JPH09185353A - Display control circuit using error diffusion method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the display control circuit with high flexibility which can adequately display characters while applying the error diffusion method. SOLUTION: An error adder 15 adds an error of an adjacent pixel to image data supplied from an image data generation part 11, etc. A converting circuit 17 supplies display data for displaying the color corresponding to the addition value to a display 25 and diffuses the difference between the addition value and display data to adjacent pixels. An exceptional color detecting circuit 21 detects image data indicating the display color of characters and outputs an exception indicating signal and exceptional display data specifying the display color. The converting circuit 17 once supplied with the exception indicating signal stops the error diffusion process and supplies the exceptional display data to the display 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display control circuit for driving a liquid crystal display element using an error diffusion method.

[0002]

2. Description of the Related Art An error diffusion method is known as a method for enabling a pseudo full-color display using a display device having a small number of display gradations. In the error diffusion method, an error between the image data of each pixel and the actual display color is diffused to an adjacent pixel so that a delicate color change is expressed by a set of pixels.

However, when a character is displayed by using the error diffusion method, there is a problem that a small character is crushed and the character becomes difficult to read.

[0004]

In order to solve this problem, a character data memory is provided in addition to the image memory, and by superimposing the character data on the image display which has been subjected to the error diffusion processing, the characters are crushed. A method for preventing this has also been proposed. However, in this method, the display system has a special configuration, and when it is applied to a display device of a personal computer, for example, a special display software interface is required from the viewpoint of application software, which is not versatile. .

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a display control circuit using the error diffusion method which can appropriately display characters while applying the error diffusion method. .

[0006]

In order to achieve the above object, a display control circuit using an error diffusion method according to a first aspect of the present invention comprises a receiving means for receiving image data and a receiving means for receiving the image data. Display data generating means for generating display data for driving a display device by applying an error diffusion method to the image data thus obtained, and determining whether the image data received by the receiving means is data forming a character And a display corresponding to the image data by stopping the application of the error diffusion method to the display data generation unit when the image data is determined to be data forming a character by the determination unit. It is characterized by comprising control means for generating a signal.

According to this structure, since a normal image is displayed by using the pixel diffusion method, it can be displayed with an appropriate gradation. On the other hand, for the character, the error diffusion process is stopped, so that the character collapse can be prevented.

Characters are displayed in a predetermined color. Therefore, by stopping the error diffusion processing for the display color of the character, it is possible to prevent the character from being crushed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A display device according to an embodiment of the present invention will be described below. FIG. 1 shows the configuration of a data processing device according to an embodiment of the present invention. As shown in the figure, this data processing device includes an image data generation unit 11,
A / D converter 13, error adder 15, and conversion circuit 17
An error calculation circuit 19, an exceptional color detection circuit 21, an exceptional color register 23, and a display (display device) 25.

The display 25 is a birefringence control type (EC
The liquid crystal display device of B) is applied, and a voltage indicated by display data is applied to each pixel, and the alignment state of the liquid crystal is changed according to the applied voltage to display an arbitrary color. The display 25 is, for example, compliant with VGA and is 64
It is composed of 0 (horizontal) × 480 (vertical) pixels.

The image data generator 11 is, for example, a VGA
Comprised of a personal computer compliant with
Three color analog image signals of (red), G (green) and B (blue) are output. The A / D converter 13 converts each analog image signal into 6-bit digital image data DR, DG, DB. The digital image signal output from the A / D converter 13 is supplied to the error adder 15, and the upper 3
The bits are supplied to the exceptional color detection circuit 21. The error adder 15 receives the supplied digital image data DR, DG,
DB is added to error data GR2, GG2, GB2 described later, and output as 7-bit image data R2, G2, B2.

The exceptional color detection circuit 21 includes an A / D converter 13
Digital image data DR, DG, DB supplied from
The color defined by the upper 3 bits of is determined, and when this color matches the color preset in the exception color register 23, the exception instruction signal and the exception display data are output.

FIG. 2 shows a configuration example of the exceptional color detection circuit 21. As illustrated, the exceptional color detection circuit 21 includes a first to fourth comparators 211 to 214 and a fixed exceptional color decoder 2
15, an exceptional color enable register 216, an encoder 217, an exceptional display color designation register 218, and first to nth AND gates AND _{1 to} AND _n .

