JP2013186416A - Device for performing gradation conversion of image data, method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow an image with high image quality to be also displayed while allowing an image subjected to halftone processing to be displayed at a high speed.SOLUTION: An image processing section acquires image data before conversion with (a) gradation. The image processing section generates first image data after conversion indicating an image obtained by performing halftone processing on an image indicated in the image data before conversion in accordance with a blue noise masking method. The display section displays the image subjected to the halftone processing according to the first image data after conversion. Subsequently, the image processing section quickly generates second image data after conversion indicating an image obtained by performing the halftone processing on the image indicated in the image data before conversion in accordance with an error diffusion method or does so after a predetermined period of time has elapsed or after waiting for instructions by a user in accordance with a power supply state. The display section overwrites the image subjected to the halftone processing according to the second image data after conversion on an image having been already displayed and displays the image overwritten thereby.

Description

  The present invention relates to a technique for converting image data representing an image by a collection of pixels having a predetermined number of gradation densities into image data having a different number of gradations.

  There is a technique (halftone technique) for converting image data having a large number of gradations (for example, image data having 16 gradations) into image data having a small number of gradations (for example, image data having two gradations). According to the halftone technology, by arranging halftone dots having different sizes and densities, image data that is illusioned with an image expressed in halftones by human eyes is generated even with two gradations.

  According to the halftone technology, an image such as a photograph including many halftones can be displayed relatively beautifully in a display device having a display capability of a small number of gradations such as 2 gradations and 4 gradations. . Further, according to the halftone technique, the number of gradations is reduced, so that the time required for rewriting the screen in the display device is shortened as compared with the case of rewriting the screen according to the image data before conversion. .

  As a document describing an image display method using a halftone technique, for example, there is Patent Document 1. In the technique described in Patent Document 1, ghosts and the like in a bistable display can be reduced by using image data after halftone processing used for previous image data generation for subsequent image data generation. .

Special table 2010-515926

  As an example of a display device having a display capability with a small number of gradations such as two gradations and four gradations, there is an electrophoretic display device, for example.

  An electrophoretic display device includes, for example, a large number of microcapsules arranged on a two-dimensional plane containing black electrophoretic particles that are positively charged and white electrophoretic particles that are negatively charged. And a large number of electrode pairs arranged so as to sandwich the microcapsule. When a voltage corresponding to the gradation value indicated by each of the pixel data included in the image data is applied to each of these electrode pairs, either black or white electrophoretic particles are subjected to Coulomb force on one electrode side. Attracted by As a result, display of an image indicated by the image data is realized.

  In an image displayed by an electrophoretic display device, for example, black and white of each pixel constituting the image is clearly distinguished as compared with an image displayed on a liquid crystal display, for example. In a display device having such characteristics, generally, when image data generated by a dot dispersion type halftone technique having blue noise characteristics such as an error diffusion method or a blue noise mask dither method is used, high image quality is obtained. An image can be displayed.

  Comparing the sufficiently optimized error diffusion method and the blue noise mask dither method, generally, an image displayed according to image data generated by the error diffusion method has higher image quality. In particular, when characters or thin lines drawn at a low density are included on a white background, the image data generated by the blue noise mask dither method may cause inconveniences such as line breaks. However, such an inconvenience does not easily occur with the error diffusion method.

  On the other hand, the time required for screen rewriting generally requires a longer time in the error diffusion method than in the blue noise mask dither method. In dithering methods such as the blue noise mask dithering method, for each pixel, the tone after conversion by simple comparison between the tone value before conversion and a predetermined threshold value corresponding to the pixel position of the pixel. The value is determined.

  On the other hand, in the error diffusion method, in the conversion of a certain pixel, the gradation value of the pixel is not compared with the threshold value, but the density generated before and after the conversion of the neighboring pixel with respect to the gradation value of the pixel. A corrected gradation value obtained by adding a correction value which is a part of an error value indicating a difference is compared with a threshold value.

  Therefore, the error diffusion method generally requires a larger amount of computation than the dither method, and conversion processing for a plurality of pixels cannot be performed in parallel at the same time, so that the conversion processing requires more time than the dither method.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a means for displaying a halftoned image at a high speed and displaying a high-quality image. .

In order to achieve the above object, the present invention provides:
pre-conversion image data acquisition means for acquiring, as pre-conversion image data, image data including a plurality of pre-conversion pixel data indicating pixels included in an image of a gradation (where a is a predetermined natural number satisfying a> 2) ,
Among the gradation values of one pre-conversion pixel data included in the pre-conversion image data and (b-1) dither threshold values (where b is a predetermined natural number satisfying a>b> 1) First pixel data conversion means for generating first converted pixel data of b gradation by comparison with one of the dither threshold values set for the pixel position of the pixel data before conversion;
A gradation value after correction that is a value obtained by adding a gradation value of the one pre-conversion pixel data and a correction value that is a diffusion error value distributed to the one pre-conversion pixel data according to an error diffusion method; Second pixel data conversion means for generating second converted pixel data of b gradation based on the magnitude relationship with one error diffusion threshold;
When the second post-conversion pixel data is generated by the second pixel data conversion means, the second post-conversion pixel data is converted to a from the post-correction gradation value related to the one pre-conversion pixel data. Pre-conversion pixel data not yet used in the conversion by the second pixel data conversion means among the plurality of pre-conversion pixel data, which is a value obtained by subtracting the gradation value in the case of gradation. In addition, each of the one or more pre-conversion pixel data selected according to a predetermined rule that forms a continuous area with the one pre-conversion pixel data on the two-dimensional array is distributed as the correction value according to the predetermined rule. Error diffusion means to
After the data including the first converted pixel data set is output as the first converted image data to the display unit capable of displaying the b-gradation image, the second converted pixel data set is output. A converted image data output means for outputting data including the image data as second converted image data is proposed.

  According to the above-described apparatus of the present invention, an image halftoned according to the dither method or the like is displayed at high speed, and then the image is overwritten and displayed by an image halftoned according to the error diffusion method. Therefore, the user does not feel the stress caused by the delay in image display, and when he wants to browse the displayed image in detail, he / she does not feel the inconvenience that it is difficult to distinguish the image by browsing the high-quality image displayed by overwriting. .

In the apparatus according to the present invention,
The second pixel data conversion unit compares the corrected gradation value with at least one of the (b-1) error diffusion threshold values, and thereby converts the second converted pixel data of b gradation. The configuration of generating the may be adopted.

  According to the apparatus having this configuration, the error diffusion threshold setting process is simplified by using (b-1) preset error diffusion thresholds.

In the apparatus according to the present invention,
A configuration is adopted in which storage means for storing threshold matrix data including a collection of dither threshold data, which is data indicating the (b-1) dither threshold values, is provided for each of the plurality of pixels arranged in a two-dimensional array. Also good.

  According to the apparatus having this configuration, since the dither threshold value is obtained by reading the dither threshold value data from the stored threshold matrix data, the process of acquiring the dither threshold value is simplified.

In the apparatus according to the present invention,
Trigger data acquisition means for acquiring trigger data indicating a trigger for generation of second converted pixel data by the second pixel data conversion means;
The second pixel data conversion unit may employ a configuration in which a process of generating second post-conversion pixel data is started in accordance with the trigger data acquired by the trigger data acquisition unit.

  According to the apparatus having this configuration, the image conversion process according to the error diffusion method is performed only when high-quality image display is necessary, so that the inconvenience of wasting power required for the conversion process is avoided. The

In the apparatus according to the present invention,
One or more power supply means each capable of supplying power;
Power supply state specifying means for specifying the state of power supply by the one or more power supply units,
The trigger data acquisition means can acquire a plurality of types of trigger data,
The second pixel data conversion means follows trigger data of a type predetermined according to the power supply state specified by the power supply state specifying means among the trigger data acquired by the trigger data acquisition means. A configuration of starting the process of generating the second post-conversion pixel data may be employed.

  According to the apparatus having this configuration, for example, when a sufficient amount of power can be obtained from an external power source, image conversion processing according to the error diffusion method can be performed quickly, and only a limited amount of power can be obtained from the built-in battery. In this case, image conversion processing according to the error diffusion method is performed at a timing suitable for the power supply, such as image conversion processing according to the error diffusion method after waiting for a user instruction. The result is a desirable balance between display comfort and device uptime.

In the apparatus according to the present invention,
Trigger data acquisition means for acquiring trigger data indicating a trigger for output of the second converted image data by the converted image data output means;
The post-conversion image data output means may be configured to start outputting the second post-conversion pixel data in accordance with the trigger data acquired by the trigger data acquisition means.

  According to the apparatus having this configuration, an image display process according to the error diffusion method is performed only when display of a high-quality image is necessary. Therefore, inconvenience that power required for the display process is wasted in the display unit. Is avoided.

In the apparatus according to the present invention,
One or more power supply means each capable of supplying power;
Power supply state specifying means for specifying the state of power supply by the one or more power supply units,
The trigger data acquisition means can acquire a plurality of types of trigger data,
The converted image data output means includes the trigger data acquired by the trigger data acquisition means according to trigger data of a type predetermined according to the power supply state specified by the power supply state specifying means. A configuration in which output of the second pixel data after conversion is started may be employed.

  According to the apparatus of this configuration, for example, when a large amount of power can be supplied from an external power source to the display means, an image according to the error diffusion method is quickly output to the display means, and the display means is limited from the built-in battery. When only the specified amount of power can be supplied, an image according to the error diffusion method is output to the display means after waiting for an instruction from the user. Is done. The result is a desirable balance between display comfort and device uptime.

In the apparatus according to the present invention,
The second pixel data converting means converts one pre-conversion pixel data into second post-conversion pixel data when at least one gradation value of b gradations is set as a target gradation value. When the gradation value indicated by the first post-conversion pixel data generated by the first pixel data conversion unit based on the one pre-conversion pixel data is one of the at least one target gradation value, The gradation band expands at least one of the upper limit gradation value and the lower limit gradation value of the a gradation band including the gradation value when the target gradation value is represented by the a gradation. After the change, it is determined whether the corrected gradation value indicated by the corrected pixel data related to the one pre-conversion pixel data is included in the gradation band, and the corrected gradation level is included in the gradation band. Pixel data indicating the target gradation value when it is determined that a tone value is included When it is determined that the corrected gradation value is not included in the gradation band, pixel data indicating gradation values other than the target gradation value is generated as the second converted pixel data. A configuration of generating as post-pixel data may be employed.

  According to the apparatus having this configuration, when converting an image by the error diffusion method, a threshold value set so as to increase the probability of being the same as the gradation value of an already displayed image is used. The number of pixels that require redrawing is reduced, and the power consumption is reduced.

In the apparatus according to the present invention,
The pre-conversion image data includes pixel data generated according to drawing instruction data for instructing drawing of a character or a line,
Drawing instruction data acquisition means for acquiring the drawing instruction data;
Based on the drawing instruction data, conversion target area specifying data for specifying a conversion target area that specifies a conversion target area in which a character or line is drawn on a two-dimensional array is generated. And generating means,
The post-conversion image data output means does not output the second post-conversion image data relating to pixels not included in the area indicated by the conversion target area designation data on the two-dimensional array to the display means. It may be adopted.

