JP2008145642A - Error diffusion apparatus and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an error diffusion apparatus and a display device which are capable of making output pixels irregularly emitting light on the basis of error components, continuous and making noise due to the error components inconspicuous. <P>SOLUTION: An error diffusion apparatus 200 includes a bit conversion circuit 11 for converting an image input signal for a target pixel, of which the number of display bits is m, to an image output signal for the target pixel, of which the number of display bits is n (n<m), and is so configured that error components corresponding to lower order (m-n) bits of the image input signal are distributed to output pixels displaying colors different from a color which the target pixel displays. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an error diffusion device and a display device, and more particularly to improvement of a halftone display technique using an error diffusion method.

  Thin panels such as liquid crystal panels and plasma display panels (hereinafter abbreviated as “PDP”) are becoming mainstream display devices for televisions in place of existing CRTs.

  Unlike the CRT driving method, the PDP driving method is a direct driving method using a digitized image input signal. Specifically, in the plasma display device, the number of bits of the image input signal that can be processed in the plasma display device is limited according to the number of gradations of the image displayed on the screen (subfield method).

  For this reason, when an image input signal having a number of bits that exceeds the number of display bits that can be processed in the plasma display apparatus is input to the plasma display apparatus, an error occurs in the gradation of the display image.

  For example, when an image input signal having a display bit number of 10 bits is input to a plasma display device in which the display bit number of one pixel is 8 bits (256 gradations), a 2-bit error component is generated. In this case, if the 2-bit data of the 10-bit image input signal is simply reduced, the tone reproducibility of the image when displayed on the screen of the plasma display device is deteriorated. On the other hand, if the number of display bits of one pixel is increased, the problem of deterioration in gradation reproducibility is solved, but the emission luminance is lowered.

  In view of this, an error diffusion method has been developed in which such error components are diffused spatially and / or temporally to a predetermined pixel so as to simulate a larger number of gradations with a smaller number of output gradations. (For example, refer to Patent Document 1). By this error diffusion method, 2-bit data, which is an error component of the image input signal, can be reflected by adding it to the 8-bit image input signal according to the signal level (luminance level) of the image input signal. Tonal reproducibility is improved.

  FIG. 6 is a block diagram showing an example of the configuration of such a conventional error diffusion device.

  The conventional error diffusion device 100 includes an R error diffusion circuit 60R and a G error diffusion circuit 60G that perform error diffusion for each of the three primary color signals of R (red), G (green), and B (blue). B error diffusion circuit 60B.

  The R error diffusion circuit 60R, the G error diffusion circuit 60G, and the B error diffusion circuit 60B receive the R, G, and B image input signals, perform the signal processing described later, and do not illustrate the R, G, and B image output signals, respectively. The data is output to a display device (hereinafter, a “plasma display device” having a PDP will be described as an example).

  Hereinafter, a detailed configuration of the error diffusion circuit 100 will be described.

  The R error diffusion circuit 60R, the G error diffusion circuit 60G, and the B error diffusion circuit 60B have the same configuration except for the type of the image input / output signal, and operate independently in the same manner. Therefore, here, the configuration and operation of the R error diffusion circuit 60R will be described as a representative example, and description of the other configurations and operations of the G error diffusion circuit 60G and the R error diffusion circuit 60B will be omitted.

  The R error diffusion circuit 60R includes an R bit conversion circuit 61, an R error detection circuit 64, and an adder 67, as shown in FIG.

  The R image input signal is input to the R bit conversion circuit 61 through the adder 67. The R bit conversion circuit 61 performs signal processing for converting (reducing) the number of display bits of the R image input signal, and outputs this signal as an R image output signal to a driver circuit (not shown) of the plasma display device. Note that an R error component described later is added to the R image input signal.

  The R error detection circuit 64 converts an R error component generated when the number of display bits is reduced in the R bit conversion circuit 61 to other pixels in the target pixel field that displays the same color as the target pixel at a predetermined ratio, or The target pixel displaying the same color as the target pixel is distributed to other pixels in the subsequent field.

The adder 67 adds the R error component thus distributed to the R image input signal, but degrades the original image for the purpose of eliminating the pseudo pattern generated in the image obtained by the pseudo halftone display. There may be provided means for adding or subtracting random correction values to such an extent that no correction is made.
JP-A-7-64505

  The plasma display device incorporating the conventional error diffusion device described above can increase the number of apparent gradations by pseudo halftone display by the error diffusion method.

  However, the plasma display apparatus can only display an image with a digitally limited number of gradations (for example, a digital signal with 256 gradations if 8 bits). For this reason, in a plasma display device incorporating a conventional error diffusion processing device, for example, the gray level of an image input signal such as a black band mask portion in the upper and lower portions of the screen or an image that occupies a dark screen as a whole is zero or If numerical values near zero are continuously included, an image that should be all black as a display image may be conspicuous as image quality interference such as periodic pattern noise peculiar to error diffusion depending on the conditions of the image input signal.

