JP5011636B2 - Image display method - Google Patents

Description

  The present invention relates to an image display method such as a plasma display panel (PDP) or a digital mirror device (DMD) that divides a one-field image into a plurality of subfield images and performs multi-gradation display.

  In an image display device such as a PDP or DMD that displays an image by binary control of light emission and non-light emission, an image based on a so-called subfield method that performs multi-gradation display by dividing an image of one field into a plurality of subfield images Display is common. In the subfield method, one field period is time-divided into a plurality of subfields weighted by the number of times of light emission or the amount of light emission, and gradation display is performed by a combination of subfields to emit light.

  FIG. 10 is a diagram illustrating an example of a subfield configuration in a conventional PDP. In the example shown in FIG. 10, one field is divided into eight subfields (SF1, SF2,..., SF8), and (1, 2, 4, 8, 16, 32, 64, 128) a luminance weight. Each subfield includes a setup period (T1) in which preliminary discharge is performed, an address period (T2) in which data is written for each pixel for light emission or non-light emission, and a pixel in which the light emission data is written is maintained at the same time. It consists of a period (T3). By combining these subfields to emit light, 256 gradation levels from “0” to “255” are displayed. For example, when displaying gradation “7”, SF1, SF2, and SF3 having luminance weights 1, 2, and 4 are emitted, and when displaying gradation “21”, luminance weights 1, 4, and 16 are set. The SF1, SF3, and SF5 possessed are emitted.

  In a display method that performs multi-gradation display using such a subfield method, it is known that a phenomenon in which image quality deteriorates and is observed during moving image display occurs. One of the causes is a pseudo contour (moving image pseudo contour). For this moving image pseudo contour, one field is divided into eight subfields (SF1, SF2,..., SF8) having luminance weights of (1, 2, 4, 8, 16, 32, 64, 128). A case will be described as an example.

  FIG. 11 is a diagram showing a case where the image pattern X moves in the horizontal direction on the screen of the PDP, and FIG. 12 is a diagram in which the image pattern X is developed into subfields. As shown in FIG. 11, the image pattern X includes a region P1 having a gradation value “127” and a region P2 having a gradation value “128”. In FIG. 12, the horizontal axis represents the screen position in the horizontal direction of the PDP, the vertical axis represents the time direction, and the hatched subfield represents a subfield that does not emit light.

  For example, when the image pattern X is stationary and the observer's viewpoint does not move in the horizontal direction and remains fixed at the screen position A as indicated by an arrow AA ′ in FIG. It is possible to observe “127” and “128” which are the original gradation values of the regions P1 and P2. On the other hand, when the image pattern X moves in the left direction and the observer follows the movement of the image pattern X and moves the viewpoint in the direction of the arrow BB ′, the observer moves the non-light-emitting subfield (region) in the region P2. (SF1 to SF7 of P2) and the non-light emitting subfield (SF8 of the region P1) of the region P1 may be observed. In this case, the observer continuously observes SF1 to SF7 in the region P2 and SF8 in the region P1, and consequently observes the gradation value “0”, that is, a dark line. Conversely, when the image pattern X moves to the right and the observer follows the movement of the image pattern X and moves the viewpoint in the direction of the arrow CC ′, the observer moves the light emission subfield (region) in the region P1. (SF1 to SF7 of P1) and the light emission subfield (SF8 of region P2) of region P2 may be observed. In this case, the observer continuously observes SF1 to SF7 in the region P1 and SF8 in the region P2, and as a result, observes the gradation value “255”, that is, a bright line. In any case, gradation values that are significantly different from the original gradation values (127 or 128) are observed, and these are recognized as false contours, that is, pseudo contours.

  As described above, the pseudo contour is generated in a place where the change of the pattern of the subfield to emit light is large although the change of the gradation is slight. For example, when the above-described weighting subfield is used, the pseudo contour is noticeably observed when the luminance gradations of adjacent pixels are “63” and “64”, or “191” and “192”. The As described above, the pseudo contour generated during the moving image display is one of the causes for the deterioration of the image quality.

As a technique for suppressing the moving image pseudo contour, the tone of the video signal is converted into the “first gradation” and the “intermediate gradation” where the moving image pseudo contour is difficult to occur, and the error caused by the conversion is peripheral) A method of interpolating gradation jumps by diffusing to pixels has been proposed (for example, Patent Document 1).
JP-A-10-171403

  In the display method that performs multi-gradation display using the subfield method, the cause of the observation that the image quality is deteriorated during the moving image display is a phenomenon in which the contour portion is observed in addition to the moving image pseudo contour described above ( Hereinafter, “abbreviated as edge blur”).