  According to the apparatus having this configuration, overwriting by an image according to the error diffusion method is performed only for an area including characters and lines in which the image quality by the error diffusion method is remarkably superior compared to the systematic dither method. Display is performed. As a result, power consumption required for redrawing is reduced without much image quality degradation.

In the apparatus according to the present invention,
An area including the edge position on the two-dimensional array, wherein a position on the two-dimensional array in which the index indicating the degree of density change is equal to or greater than a predetermined threshold is specified as an edge position in the image indicated by the pre-conversion image data. Conversion target area specifying data generating means for generating conversion target area specifying data, which is data indicating the conversion target area,
The post-conversion image data output means does not output the second post-conversion image data relating to pixels not included in the area indicated by the conversion target area designation data on the two-dimensional array to the display means. It may be adopted.

  According to the apparatus having this configuration, overwriting display with an image in accordance with the error diffusion method is performed only on a region including an edge in which the image quality by the error diffusion method is remarkably superior as compared with the systematic dither method. Done. As a result, power consumption required for redrawing is reduced without much image quality degradation.

In the apparatus according to the present invention,
The second pixel data converting means converts the pre-conversion pixel data into the second post-conversion pixel data based on the gradation value indicated by the one pre-conversion pixel data. A configuration in which at least one of the upper limit gradation value and the lower limit gradation value is determined may be employed.

  According to the apparatus having this configuration, since the threshold value corresponding to the gradation value before conversion of the pixel to be converted is used in the conversion, for example, the gradation value before the conversion has a density at which the gradation changes in the converted image. In the case of the vicinity of the indicated gradation value, the number of pixels that need to be redrawn can be effectively reduced by a method such as using a threshold value for maintaining the current gradation value for conversion.

In the apparatus according to the present invention,
The pre-conversion image data is the (i + 1) -th pre-conversion image data, and the second post-conversion image data generated based on the (i + 1) -th pre-conversion image data is the (i + 1) -th post-conversion image data. Until the (i + 1) th converted image data is output to the display means by the converted image data output means, the image data indicating the image displayed on the display means is i-th When the pre-conversion image data obtained by the pre-conversion image data acquisition means and used for the conversion of the i-th post-conversion image data is used as the post-conversion image data,
The second pixel data conversion means converts the first pre-conversion pixel data into the second post-conversion pixel data in the conversion related to the (i + 1) th pre-conversion image data. The upper limit gradation value and the lower limit gradation of the gradation band based on the gradation value indicated by the pixel data whose position in the two-dimensional array is the same as the one pre-conversion pixel data among the pixel data included in A configuration in which at least one of the values is determined may be employed.

  According to the apparatus having this configuration, the gradation value of the pixel at the same position in the converted image of the newly displayed image is determined according to the gradation value of the image before conversion of the currently displayed image. The Therefore, for example, the gradation value of the image before conversion of the currently displayed image is compared with the gradation value of the image before conversion of the newly displayed image, and the threshold value is set according to the direction in which they change. By changing the number of pixels, the number of pixels that need to be redrawn can be effectively reduced.

In the apparatus according to the present invention,
The pre-conversion image data is the (i + 1) -th pre-conversion image data, and the second post-conversion image data generated based on the (i + 1) -th pre-conversion image data is the (i + 1) -th post-conversion image data. Until the (i + 1) th converted image data is output to the display means by the converted image data output means, the image data indicating the image displayed on the display means is i-th When the pre-conversion image data obtained by the pre-conversion image data acquisition means and used for the conversion of the i-th post-conversion image data is used as the post-conversion image data,
The second pixel data converting means converts the pre-conversion pixel data into the second post-conversion pixel data in the conversion related to the (i + 1) -th pre-conversion image data. Among the gradation bands used for each pixel data in the conversion related to the i-th pre-conversion image data, the one of the gradation bands indicated by the same pixel data as the one-dimensional pixel data and the position on the two-dimensional array. Based on at least one of the upper limit gradation value and the lower limit gradation value, at least one of the upper limit gradation value and the lower limit gradation value of the gradation band used for the conversion of the one pre-conversion pixel data is determined. Such a configuration may be adopted.

  According to the apparatus having this configuration, for example, in the conversion of each of two images displayed in succession, the gradation band used for conversion of a certain pixel of the image displayed earlier is the same as the image displayed later. Data indicating a suitable combination with the gradation band used for pixel conversion is prepared in advance, and a gradation band used for each pixel in the conversion of a new image is determined according to the combination. Thus, it is possible to effectively reduce the number of pixels that require redrawing.

In the apparatus according to the present invention,
A configuration including the display means may be employed.

  According to the apparatus having this configuration, a display apparatus capable of both high-speed display and high-quality display of a halftoned image can be obtained.

In the apparatus according to the present invention,
The display means displays the image among the currently displayed pixels when displaying an image according to the first converted image data or the second converted image data received from the converted image data output means. Redrawing is performed on at least some of the pixels displayed with the same gradation value as the gradation value indicated by the pixel data included in the first converted image data or the second converted image data. A configuration of “not present” may be adopted.

  According to the apparatus having this configuration, at least a part of pixels in which the gradation value in the currently displayed image and the gradation value in the next image to be displayed do not change are applied for redrawing. This saves energy consumption for redrawing.

In the apparatus according to the present invention,
The display means displays the image among the currently displayed pixels when displaying an image according to the first converted image data or the second converted image data received from the converted image data output means. A pixel that is displayed with a gradation value different from the gradation value indicated by the pixel data included in one converted image data or the second converted image data, and a region that is continuous with the pixel and defined by a predetermined rule A configuration may be adopted in which redrawing is performed only with respect to pixels included in.

  According to the apparatus of this configuration, the application for redrawing or the like is performed only with respect to a pixel in which the gradation value in the currently displayed image is different from the gradation value in the image to be displayed next and pixels around the pixel. Since other pixels are not applied for redrawing, energy consumption required for redrawing is reduced, and only pixels with different gradation values are redrawn in the preceding and following images. In comparison, for example, when the display means has a characteristic that the outer edge portion of the rewritten pixel is likely to be blurred, it may be desirable to suppress deterioration in image quality due to bleeding.

The present invention also provides:
a pre-conversion image data acquisition step of acquiring, as pre-conversion image data, image data including a plurality of pre-conversion pixel data indicating pixels included in an image of a gradation (where a is a predetermined natural number satisfying a>2); ,
Among the gradation values of one pre-conversion pixel data included in the pre-conversion image data and (b-1) dither threshold values (where b is a predetermined natural number satisfying a>b> 1) A first pixel data conversion step of generating first converted pixel data of b gradation by comparison with one dither threshold value set for the pixel position of the pixel data before conversion;
A gradation value after correction that is a value obtained by adding a gradation value of the one pre-conversion pixel data and a correction value that is a diffusion error value distributed to the one pre-conversion pixel data according to an error diffusion method; A second pixel data conversion step of generating second converted pixel data of b gradation based on a magnitude relationship with one error diffusion threshold;
When the second post-conversion pixel data is generated in the second pixel data conversion step, the second post-conversion pixel data is converted from the post-correction gradation value related to the one pre-conversion pixel data. Pre-conversion pixel data that has not yet been used in the conversion in the second pixel data conversion step among the plurality of pre-conversion pixel data, which is a value obtained by subtracting the gradation value in the case of gradation In addition, each of the one or more pre-conversion pixel data selected according to a predetermined rule that forms a continuous area with the one pre-conversion pixel data on the two-dimensional array is distributed as the correction value according to the predetermined rule. An error diffusion step to
After the data including the first converted pixel data set is output as the first converted image data to the display unit capable of displaying the b-gradation image, the second converted pixel data set is output. A post-conversion image data output step of outputting data including the image data as second post-conversion image data is proposed.

  According to the method according to the present invention, the same effects as those of the device according to the present invention can be obtained.

The present invention also provides:
On the computer,
pre-conversion image data acquisition processing for acquiring, as pre-conversion image data, image data including a plurality of pre-conversion pixel data indicating pixels included in an image of a gradation (where a is a predetermined natural number satisfying a> 2) ,
Among the gradation values of one pre-conversion pixel data included in the pre-conversion image data and (b-1) dither threshold values (where b is a predetermined natural number satisfying a>b> 1) A first pixel data conversion process for generating first converted pixel data of b gradation by comparison with one dither threshold value set for the pixel position of the pixel data before conversion;
A gradation value after correction that is a value obtained by adding a gradation value of the one pre-conversion pixel data and a correction value that is a diffusion error value distributed to the one pre-conversion pixel data according to an error diffusion method; A second pixel data conversion process for generating second converted pixel data of b gradation based on a magnitude relationship with one error diffusion threshold;
When the second post-conversion pixel data is generated in the second pixel data conversion process, the second post-conversion pixel data is converted from the post-correction gradation value related to the one pre-conversion pixel data. Pre-conversion pixel data that has not yet been used in the conversion in the second pixel data conversion processing among the plurality of pre-conversion pixel data, which is a value obtained by subtracting the gradation value in the case of gradation. In addition, each of the one or more pre-conversion pixel data selected according to a predetermined rule that forms a continuous area with the one pre-conversion pixel data on the two-dimensional array is distributed as the correction value according to the predetermined rule. Error diffusion processing to
After the data including the first converted pixel data set is output as the first converted image data to the display unit capable of displaying the b-gradation image, the second converted pixel data set is output. A program that executes post-conversion image data output processing for outputting data including a second post-conversion image data is proposed.

  According to the program according to the present invention, the apparatus according to the present invention is realized using a general-purpose computer.

It is the figure which showed the external appearance of the electronic device concerning one Embodiment of this invention. It is the block diagram which showed the hardware constitutions of the electronic device concerning one Embodiment of this invention. It is the figure which showed the cross section of the display part concerning one Embodiment of this invention. It is a figure for demonstrating the structure of the circuit of the circuit layer concerning one Embodiment of this invention. It is a figure for demonstrating the structure of the pixel drive circuit concerning one Embodiment of this invention. It is the block diagram which showed the function structure of the image process part concerning one Embodiment of this invention. It is the flowchart which showed the flow of the process which the 2nd conversion part concerning one Embodiment of this invention performs. It is the flowchart which showed the flow of the process which the 2nd conversion part concerning one Embodiment of this invention performs. It is the figure which illustrated a part of dither matrix data which the 2nd conversion part concerning one Embodiment of this invention uses. It is the block diagram which showed the function structure of the 2nd conversion part concerning one Embodiment of this invention. It is the flowchart which showed a part of flow of the process which the 2nd conversion part concerning one Embodiment of this invention performs. It is the figure which showed the mode of conversion of the gradation value performed in the image processing part concerning one Embodiment of this invention. It is the figure which showed the mode of the change of the threshold value used for the conversion of the gradation value performed in the image process part concerning the modification of this invention. It is the block diagram which showed the function structure of the image process part concerning the modification of this invention. It is the block diagram which showed the function structure of the image process part concerning the modification of this invention. It is the block diagram which showed the structure of the electronic device and display apparatus concerning one modification of this invention.

[First Embodiment]
FIG. 1 is a diagram illustrating an appearance of an electronic device 1000 according to an embodiment of the present invention. The electronic device 1000 is a display device that displays an image including characters, lines, figures, photographs, and the like. The electronic device 1000 includes a display unit 101 that displays an image. In addition, the electronic device 1000 includes buttons 9A to 9F as operation units operated by the user.