  In addition, error diffusion itself is a technique used to reduce the influence of quantization noise caused by a reduction in the number of bits of displayed resolution. In some cases, high-frequency and low-amplitude noise that can be visually recognized by a viewer who is watching at

  The cause of such image quality degradation is considered to be related to the diffusion range of the error diffusion method.

  A stripe-shaped pixel displaying the same color of a display panel of a plasma display device usually repeats R, G, and B in a direction orthogonal to the direction extending in the stripe shape (hereinafter referred to as “lateral direction” for convenience). Discretely arranged based on. As a result, the diffusion range of the conventional error diffusion method such as error component diffusion to the output pixel in the horizontal direction, which displays the same color as the target pixel, inevitably becomes discrete. This widens the diffusion range of the error component, and it is estimated that irregular pixel emission based on the diffused error component is easily recognized as noise.

  The present invention has been made in view of such circumstances, and an error diffusion device and a display device that can continuously output pixels that emit light irregularly based on an error component and make noise due to the error component less noticeable. The purpose is to provide.

  In order to solve the above problems, an error diffusion device according to the present invention provides an image input signal for a pixel of interest having a display bit number of (m) bits, and the display bit number of (n) bits (n <m). A bit conversion circuit for converting into an image output signal for the target pixel, and distributing an error component corresponding to the lower (mn) bits of the image input signal to an output pixel displaying a color different from the target pixel It is configured.

  Here, the error component includes a first error component for diffusion to an output pixel that displays the same color as the target pixel and a second error for diffusion to an output pixel that displays a color different from the target pixel. An error divider for allocating the components, and an error for acquiring the first and second error components and determining the output pixel for diffusing the first and second error components based on a switching signal of a controller An error detection circuit comprising: a selector; and a delay unit that delays output timings of the first and second error components given by the error selector in accordance with selection of the output pixel by the error selector. A first adder that adds the first error component provided by the delay unit to the image input signal of an output pixel that displays the same color as the target pixel, and the first adder provided by the delay unit. Second error A second adder for adding the partial to the image input signal of the output pixels displaying different colors and the pixel of interest, may be provided.

  Thereby, the error component of the target pixel can be diffused to the output pixel that displays a color different from that of the target pixel.

  According to such a configuration, the second adder can add the second error component to the image input signal of the output pixel spatially adjacent to the target pixel, and as a result, error diffusion. It is possible to prevent the region from being separated due to the influence of the arrangement pattern of the R, G, and B output pixels. Therefore, the output pixels that emit light irregularly based on the diffused error component are continuous, and noise due to the diffused error component is less noticeable. Further, compared with the conventional error diffusion method, the diffusion range of the error component is narrowed, and irregular output pixel light emission based on the diffused error component can be hardly recognized as noise.

  The first adder may add the first error component to the image input signal of an output pixel that is spatially separated from the target pixel.

  As a result, the error component is distributed by being divided into a component that diffuses to an output pixel that is spatially separated from the target pixel and displays the same color, and a component that diffuses to an output pixel that is spatially adjacent to the target pixel. That is, it is possible to appropriately suppress screen coloring of unnecessary noise due to error diffusion to an output pixel that displays a different color spatially adjacent to the target pixel.

  The error divider may distribute the error component into the first error component and the second error component based on the number of bits of the error component.

  For example, when the number of bits of the error component is only the minimum bit, the error divider may distribute the error component as the second error component.

  In this way, since the emission luminance of the minimum bit is low, even if the error component based on the minimum bit is diffused to the output pixel that is spatially adjacent to the target pixel and displays a different color, the screen color of unnecessary noise is appropriately displayed. While it can be suppressed, output pixels that emit light irregularly based on the diffused error component can be continued, and noise due to the diffused error component is less noticeable.

  The error divider may convert the error component from the first error component so that the ratio of the first error component for each output pixel differs from the ratio of the second error component for each output pixel. You may distribute to the said 2nd error component.

  For example, the output pixel that diffuses the second error component includes pixels that display red, green, and blue, respectively, and the ratio of the second error component for each output pixel is red, green, and blue. It may be set based on white balance.

  By determining the ratio of error components for each output pixel in consideration of white balance, coloring due to unnecessary noise when error components are diffused to output pixels that are spatially adjacent to the target pixel and display different colors It can be suppressed more appropriately.

  According to another aspect of the present invention, there is provided a display device that incorporates the error diffusion device described above and drives the display panel to perform gradation display using the image output signal.

  According to the present invention, it is possible to obtain an error diffusion device and a display device in which output pixels that emit light irregularly based on an error component can be continuously formed, and noise due to the error component is less noticeable.

  Hereinafter, first and second embodiments will be described with reference to the drawings. However, the present invention is not limited to the description of these embodiments.