  This edge blur will be described. FIG. 13 is a diagram showing an apparent luminance level when the contour portion is stationary on the PDP screen, and FIG. 14 is an appearance when the contour portion moves rightward on the PDP screen. FIG. 15 is a diagram showing the apparent luminance level when the contour portion moves to the left on the PDP screen. 13 to 15, each (a) represents a gradation value in the horizontal scanning direction of the contour portion, and each (b) is a diagram in which the contour portion is developed into subfields. c) is a diagram showing an apparent luminance level when the observer observes the contour portion. 13 to 15, the horizontal axis represents the screen position in the horizontal direction of the PDP, and the vertical axis represents the time direction in FIGS. 13 to 15 (a) and (b). In (c), the luminance level of the observer's appearance is shown. In each (b) of FIGS. 13 to 15, the broken arrow indicates the observer's viewpoint movement, and the hatched subfield indicates the subfield that does not emit light. Yes. In addition, here, it is assumed that one field is divided into five subfields (SF1, SF2,..., SF5) having luminance weights of (1, 2, 4, 8, 16).

  Further, as shown in FIGS. 13 to 15A, the gradation value of the contour portion is 0 in the (n) field up to (m−1) pixels, and from (m) pixels. The gradation value increases to 1, 3, 7, 15, and 31 up to (m + 4) pixels, and the gradation value 31 after (m + 5) pixels. The light emission subfields in the (n) field are SF1 (luminance weight 1) and (m + 1) pixels (floor) for (m) pixels (gradation value 1) as shown in FIGS. In the tone value 3), the light emission subfield is increased by 1 to SF1 and SF2 (luminance weight 1 + 2) and thereafter (m + 4) pixels (gradation value 31), and the pixels after (m + 4) pixels (gradation value 31). Then, all subfields (SF1 to SF5) emit light (luminance weight 1 + 2 + 4 + 8 + 16).

  In the state where the contour portion is stationary, as shown in FIGS. 13A and 13B, there is no change in the gradation value and the light emission subfield between the (n) field and the (n + 1) field. At this time, if the observer's viewpoint does not move in the horizontal direction as shown by the dashed arrow in FIG. 13B, the change in the brightness level of the observer's appearance is as shown in FIG. 13C. This is the same as the change in gradation value.

  When the contour portion moves to the right on the screen, for example, if the moving speed is 4) the pixel speed in one field period, the region where the gradation value increases to 1, 3, 7, 15, 31 is As shown in FIG. 14A, the number of pixels is from (m + 4) pixels to (m + 8) pixels in the (n + 1) field. The light emission subfield in the (n + 1) field also changes in the same manner. At this time, if the observer's viewpoint moves to the right according to the moving speed of the contour portion as indicated by the dashed arrow in FIG. The non-light emitting subfield is continuously observed up to SF5 of the (m + 7) pixel, and the light emitting subfield is continuously observed from SF1 of the (m + 2) pixel to SF5 of the (m + 10) pixel. Accordingly, as shown in FIG. 14C, the apparent contour width from the apparent luminance level 0 that continuously observes the non-light-emitting subfield to the apparent luminance level 31 that continuously observes the light-emitting subfield is about 2) The pixel portion is observed, and a contour portion that is sharper than the original contour portion is observed. In such a case, the observer observes an image different from the original image, but since it is an image with a sharper outline than the original image, it is not particularly recognized as image quality deterioration, and is not much of a problem. Don't be.

  On the other hand, when the contour portion moves leftward on the screen, for example, if the moving speed is 4 pixels in one field period, the gradation value is increased to 1, 3, 7, 15, 31 As shown in FIG. 15A, in the (n + 1) field, from (m−4) pixels to (m) pixels. The light emission subfield in the (n + 1) field also changes in the same manner. At this time, if the observer's viewpoint moves to the left in accordance with the moving speed of the contour portion as indicated by the dashed arrow in FIG. m-9) The non-light emitting subfield is continuously observed up to SF5 of the pixel, and the light emitting subfield is continuously observed from SF1 of the (m + 8) pixel to SF5 of the (m) pixel. Therefore, as shown in FIG. 15C, the apparent contour width from the apparent luminance level 0 in which the non-light emitting subfield is continuously observed to the apparent luminance level 31 in which the light emitting subfield is continuously observed is about 8) A contour portion that is a pixel portion and rises more slowly than the original contour portion is observed. In such a case, the observer observes an image with a blurred outline portion, that is, an edge blur, and recognizes it as a deterioration in image quality.