The exceptional color register 23 is provided with four registers, stores exceptional color data of exceptional colors 1 to 4 (6 bits for each of RGB, 18 bits in total), and corresponds to the first to fourth comparators 211 to 211. To 214. The first to fourth comparators 211 to 214 compare the supplied exceptional color data with the RGB image data supplied from the A / D converter 13, and when they match, output a match signal.

The fixed exceptional color decoder 215 decodes the RGB image data, and turns on the decode signals 1 to (n-4) when the RGB image data has a predetermined value.

The matching signals output from the first to fourth comparators 211 to 214 and the decode signals 1 to (n-4) output from the fixed exceptional color decoder 215 correspond to the corresponding AND gate AN.
It is supplied to one input terminal of D _{1 to} AND _n . On the other hand, an enable signal is supplied from the exceptional color enable register 216 to the other input ends of the AND gates AND _{1 to} AND _n . Therefore, by setting the exceptional color enable register 216, each match signal and decode signal are arbitrarily set to be valid or invalid.

The output signals of the AND gates AND _{1 to} AND _n are supplied to the encoder 217. Encoder 217
Encodes the outputs of the AND gates AND _{1 to} AND _n and supplies the code data to the exception display color designation register 218. The encoder 217 is an AND gate AN.
When a "1" level signal is output from any of D _{1 to} AND _n , the exception instruction signal is turned on.

The exceptional color display color designation register 218 has n entries, and the exceptional display data (displayed when the image data constitutes a character) stored in the entry designated by the signal from the encoder 217. Data that indicates the color to be output).

Referring again to FIG. 1, the conversion circuit 17
It operates according to the exception instruction signal supplied from the exception color detection circuit 21, and when the exception instruction signal is off, the error adder 15
Image data R2, G2, B supplied from the error adder 15 while generating display data to be supplied to the display 25 from the image data R2, G2, B2 supplied from
Error data GR1, GG1, GB1 corresponding to the error between 2 and the generated display data is generated. On the other hand, when the exception instruction signal is on, the exceptional display data supplied from the exceptional color detection circuit 21 is supplied to the display 25 as display data, and the error data GR1, GG1, GB1 are set to "0".

FIG. 3 shows a configuration example of the conversion circuit 17. As shown in the figure, the 7-bit image data R2, G2, B2 supplied from the error adder 15 is converted into the bit number conversion circuit 17
1 to 173. Bit number conversion circuits 171-1
73 compares input data with a predetermined threshold value, converts 7-bit data into 2-bit (4 steps) image data R3, G3, B3, and outputs it to the display data generation table 174.

The display data generation table 174 has the structure shown in FIG. 4, for example, and has image data R3, G3, B.
Display data capable of displaying a color closest to the color indicated by the image data in the entry indicated by the concatenated data of 3 (display voltage indicates the applied voltage because the display 25 is a birefringence control type liquid crystal display element). Voltage data). That is, the data that indicates the colors that can be actually displayed is stored. Further, in each entry, the difference between the image data R3, G3, B3 and the RGB data representing the color defined by the display data (image data R3, G3,
Error data R4, G4, B4 corresponding to the difference between the color designated by B3 and the color actually displayed) is stored.

The display data generation table 174 supplies the display data stored in the entry designated by the concatenated data of the image data R3, G3, B3 to the selector 175, and subtracts the error data R4, G4, B4 from the subtractor 176. ~
Supply to 178.

The selector 175 outputs the exception display data from the exception color detection circuit 21 when the exception instruction signal from the exception color detection circuit 21 is at "1" level, that is, when the image data indicates the exception color. When the exceptional instruction signal from the exceptional color detection circuit 21 is at "0" level, the display data from the display data generation table 174 is selected and supplied to the display 25. The subtracters 176 to 178 are cleared by the exception instruction signal from the exception color detection circuit 21, and the image data R2, G2, B2 to the error data R4, respectively.
G4, B4 are subtracted, and error data GR1, GG1, GB
Output as 1.

Referring again to FIG. 1, the error calculation circuit 19
Generates error data of each color of RGB to be added to the image data of the pixel to be processed by multiplying the error data of pixels in the vicinity of the pixel to be processed by a weight and further adding them.