(First embodiment)
FIG. 1 is a block diagram showing a configuration example of an error diffusion device according to the first embodiment of the present invention.

  As shown in FIG. 1, the error diffusion device 200 of this embodiment includes an R error diffusion circuit 10R that performs error diffusion processing on an R image input signal, and a G error diffusion circuit 10G that performs error diffusion processing on a G image input signal. And a B error diffusion circuit 10B that performs error diffusion processing on the B image input signal.

  Next, the configuration of the R error diffusion circuit 10R will be described.

  Note that the G error diffusion circuit 10G and the B error diffusion circuit 10B can be understood from the following description of the R error diffusion circuit 10G, and thus detailed description thereof will be omitted.

  The R error diffusion circuit 10R converts an R bit conversion circuit 11 for converting (reducing) the display bit number of the R image input signal, and an R error component generated when the display bit number is reduced in the R bit conversion circuit 11 as R R to be distributed to other pixels in the field of interest (hereinafter abbreviated as “R pixel of interest”), or to other pixels subsequent to the R pixel of interest (for example, the next frame of the current frame) at a predetermined ratio. An error detection circuit 14 and an adder 17 that adds the distributed R error component to the subsequent R image input signal are provided.

  Here, the R error detection circuit 14 is connected to an adder 17 corresponding to the R error diffusion circuit 10R, an adder 18 corresponding to the G error diffusion circuit 10G, and an adder 19 corresponding to the B error diffusion circuit 10B by the wiring 301. On the other hand, the R error component can be distributed to an appropriate ratio.

  Similarly, the G error detection circuit 15 of the G error diffusion circuit 10G is connected to the adder 18 corresponding to the R error diffusion circuit 10R and the B error diffusion in addition to the adder 18 corresponding to the G error diffusion circuit 10G through the wiring 302. For the adder 19 corresponding to the circuit 10B, the G error component can be distributed to an appropriate ratio. Also, the B error detection circuit 16 of the B error diffusion circuit 10B is connected to the adder 19 corresponding to the B error diffusion circuit 10B, the adder 17 corresponding to the R error diffusion circuit 10R, and the G error diffusion circuit 10G via the wiring 303. The B error component can be distributed to an appropriate ratio for the adder 18 corresponding to.

  Next, the configuration of the R error detection circuit 14 will be described with reference to FIG.

  FIG. 2 is a block diagram showing a configuration example of the R error detection circuit and a connection example between the R error detection circuit and each adder.

  However, in FIG. 2, the R bit conversion circuit 11 of FIG. 1 is omitted for the purpose of simplifying the illustration.

  In the following description, after the digitized R image input signal (original image data) having the number of display bits of (m) bits passes through the R bit conversion circuit 11, finally, (m) bits Are output to the plasma display device as digitized R image output signals of upper (n) bits.

  As shown in FIG. 2, the R error detection circuit 14 includes an error divider 21, an error selector 22, an in-field delay unit 23, and an inter-field delay unit 24.

  The error divider 21 receives the lower (mn) bit data of the (m) bit R image input signal as the R error component from the R bit conversion circuit 11 (see FIG. 1), and this lower (m−). n) The R error component of the bit is divided into an intra-field error component and an inter-field error component.

  In this case, each of the inter-field error component and the intra-field error component is further diffused by the error divider 21 to an output pixel that displays the same color as the R target pixel based on a predetermined method (described later). An error component (first error component) and an error component (second error component) for diffusion to an output pixel that displays a color different from that of the R target pixel are sorted.

  Here, the in-field error component refers to a signal of an error component that is to be spatially diffused to output pixels in the same field as the field in which the target pixel exists. The inter-field error refers to a signal of an error component that is scheduled to be temporally diffused to output pixels in a field subsequent to the field where the target pixel exists.

  The first error component is input to the adder 17, and the second error component is input to the adder 18 or the adder 19.

  When the error divider 21 distributes the intra-field error component and the inter-field error component to the first and second error components, an error diffusion device (not shown) shows the ratio of the first and second error components. Appropriately set for each output pixel based on the ratio representing the diffusion ratio of the error component stored in the 200 internal memory (ROM or RAM). An example of setting the ratio of error components will be described in detail later.

  The error selector 22 receives the first and second error components given by the error divider 21 and the switching signal output from the controller 25, whereby the error selector 22 controls the switching of the controller 25. Based on the above, one of the plurality of intra-field error components and one of the plurality of inter-field error components are respectively associated with the R, G, and B output pixels of the diffusion destination. To select.