  Thus, when the contour portion that changes from a low gradation value to a high gradation value moves and the observer moves the viewpoint accordingly, the observer moves in the direction of the higher gradation value. When an image is observed (example shown in FIG. 14), a contour portion narrower than the contour portion of the original image is observed, and conversely when moving in the direction of a lower gradation value (example shown in FIG. 15). Observes a contour portion that is wider than the contour portion of the original image. When the observer observes a contour portion that is wider than the contour portion of the original image, it is recognized as an edge blur and looks as if the image quality has deteriorated.

  The above-described conventional technique can obtain an effect of suppressing the pseudo contour generated when pixels having specific gradation values are adjacent to each other. However, the edge blur as described above has a problem that no improvement effect can be obtained.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an image display method in which edge blurring is suppressed and the quality of a moving image is improved.

In order to achieve such an object, the image display method of the present invention is an image that is displayed in multiple gradations by configuring one field with a plurality of subfields having different luminance weights and controlling each subfield to emit or not emit light. A display method for detecting an area that is a contour area in an image of the current field and has a gradation value larger than that of the previous field, and the detection of the outline area is performed more than adjacent pixels that are adjacent pixels in the horizontal direction. This is done by detecting pixels whose gradation value has increased by a predetermined value or more, and in the detected area, the pixels in which the subfields having a luminance weight equal to or higher than the predetermined luminance weight are lit are brighter than the luminance that should originally be emitted. A combination of light emission subfields that emit light at a luminance is used to display the luminance that should be emitted. The combination of the light emission subfields, by shifting the sub-fields it is luminance weight larger, making the large sub-field luminance weight than the light-emitting sub-field that displays the brightness should be originally emitted in the light-emitting subfields In the detected region, a light emitting subfield that emits light with a luminance lower than the luminance that should originally be emitted in pixels other than the pixel in which the subfield having a luminance weight greater than or equal to a predetermined luminance weight in the detected region is lit The combination of the light emission subfields is displayed by shifting the combination of the light emission subfields for displaying the luminance to be originally emitted to the subfield having the smaller luminance weight, thereby displaying the luminance to be originally emitted. small differences of brightness weight than the light emitting sub-fields for Characterized in that it is a combination obtained by the field emission subfields.

  According to this method, the contour region in the image of the current field and the region having a larger gradation value than the previous field can be set as a sharper rising contour, effectively preventing edge blurring during moving image display. It can be suppressed and image quality degradation can be improved.

In addition, a pixel in which the gradation value of the video signal is increased by a first threshold value or more than the previous field, and is detected by a second threshold value or more than the adjacent pixels that are adjacent pixels adjacent in the horizontal direction is detected. In the current field image, a region that is a contour region and has a gradation value larger than that of the previous field is detected, and in the detected region, light emission and non-light emission of each subfield is generated as numerical information. If the subfield data is greater than or equal to the third threshold value, the subfield data is multiplied by a constant to make a combination of light emission subfields that emit light at a brightness brighter than the original light emission, and the subfield data is less than the third threshold value. If this is the case, a combination of emission subfields that emit light with a luminance lower than the luminance that should be emitted by multiplying it by a constant number, In the output area, each subfield is controlled to emit or not emit light based on the subfield data multiplied by a constant or subfield data multiplied by a constant, and in the area other than the detected area, from the video signal based on the subfield data generated by emission or non-emission control each sub-field, is the weight of the power of the luminance weights 2 of each sub-field, the constant may be set to a power of 2. According to this method, the subfield data is multiplied by a constant or a factor of a constant to obtain a combination of light emitting subfields that emit light with a luminance that is brighter or darker than the luminance that should be emitted. The contour area in the field image that has a larger gradation value than the previous field can be made to have a steeper rising edge, effectively reducing edge blurring during video display and improving image quality degradation. can do.