FIG. 5 shows the configuration of the error calculation circuit 19.
As shown in the figure, the error calculation circuit 19 is composed of arithmetic circuits of the same configuration arranged in each of RGB, and each arithmetic circuit has one line (one scanning line of the display 25).
A shift register 191 that stores error data of +1 pixel (that is, 641 pixels), a multiplier 192 that multiplies the error data of the upper right pixel of the pixel of interest (the pixel currently being processed) by a weight Wa, A multiplier 193 that multiplies the error data of the upper pixel of the pixel by the weight Wb, and a multiplier 194 that multiplies the error data of the upper left pixel of the target pixel by the weight Wc.
And a multiplier 195 that multiplies the error data of the pixel on the left side of the pixel of interest by a weight Wd, and an adder 196 that adds the outputs of the multipliers 192 to 195 and outputs the error data GR2, GG2, and GB2. It

Since the error data of each pixel is sequentially transferred in the shift register, the error data of the left pixel of the pixel of interest is stored in the first register regardless of the position of the pixel to be processed, and the error data of the upper right pixel is stored. The error data is stored in the 639th register, the error data of the upper pixel is stored in the 640th register, and the error data of the upper left pixel is stored in the 641st register.

With such a configuration, the error Wa of the upper right pixel of the pixel of interest X shown in FIG. 6, the error Wb of the upper pixel, the error Wc of the upper left pixel, and the error Wc of the left pixel of FIG. The sum of Wd is added to the image data of the target pixel X. Also, the error data Wa of the target pixel X is diffused to the lower left pixel, the error data Wb of the target pixel X is diffused to the lower pixel, and the error data Wc of the target pixel X is diffused to the lower right pixel. , Wd of the error data of the target pixel X is diffused to the right pixel.

Next, the operation of the data processing device having the configuration shown in FIGS. 1 to 5 will be described. First, the fixed exceptional color decoder 215 of the exceptional color detection circuit 21 is programmed to turn on a corresponding decode signal when image data defining a color representing a character is input. In addition, the image data of the display color of the character is set in the exceptional color register 23 with 3 bits for each RGB. Further, a signal for effectively setting either the fixed exception color set in the fixed exception color decoder 215 or the exception color set in the exception color register 23 is set in the exception color enable register 216.

For ease of understanding, as shown in FIG. 7A, it is assumed that characters are displayed in a dark red color on a black background of the original image. In such a setting, image data indicating dark red is set in either the fixed exception color decoder 215 or the exception color register 23. Also, a signal for activating "dark red" set in the exceptional color enable register 216 is set. In this example, image data corresponding to "dark red" is set in the first register of the exceptional color register 23.

When the image data generator 11 outputs the analog image signal RGB representing the background "black", this signal is
The A / D converter 13 converts each 6-bit digital image data DR, DG, DB. Converted RGB
The upper 3 bits of the digital image data DR, DG, DB are supplied to the exceptional color detection circuit 21.

In this example, no image data representing black is set in the exceptional color register 23. Therefore, the comparators 211 to 214 output the "0" level coincidence signal. The fixed exceptional color decoder 215 also sets all output signals to the "0" level. Therefore, regardless of the setting of the exceptional color enable register 216, the outputs of the AND gates AND _{1 to} AND _n are all at the “0” level.

The encoder 217 outputs an exception instruction signal of "0" level because all the input data is "0" level.

The error calculation circuit 19 uses the error diffusion method to
Calculate the error to be added to the image data. To calculate this error, the multipliers 192 to 195 of the error calculation circuit 19 are used.
Multiplies the data of the first register of the shift register 191 by the weight Wd, and the data of the 639th register is weighted by Wa.
, The data in the 640th register is multiplied by the weight Wc, the data in the 641st register is multiplied by the weight Wc, the adder 196 adds the multiplication results, and the error data GR2, G2
Output as G2 and GB2.

The error adder 15 receives the 6-bit image data DR, DG, DB supplied from the A / D converter 13 and the error data GR2, G supplied from the error calculation circuit 19.
G2 and GB2 are added, and addition data R2, G2 and B2 are output. The bit number conversion circuits 171 to 173 convert the supplied addition data R2, G2, B2 into 2-bit image data R3, G3, B3, and supply them to the display data generation table 174.

The display data generation table 174 reads the display data stored in the entries of the image data R3, G3, B3 which are addressed by a total of 6 bits.
This display data is data indicating a voltage for displaying a color (here, “black”) closest to “black” defined by the image data R3, G3, and B3 among colors that can be displayed on the display 25. . The selector 175 selects the display data (voltage data for displaying “black”) output from the display data generation table 174 because the exception instruction signal is at “0” level and supplies it to the display 25. The display 25 A / D-converts the display data and applies it to the corresponding pixel to display "black".