  For example, whether the error selector 22 diffuses a part of the R error component generated in the R attention error to the output pixel in the field of the R attention pixel as an in-field error component based on the switching signal of the controller 25. And whether or not a part of the R error component generated in the R attention error is diffused as an inter-field error component to an output pixel in a field subsequent to the field where the R attention pixel exists. Further, the error selector 22 determines, based on the switching signal from the controller 25, the output component in the field of the R pixel of interest as the one in-field error component, and the one of the above-mentioned ones. One inter-field error component is used to determine which output pixel in the field subsequent to the field in which the R pixel of interest exists is the diffusion destination.

  The intra-field delay unit 23 receives the one intra-field error component from the error selector 22, and according to the output pixel that diffuses the one intra-field error component (according to the output pixel selection by the error selector 22). ) The output timing of the one intra-field error component to the adder is delayed as appropriate and output to any one of the adders 17, 18, 19.

  For example, the intra-field delay unit 23 is a circuit capable of delaying the one intra-field error component in the row (horizontal) direction by one or more dot periods, or the one intra-field error component in the column (vertical) direction. Includes a circuit capable of delaying by one or a plurality of scanning periods, so that when the one intra-field error component is diffused to the output pixel adjacent to the R target pixel in the row direction, the intra-field delay The unit 23 delays the output timing of the one intra-field error component to the adder by one dot period, and diffuses the one intra-field error component to the output pixel adjacent to the R target pixel in the column direction. In this case, the intra-field delay unit 23 delays the output timing of this one intra-field error component to the adder by one scanning period.

  The inter-field delay unit 24 receives the one inter-field error component from the error selector 22, and according to the output pixel that diffuses this one inter-field error component (according to the selection of the output pixel by the error selector 22). ) The output timing of the one inter-field error component to the adder is delayed as appropriate and output to any one of the adders 17, 18, and 19.

  For example, the inter-field delay unit 24 includes a circuit that delays the one inter-field error component in the time direction by one to a plurality of field periods, and thereby outputs the output pixel of the next field corresponding to the R target pixel. When the one inter-field error component is diffused, the inter-field delay unit 24 delays the output timing of the one inter-field error component to the adder by one field period.

  When the adder 17 receives the one intra-field error component from the intra-field delay unit 23, the adder 17 adds the one intra-field error component to the R image input signal, and the inter-field delay unit 24 adds the one intra-field error component. When an inter-field error component is received, the one inter-field error component is added to the R image input signal.

  Although the adder 17 is not shown here, the G error detection circuit 15 shown in FIG. When one intra-field error component and one inter-field error component are received from (1), these error components are added to the R image input signal.

  Further, although not shown here, the adder 17 is omitted from the B error detection circuit 16 of FIG. 1 (more precisely, an intra-field delay device and an inter-field delay device built in the B error detection circuit 16 (not shown)). When one intra-field error component or one inter-field error component is received from (1), these error components are also added to the R image input signal.

  In this way, the R image input signal to which the R, G, and B error components are added is converted (reduced) in the number of display bits by the R bit conversion circuit 11, and is output to the plasma display device as an R image output signal.

  The controller 25 is constituted by a microprocessor, for example, and outputs a control signal (switching signal) for controlling the switching operation of the error selector 22 to the error selector 22. The controller 25 may control the overall operation of the error diffusion device 100 in addition to the switching operation of the error selector 22.

  Next, an example of diffusing the in-field error component and the inter-field error component of the target pixel to the output pixel spatially and temporally adjacent to the target pixel will be described with reference to FIG.

  FIG. 3 is a perspective view schematically showing an example of diffusion of the in-field error component and the inter-field error component by the error diffusion device of this embodiment to the output pixel spatially and temporally adjacent to the target pixel. is there. The rectangular perspective plane shown in FIG. 3 assumes one screen of the display device in one field period. In FIG. 3, the screen of the Lth field period (hereinafter abbreviated as “L field”) and the next A screen of the (L + 1) -th field period (hereinafter abbreviated as “(L + 1) field”) is drawn.

  One screen of the display device displays an image based on a large number of pixels (picture elements) of R, G, and B, which are the minimum display units. In FIG. The extending direction of the phosphor regions is the “Y; column direction” direction, and the direction in which the R, G, and B phosphor regions are arranged in this order perpendicular to the “Y” direction is “X; row direction”. As directions, nine regions divided into 3 rows × 3 columns in the XY direction are each drawn as one pixel. A region of G pixels corresponding to the center (2 rows × 2 columns) of the (L) field and the (L + 1) field is set as a target pixel P0 here.

  However, the pixel arrangement pattern in FIG. 3 is merely an example described for the purpose of explaining the diffusion of the error component of the present embodiment, and the pixel arrangement pattern is not limited to this.

  As shown in FIG. 3, the in-field error component E2 due to the target pixel P0 in the (L) field is spatially located in a region adjacent to the target pixel P0 (including an output pixel that displays a different color from the target pixel P0). Specifically, the B output pixel P1 adjacent to the target pixel P0 in the X direction, the B output pixel P2 adjacent to the B output pixel P1 in the Y reverse direction, and the target pixel P0 in the Y reverse direction are diffused. The G output pixel P3 and the R output pixel P4 adjacent to the G output pixel P3 in the X reverse direction are each spatially diffused at a predetermined ratio.

