amount.
And before the quantization by the error calculation means.
When the quantization error is calculated from the subsequent data, the gradation conversion means
Image is displayed with low gradation image data converted by
The vertical synchronizing signal of the display means generated when displaying on the means
Synchronously, the limit is
No processing is performed, and the limiter is used for other frames.
Specify that processing is performed and this limiter processing is not performed
In the frame of the other frame by the limiter
The truncated error is turned off by the offset addition means
Because it was configured to be added as a set ,
Notch noise in a character area due to a large accumulation error can be reduced, and excellent gradation conversion can be performed visually even in a photographic area.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an image recording / display device to which the present invention is applied.

FIG. 2 is a block diagram illustrating a configuration of a first embodiment of a multi-tone image data conversion device according to the present invention.

FIG. 3 is a block diagram showing a configuration of a multi-tone image data conversion device according to a second embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of the present invention.

FIG. 5 is a block diagram showing a configuration of a third embodiment of the multi-tone image data conversion device of the present invention.

[Explanation of symbols]

 100 CCD camera 101 Video RAM 102 Error diffusion unit 103 LCD unit 200 Image input unit 201 Offset addition unit 202 Quantization unit 203 Display means 204 Error storage unit 205 One-line delay unit 206 Error calculation unit 207 Adder 300 Image input unit 301 Error Accumulation section 302 Quantization section 303 Error calculation section 304 One-line delay section 305 Display means 306 Coefficient multiplier 307 Coefficient multiplier 308 Adder 400 Image input section 501 Error storage section 502 Quantization section 503 Error calculation section 504 One-line delay section 505 coefficient multiplier 506 limiter 507 offset adder 508 display means 509 adder

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masako Nakanishi 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-6-165089 (JP, A) JP-A-6-160 242754 (JP, A) JP-A-4-54768 (JP, A) JP-A-3-149966 (JP, A) JP-A-8-44313 (JP, A) (58) Fields investigated (Int. ^7, DB name) G09G 5/00 G06T 5/00 G09G 3/20 G09G 3/36 G09G 5/36

Claims (2)

(57) [Claims] 1. Image input means for inputting a captured image
And quantizing the image input by the image input means.
Of in a gradation converting means for converting the multi-tone image data to the low tone image data in the pixel of interest from the data after the data and the quantization before quantization
Error calculating means for calculating a quantization error, and error accumulating means for accumulating the calculation result as a quantization error
And a quantization error generated in the pixel of interest is determined in advance.
Error diffusion means to absorb by adding the offset value
From the quantized multi-tone image data to the low-tone image data.
Bei display means, the displaying the converted image data to the data
The error is calculated from the data before and after the quantization by the error calculation means.
The quantization error data stored in the error storage means is
Serial adds the image data input by the image input means, said <br/> display unit that occurs when an image is displayed on the display unit by the low tone image data converted by the gradation conversion means The data of the quantization error is added by the error diffusion means in synchronization with the vertical synchronization signal.
By periodically switching and adding a predetermined offset value to the calculated image data and adding it,
A multi-gradation image data conversion device for generating an image. 2. An image input means for inputting a captured image.
And quantizing the image input by the image input means.
Of in a gradation converting means for converting the multi-tone image data to the low tone image data in the pixel of interest from the data after the data and the quantization before quantization
Error calculating means for calculating a quantization error, and error accumulating means for accumulating the calculation result as a quantization error
And a quantization error generated in the pixel of interest is determined in advance.
Error diffusion means to absorb by adding the offset value
From the quantized multi-tone image data to the low-tone image data.
Bei display means, the displaying the converted image data to the data
The error accumulating means is calculated by the error calculating means.
If the error amount is outside the specified range,
Add a limiter to cut off and a predetermined offset amount
It has an offset adding unit, a quantization from the quantization data before and after by said error calculating means
When the quantization error is calculated, the predetermined error is determined in synchronization with the vertical synchronization signal of the display unit, which is generated when an image is displayed on the display unit using the low gradation image data converted by the gradation conversion unit . Limiter processing is performed on the specific frame
No limiter processing is performed for other frames.
We, its in certain frames the limiter processing is not performed
Be cut off by the limiter in other frames
Error is offset by the offset adding means.
A multi-gradation image data conversion device characterized in that a fine quantized image is generated by performing an addition process .