In addition, a pixel in which the gradation value of the video signal is increased by a first threshold value or more than the previous field, and is detected by a second threshold value or more than the adjacent pixels that are adjacent pixels adjacent in the horizontal direction is detected. Then, an area that is a contour area in the image of the current field and has a gradation value larger than that of the previous field is detected. If the gradation value of the video signal is equal to or greater than the third threshold value in the detected area, By multiplying by a constant and generating subfield data based on the gradation value multiplied by the constant, a combination of light emitting subfields that emit light with a brightness brighter than the brightness that should originally be emitted, and the gradation value of the video signal is If it is less than the third threshold, it is multiplied by a constant and the subfield data is generated based on the gradation value multiplied by the constant, thereby emitting light with a luminance lower than the luminance that should originally be emitted. In the detected area, each subfield emits light based on subfield data created from a gradation value multiplied by a constant or a gradation value multiplied by a constant. Alternatively, non-emission control is performed, and in the areas other than the detected area, each sub-field is controlled to emit or non-emission based on the sub-field data created from the video signal, and the luminance weight of each sub-field is a power of 2. is a weight, constant may be assumed to be a power of 2. According to this method, the gradation value of the video signal is multiplied by a constant or a constant, and the subfield data is created from the gradation value, so that the luminance is brighter or darker than the luminance that should originally be emitted. By combining light-emitting subfields that emit light, the contour region in the current field image and the region having a larger gradation value than the previous field can be made a sharper rising contour. It is possible to effectively suppress the edge blur at the time of image quality and to improve image quality degradation.

  According to the present invention, in an image display apparatus that performs multi-gradation display by dividing an image of one field into a plurality of sub-field images, such as PDP and DMD, image quality deterioration at the time of moving image display is suppressed by suppressing edge blurring. An image display method that can be improved can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a perspective view showing the structure of the PDP of the plasma display device in accordance with the first exemplary embodiment of the present invention. On the glass front plate 20 which is the first substrate, a plurality of display electrodes which are paired with a stripe-shaped scan electrode 22 and a stripe-shaped sustain electrode 23 are formed. A dielectric layer 24 is formed so as to cover the scan electrode 22 and the sustain electrode 23, and a protective layer 25 is formed on the dielectric layer 24. A plurality of stripe-shaped data electrodes 32 covered with a dielectric layer 33 are formed on the back plate 30 as the second substrate so as to three-dimensionally intersect the scan electrodes 22 and the sustain electrodes 23. A plurality of barrier ribs 34 are disposed on the dielectric layer 33 in parallel with the data electrodes 32, and a phosphor layer 35 is provided on the dielectric layer 33 between the barrier ribs 34. Further, the data electrode 32 is disposed at a position between the adjacent partition walls 34.

  The front plate 20 and the back plate 30 are arranged to face each other with a minute discharge space so that the scan electrode 22, the sustain electrode 23, and the data electrode 32 are orthogonal to each other, and the outer peripheral portion thereof is made of glass frit or the like. It is sealed with a sealing material. In the discharge space, for example, a mixed gas of neon (Ne) and xenon (Xe) is sealed as a discharge gas. The discharge space is partitioned into a plurality of sections by partition walls 34, and phosphor layers 35 that emit red (R), green (G), and blue (B) light are sequentially disposed in each section. A discharge cell is formed at a portion where the scan electrode 22 and the sustain electrode 23 intersect with the data electrode 32, and one adjacent pixel is formed by three adjacent discharge cells on which the phosphor layers 35 that emit light of each color are formed. The An area where the discharge cells constituting this pixel are formed becomes an image display area, and the periphery of the image display area becomes a non-display area where image display is not performed, such as an area where glass frit is formed.

FIG. 2 is an electrode array diagram of the PDP in Embodiment 1 of the present invention. M columns of data electrodes D _{1 to} D _m (data electrodes 32 in FIG. 1) are arranged in the column direction, and n rows of scan electrodes SC _{1 to} SC _n (scan electrodes 22 in FIG. 1) and n rows of data electrodes are arranged in the row direction. Sustain electrodes SU _{1 to} SU _n (sustain electrodes 23 in FIG. 1) are alternately arranged. A discharge cell C _{i, j} including a pair of scan electrodes SC _i , sustain electrodes SU _i (i = 1 to n) and one data electrode D _j (j = 1 to m) is formed in the discharge space. The total number of discharge cells C is (m × n).

  In the PDP having such a configuration, color display is performed by generating ultraviolet rays by gas discharge and exciting the phosphors of R, G, and B colors with the ultraviolet rays to emit light.