  The inter-field error component E1 due to the target pixel P0 in the (L) field is temporally diffused from the L field to the pixel P5 in the (L + 1) field by one field period, and then the same as the in-field error component E2. The B output pixel P6 adjacent to the pixel P5 in the X direction, the B output pixel P7 adjacent to the B output pixel P6 in the Y reverse direction, the G output pixel P8 adjacent to the pixel P5 in the Y reverse direction, and the X reverse In the direction, the G output pixel P8 and the R output pixel P9 adjacent to the G output pixel P8 are spatially diffused at a predetermined ratio.

  Here, numerical values obtained by multiplying the in-field error component E2 by a predetermined coefficient K1, K2, K3, or K4 are diffused to the B output pixel P1, the B output pixel P2, the G output pixel P3, and the R output pixel P4, respectively. ing. Similarly, numerical values obtained by multiplying the inter-field error component E1 by a predetermined coefficient K1, K2, K3, or K4 are diffused to the B output pixel P6, the B output pixel P7, the G output pixel P8, and the R output pixel P9, respectively. Yes. The coefficients K1, K2, K3, and K4 for each output pixel of such error components are set to appropriate values that satisfy the relationship of K1 + K2 + K3 + K4 = 1. For example, the coefficients K1, K2, K3 and K4 are based on the known error diffusion method published by Floyd and Steinberg, and K1 = 7/16, K2 = 1/16, K3 = 5/16 and K4 = It may be set to 3/16. These coefficient data are stored in the internal memory of the error diffusion device 200, for example.

  As described above, the error diffusion device 200 of the present embodiment can diffuse the error component of the target pixel P0 to output pixels that are spatially adjacent to the target pixel P0 and display different colors. For this reason, the error diffusion region is prevented from being separated by being affected by the arrangement pattern of the R, G, and B output pixels, and as a result, an output that emits light irregularly based on the diffused error component. Pixels become continuous, and noise due to diffused error components is less noticeable. Further, compared with the conventional error diffusion method, the diffusion range of the error component is narrowed, and irregular output pixel light emission based on the diffused error component can be hardly recognized as noise.

(Modification 1)
In the present embodiment, the error diffusion device that can diffuse the error component of the target pixel P0 to the output pixel spatially and temporally adjacent to the target pixel P0 at a predetermined ratio has been described. Here, as a first modification, in addition to an output pixel that is spatially and temporally adjacent to the target pixel P0, an output pixel that is spatially separated from the target pixel P0 and displays the same color as the target pixel P0. An error diffusion device capable of diffusing errors will be described.

  FIG. 4 shows the output pixel and the target pixel spatially and temporally adjacent to the target pixel for the intra-field error component and the inter-field error component by the error diffusion device of this embodiment. It is the perspective view which showed typically the example of the spreading | diffusion to the output pixel which displays the same color.

  In FIG. 4, the extending direction of the stripe-shaped R, G, and B phosphor regions is defined as “Y; column direction”, and the R, G, and B phosphor regions are orthogonal to the “Y” direction. , G and B are arranged in the order of “X; row direction”, and 27 regions divided into 3 rows × 9 columns in the XY direction are drawn as one pixel. A region of G pixels corresponding to the center (2 rows × 5 columns) of the (L) field and the (L + 1) field is set as a target pixel P0 here.

  As shown in FIG. 4, the in-field error component E2 due to the target pixel P0 in the (L) field is spatially located in a region adjacent to the target pixel P0 (including an output pixel that displays a different color from the target pixel P0). Specifically, the B output pixel P1 adjacent to the target pixel P0 in the X direction, the B output pixel P2 adjacent to the B output pixel P1 in the Y reverse direction, and the target pixel P0 in the Y reverse direction are diffused. The G output pixel P3 and the R output pixel P4 adjacent to the G output pixel P3 in the X reverse direction are each spatially diffused at a predetermined ratio.

  The in-field error component E2 is also spatially diffused in a region separated from the pixel of interest P0 (however, an output pixel displaying the same color as the pixel of interest P0), specifically, in the X direction. A G output pixel P5 separated by 3 pixels from the pixel P0, a G output pixel P6 adjacent to the G output pixel P5 in the Y reverse direction, and 3 pixels from the target pixel P0 in the X reverse direction. Are spatially diffused to the G output pixel P7 adjacent to each other at a predetermined ratio.