  FIG. 2 is a block diagram illustrating a hardware configuration of the electronic device 1000. As shown in FIG. 2, each unit of the electronic device 1000 (excluding the external power input unit 110 and the battery 111) is connected to the BUS. Each unit of the electronic device 1000 exchanges data between the units via the BUS.

  The display unit 101 includes a display element having a memory property, and is a display device that maintains a displayed image even when no voltage is applied to the display element. In the present embodiment, the display unit 101 includes a display element having electrophoretic particles and displays a monochrome image.

  FIG. 3 is a view showing a cross section of the display unit 101. As shown in FIG. 3, the display unit 101 is roughly composed of a first substrate 10, an electrophoretic layer 20, and a second substrate 30. The first substrate 10 is a substrate in which a circuit layer is formed on an insulating and flexible substrate 11. The substrate 11 is made of polycarbonate in this embodiment. The substrate 11 is not limited to polycarbonate, and a resin material having lightness, flexibility, elasticity, and insulation can be used. Moreover, the board | substrate 11 may be formed with the glass which does not have flexibility. An adhesive layer 11a is provided on the surface of the substrate 11, and a circuit layer 12 is laminated on the surface of the adhesive layer 11a.

  FIG. 4 is a diagram for explaining a circuit configuration of the circuit layer 12. The circuit layer 12 includes a plurality of scanning lines 64 provided in the horizontal direction so as to cover the display region 55 and a plurality of data lines 65 provided in the vertical direction so as to be electrically insulated from the respective scanning lines. have. The circuit layer 12 includes a pixel electrode 13a (first electrode, see FIG. 3) and a TFT (Thin Film Transistor) corresponding to each intersection of the m rows of scanning lines 64 and the n columns of data lines 65. And a pixel driving circuit 66 configured as described above.

  Returning to FIG. 3, the description of the overall configuration of the display unit 101 will be continued. The electrophoretic layer 20 includes a binder 22 and a plurality of microcapsules 21 fixed by the binder 22, and is formed on the pixel electrode 13a. Note that an adhesive layer formed of an adhesive may be provided between the microcapsule 21 and the pixel electrode 13a.

  The binder 22 is not particularly limited as long as it has a good affinity with the microcapsule 21, an excellent adhesion with the electrode, and an insulating property. A dispersion medium and electrophoretic particles are stored in the microcapsule 21. As a material constituting the microcapsule 21, it is preferable to use a flexible material such as a gum arabic / gelatin compound or a urethane compound.

  Dispersion media include water, alcohol solvents (methanol, ethanol, isopropanol, butanol, octanol, methyl cellosolve, etc.), esters (ethyl acetate, butyl acetate, etc.), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.) , Aliphatic hydrocarbons (pentane, hexane, octane, etc.), alicyclic hydrocarbons (cyclohexane, methylcyclohexane, etc.), aromatic hydrocarbons (benzene, toluene, benzenes with long chain alkyl groups (xylene) Hexylbenzene, hebutylbenzene, octylbenzene, nonylbenzene, decylbenzene, undecylbenzene, dodecylbenzene, tridecylbenzene, tetradecylbenzene)), halogenated hydrocarbons (methylene chloride, chloroform, carbon tetrachloride) 1,2-dichloroethane, etc.), it can be any of such carboxylates, and the dispersion medium may be other oils. These substances can be used alone or in combination as a dispersion medium, and a surfactant or the like may be further blended to form a dispersion medium.

  Electrophoretic particles are particles (polymer or colloid) having the property of moving by an electric field in a dispersion medium. In the present embodiment, white electrophoretic particles and black electrophoretic particles are stored in the microcapsule 21. The black electrophoretic particles are particles made of a black pigment such as aniline black or carbon black, and are positively charged in this embodiment. The white electrophoretic particles are particles made of a white pigment such as titanium dioxide or aluminum oxide, and are negatively charged in this embodiment.

  The second substrate 30 includes a film 31 and a transparent electrode layer 32 (second electrode) formed on the lower surface of the film 31. The film 31 plays a role of sealing and protecting the electrophoretic layer 20 and is, for example, a polyethylene terephthalate film. The film 31 is transparent and has an insulating property. The transparent electrode layer 32 is made of a transparent conductive film such as an indium oxide film (ITO film).

  As described above, the display area 55 is provided with a plurality of data lines 65 arranged in parallel along the vertical direction and a plurality of scanning lines 64 arranged in parallel along the horizontal direction (see FIG. 4). The display area 55 is provided with a pixel driving circuit 66 corresponding to the intersection of the data line 65 and the scanning line 64.

  FIG. 5 is a diagram for explaining the configuration of the pixel driving circuit 66. In the present embodiment, in order to distinguish each scanning line 64, the scanning lines 64 shown in FIG. 4 are called the first, second, third,. You may want to Similarly, in order to distinguish each data line 65, the data lines shown in FIG. 4 are referred to as 1, 2, 3,..., (N−1), nth column in order from the left. There is.

  FIG. 5 shows a pixel driving circuit 66 corresponding to the intersection of the scanning line 64 in the first row and the data line 65 in the first column. The same pixel driving circuit 66 is provided at the intersection of the other data line 65 and the scanning line 64. However, since the configuration of each pixel driving circuit 66 is the same, the data in the first row is representatively shown here. The pixel driving circuit 66 corresponding to the intersection of the line and the first scanning line will be described, and the description of the other pixel driving circuits 66 will be omitted.

  In the pixel driving circuit 66, the gate of the TFT 61 is connected to the scanning line 64, and the source of the TFT 61 is connected to the data line 65. The drain of the TFT 61 is connected to the pixel electrode 13a. The pixel electrode 13 a faces the transparent electrode layer 32, and the electrophoretic layer 20 is sandwiched between the pixel electrode 13 a and the transparent electrode layer 32. The microcapsule 21 between the one pixel electrode 13 a and the transparent electrode layer 32 becomes one pixel in the display unit 101. In the pixel drive circuit 66, a storage capacitor 63 is connected in parallel with the electrophoretic layer 20. The potential of the transparent electrode layer 32 is set to a predetermined potential Vcom.

  The scanning line driving circuit 53 (see FIG. 4) is connected to each scanning line 64 in the display area 55, and scan signals Y1, Y2,.・ Supply Ym. Specifically, the scanning line driving circuit 53 selects the scanning line 64 in the order of 1, 2,..., M-th row, and selects the voltage of the scanning signal of the selected scanning line 64 as the selection voltage VH (H level). ), And the voltage of the scanning signal of the scanning line that is not selected is the non-selection voltage VL (L level).

  The data line driving circuit 54 (see FIG. 4) is connected to each data line 65 of the display area 55, and data signals X1, X2,.・ Supply Xn. A data signal is supplied from the data line 65 to the pixel driving circuit 66 connected to the scanning line 64 whose potential is the selection voltage VH. Specifically, when the scanning line 64 becomes H level, the TFT 61 whose gate is connected to the scanning line 64 is turned on, and the pixel electrode 13 a is connected to the data line 65. For this reason, when a data signal is supplied to the data line 65 when the scanning line 64 is at the H level, the data signal is applied to the pixel electrode 13a via the TFT 61 that is turned on. When the scanning line 64 becomes L level, the TFT 61 is turned off, but the voltage applied to the pixel electrode 13a by the data signal is accumulated in the storage capacitor 63, and the potential of the pixel electrode 13a and the potential of the transparent electrode layer 32 are stored. Electrophoretic particles move according to the potential difference (voltage).

  For example, when the potential of the pixel electrode 13 a is higher than the potential Vcom of the transparent electrode layer 32, the negatively charged white electrophoretic particles move to the pixel electrode 13 a side, and the positively charged black electricity The migrating particles move to the transparent electrode layer 32 side, and the pixel is displayed in black. When the potential of the pixel electrode 13a is lower than the potential Vcom of the transparent electrode layer 32, the positively charged black electrophoretic particles move to the pixel electrode 13a side, and the negatively charged white electricity The migrating particles move to the transparent electrode layer 32 side, and the pixel is displayed in white.

  A period from when the scanning line driving circuit 53 selects the first scanning line to when the selection of the Yth scanning line is completed is referred to as “frame period” or simply “frame”. Each scanning line 64 is selected once per frame, and a data signal is supplied to each pixel driving circuit 66 once per frame.

  Returning to FIG. 2, the description of the overall hardware configuration of the electronic device 1000 will be continued. The control unit 103 is a microcomputer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and controls each unit of the electronic device 1000 according to a program stored in the ROM. A VRAM 104 (Video RAM) is a memory that stores display image data indicating a two-tone monochrome image to be displayed on the display unit 101. The storage unit 108 is a non-volatile memory, and stores image data indicating an original image used for generating image data for display. Note that the image data indicating the original image may indicate either a color image or a monochrome image. The image data indicating the original image may be in a raster format or a vector format. The storage unit 108 can store a plurality of different image data.

  The controller 102 controls the scanning line driving circuit 53 and the data line driving circuit 54 and displays an image on the display area 55 according to the image data stored in the VRAM 104. The communication unit 105 is a communication interface for communicating with other computer apparatuses. The communication unit 105 performs data communication with another computer device by wireless communication or wired communication using a communication cable, and receives image data. The received image data is stored in the storage unit 108.

  The operation unit 109 includes the buttons 9A to 9F illustrated in FIG. When this button is operated, a signal indicating the operated button is sent to the control unit 103. The control unit 103 acquires the signal sent from the operation unit 109 and identifies the operated button. The control unit 103 specifies an instruction from the user according to the specified button, and executes a process corresponding to the specified instruction.

  The external power input unit 110 receives external power supply and outputs power to the battery 111 described below.

  The battery 111 stores the power input from the external power input unit 110 and supplies the stored power to other components of the electronic device 1000.

  The power supply monitor unit 112 monitors the presence / absence of power supplied from the outside to the external power input unit 110 and the remaining amount of power stored in the battery 111, and generates power supply state data indicating these states To do.

  The time measuring unit 113 constantly measures the elapsed time from the reference time, and generates elapsed time data indicating the measurement result.

  In this embodiment, the image processing unit 106 is an ASIC (Application Specific Integrated Circuit), and color or monochrome image data of a gradation (where a is a natural number satisfying a> 2) is represented by halftone dots. A process of converting the image data into a two-gradation raster format that expresses gradation is performed.

  FIG. 6 is a block diagram illustrating a functional configuration of the image processing unit 106. The acquisition unit 6a acquires the image data to be converted stored in the storage unit 108. If the acquired image data is in the vector format, the acquisition unit 6a passes the image data to the expansion unit 6b. The acquired image data is in the raster format. If there is, the image data is developed in the VRAM 104.

  The expansion unit 6 b receives vector format image data from the acquisition unit 6 a, rasterizes the received image data to generate raster format image data, and expands the image data in the VRAM 104. When the raster format image data developed in the VRAM 104 indicates a color image, the first conversion unit 6c converts the image data into grayscale image data. The gamma correction unit 6 d performs gamma correction according to the characteristics of the display unit 101 on the grayscale image data developed in the VRAM 104. The second conversion unit 6e performs a halftoning process on the grayscale image data after the gamma correction. The expansion unit 6b to the second conversion unit 6e store data that needs to be temporarily stored in the process in a working area (RAM) of the storage unit 108, and read and use the data as appropriate.