  FIG. 3 is a diagram showing a driving voltage waveform of each electrode of the PDP in the first embodiment of the present invention. As shown in FIG. 3, each subfield has an initialization period, an address period, and a sustain period. Each subfield performs substantially the same operation except that the number of sustain pulses in the sustain period is changed in order to change the weight of the light emission period, and the operation principle in each subfield is also substantially the same. Accordingly, only the operation for one subfield will be described here.

First, in the half of the initializing period, holds the data electrodes _D 1 to D _m, sustain electrodes _SU 1 to SU _n in each 0 (V), the scan electrodes _SC 1 to SC _n, data electrodes _D 1 to D A ramp waveform voltage that gradually rises from a voltage V _{i1 that is} equal to or lower than the discharge start voltage to a voltage V _i2 that exceeds the discharge start voltage is applied to _m . While this ramp waveform voltage rises, the _first weak initializing discharge occurs between scan electrodes SC _{1 to} SC _n and sustain electrodes SU _{1 to} SU _n and data electrodes D _{1 to} D _m , respectively. Negative wall voltage is accumulated on scan electrodes _SC 1 to SC _n top, to the data electrodes _D 1 to D _m and sustain electrodes _SU 1 to SU _n positive wall voltage is accumulated. Here, the wall voltage at the top of the electrode represents a voltage generated by wall charges accumulated on the dielectric layer covering the electrode.

In the second half of the initializing period, maintaining the sustain electrodes _SU 1 to SU _n to a positive voltage Ve, the scan electrodes _SC 1 to SC _n, the voltage _{V i3} which is a discharge start voltage or less with respect to sustain electrodes _SU 1 to SU _{n Is} applied with a ramp waveform voltage that gradually falls toward voltage V _i4 exceeding the discharge start voltage. During this time, the second weak initializing discharge occurs between the scan electrodes SC _{1 to} SC _n and the sustain electrodes SU _{1 to} SU _n and the data electrodes D _{1 to} D _m , respectively. Then, negative wall voltage and sustain electrodes _SU 1 to SU _n positive wall voltage on scan electrodes _SC 1 to SC _n upper are weakened, positive wall voltage on data electrodes _D 1 to D _m upper address operation It is adjusted to a suitable value. Thus, the initialization operation ends (hereinafter, the drive voltage applied to each electrode during the initialization period is abbreviated as “initialization pulse”).

In the address period, scan electrodes SC _{1 to} SC _n are temporarily held at voltage Vc. Next, in the write operation of the discharge cell _C p, 1 _{-C p, m,} with scan pulse voltage Va is applied to scan electrode SC _p, to be displayed on the p-th row among data electrodes _D 1 to D _m video A positive address pulse Vd is applied to the data electrode D _k (k is an integer of 1 to m) corresponding to the signal. Accordingly, discharge cells corresponding to the intersections of the address pulse voltage to the data electrode D _k of applying a scan electrode SC _P C _p, address discharge in _k is generated. Discharge cells C _p The write _discharge, a positive voltage to the scan electrodes SC _p top of _k is accumulated, and a negative voltage is accumulated on sustain electrode SU _p top, the write operation is completed. Thereafter, the same address operation is performed until the discharge cell C _{n, k} in the _n- th row _, and the address operation is completed.

In the sustain period, scan electrodes SC _{1 to} SC _n are once returned to 0 (V), then positive sustain pulse voltage Vs is applied to scan electrodes SC _{1 to} SC _n , and then sustain electrodes SU _{1 to} SU _n are applied. Return to 0 (V). At this time, the voltage between the upper portion of scan electrode SC _{i and} upper portion of sustain electrode SU _i in discharge cell C _{i, j} in which the address discharge has occurred is in addition to positive sustain pulse voltage Vs, and scan electrode SC _i in the address period. The wall voltage accumulated on the upper part and the upper part of the sustain electrode SU _i is added to become higher than the discharge start voltage, and the first sustain discharge is generated. After the first sustain discharge, the Vs is applied to sustain electrodes _SU 1 to SU _n, then returned to the scan electrodes _SC 1 to SC _n to 0 (V). At this time, the voltage between the upper portion of scan electrode SC _{i and} upper portion of sustain electrode SU _i in discharge cell C _{i, j} in which the address discharge has occurred is in addition to positive sustain pulse voltage Vs, and scan electrode SC _i in the address period. The wall voltage accumulated in the upper part and the upper part of the sustain electrode SU _i is added to become higher than the discharge start voltage, and a second sustain discharge is generated. Thereafter, in the same manner, by applying sustain pulses alternately to scan electrodes SC _{1 to} SC _n and sustain electrodes SU _{1 to} SUn, the _number of sustain pulses is _equal to the number of sustain pulses for discharge cells C _{i, k} that have caused address discharge. The sustain discharge is continuously performed.