  The inter-field error component E1 due to the pixel of interest P0 in the (L) field is temporally diffused from the L field to the pixel P8 in the (L + 1) field so as to be delayed by one field period, and then adjacent to the pixel P8. Are spatially diffused in a region (including an output pixel that displays a different color from the target pixel P0), specifically, a G output pixel P9 adjacent to the pixel P8 in the X direction, and a G output pixel in the Y reverse direction. G output pixel P10 that is adjacent to P9, G output pixel P11 that is adjacent to pixel P8 in the Y reverse direction, and R output pixel P12 that is adjacent to G output pixel P11 in the X reverse direction are spatially spaced at a predetermined ratio. Is diffused.

  Further, the inter-field error component E1 is temporally diffused from the L field to the (L + 1) field pixel P8 so as to be delayed by one field period, and then separated from the pixel P8 (provided that it is different from the target pixel P0). Output pixels that display the same color), specifically, the G output pixel P13 that is separated from the pixel P8 by 3 pixels in the X direction and the G output pixel P13 that is adjacent to the G output pixel P13 in the Y reverse direction. The output pixel P14 and the G output pixel P15 that is separated from the pixel P8 in the X reverse direction by 3 pixels and is adjacent in the Y reverse direction from this position are spatially diffused at a predetermined ratio.

  Here, numerical values obtained by multiplying the in-field error component E2 by predetermined coefficients K1, K2, K3, K4, K5, K6, and K7 are the G output pixel P5, the G output pixel P7, the G output pixel P3, G, respectively. The output pixel P6, the B output pixel P1, the R output pixel P4, and the B output pixel P2 are diffused. Similarly, numerical values obtained by multiplying the inter-field error component E1 by predetermined coefficients K1, K2, K3, K4, K5, K6, and K7 are the G output pixel P13, the G output pixel P15, the G output pixel P11, and the G output, respectively. The pixel P14, the B output pixel P9, the R output pixel P12, and the B output pixel P10 are diffused. The coefficients K1, K2, K3, K4, K5, K6, and K7 for each output pixel of such error components are set to appropriate values that satisfy the relationship of K1 + K2 + K3 + K4 + K5 + K6 + K7 = 1. For example, each coefficient K1, K2, K3, K4, K5, K6, and K7 is based on the known error diffusion method published by Floyd and Steinberg and K1 = 6/16, K2 = 1/16, K3 = 4/16, K4 = 2/16, K5 = 1/16, K6 = 1/16 and K7 = 1/16. These coefficient data are stored in the internal memory of the error diffusion device 200, for example.

  The error diffusion device of the present modification can diffuse the error component of the target pixel P0 to output pixels that are spatially adjacent to the target pixel P0 and display different colors. For this reason, the error diffusion region is prevented from being separated by being affected by the arrangement pattern of the R, G, and B output pixels, and as a result, an output that emits light irregularly based on the diffused error component. Pixels become continuous, and noise due to diffused error components is less noticeable. Further, compared with the conventional error diffusion method, the diffusion range of the error component is narrowed, and irregular output pixel light emission based on the diffused error component can be hardly recognized as noise.

  Further, the error diffusion device of the present modified example diffuses the error component to an output pixel that is spatially separated from the target pixel P0 and displays the same color, and to an output pixel that is spatially adjacent to the target pixel P0. By allocating and diffusing components to diffuse, it is possible to appropriately suppress screen coloring of unnecessary noise due to error diffusion to output pixels that display different colors spatially adjacent to the target pixel P0.

(Modification 2)
The feature of the error diffusion device of this modification is that the error diffusion operation is different between the case where only the minimum bit of the display bits of the image input signal is used as the error component and the other case.

  Specifically, when only the minimum bit is used as an error component, the controller 25 (see FIG. 2) displays an output pixel (a color different from the target pixel) spatially adjacent to the target pixel P0 as shown in FIG. The error diffusion device is controlled so that error diffusion is performed only on the output pixel (including the output pixel to be output), and in other cases, as shown in FIG. 4, in addition to the output pixel spatially adjacent to the target pixel P0, the target pixel The error diffusion device 200 is controlled so that error diffusion is performed on output pixels that are spatially separated from P0 and display the same color.

  In this way, since the light emission luminance of the minimum bit is low, even if an error component based on the minimum bit is diffused to an output pixel that is spatially adjacent to the target pixel P0 and displays a different color, the screen color of unnecessary noise is appropriately obtained. On the other hand, compared to the first modification, output pixels that emit light irregularly based on the diffused error component can be more positively continued, and noise due to the diffused error component is less noticeable.

(Modification 3)
In this embodiment, the known error diffusion published by Floyd and Steinberg for each coefficient K1, K2, K3 and K4 for each output pixel of the error component stored in advance in the internal memory of the controller 25 (FIG. 2). An example in which K1 = 7/16, K2 = 1/16, K3 = 5/16 and K4 = 3/16 has been described based on the law.

  In the error diffusion device of the present modification, an example will be described in which the coefficients K1, K2, K3, and K4 are corrected by considering the white balance of the output pixels.