  The grayscale image data after gamma correction is for each pixel that represents an image. The grayscale indicates the density according to the scale of a gradation (where a is the natural number satisfying a> 2). It is a collection of pixel data indicating a value (for example, any integer between 0 and 255 for 256 gradations). That is, in each pixel data, data indicating a gradation value is associated with data indicating a pixel position. Hereinafter, the pixel data included in the pre-conversion image data is referred to as pre-conversion pixel data.

  7 and 8 are flowcharts showing the flow of the halftoning process performed by the second conversion unit 6e. Hereinafter, the flow of the halftoning process performed by the second conversion unit 6e will be described with reference to FIGS.

  When the second conversion unit 6e detects that the new gamma-corrected grayscale image data has been written in the VRAM 104 as pre-conversion image data by the gamma correction unit 6d (S101), the second conversion unit 6e reads out the pre-conversion image data from the VRAM 104. (S102).

  Subsequently, the second conversion unit 6e substitutes the gradation value indicated by the pixel data included in the read image data into input_ [y] [x] corresponding to the pixel position (S103).

  Here, [y] [x] indicates the pixel position on the two-dimensional array in the display area 55, y indicates the row number of the scanning line 64 (therefore, y is a natural number between 1 and m), and x is data Indicates the column number of the line 65 (therefore, x is a natural number between 1 and n). Further, input_ [y] [x] is a variable indicating the gradation value of the pixel position [y] [x] of the pre-conversion image data.

  Subsequently, the second conversion unit 6e selects one pixel position according to a predetermined rule (S104). Here, the predetermined rule is that the first row of the display area 55 is sequentially selected from the left to the right in FIG. 4 as pixel position [1] [1] → pixel position [1] [n] After reaching the rightmost edge of the row, the second row is successively selected from left to right in FIG. 4 as pixel position [2] [1] → pixel position [2] [n]. Suppose that the rule repeats the selection up to the m-th line. However, this selection rule is an example, and any other rule may be adopted as long as it is a rule that selects all pixels once. Hereinafter, the pixel position selected in step S104 (and step S113 described later) is referred to as a “conversion target pixel position”.

  Subsequently, the second conversion unit 6e has threshold data (dither threshold data) corresponding to the conversion target pixel position included in dither matrix data (hereinafter simply referred to as “dither matrix data”) stored in the storage unit 108 in advance. Is read. In the present application, in order to distinguish between a threshold value used for the error diffusion method and a threshold value used for the dither method, the former threshold value is called an “error diffusion threshold value”, and the latter threshold value is called a “dither threshold value”.

  FIG. 9 is a diagram illustrating a part of the dither matrix data. The dither matrix data is relatively large two-dimensional array data such as 128 rows × 128 columns and 256 rows × 256 columns, for example, and FIG. 9 shows a portion of 16 rows × 16 columns extracted from these two-dimensional arrays. Yes. Each element data (dither threshold data) of the dither matrix data indicates any numerical value of a natural number between 1 and 100. This numerical value indicates a dither threshold value that divides the entire gradation band of the a gradation into two gradation bands, a lower side and an upper side.

  Further, the dither matrix data is arranged such that the dither threshold values have a blue noise characteristic on the two-dimensional array. Note that the blue noise characteristic is a distribution characteristic of a pseudo random pattern adjusted so that the spatial frequency distribution is equal to or higher than the spatial frequency that can be sensed by human vision. For example, in FIG. 9, element data indicating a dither threshold value of 10 or less is displayed in gray. It can be seen that the element data displayed in gray are randomly arranged at an appropriate distance without following a regular pattern as long as it is judged at least by human vision.

The second conversion unit 6e performs the following determination regarding the conversion target pixel position (S105).
input_ [y] [x]> = dither_threshold [y] [x] * (a / 100)

  Where dither_mask [p] [q] (where p and q are 1 <= p <= k, 1 <= q <= k, where k is the dither matrix data) Dither_threshold [y] [x] = dither_mask [y% k] [x% k], where p is the element data of the pth and qth columns included in the dither matrix data. In step S106, the gradation value indicated by the pixel data related to the conversion target pixel position of the pre-conversion image data is set to a scale of a gradation from the dither threshold value indicated by the dither threshold data corresponding to the conversion target pixel position of the dither matrix data. This is a process for determining whether or not the converted dither threshold value is exceeded.

  When it is determined in step S105 that the gradation value is equal to or greater than the dither threshold (S105; Yes), the second conversion unit 6e sets output1_ [y] [x] related to the conversion target pixel position [y] [x]. A gradation value 1 indicating black is substituted (S106).

  Here, output1_ [y] [x] is a variable indicating first converted pixel data which is pixel data after conversion obtained by conversion according to dither matrix data (conversion according to the blue noise mask dither method). is there.

  On the other hand, when it is determined in step S105 that the gradation value is less than the dither threshold (S105; No), the second conversion unit 6e outputs the output1_ [y] [x related to the conversion target pixel position [y] [x]. ] Is substituted with a gradation value 0 indicating white (S107).

  When the process of step S106 or S107 is completed, the second conversion unit 6e determines whether the generation process of the first converted pixel data regarding all the pixel positions is completed (S108). If there is a pixel position for which the first converted pixel data has not yet been generated (S108; No), the second conversion unit 6e returns the process to step S104 to perform the first conversion relating to the new conversion target pixel position. The subsequent pixel data generation process is repeated.

  On the other hand, when the generation of the second post-conversion pixel data is completed for all pixel positions (S108; Yes), the second conversion unit 6e uses the data stored in the array output1_ [y] [x] as the first After the image data is expanded in the VRAM 104 as converted image data, the controller 102 is notified of this (S109).

  Upon receiving the notification, the controller 102 controls the display unit 101 based on the first converted image data developed in the VRAM 104, and displays the monochrome image halftoned by the blue noise mask dither method on the display unit 101. Let At that time, the controller 102 performs redrawing by applying a voltage only for pixels in which the gradation value of the image displayed so far is different from the gradation value of the image to be displayed now.

  In addition, the controller 102 instructs the power supply monitor unit 112 to deliver power supply state data to the second conversion unit 6e. In response to this instruction, the power supply monitoring unit 112 supplies power indicating either “power supply from external power source”, “battery remaining power”, or “battery remaining power” is low depending on the current power supply state. State data is generated, and the generated power supply state data is delivered to the second conversion unit 6e.

  Furthermore, the controller 102 instructs the time measuring unit 113 to start measuring elapsed time. In response to this instruction, the timing unit 113 measures the elapsed time since the display of the image according to the first converted image data is started, and sequentially passes the elapsed time data indicating the result to the second conversion unit 6e. To hand over.

  Following the processing of step 109, the second conversion unit 6e determines whether the power supply state data delivered from the power supply monitoring unit 112 is “power supply from an external power supply”, “battery remaining amount”, or “battery remaining amount” is low. It is determined whether or not to show (S110).

  If it is determined in step S110 that “the power supply from the external power supply is present”, the second conversion unit 6e immediately moves the process to step S113 described later.

  If it is determined in step S110 that “battery remaining amount is high”, the second conversion unit 6e has exceeded the predetermined time (for example, 5 seconds) indicated by the elapsed time data sequentially delivered from the time measuring unit 113. It is determined whether or not (S111). When it is determined that the elapsed time has exceeded the predetermined time (S111; Yes), the second conversion unit 6e moves the process to step S113 described later.

  If it is determined in step S110 that the battery level is low, the second conversion unit 6e determines whether or not high-quality display instruction data has been delivered from the operation unit 109 (step S112). The high image quality display instruction data is data generated by the operation unit 109 and delivered to the second conversion unit 6e when the user performs a predetermined operation to instruct the operation unit 109 to overwrite with a high quality image. . If it is determined that the high-quality display instruction data has been delivered (S112; Yes), the second conversion unit 6e moves the process to step S113 described later.

  The second conversion unit 6e determines that “the power supply from the external power supply is present” in the determination in step S110, determines that the elapsed time exceeds the predetermined time in the determination in step S111, or determines in the determination in step S112. If it is determined that the high-quality display instruction data has been delivered, a process for halftoning the image indicated by the pre-conversion image data read in step S102 and substituted for input_ [y] [x] in step S103 by the error diffusion method I do.

  Therefore, first, the second conversion unit 6e performs substitution of error_buffer [y] [x] = 0 for all pixel positions [y] [x] as an initialization process (S113). Here, error_buffer [y] [x] is a variable indicating a cumulative value of correction values relating to the pixel position [y] [x] (hereinafter referred to as “cumulative correction value”).

  Subsequently, the second conversion unit 6e selects a conversion target pixel position according to a predetermined rule (for example, the same rule as that used in selection of the conversion target pixel position in step S104) (S114).

Subsequently, the second conversion unit 6e performs the following determination regarding the conversion target pixel position [y] [x] (S115).
threshold_ [y] [x] = a / 2
input_ [y] [x] + error_buffer [y] [x]> = threshold_ [y] [x]

  The left side of the above second equation is a value obtained by adding the cumulative correction value to the gradation value indicated by the pre-conversion pixel data. Hereinafter, the value is referred to as “corrected gradation value”, and data indicating the corrected gradation value is referred to as “corrected pixel data” in order to distinguish it from pixel data indicating the gradation value before correction. Since the correction value is added to the variable error_buffer [y] [x] in the process of step S119 described later, for example, in the process of step S115 regarding the pixel position [1] [1], error_buffer [1] [1] = 0 (initial value).

  threshold_ [y] [x] is the error diffusion on the scale of a gradation used when converting the pixel data (a gradation) of the conversion target pixel position [y] [x] into two gradations by the error diffusion method It is a variable indicating a threshold value. For example, if the pre-conversion image data is 256 gradations, a = 256. The reason why the value obtained by dividing a by 2 is used as the error diffusion threshold is that the number of gradations of the converted image data is 2.

  When it is determined in step S115 that the corrected gradation value is equal to or greater than the error diffusion threshold (S115; Yes), the second conversion unit 6e outputs output2_ [y] [related to the conversion target pixel position [y] [x]. A gradation value 1 indicating black is substituted for x] (S116).

  Here, output2_ [y] [x] is a variable indicating second converted pixel data which is pixel data after conversion by conversion according to the error diffusion method.

  On the other hand, when it is determined in step S115 that the corrected gradation value is less than the error diffusion threshold (S115; No), the second conversion unit 6e outputs output2_ [y related to the conversion target pixel position [y] [x]. ] [x] is substituted with a gradation value 0 indicating white (S117).

  Subsequently, the second conversion unit 6e includes a corrected gradation value indicated by the corrected pixel data corrected by adding the error value distributed from the neighboring processed pixel to the pre-conversion pixel data of the conversion target pixel position, An error value (hereinafter, this error value is referred to as a “diffusion error value”) that is a difference from a gradation value obtained by converting the gradation value indicated by the second pixel data after conversion into a gradation scale a is The process of distributing as a correction value to the pixel positions that have not yet been selected as the conversion target pixel position in the region continuous to the conversion target pixel position is performed.