  The above is the electrode arrangement of the PDP 10, the drive voltage waveform for driving the PDP 10, and the timing thereof.

  FIG. 4 is a block diagram showing the configuration of the plasma display device in accordance with the first exemplary embodiment of the present invention. The plasma display device shown in FIG. 4 includes an AD converter 1, a video signal processing circuit 2, a subfield processing circuit 3, a data electrode driving circuit 4, a scanning electrode driving circuit 5, a sustain electrode driving circuit 6, and a PDP 10.

  The AD converter 1 converts the input analog video signal into a digital video signal. The video signal processing circuit 2 emits and displays the input digital video signal on the PDP 10 by a combination of a plurality of subfields having different light emission period weights, and controls each subfield from the video signal of one field. Convert to data.

  The subfield processing circuit 3 generates a data electrode drive circuit control signal, a scan electrode drive circuit control signal, and a sustain electrode drive circuit control signal from the subfield data created by the video signal processing circuit 2, and drives the data electrode Output to the circuit 4, the scan electrode drive circuit 5, and the sustain electrode drive circuit 6, respectively.

As described above, the PDP 10 has m columns of data electrodes D _{1 to} D _m (data electrodes 32 in FIG. 1) arranged in the column direction, and n rows of scan electrodes SC _{1 to} SC _n (scan in FIG. 1). Electrodes 22) and n rows of sustain electrodes SU _{1 to} SU _n (sustain electrodes 23 in FIG. 1) are alternately arranged. A discharge cell C _{i, j} including a pair of scan electrodes SC _i , sustain electrodes SU _i (i = 1 to n) and one data electrode D _j (j = 1 to m) is formed in the discharge space (m Xn) One pixel is composed of three discharge cells that are formed and emit light in red, green, and blue colors.

  The data electrode drive circuit 4 includes a drive circuit that can drive each data electrode 32 independently, and drives each data electrode 32 independently based on a data electrode drive circuit control signal. Sustain electrode drive circuit 6 internally includes a drive circuit that can drive all sustain electrodes 23 of PDP 10 together, and drives sustain electrode 23 based on a control signal for the sustain electrode drive circuit. The scan electrode drive circuit 5 includes a drive circuit that can drive each scan electrode 22 independently, and independently drives each scan electrode 22 based on a scan electrode drive circuit control signal. Each drive is as described in FIG.

  FIG. 5 is a block diagram of the video signal processing circuit according to Embodiment 1 of the present invention.

  As shown in FIG. 5, the video signal processing circuit 2 according to the first embodiment of the present invention includes a field memory 101, a gradation value increasing region detecting unit 102, a contour region detecting unit 103, a specific region detecting unit 104, a subfield conversion. Unit 105, subfield shift unit 106, and selector 107.

  The field memory 101 delays the input digital video signal for one field period. The gradation value increasing area detection unit 102 obtains a difference in gradation value between the input digital video signal and the video signal delayed by one field period by the field memory 101, and uses the difference value and the first threshold value. Compare with threshold A. Then, a pixel whose difference value is greater than or equal to the threshold value A is detected as a gradation value increasing region in which the gradation value is higher in the current field than in the previous field. The contour region detection unit 103 obtains a difference in gradation value between the current pixel of the input digital video signal and a pixel adjacent to the current pixel, and compares the difference value with a threshold value B that is a second threshold value. . If the difference value is greater than or equal to the threshold value B, the pixel is detected as a contour region. The specific area detection unit 104 detects a pixel detected as a gradation value increase area by the gradation value increase area detection unit 102 and detected as a contour area by the outline area detection unit 103 as a specific area.

  The subfield conversion unit 105 converts the input digital video signal into subfield data indicating a combination of subfields to emit light. For example, one field is divided into eight subfields (SF1, SF2,..., SF8) having luminance weights of (1, 2, 4, 8, 16, 32, 64, 128). When the key is displayed, the subfield data is represented by an 8-bit binary number. If the light emission subfield is SF7, SF6, and the non-light emission subfield is SF8, SF5 to SF1, the subfield data is represented as 01100000.