  White light is generally composed of a balance in which the amounts of red, green, and blue light are set to 3: 6: 1. For this reason, when the error component is diffused to the output pixel that displays a different color spatially adjacent to the green pixel of interest P0, the coefficients K1, K2, K3, and K4 are considered in consideration of such a white balance ratio. For example, K1 = 1/16, K2 = 1/16, K3 = 9/16, K4 = 5/16.

  These coefficient data are stored in the internal memory of the error diffusion device 200, for example. These coefficient data are merely examples, and optimum coefficients may be obtained in accordance with individual characteristics of the display device.

  The error diffusion device according to the present modification determines the error component coefficient for each output pixel in consideration of white balance, so that the error component is output to an output pixel that is spatially adjacent to the target pixel P0 and displays a different color. When diffused, coloring due to unnecessary noise can be suppressed more appropriately.

(Second Embodiment)
FIG. 5 is a block diagram showing a configuration example of a display device according to the second embodiment of the present invention. Here, the configuration of the display device will be described taking the plasma display device 300 (hereinafter, abbreviated as “PDP device 300”) as an example.

  As shown in FIG. 5, the PDP device 300 includes an inverse γ (gamma) conversion unit 51, the error diffusion device 200 configured as described above, a subfield conversion unit 53, a discharge control timing generation circuit 54, and a PDP 55. A data driver circuit 56, a sustain driver circuit 57, and a scan driver circuit 58 are provided.

  First, an outline of the configuration of the PDP 55 will be described.

The PDP 55 is configured such that a front surface 2 made of glass and a rear surface substrate 3 are disposed so that their main surfaces face each other and a discharge space is formed therebetween. On the main surface of the front substrate 2, formed in plural in rows (horizontal) of the n extending in the direction scanning electrodes SCN ₁ ~SCN _n and n sustain electrodes SUS ₁ ~SUS _n and is parallel to pair with one another Yes. Further, m data electrodes D _{1 to} D _m extending in the column (vertical) direction are formed on the main surface of the back substrate 3.

In this way, n scan electrodes SCN _{1 to} SCN _n and n sustain electrodes SUS _{1 to} SUS _n are alternately arranged in the horizontal direction, and m data electrodes D _{1 to} D _m are arranged in the vertical direction. Has been. A region where the scan electrode SCN _i and the sustain electrode SUS _i (i = 1 to n) and one data electrode D _j (j = 1 to _m ) forming a pair intersect with each other across the discharge space and its vicinity region Becomes one discharge cell (pixel) contributing to image display. That is, each pixel includes a pair of display electrodes (scan electrode SCN _i and sustain electrode SUS _i ) and one data electrode D _m , and includes a discharge space between them. Therefore, m × n pixels are formed on the PDP 55.

  In the PDP 55 having such a configuration, ultraviolet rays are generated by gas discharge in each pixel, and phosphors in a phosphor layer (not shown) are excited and emitted by the ultraviolet rays. Color display can be performed by separately coating the phosphor layer for each pixel, for example, red, green, and blue (RGB), which are the three primary colors of light.

  Next, a configuration for driving the PDP 55 in the PDP apparatus 300 will be described.

  In FIG. 5, the horizontal synchronization signal H and the vertical synchronization signal V are output to the discharge control timing generation circuit 54, the inverse γ conversion unit 51, the error diffusion device 200, and the subfield conversion unit 53.

  The discharge control timing generation circuit 54 generates the timing signals SU and SC of the sustain driver circuit 57 and the scan driver circuit 58 on the basis of the horizontal synchronization signal H and the vertical synchronization signal V, and outputs the timing signals SU and SC to these timing signals SU and SC. To the circuits 57 and 58.

The scan driver 58 drives the scan electrodes SCN _{1 to} SCN _n based on the applied timing signal SC. The sustain driver 57 drives the sustain electrodes SUS _{1 to} SUS _n based on the applied discharge control timing signal SU.

  The analog R, G, and B image signals are input to an appropriate A / D converter (not shown), where they are converted into digitized R, G, and B image signals.

  Then, the R, G, and B image signals are input to the inverse gamma conversion unit 51. The inverse gamma conversion unit 51 performs inverse gamma conversion on the (l) -bit input signal, whereby R, G, and B image input signals (m) having a display bit number (m) larger than the input signal > L) is output. In other words, the R, G, and B image input signals are each input to the error diffusion device 200 with a display bit number of (m) bits.

  The error diffusion device 200 converts the (m) -bit R, G, and B image input signals output from the inverse gamma conversion unit 51 into fewer (n) bits (n <m). (N) The R, G, and B image output signals of bits are output to the subfield conversion unit 53. In this case, since the error diffusion device 200 has the configuration described in the first embodiment, as described above, the error component corresponding to the lower bits (mn) is spatially adjacent to the target pixel. Are diffused to output pixels displaying different colors. The numerical values of (l), (m), and (n) are all positive integers.