That is, the second conversion unit 6e first calculates the diffusion error value error as follows (S117).
error = input_ [y] [x] + error_buffer [y] [x]-a * output2_ [y] [x]

Subsequently, the second conversion unit 6e applies the error error value error to each of the pre-conversion pixel data at the four adjacent pixel positions (pixel positions not yet selected as the conversion target pixel positions in step S114) as follows. On the other hand, it distributes as a correction value (S119).
error_buffer [y] [x + 1] = error_buffer [y] [x + 1] + error / 4
error_buffer [y + 1] [x-1] = error_buffer [y + 1] [x-1] + error / 4
error_buffer [y + 1] [x] = error_buffer [y + 1] [x] + error / 4
error_buffer [y + 1] [x + 1] = error_buffer [y + 1] [x + 1] + error / 4

  Each of the first to fourth expressions above relates to the pixel position on the right side of the current pixel position to be converted, the pixel position on the lower left, the pixel position on the lower right, and the pixel position on the lower right in FIG. The process of adding a newly distributed correction value to the cumulative correction value of the pixel position is shown.

  In addition, regarding pixel positions located at the left edge, right edge, or lower edge of the display area 55 in FIG. 4, the adjacent pixel positions that are not yet selected as the conversion target pixel positions are 3 or less. In that case, in step S119, for example, if there are three pixel positions, the diffusion error values are distributed as error_buffer [] [] = error_buffer [] [] + error / 3 for those three pixel positions. Is called.

  As described above, when the conversion process of a series of pixel data related to the current conversion target pixel position is completed, the second conversion unit 6e determines whether the generation process of the second converted pixel data is completed for all the pixel positions. Determine (S120). If there is a pixel position for which the generation of the second converted image data has not yet been performed (S120; No), the second conversion unit 6e returns the process to step S114, and the second conversion position regarding the new conversion target pixel position. The process of generating the converted pixel data is repeated. On the other hand, when the generation of the second converted pixel data is completed for all pixel positions (S120; Yes), the second conversion unit 6e uses the data stored in the array output2_ [y] [x] as the second After the image data is expanded in the VRAM 104 as converted image data, the controller 102 is notified of this (S121).

  Upon receiving the notification, the controller 102 controls the display unit 101 based on the second converted image data developed in the VRAM 104 and causes the display unit 101 to display a monochrome image halftoned by the error diffusion method. At that time, the controller 102 performs redrawing by applying a voltage only for pixels in which the gradation value of the image displayed so far is different from the gradation value of the image to be displayed now.

  FIG. 10 is a block diagram illustrating a configuration of functions related to the halftoning process of the second conversion unit 6e described above. The second conversion unit 6e includes, as its function component, a pre-conversion image data acquisition unit 601, a first pixel data conversion unit 602, a second pixel data conversion unit 603, an error diffusion unit 604, and a post-conversion image data output unit 605. A trigger data acquisition unit 606 and a power supply state specifying unit 607.

  The pre-conversion image data acquisition unit 601 executes step S102. The first pixel data conversion unit 602 executes Steps S104 to S107. The second pixel data conversion unit 603 executes steps S114 to S117. Error diffusion unit 604 executes steps S117, S119, and S115. The post-conversion image data output unit 605 executes steps S109 and S121. The trigger data acquisition unit 606 executes steps S111 and S112. The power supply state specifying unit 607 executes Step S110.

  As described above, according to the present embodiment, an image halftoned by the blue noise mask dither method is first displayed at high speed. Thereafter, an image halftoned by the error diffusion method is displayed promptly or after waiting for a predetermined time or a predetermined operation by the user according to the state of power supply.

  An image halftoned by the error diffusion method is superior to an image halftoned by the blue noise mask dither method, particularly in displaying characters and fine lines. Therefore, the error diffusion method is used when a user wants to browse a specific image without feeling the stress caused by the display delay even when the page is quickly turned by displaying the image halftoned by the blue noise mask dither method. Thus, it is possible to view the image comfortably by displaying the halftoned image.

[Second Embodiment]
Next, an electronic apparatus 1000 according to the second embodiment of the present invention will be described. The electronic apparatus 1000 according to the second embodiment has the same hardware configuration as that of the first embodiment. The electronic device 1000 according to the second embodiment differs from the electronic device 1000 according to the first embodiment in the processing performed by the second conversion unit 6e. Therefore, in the following, this different processing will be mainly described. Hereinafter, simply referring to the second conversion unit 6e means the second conversion unit 6e of the electronic apparatus 1000 according to the second embodiment.

  FIG. 11 is a flowchart showing a part of the processing performed by the second conversion unit 6e. The second conversion unit 6e according to the second embodiment performs the process shown in FIG. 11 between step S114 and step S115 of the process shown in FIGS.

  When the second conversion unit 6e selects the conversion target pixel position to be the generation target of the second converted pixel data in step S114, the first converted pixel data regarding the selected conversion target pixel position [y] [x]. It is determined whether (output1_ [y] [x]) is 0 or 1 (S201).

When the first post-conversion pixel data related to the conversion target pixel position [y] [x] is 1 (S201; 1), the second conversion unit 6e uses threshold_ [y] related to the conversion target pixel position [y] [x]. A value is substituted into [x] as follows (S202).
threshold_ [y] [x] = a / 2-0.2a

On the other hand, when the first post-conversion pixel data regarding the conversion target pixel position [y] [x] is 0 (S201; 0), the second conversion unit 6e uses threshold_ [regarding the conversion target pixel position [y] [x]. A value is substituted into y] [x] as follows (S203).
threshold_ [y] [x] = a / 2 + 0.2a

  In the processing of steps 202 and S203, the gradation width of the gradation band corresponding to the gradation value indicated by the first converted pixel data (hereinafter referred to as “target gradation value”) is the gradation width of all gradation bands. Is a process of setting an error diffusion threshold so as to be wider than the gradation width that is divided into two.

  In the present application, the “gradation band” is a gradation defined between the lower limit threshold and the upper limit threshold when converting the corrected gradation value of the a gradation to the gradation value of the b gradation. Means a range of values.

  FIG. 12 shows a state in which the corrected gradation value of 256 gradations (that is, a = 256) is converted into a gradation value of 2 gradations according to the error diffusion threshold changed by the processing in steps S202 and S203. FIG.

  FIG. 12A shows the case where the error diffusion threshold value 128 (corresponding to threshold_ [y] [x] = a / 2) is used so as to divide the entire 256-tone range (0 to 255) into two equal parts. In the figure, a state in which the corrected gradation value of 256 gradations is converted into a gradation value of 2 gradations is shown. That is, when the corrected gradation value before conversion is 0 to 127, the gradation value after conversion is 0. Further, when the post-correction gradation value before conversion is 128 to 255, the gradation value after conversion is 1. This is the error diffusion threshold used in step S115 in the first embodiment. According to this error diffusion threshold, the gradation bands having the same gradation width (the gradation bands 0 to 127 and the gradation bands 128 to 255) are the same. Is set.

  FIG. 12B shows 256 corrected gradations when the error diffusion threshold 77 (corresponding to threshold_ [y] [x] = a / 2−0.2a) set in step S202 is used. This shows how the value is converted into a two-tone gradation value. That is, when the corrected gradation value before conversion is 0 to 76, the converted gradation value is 0. Further, when the corrected gradation value before conversion is 77 to 255, the gradation value after conversion is 1. Thus, according to the error diffusion threshold set in step S202, the gradation width corresponding to the target gradation value 1 (upper gradation width) is 20% wider than that shown in FIG. As a result, the probability that the converted gradation value matches the target gradation value 1 is increased.

  FIG. 12 (c) shows 256 corrected gradations when the error diffusion threshold 179 (corresponding to threshold_ [y] [x] = a / 2 + 0.2a) set in step S203 is used. This shows how the value is converted into a two-tone gradation value. That is, when the gradation value after correction before conversion is 0 to 178, the gradation value after conversion is 0. When the corrected gradation value before conversion is 179 to 255, the converted gradation value is 1. Thus, according to the error diffusion threshold set in step S203, the gradation width corresponding to the target gradation value 0 (lower gradation width) is 20% wider than that shown in FIG. . As a result, the probability that the converted gradation value matches the target gradation value 0 increases.

  The second conversion unit 6e uses the error diffusion threshold selected according to the first pixel data after conversion at the same pixel position as described above, and performs the second post-conversion according to the error diffusion method after step S115. Pixel data is generated. As a result, the image indicated by the generated second converted image data has more pixels whose gradation values match the image indicated by the first converted image data than in the first embodiment. It becomes an image. Accordingly, the number of pixels that require redrawing in the display unit 101 is reduced, and the power consumption is reduced.

  As described above, even if the second converted image data is generated so that the gradation value of the same pixel position included in the first converted image data is maintained with a high probability, for example, The image indicated by the second post-conversion image data does not become darker or lighter as a whole than the image indicated by the pre-conversion image data. This is because, as a result of the diffusion error values being distributed to neighboring pixels in steps S118 and S119, the overall density of the image indicated by the pre-conversion image data and the overall density of the image indicated by the second post-conversion image data This is because the difference falls within the shade range of one pixel at the maximum.

[Modification]
The above-described embodiments can be variously modified within the scope of the technical idea of the present invention. Examples of these modifications are shown below.

[First Modification]
In the embodiment described above, the first and second converted image data (hereinafter simply referred to as “converted image data”) has two gradations. On the other hand, in the first modified example, even if the number of gradations of the converted image data is 3 gradations or more, the corresponding image data is converted.

  When the number of gradations of the converted image data is 3 gradations or more, the processes in steps S105 to S110 and S115 to S117 in FIGS. 7 and 8 in the above-described embodiment are modified. In addition, the processes in steps S201 to S203 of FIG. 11 in the second embodiment described above are also modified. Hereinafter, a case where the number of gradations of the converted image data is 4 will be described as an example.

  First, in the first modification, dither matrix data including three dither threshold value data in each element data is used in the process of step S105. The dither threshold indicated by the dither threshold data included in each element data is randomly arranged on the two-dimensional array with respect to each of the minimum, middle, and maximum among the three dither thresholds. Yes.

  In step S105, the second conversion unit 6e indicates that the gradation value (input_ [y] [x]) indicated by the pre-conversion pixel data is indicated by element data corresponding to the conversion target pixel position included in the dither matrix data. It is determined which of the four gradation bands divided by one dither threshold is included.

  According to the determination result of step S105, the second conversion unit 6e performs a process of substituting one of 0 to 3 for output1_ [x] [x] instead of the processes of steps S106 and S107.

  In the case of a modification to the second embodiment, the second conversion unit 6e indicates the first converted pixel data (output1_ [x] [x]) determined as described above, instead of the process of step S201. It is determined whether the gradation value is 0 to 3, and instead of steps S202 and S203, gradation band setting processing corresponding to each of those gradation values (that is, error diffusion threshold setting processing) I do.

  In addition, in the determination in step S115, the second conversion unit 6e determines which of the gradation bands divided into four by the three thresholds is included in the corrected gradation value, and the second conversion unit 6e performs the first conversion according to the determination result. The process of substituting one of the gradation values 0 to 3 into the post-conversion pixel data (output2_ [x] [x]) of 2 is performed in place of the processes of steps S116 and S117.