Further, the display data generation table 174 includes image data R4 representing the color displayed by the display data,
The G4 and B4 are supplied to the subtractors 176 to 178.

If there is an error between the color defined by the image data R3, G3, B3 and the display data, the subtracter 17
6 to 178 subtract the image data R4, G4, B4 from the image data R2, G2, B2 supplied from the error adder 15 and output error data GR1, GG1, GB1. These error data GR1, GG1, GB1 are A / D
Image data DR, DG, DB supplied from the converter 13
And the error data of neighboring pixels (upper left, upper, upper right, left pixels) and those diffused to this pixel and the error of the color actually displayed. Down, down,
This is the error that should be distributed to the lower left pixels. This error data GR1, GG1, GB1 is stored in the error calculation circuit 19
Of the shift register 191.

The operation described above is performed by the image data generator 11
Is repeated each time the analog image signal RGB is output, and the display is performed while sequentially diffusing the error between the analog image signal RGB and the color actually displayed to the adjacent pixels.

Next, when the image data generator 11 outputs an analog image signal RGB representing the character "dark red", this image signal is converted by the A / D converter 13 into 6-bit digital image data DR, DG. , Converted to DB. Converted RGB digital image data DR, DG, DB
The upper 3 bits of are supplied to the exceptional color detection circuit 21. As described above, data representing "dark red" is set in the first register of the four registers forming the exceptional color register 23. Therefore, the comparator 211 outputs a "1" level coincidence signal.

The exceptional color enable register 216 sets the signal supplied to the AND gate AND ₁ to "1" level to open the AND gate AND ₁ . Therefore, the output of AND ₁ is at "1" level. Therefore, the encoder 21
7 sets the exception instruction signal to the "1" level.

Further, the encoder 217 encodes the outputs of the AND gates AND _{1 to} AND _n and supplies them to the exceptional display color designation register 218. The exceptional display color designation register 218 reads and outputs the display data set in the corresponding register using the supplied encoded data as an address. Here, the display data representing “bright red” is output as the display data.

The selector 175 of the conversion circuit 17 selects and outputs this exception display data because the exception instruction signal is at "1" level, and supplies it to the display 25. Therefore, the display 25 displays "bright red" on the corresponding pixel. Since the exception instruction signal is at "1" level,
The subtracters 176 to 178 are cleared and the error data GR
1, GG1 and GB1 are “0”. Therefore, “0” is newly input to the shift register 191 of the error calculation circuit 19.

In this way, the application of the error diffusion method is excluded for "dark red" for displaying characters, and the characters are displayed in predetermined "bright red".

In the prior art, the original image is the image shown in FIG. 7 (A), and like the present embodiment, it can display "black" and "bright red", but drives a display element that cannot display "dark red". In this case, in the background portion, an error does not occur between "black" which is the color to be displayed and "black" which is the displayed color, and no particular problem occurs. However, in the dots forming the character, an error occurs between the desired color "dark red" and the displayable color "bright red". In this case, the difference in brightness becomes an error and is distributed to the adjacent pixels. Therefore, a part of the characters is displayed darker than "dark red". For this reason, as shown in FIG. 7B, it becomes impossible to distinguish between the character and the background, and the character is crushed and displayed. On the other hand, according to the present invention, it is possible to prevent the characters from being crushed as shown in FIG. That is, when the liquid crystal display element is a birefringence control type, since the voltage applied to the liquid crystal and the display color have a one-to-one correspondence, the characters are displayed when the error diffusion method is applied to the data displaying the background. The same voltage may be selected corresponding to the data for displaying and the data for displaying the background, and the characters are displayed discontinuously as shown in FIG. 7B, which makes it difficult to read. . On the other hand, if the display control circuit of this embodiment is used, the error diffusion method is not applied to the character portion, and the character is displayed in a color corresponding to one predetermined voltage. Is clearly displayed and can be clearly read.

In the above embodiment, in order to determine whether or not the image data identifies a character, it is determined whether or not the color designated by the image data is a specific color. You may use the discrimination method of. For example, the image data generation unit 11 may determine whether or not the image data forms a character by using a specific bit of the image data as a flag and determining whether the specific bit is on or off. . Further, when the image data is detected by the exceptional color detection circuit 21, the exceptional color detection circuit 21 outputs the exceptional display data, but the conversion circuit 17 corresponds to the image data R2, G2, D2 in which no error is added. Display data may be output.