  The subfield conversion unit 53 converts the R, G, and B image output signals of each pixel into serial data corresponding to a plurality of subfields, and provides this serial data to the data driver circuit 56.

The data driver circuit 56 converts the serial data supplied from the subfield conversion unit 54 into parallel data, and selectively applies a write pulse to the plurality of data electrodes D _{1 to} D _m based on the parallel data.

  In the PDP device 300 of the present embodiment described above, the error diffusion device 200 can diffuse the error component of the pixel of interest P0 to output pixels that are spatially adjacent to the pixel of interest P0 and display different colors. For this reason, the error diffusion region is affected by the arrangement pattern of the R, G, and B pixels and is prevented from being separated, and as a result, the PDP 55 that emits light irregularly based on the diffused error component is prevented. Discharge cells (output pixels) are continuous, and noise due to diffused error components is less noticeable. Further, compared with the conventional error diffusion method, the diffusion range of the error component is narrowed, and irregular pixel light emission based on the diffused error component can be made difficult to visually recognize as noise.

  In the present embodiment, the PDP device 300 is exemplified as the display device. However, the gradation display technology described here is not limited to this, and a field emission display (FED), digital light processing (DLP), electroluminescence (EL) ), And a display device using a digital display device such as a light emission diode (LED).

  The error diffusion device of the present invention makes noise due to the diffused error component inconspicuous, and can be used, for example, in an image display device capable of obtaining good image quality.

It is the block diagram which showed one structural example of the error diffusion apparatus by the 1st Embodiment of this invention. FIG. 5 is a block diagram showing a configuration example of a first R error detection circuit and a connection example between the R error detection circuit and each adder. It is the perspective view which showed typically the example of the spreading | diffusion to the output pixel which adjoins the attention pixel spatially and temporally about the error component in a field by the error diffusion apparatus of 1st Embodiment, and an error component between fields. Regarding the in-field error component and the inter-field error component by the error diffusion device of the first embodiment, the same color is displayed spatially separated from the target pixel and the target pixel spatially and temporally adjacent to the target pixel. It is the perspective view which showed the example of the spreading | diffusion to an output pixel typically. It is the block diagram which showed the outline | summary of the example of 1 structure of the display apparatus by the 2nd Embodiment of this invention. It is the block diagram which showed one structural example of the conventional error diffusion apparatus.

Explanation of symbols

11 R bit conversion circuit 12 G bit conversion circuit 13 B bit conversion circuit 14 R error detection circuit 15 G error detection circuit 16 B error detection circuit 17, 18, 19 Adder 21 Error divider 22 Error selector 23 In-field delay unit 24 Inter-field delay device 25 Controller

Claims (9)

A bit conversion circuit for converting an image input signal for a pixel of interest having a display bit number of (m) into the image output signal for the pixel of interest having a display bit number of (n) bits (n <m); ,
An error diffusion device that distributes an error component corresponding to lower (mn) bits of the image input signal to an output pixel that displays a color different from that of the target pixel. The error component is converted into a first error component for diffusion to an output pixel that displays the same color as the pixel of interest and a second error component for diffusion to an output pixel that displays a color different from the pixel of interest. An error divider that distributes, and an error selector that obtains the first and second error components and determines the output pixel that diffuses the first and second error components based on a controller switching signal; A delay unit that delays output timing of the first and second error components given by the error selector in accordance with selection of the output pixel by the error selector;
A first adder that adds the first error component provided by the delay unit to the image input signal of an output pixel that displays the same color as the target pixel;
A second adder that adds the second error component provided by the delay unit to the image input signal of an output pixel that displays a color different from the target pixel;
The error diffusion apparatus according to claim 1, comprising:   The error diffusion apparatus according to claim 2, wherein the second adder adds the second error component to the image input signal of an output pixel spatially adjacent to the target pixel.   The error diffusion apparatus according to claim 3, wherein the first adder adds the first error component to the image input signal of an output pixel spatially separated from the target pixel.   The error diffusion device according to claim 2, wherein the error divider distributes the error component into the first error component and the second error component based on the number of bits of the error component.   6. The error diffusion device according to claim 5, wherein when the number of bits of the error component is only the minimum bit, the error divider distributes the error component as the second error component.   The error divider converts the error component into the first error component and the first error component so that a ratio of the first error component for each output pixel is different from a ratio of the second error component for each output pixel. The error diffusion device according to claim 2, wherein the error diffusion device is divided into two error components.   The output pixels that diffuse the second error component include pixels that display red, green, and blue, respectively, and the ratio of the second error component for each output pixel is a white balance of red, green, and blue The error diffusion device according to claim 7, which is set based on Incorporating the error diffusion device according to any one of claims 1 to 8,
A display device that drives the display of gradation on the display panel using the image output signal.

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