  FIG. 13 shows, as an example, the gradation set in the processing performed in place of steps S202 and S203 in FIG. 11 when the pre-conversion image data has 256 gradations and the post-conversion image data has 4 gradations. It is the figure which showed the belt | band | zone.

  FIG. 13A shows four gradation bands with a gradation width of 64 obtained by equally dividing 256, which is the number of gradations of the pre-conversion image data, by 4 that is the number of gradations of the converted image data. The case where it is set is shown.

  FIGS. 13B to 13E show output1_ [y] [x] = 0, output1_ [y] [x] = 1, output1_ [y] [x] = 2, output1_ [y] [x] = 3 shows the gradation band set by the second converter 6e.

  That is, when the first post-conversion pixel data (output1_ [y] [x]) is k (where k is a natural number not less than 0 and not more than 3), the second conversion unit 6e is shown in FIG. The error diffusion gradation value is set so that, for example, the gradation width of the gradation band that converts the pre-conversion pixel data (input_ [y] [x]) to k is expanded by 20%, for example. To do.

  As described above, when converting the pre-conversion pixel data into the second post-conversion pixel data, the pre-conversion image data differs by expanding the gradation band width according to the first post-conversion pixel data. However, the probability that the second converted pixel data at the same pixel position matches is increased.

  According to the first modification, even when the pre-conversion image data with a gradation is converted into the converted image data with three or more gradations and displayed, the gradation value is changed before and after the display. The number of changing pixels is reduced compared to the case of following the conventional error diffusion method.

  The case where the first converted pixel data and the second converted pixel data have four gradations has been described above. However, if the above is generalized, the first converted pixel data and the second converted pixel data will be described. When the number of gradations of pixel data is b, first to b-th gradation bands formed by (b-1) error diffusion thresholds are set.

  Then, when the first converted pixel data is c (where c is an integer satisfying 0 ≦ c ≦ (b−1)), the (c + 1) -th gradation band is increased. At least one of the lower error diffusion threshold and the upper error diffusion threshold forming the (c + 1) gradation band is changed.

  After that, b after the corrected gradation value of the conversion target pixel position belongs to any of the first to b-th gradation bands formed by (b-1) error diffusion thresholds, b Pixel data indicating the gradation value of the gradation is generated as second converted pixel data.

  Here, the width of the gradation band before the gradation width is expanded according to the first converted pixel data (output (i) _ [y] [x]) seems to be adopted in the above-described embodiment. It is not limited to an equal split. In other words, a configuration may be employed in which a gradation band having a different gradation width from the beginning is set as the initial gradation band.

  In addition, when generating the second converted image data of b gradation, it is not always necessary to use (b-1) error diffusion threshold values. For example, binarization using one threshold value is performed. A configuration that obtains a similar result by another method, such as repeating the process a plurality of times, may be employed.

[Second Modification]
In the second embodiment described above, overwriting of the entire image is performed with the image halftoned by the improved error diffusion method according to the present invention. On the other hand, in the second modification, when the pre-conversion image data read from the storage unit 108 by the acquisition unit 6a is vector format image data, a region including characters or lines is generated according to the error diffusion method. An image (image indicated by the second post-conversion pixel data) is subjected to a rewrite process, and the other regions are generated according to the blue noise mask dither method (an image indicated by the first post-conversion pixel data). The rewriting process by is performed.

  FIG. 14 is a block diagram illustrating a functional configuration of the image processing unit 106 of the electronic apparatus 1000 according to the second modification. The image processing unit 106 according to the second modification includes a drawing instruction data acquisition unit 608 and a conversion target area designation data generation unit 609 in addition to the functional configuration unit included in the image processing unit 106 according to the above-described embodiment. .

  When the pre-conversion image data acquisition unit 601 acquires the pre-conversion image data in the vector format, the drawing instruction data acquisition unit 608 is data for instructing the drawing of characters or lines included in the pre-conversion image data in the vector format. Certain drawing instruction data is read out and transferred to the conversion target area designation data generation unit 609.

  Based on the drawing instruction data received from the drawing instruction data acquisition unit 608, the conversion target area specifying data generation unit 609 is configured to display the position of the character or line included in the image on the two-dimensional plane, that is, the pixel group that displays the character or line. A pixel position group indicating a position on the two-dimensional array is specified.

  Subsequently, the conversion target area designating data generation unit 609 determines the pixel position group thus identified and an area identified by a predetermined rule continuing from the pixel position group (for example, from the outer edge of the character or line pixel position group). A region formed by a pixel position group included in a region within a range of a predetermined distance is specified as a conversion target region. The conversion target area designation data generation unit 609 generates conversion target area designation data that is data indicating the conversion target area specified as described above, and delivers the conversion target area designation data to the second pixel data conversion unit 603.

  In step S114 of FIGS. 7 and 8, the second pixel data conversion unit 603 selects a conversion target pixel position from the conversion target area indicated by the conversion target area specifying data, and converts the conversion target pixel position from other areas. Do not select.

  As a result, according to the second modified example, the image by the error diffusion method is overwritten and displayed only for the region where the image by the error diffusion method is predicted to be noticeably higher quality than the blue noise mask dither method, For other areas, the image by the blue noise mask dither method is continuously displayed. Therefore, the power consumption required for the conversion process and redrawing is reduced as compared with the case where the entire image is overwritten and displayed by the image by the error diffusion method.

[Third Modification]
In the second modification, an area including characters or lines is specified as a conversion target area, an image by the error diffusion method according to the present invention is displayed for the conversion target area, and a blue noise mask dither method is used for the other areas. The image by is displayed. On the other hand, in the third modification, a region including the edge position of the image indicated by the pre-conversion image data is specified as a conversion target region, and an image by the error diffusion method according to the present invention is displayed for the conversion target region. For other regions, an image by the blue noise mask dither method is displayed.

  FIG. 15 is a block diagram illustrating a functional configuration of the image processing unit 106 of the electronic apparatus 1000 according to the third modification. The image processing unit 106 according to the third modification includes a conversion target area designation data generation unit 610 in addition to the functional configuration unit included in the image processing unit 106 according to the above-described embodiment.

  The conversion target area designation data generation unit 610 performs a known edge detection process using, for example, bluelet conversion on the image data indicated by the pre-conversion image data acquired by the pre-conversion image data acquisition unit 601, A pixel position group indicating a position where an edge position on the two-dimensional plane (edge position), that is, an index indicating the degree of change in image density is equal to or greater than a predetermined threshold is specified.

  Subsequently, the conversion target area designating data generation unit 610 performs the pixel position group specified as described above and an area specified by a predetermined rule continuing from the pixel position group (for example, from the outer edge of the character or line pixel position group). A region formed by a pixel position group included in a region within a range of a predetermined distance is specified as a conversion target region. The conversion target area specifying data generation unit 610 generates conversion target area specifying data that is data indicating the conversion target area specified as described above, and passes it to the second pixel data conversion unit 603.

  Subsequent processing is the same as in the case of the second modification described above.

  According to the third modified example, as in the second modified example, the image by the error diffusion method is only used for the region where the image by the error diffusion method is predicted to be noticeably higher in quality than the blue noise mask dither method. Is overwritten and the image by the blue noise mask dither method is continuously displayed for the other areas. Therefore, the power consumption required for the conversion process and redrawing is reduced as compared with the case where the entire image is overwritten and displayed by the image by the error diffusion method.

[Fourth Modification]
In the second embodiment described above, the setting of the error diffusion threshold value performed in steps S202 and S203 in FIG. 11 is expressed as follows when it is more generalized.
threshold_ [y] [x] = f (output1_ [y] [x])
However, f () indicates a function that takes the variables shown in ().

  That is, in the second embodiment described above, the error diffusion threshold used for conversion from the pre-conversion pixel data at the certain conversion target pixel position to the second post-conversion pixel data is the first conversion at the conversion target pixel position. It changes according to the post-pixel data.

In the fourth modified example, the setting of the error diffusion threshold performed in steps S202 and S203 in FIG. 11 is performed according to the following equation.
threshold_ [y] [x] = f (output1_ [y] [x], input_ [y] [x])

  That is, in the fourth modification, the error diffusion threshold used for conversion from the pre-conversion pixel data at the certain conversion target pixel position to the second conversion pixel data is the first post-conversion pixel at the conversion target pixel position. In addition to the data, it also changes according to the pre-conversion pixel data at the conversion target pixel position.

  For example, when the converted image data has two gradations, the input_ [y] [x] indicates a value around a / 2, compared to the case where the value is a distance away from a / 2, and after the second conversion The probability that the pixel data becomes 0 and the probability that it becomes 1 conflict. Therefore, when input_ [y] [x] indicates a value around a / 2, the threshold_ [y] [x] and output1_ [y when output1_ [y] [x] = 0 are compared to the case when it is not By setting the error diffusion threshold so that the difference from threshold_ [y] [x] in the case of] [x] = 1 is widened, the number of pixels that need to be rewritten can be reduced more effectively.

[Fifth Modification]
In the fifth modification, the error diffusion threshold value set in steps S202 and S203 of FIG. 11 in the second embodiment is set according to the following equation.
threshold_ [y] [x] = f (output1_ [y] [x], input (i) _ [y] [x], input (i + 1) _ [y] [x])

  However, input (i) _ [y] [x] is an array indicating the gradation value of the pre-conversion image data used to generate the post-conversion image data indicating the currently displayed image, and input (i + 1) _ [y] [x] is an array indicating the gradation value of the pre-conversion image data used for generating the post-conversion image data indicating the image to be displayed.

  That is, in the fifth modification, the error diffusion threshold used for conversion from the pre-conversion pixel data at the certain conversion target pixel position to the second post-conversion pixel data is the first post-conversion pixel at the conversion target pixel position. In addition to the data and the pre-conversion pixel data of the conversion target pixel position, the pre-conversion pixel data of the conversion target pixel position included in the pre-conversion image data used to generate the currently displayed image Change.

  For example, when the converted image data has two gradations, it is conceivable to set the error diffusion threshold as follows.

When output1_ [y] [x] = 0 and input (i) _ [y] [x] = <input (i + 1) _ [y] [x]
threshold_ [y] [x] = a / 2 + 0.2a

When output1_ [y] [x] = 0 and input (i) _ [y] [x]> input (i + 1) _ [y] [x]
threshold_ [y] [x] = a / 2 + 0.4a

When output1_ [y] [x] = 1 and input (i) _ [y] [x] => input (i + 1) _ [y] [x]
threshold_ [y] [x] = a / 2-0.2a

When output1_ [y] [x] = 1 and input (i) _ [y] [x] <input (i + 1) _ [y] [x]
threshold_ [y] [x] = a / 2-0.4a

  When the above-mentioned conditions are followed, when the first converted pixel data indicates white and the pixel at the same pixel position in the image before conversion changes from black to white, the pixel is white with a higher probability. The error diffusion threshold is raised to a 40% increase, which is higher than the normal 20% increase. In addition, when the first converted pixel data indicates black and the pixel at the same pixel position in the image before conversion changes from white to black, the error diffusion threshold is usually set so that the pixel becomes black with higher probability. Will be reduced to a 40% reduction, which is even lower than the 20% reduction.

  As a result, the pixel under the condition where black increases in the image before conversion is converted to black with a higher probability, and the pixel under the condition where white increases is converted to white with a higher probability. A quality halftoned image may be obtained.