In the above-mentioned embodiment, the case where the liquid crystal display element of the multiple control system is used as the display 25 has been described, but it is also possible to use a liquid crystal display element using a color filter, a CRT or the like. In this case, the display data generation table shown in FIG. 5 is not used,
For example, the main data R3, G of the bit number conversion circuit 174
3 and B3 are supplied to the selector and subtraction circuits 176 to 178.

The circuit configuration, the number of bits, and the like shown in the above embodiments can be arbitrarily changed. For example, in the above embodiment, the application of the error diffusion is excluded only for the colors set in the exceptional color register 23 and the fixed exceptional color decoder 215, which are set active by the exceptional color enable register 216. However, the exceptional color enable register 216 and AND gates AND _{1 to} AND _n
Need not necessarily be provided. Also, exception color register 2
3 and comparators 211 to 214, and fixed exception color decoder 2
One of 15 may be removed.

[0048]

According to the present invention, in the display control circuit applying the error diffusion method, the application of the error diffusion is stopped for the image data forming the character, so that the character is prevented from being crushed due to the error diffusion. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a display device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an exceptional color detection circuit shown in FIG.

FIG. 3 is a block diagram showing a configuration of a conversion circuit shown in FIG.

FIG. 4 is a diagram showing a configuration example of a display data generation table shown in FIG.

5 is a block diagram showing a configuration of an error calculation circuit shown in FIG.

FIG. 6 is a diagram for explaining error diffusion.

FIG. 7 is a diagram showing an original image and a display example.

[Explanation of symbols]

11 ... Image data generation unit, 13 ... A / D converter, 15
... Error adder, 17 ... Conversion circuit, 19 ... Error calculation circuit, 21 ... Exception color detection circuit, 23 ... Exception color register,
25 ... Display, 171-173 ... Bit number conversion circuit, 174 ... Display data generation table, 175 ... Selector, 176-178 ... Subtractor, 191 ... Shift register, 192 ... 195 ... Multiplier, 196 ... Adder,
211 to 214 ... Comparator, 215 ... Fixed exception color decoder, 216 ... Exception color enable register, 217 ... Encoder, 218 ... Exception color display color designation register

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04N 5/66 102 G06F 15/68 310A

Claims (8)

[Claims] 1. Receiving means for receiving image data; display data generating means for applying a error diffusion method to the image data received by the receiving means to generate display data for driving a display device; and the receiving means. Discriminating means for discriminating whether or not the image data received by the image forming device is character data, and the display data when the image data is discriminating by the judging device. A display control circuit using the error diffusion method, comprising: a control means for stopping application of the error diffusion method to the generation means and generating a display signal corresponding to the image data. 2. The discriminating means discriminates that the image data is data forming a character when the image data indicates a predetermined color. A display control circuit using the error diffusion method described in 1. 3. The display data generating means includes an error calculating means for obtaining a sum of errors diffused to the pixel to be processed from error data of pixels in the vicinity of the pixel to be processed, and the error calculating means for the image data. An addition means for adding the sum of the errors calculated by, a display data output means for outputting display data for displaying a color close to a color defined by the output data of the addition means, and an output of the addition means. An error generating means for obtaining an error from data defining a color displayed by the display data output by the output means, and supplying the error to the error calculating means in order to diffuse the obtained error to adjacent pixels. A display control circuit using the error diffusion method according to claim 1 or 2. 4. The error generating means comprises means for setting the error supplied to the error calculating means to 0 when the determining means determines that the image data constitutes a character.
A display control circuit using the error diffusion method according to claim 3. 5. The determining means determines, based on a decoding means for decoding the image data received by the receiving means, and an output signal of the decoding means, whether or not the image data constitutes a character. The display control circuit using the error diffusion method according to claim 1, further comprising: 6. The discrimination means compares the exceptional color storage means for storing data with the data stored in the exceptional color storage means and the image data received by the receiving means,
6. A display control circuit using the error diffusion method according to claim 1, further comprising: a comparison unit that determines that the image data forms a character when they match. 7. The determining means determines, from the decoding means for decoding the image data received by the receiving means, and the output signal of the decoding means, whether or not the image data constitutes a character. The display control circuit using the error diffusion method according to claim 1, further comprising: 8. A display device is constituted by a display device for displaying a color according to an applied voltage, and the display data generating means applies the error diffusion method to the image data to obtain a color closest to a color to be displayed. 8. The display control circuit using the error diffusion method according to claim 1, wherein display data representing a voltage for displaying is output.