[Sixth Modification]
In the sixth modification, the error diffusion threshold value set in steps S202 and S203 of FIG. 11 in the second embodiment is set according to the following equation.
threshold (i + 1) _ [y] [x] = f (output1_ [y] [x], threshold (i) _ [y] [x])

  Here, threshold (i) _ [y] [x] is an array indicating the error diffusion threshold used to generate the converted image data indicating the currently displayed image, and threshold (i + 1) _ [y ] [x] is an array indicating the error diffusion threshold used to generate the converted image data indicating the image to be displayed.

  That is, in the sixth modification, the error diffusion threshold used for conversion from the pre-conversion pixel data at the certain conversion target pixel position to the second conversion pixel data is the first post-conversion pixel at the conversion target pixel position. In addition to the data, it also changes in accordance with the error diffusion threshold used for generating the second converted pixel data at the conversion target pixel position included in the converted image data indicating the currently displayed image.

  For example, for each threshold_y [x] having different values, an increase / decrease rate list in which an increase rate of an error diffusion threshold and a decrease rate of an error diffusion threshold that have a high probability of bringing a desired image quality by an investigation are associated in advance is stored. deep. When output (i) _ [y] [x] = 0, the error diffusion threshold is increased according to the increase rate associated with threshold (i) _ [y] [x] in the increase / decrease rate list, and output ( When i) _ [y] [x] = 1, the error diffusion threshold is lowered according to the decrease rate associated with threshold (i) _ [y] [x] in the increase / decrease rate list.

  Thereby, by adjusting the increase / decrease rate list, a higher quality halftoned image may be obtained.

[Seventh Modification]
In the embodiment and the modification described above, when the image data after conversion is expanded in the VRAM 104 by the second conversion unit 6e, the display unit 101 is configured to display the currently displayed image according to the application of the voltage controlled by the controller 102. Redrawing is performed only for pixels whose gradation values change.

  That is, for pixels whose gradation value does not change before and after rewriting (for example, in the case of 2 gradations, a pixel which is white → white or black → black), redrawing processing by applying a voltage is not performed. The redrawing process by applying a voltage is performed only for a pixel whose gradation value changes (for example, in the case of two gradations, a pixel that is white → black or black → white).

  Therefore, the controller 102 copies the converted image data indicating the currently displayed image to the storage unit 108, and then instructs the display unit 101 to display a new image, and then the conversion newly developed in the VRAM 104. Comparison is performed for each pixel position between the post-image data and the post-conversion image data stored in the storage unit 108, and a voltage is applied only to pixels at different pixel positions.

  By the way, when redrawing is performed with respect to a certain pixel position and redrawing is not performed with respect to surrounding pixel positions adjacent to the pixel position, depending on the characteristics of the display unit 101, the redrawing may be performed around the redrawn pixel. In some cases, image quality such as blurring may be deteriorated.

  In order to alleviate the above problem, in the seventh modified example, in addition to the pixel whose gradation value changes before and after the rewriting of the image, the voltage of the pixel in the region that is continuous with the pixel and defined by a predetermined rule is also applied. Application is performed by the controller 102, and as a result, redrawing by the display unit 101 is performed.

  According to the seventh modification, application is not performed for some of the pixels whose gradation values do not change before and after rewriting of the image, and consumption is performed as compared with the case where application for redrawing is performed for all the pixels. In addition to saving power, image quality degradation such as blurring that may occur when redrawing by pixels alone may be reduced.

[Eighth Modification]
The electronic apparatus 1000 according to the embodiment and the modification described above includes the display unit 101 that displays an image according to the converted image data generated by the image processing unit 106.

  On the other hand, the electronic device 1000 according to the eighth modified example does not include the display unit 101, and transmits the generated converted image data to the external display device 1001 that performs data communication with the electronic device 1000, for example, wirelessly.

  FIG. 16 is a block diagram showing configurations of the electronic apparatus 1000 and the display device 1001 according to the eighth modification. The electronic device 1000 according to the eighth modification includes a control unit 103, a communication unit 105, an image processing unit 106, and a storage unit 108 among the components included in the electronic device 1000 according to the above-described embodiment. In addition, the display device 1001 includes components other than the image processing unit 106 among the components included in the electronic apparatus 1000 according to the above-described embodiment.

  The control unit 103, the communication unit 105, and the storage unit 108 are provided in both the electronic device 1000 and the display device 1001. In FIG. 16, in order to distinguish them, “a” (electronic device 1000) is used for their reference numerals. Or “b” (display device 1001) is attached.

  The electronic device 1000 may be manufactured as a dedicated device, but may be realized by causing a PC (Personal Computer) such as a smartphone to execute processing according to the application program according to the present invention.

  The electronic device 1000 acquires the pre-conversion image data, and transmits the post-conversion image data obtained by performing the halftoning process to the display device 1001 via the wireless LAN, for example, via the communication unit 105a. When the display device 1001 receives the converted image data transmitted from the electronic device 1000 by the communication unit 105b, the display device 1001 develops the received converted image data in the VRAM 104 and displays the image.

  When the user performs an operation such as page turning on the operation unit 9 included in the display device 1001, command data indicating the operation content is transmitted from the display device 1001 to the electronic apparatus 1000. The electronic device 1000 performs image conversion processing on the next page in accordance with the command data received from the display device 1001, and transmits the result to the display device 1001.

  Since the display device 1001 does not include the image processing unit 106 and does not perform image conversion processing, the display device 1001 consumes less power and can be easily reduced in weight compared to the electronic apparatus 1000 including the display unit 101. Therefore, the user is less tired when holding the device to view the image, and the frequency with which charging is required when using the device with a battery can be reduced.

[Ninth Modification]
In the embodiment and the modification described above, after the first converted image data is generated, the second converted image data is generated. In addition, after the first converted pixel data is generated for all pixel positions, the first converted data is expanded into the VRAM 104, and the second converted pixel data is generated for all pixel positions. Then, the second converted data is developed into the VRAM 104.

  In the ninth modification, for example, when power is supplied from an external power source, when the first converted pixel data or the second converted pixel data relating to a certain pixel position is generated, the converted pixel data is This is immediately reflected in the VRAM 104. The generation of the second converted pixel data is performed in parallel with the generation of the first converted pixel data.

  According to the ninth modification, as a result of the processing related to the conversion and display of the image data being performed in parallel, the image according to the second converted image data is faster compared to the case of the serial processing in the above-described embodiment. Overwrite display is performed.

[Tenth Modification]
In the embodiment and the modification described above, in the determination in step S111 or S112, elapsed time data indicating the passage of a predetermined time or high image quality indicating that the user has performed a predetermined operation for instructing overwriting with a high image quality image. When the display instruction data is acquired as the trigger data, a configuration is adopted in which generation of the second post-conversion pixel data is started.

  In the tenth modification, the second conversion unit 6e starts generating the second post-conversion pixel data without waiting for the acquisition of the trigger data, and the process of step S121, ie, the second, is triggered by the acquisition of the trigger data. Development of the converted image data into the VRAM 104 is started.

  Accordingly, the processes in steps S110 to S112 in FIGS. 7 and 8 are performed after step S120, not after step S109.

  According to the tenth modified example, as compared with the case of the above-described embodiment and modified example, the overwriting display of the image according to the second converted image data is promptly performed in accordance with the passage of a predetermined time or the instruction from the user. Is done. Therefore, for example, in the eighth modification, when the power consumption in the display process is restricted but the power consumption in the conversion process is not restricted, the power consumption and the displayable time are more desirably balanced.

[Other variations]
In the second embodiment described above, when the gradation value indicated by the first converted pixel data is 0 and 1, the increase / decrease width of the error diffusion threshold is determined according to the same rule. Configuration is adopted. On the other hand, for example, when the gradation value indicated by the first converted pixel data is 0, the error diffusion threshold is not adjusted and is always fixed to a / 2 and indicated by the first converted pixel data. When the gradation value is 1, a configuration in which an asymmetric error diffusion threshold is adjusted such that the error diffusion threshold is decreased by 20% and reduced may be employed.

  In the embodiment and the modification described above, when the error value is distributed in step S119 of FIGS. 7 and 8, the error value is equally divided for the four pixel positions adjacent to the conversion target pixel position. A configuration in which values are distributed is adopted. Instead of this, various other error value distribution methods proposed in the existing error diffusion method may be employed in the present invention. For example, a pixel position that is directly adjacent to the conversion target pixel position and a pixel position that is adjacent (indirectly adjacent) outside the directly adjacent pixel position are widely used as a distribution method of those error values. For example, there is a method of assigning a larger weight to a pixel position to be distributed to a directly adjacent pixel position than to a jointly adjacent pixel position and distributing an error value according to those weights.

  In the embodiment and the modification described above, the display unit 101 that performs display in accordance with the electrophoresis method is employed, but various other display methods can be employed in the present invention. According to the second embodiment, since the number of pixels that need to be redrawn is reduced, a display method in which the amount of energy required for redrawing is greater than the amount of energy required to maintain the once drawn image, This is particularly effective in a display method in which the time required for redrawing increases according to the number of pixels.

  Further, in the above-described embodiment and its modification, the blue noise mask dither method is employed for generating the first converted image data. However, the conversion target pixel position such as other systematic dither methods is used. In other words, another method of determining the gradation value of the pixel after conversion by simply comparing the gradation value of the pixel before conversion with a fixed threshold value may be employed.

  In the second embodiment described above, a configuration is adopted in which it is determined whether or not to perform the processing of steps S201 to S203, that is, the adjustment processing of the error diffusion threshold used in the error diffusion method, according to the state of power supply. Also good. For example, when there is an external power supply, display speed may be more important than reduction in power consumption required for redrawing. In such a case, the need can be met by not performing the adjustment process of the error diffusion threshold.

  It should be noted that the order of the processing flows shown in the above-described embodiments and modifications, the conditional expressions and numerical values adopted in each processing are merely examples, and do not limit the present invention.

DESCRIPTION OF SYMBOLS 10 ... 1st board | substrate, 11 ... Board | substrate, 12 ... Circuit layer, 20 ... Electrophoresis layer, 21 ... Microcapsule, 22 ... Binder, 30 ... 2nd board | substrate, 31 ... Film, 32 ... Transparent electrode layer, 53 ... Scanning line Driving circuit 54... Data line driving circuit 55. Display area 61. TFT 61 63 Holding capacitor 64 Scan line 65 Data line 66 Pixel driving circuit 101 Display unit 102 Controller 103 ... Control part 104 ... VRAM 105 ... Communication part 106 ... Image processing part 108 ... Storage part 109 ... Operation part 110 ... External power input part 111 ... Battery 112 ... Power supply monitoring part 113 ... Timekeeping 601 ... pre-conversion image data acquisition unit, 602 ... first pixel data conversion unit, 603 ... second pixel data conversion unit, 604 ... error diffusion unit, 605 ... post-conversion image data output unit, 6 6 ... trigger data acquisition unit, 607 ... power supply state identification unit, 608 ... drawing instruction data acquisition unit, 609 ... conversion target region designation data generation unit, 610 ... conversion target region specification data generation unit, 1000 ... electronic device, 1001 ... Display device

Claims (18)

pre-conversion image data acquisition means for acquiring, as pre-conversion image data, image data including a plurality of pre-conversion pixel data indicating pixels included in an image of a gradation (where a is a predetermined natural number satisfying a> 2) ,
Among the gradation values of one pre-conversion pixel data included in the pre-conversion image data and (b-1) dither threshold values (where b is a predetermined natural number satisfying a>b> 1) First pixel data conversion means for generating first converted pixel data of b gradation by comparison with one of the dither threshold values set for the pixel position of the pixel data before conversion;
A gradation value after correction that is a value obtained by adding a gradation value of the one pre-conversion pixel data and a correction value that is a diffusion error value distributed to the one pre-conversion pixel data according to an error diffusion method; Second pixel data conversion means for generating second converted pixel data of b gradation based on the magnitude relationship with one error diffusion threshold;
When the second post-conversion pixel data is generated by the second pixel data conversion means, the second post-conversion pixel data is converted to a from the post-correction gradation value related to the one pre-conversion pixel data. Pre-conversion pixel data not yet used in the conversion by the second pixel data conversion means among the plurality of pre-conversion pixel data, which is a value obtained by subtracting the gradation value in the case of gradation. In addition, each of the one or more pre-conversion pixel data selected according to a predetermined rule that forms a continuous area with the one pre-conversion pixel data on the two-dimensional array is distributed as the correction value according to the predetermined rule. Error diffusion means to
After the data including the first converted pixel data set is output as the first converted image data to the display unit capable of displaying the b-gradation image, the second converted pixel data set is output. And a post-conversion image data output means for outputting data including the second post-conversion image data. The second pixel data conversion unit compares the corrected gradation value with at least one of the (b-1) error diffusion threshold values, and thereby converts the second converted pixel data of b gradation. The apparatus of claim 1. The storage means which memorize | stores the threshold value matrix data containing the collection of the dither threshold value data which is the data which show the said (b-1) dither threshold value regarding each of the said two-dimensionally arranged several pixel. The device described. Trigger data acquisition means for acquiring trigger data indicating a trigger for generation of second converted pixel data by the second pixel data conversion means;
4. The apparatus according to claim 1, wherein the second pixel data conversion unit starts a process of generating second converted pixel data in accordance with the trigger data acquired by the trigger data acquisition unit. 5. One or more power supply means each capable of supplying power;
Power supply state specifying means for specifying the state of power supply by the one or more power supply units,
The trigger data acquisition means can acquire a plurality of types of trigger data,
The second pixel data conversion means follows trigger data of a type predetermined according to the power supply state specified by the power supply state specifying means among the trigger data acquired by the trigger data acquisition means. The apparatus according to claim 4, wherein a process for generating second converted pixel data is started. Trigger data acquisition means for acquiring trigger data indicating a trigger for output of the second converted image data by the converted image data output means;
The apparatus according to claim 1, wherein the post-conversion image data output unit starts outputting the second post-conversion pixel data in accordance with the trigger data acquired by the trigger data acquisition unit. One or more power supply means each capable of supplying power;
Power supply state specifying means for specifying the state of power supply by the one or more power supply units,
The trigger data acquisition means can acquire a plurality of types of trigger data,
The converted image data output means includes the trigger data acquired by the trigger data acquisition means according to trigger data of a type predetermined according to the power supply state specified by the power supply state specifying means. The apparatus according to claim 6, wherein the output of the second converted pixel data is started. The second pixel data converting means converts one pre-conversion pixel data into second post-conversion pixel data when at least one gradation value of b gradations is set as a target gradation value. When the gradation value indicated by the first post-conversion pixel data generated by the first pixel data conversion unit based on the one pre-conversion pixel data is one of the at least one target gradation value, The gradation band expands at least one of the upper limit gradation value and the lower limit gradation value of the a gradation band including the gradation value when the target gradation value is represented by the a gradation. After the change, it is determined whether the corrected gradation value indicated by the corrected pixel data related to the one pre-conversion pixel data is included in the gradation band, and the corrected gradation level is included in the gradation band. Pixel data indicating the target gradation value when it is determined that a tone value is included When it is determined that the corrected gradation value is not included in the gradation band, pixel data indicating gradation values other than the target gradation value is generated as the second converted pixel data. The device according to claim 1, wherein the device is generated as post-pixel data. The pre-conversion image data includes pixel data generated according to drawing instruction data for instructing drawing of a character or a line,
Drawing instruction data acquisition means for acquiring the drawing instruction data;
Based on the drawing instruction data, conversion target area specifying data for specifying a conversion target area that specifies a conversion target area in which a character or line is drawn on a two-dimensional array is generated. And generating means,
2. The post-conversion image data output unit does not output the second post-conversion image data regarding the pixels not included in the region indicated by the conversion target region designation data on the two-dimensional array to the display unit. The apparatus in any one of thru | or 8. An area including the edge position on the two-dimensional array, wherein a position on the two-dimensional array in which the index indicating the degree of density change is equal to or greater than a predetermined threshold is specified as an edge position in the image indicated by the pre-conversion image data. Conversion target area specifying data generating means for generating conversion target area specifying data, which is data indicating the conversion target area,
2. The post-conversion image data output unit does not output the second post-conversion image data regarding the pixels not included in the region indicated by the conversion target region designation data on the two-dimensional array to the display unit. The apparatus in any one of thru | or 8. The second pixel data converting means converts the pre-conversion pixel data into the second post-conversion pixel data based on the gradation value indicated by the one pre-conversion pixel data. The apparatus according to claim 8, wherein at least one of an upper limit gradation value and a lower limit gradation value is determined. The pre-conversion image data is the (i + 1) -th pre-conversion image data, and the second post-conversion image data generated based on the (i + 1) -th pre-conversion image data is the (i + 1) -th post-conversion image data. Until the (i + 1) th converted image data is output to the display means by the converted image data output means, the image data indicating the image displayed on the display means is i-th When the pre-conversion image data obtained by the pre-conversion image data acquisition means and used for the conversion of the i-th post-conversion image data is used as the post-conversion image data,
The second pixel data conversion means converts the first pre-conversion pixel data into the second post-conversion pixel data in the conversion related to the (i + 1) th pre-conversion image data. The upper limit gradation value and the lower limit gradation of the gradation band based on the gradation value indicated by the pixel data whose position in the two-dimensional array is the same as the one pre-conversion pixel data among the pixel data included in The apparatus of claim 8, wherein at least one of the values is determined. The pre-conversion image data is the (i + 1) -th pre-conversion image data, and the second post-conversion image data generated based on the (i + 1) -th pre-conversion image data is the (i + 1) -th post-conversion image data. Until the (i + 1) th converted image data is output to the display means by the converted image data output means, the image data indicating the image displayed on the display means is i-th When the pre-conversion image data obtained by the pre-conversion image data acquisition means and used for the conversion of the i-th post-conversion image data is used as the post-conversion image data,
The second pixel data converting means converts the pre-conversion pixel data into the second post-conversion pixel data in the conversion related to the (i + 1) -th pre-conversion image data. Among the gradation bands used for each pixel data in the conversion related to the i-th pre-conversion image data, the one of the gradation bands indicated by the same pixel data as the one-dimensional pixel data and the position on the two-dimensional array Based on at least one of the upper limit gradation value and the lower limit gradation value, at least one of the upper limit gradation value and the lower limit gradation value of the gradation band used for the conversion of the one pre-conversion pixel data is determined. The apparatus according to claim 8. The apparatus according to claim 1, comprising the display unit. The display means displays the image among the currently displayed pixels when displaying an image according to the first converted image data or the second converted image data received from the converted image data output means. Redrawing is performed on at least some of the pixels displayed with the same gradation value as the gradation value indicated by the pixel data included in the first converted image data or the second converted image data. The apparatus of claim 14. The display means displays the image among the currently displayed pixels when displaying an image according to the first converted image data or the second converted image data received from the converted image data output means. A pixel that is displayed with a gradation value different from the gradation value indicated by the pixel data included in one converted image data or the second converted image data, and a region that is continuous with the pixel and defined by a predetermined rule The apparatus according to claim 15, wherein redrawing is performed only with respect to pixels included in. a pre-conversion image data acquisition step of acquiring, as pre-conversion image data, image data including a plurality of pre-conversion pixel data indicating pixels included in an image of a gradation (where a is a predetermined natural number satisfying a>2); ,
Among the gradation values of one pre-conversion pixel data included in the pre-conversion image data and (b-1) dither threshold values (where b is a predetermined natural number satisfying a>b> 1) A first pixel data conversion step of generating first converted pixel data of b gradation by comparison with one dither threshold value set for the pixel position of the pixel data before conversion;
A gradation value after correction that is a value obtained by adding a gradation value of the one pre-conversion pixel data and a correction value that is a diffusion error value distributed to the one pre-conversion pixel data according to an error diffusion method; A second pixel data conversion step of generating second converted pixel data of b gradation based on a magnitude relationship with one error diffusion threshold;
When the second post-conversion pixel data is generated in the second pixel data conversion step, the second post-conversion pixel data is converted from the post-correction gradation value related to the one pre-conversion pixel data. Pre-conversion pixel data that has not yet been used in the conversion in the second pixel data conversion step among the plurality of pre-conversion pixel data, which is a value obtained by subtracting the gradation value in the case of gradation In addition, each of the one or more pre-conversion pixel data selected according to a predetermined rule that forms a continuous area with the one pre-conversion pixel data on the two-dimensional array is distributed as the correction value according to the predetermined rule. An error diffusion step to
After the data including the first converted pixel data set is output as the first converted image data to the display unit capable of displaying the b-gradation image, the second converted pixel data set is output. A post-conversion image data output step for outputting data including the second post-conversion image data. On the computer,
pre-conversion image data acquisition processing for acquiring, as pre-conversion image data, image data including a plurality of pre-conversion pixel data indicating pixels included in an image of a gradation (where a is a predetermined natural number satisfying a> 2) ,
Among the gradation values of one pre-conversion pixel data included in the pre-conversion image data and (b-1) dither threshold values (where b is a predetermined natural number satisfying a>b> 1) A first pixel data conversion process for generating first converted pixel data of b gradation by comparison with one dither threshold value set for the pixel position of the pixel data before conversion;
A gradation value after correction that is a value obtained by adding a gradation value of the one pre-conversion pixel data and a correction value that is a diffusion error value distributed to the one pre-conversion pixel data according to an error diffusion method; A second pixel data conversion process for generating second converted pixel data of b gradation based on a magnitude relationship with one error diffusion threshold;
When the second post-conversion pixel data is generated in the second pixel data conversion process, the second post-conversion pixel data is converted from the post-correction gradation value related to the one pre-conversion pixel data. Pre-conversion pixel data that has not yet been used in the conversion in the second pixel data conversion processing among the plurality of pre-conversion pixel data, which is a value obtained by subtracting the gradation value in the case of gradation. In addition, each of the one or more pre-conversion pixel data selected according to a predetermined rule that forms a continuous area with the one pre-conversion pixel data on the two-dimensional array is distributed as the correction value according to the predetermined rule. Error diffusion processing to
After the data including the first converted pixel data set is output as the first converted image data to the display unit capable of displaying the b-gradation image, the second converted pixel data set is output. A program for executing post-conversion image data output processing for outputting data including a second post-conversion image data.

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