  The subfield shift unit 106 compares the subfield data created by the subfield conversion unit 105 with a threshold value C that is a third threshold value. Here, the threshold C represents a subfield number, and when the subfield data is a subfield equal to or greater than the subfield number represented by the threshold C, the subfield data is determined to be greater than or equal to the threshold C. . If the subfield data is greater than or equal to the threshold value C, the subfield data is multiplied by a constant represented by a power of 2, and 1 is put in the lower bits that become blank by multiplying by a constant. For example, if the subfield data is 01100000, the threshold C is 01000000 representing SF7, and the constant is 2 as in the above example, the subfield data (01100000) is equal to or greater than the threshold C (01000000). The unit 106 determines that the subfield data is equal to or greater than the threshold value C and multiplies the subfield data by a constant (twice), and puts 1 in the least significant bit. Therefore, the subfield data 01100000 becomes 11000001. If the subfield data overflows (digit overflow) by multiplying the subfield data by a constant, the maximum value is assigned to the subfield data to prevent overflow. Also, the reason why the lower bits are set to 1 when subfield data is multiplied by a constant is to improve the stability of discharge by setting each subfield to a light emitting state as continuously as possible.

  Also, if the subfield data is less than the threshold value C, the subfield data is multiplied by one of the constants, and 0 is put in the upper bits that are blank by being multiplied by the constant. For example, if the subfield data is 0000111, SF3 to SF1 are light emission subfields. Therefore, the subfield shift unit 106 determines that the subfield data is less than the threshold value C (SF7), and is 1 times the constant (2 1) and put 0 in the most significant bit. Therefore, the subfield data 00000111 is 00000011.

  The selector 107 selects the subfield data that has passed through the subfield shift unit 106 in the region detected as the specific region by the specific region detection unit 104, and the subfield that has not passed through the subfield shift unit 106 in other regions. Data is selected and output to the subfield processing circuit 3 at the subsequent stage.

  In the first embodiment of the present invention, the above-described configuration reduces edge blur and improves the image quality when displaying a moving image.

  In the first embodiment of the present invention, when the maximum gradation value is 255, the threshold A is preferably about 50 and the threshold B is preferably about 20. Further, the constant in the subfield shift unit 106 is preferably 2 or 4, and the threshold C is preferably any one of the subfield having the fourth largest weighting to the subfield having the fourth largest weighting. However, since this value differs optimally depending on the number of subfields, the weight of each subfield, the number of pixels, discharge characteristics, etc., it is desirable to optimize for each model.

  Next, the appearance of the contour portion when the edge blur improvement process is performed in the video signal processing circuit 2 will be described in comparison with the case where the process is not performed.

  FIG. 6 is a diagram showing how the contour portion moves to the left on the screen of the PDP, and FIG. 7 shows how the contour portion looks when the signal processing according to Embodiment 1 of the present invention is performed. FIG. 6 and 7, each (a) is a diagram showing the gradation value of the contour portion in the horizontal scanning direction, and each (b) is a diagram in which the contour portion is developed into subfields. c) is a diagram showing an apparent luminance level when an observer observes a contour portion. 6 and 7, the horizontal axis represents the screen position in the horizontal direction of the PDP, and the vertical axis represents each of (a) and (b in FIG. 6 and FIG. 7. ) In FIG. 6 and FIG. 7 (c) shows the luminance level of the observer's appearance, and the broken arrows in FIG. 6 and FIG. 7 (b) indicate the observer's viewpoint movement. The hatched subfield represents a subfield that does not emit light. Also, here, one field is described as being divided into eight subfields (SF1, SF2,..., SF8) having luminance weights of (1, 2, 4, 8, 16, 32, 64, 128). I do.

  Further, as shown in FIG. 6A, the gradation value of the contour portion is 0 in the (n) field up to (m−1) pixels and from (m) pixels to (m + 6) pixels. Gradually increases to gradation values 1, 3, 7, 15, 31, 63, 127, and the gradation value 255 is obtained after (m + 7) pixels. In addition, as shown in FIG. 6B, the light emission subfield is SF1 (luminance weight 1) and (m + 1) pixels (gradation value 3) in the (m) pixel (gradation value 1) in the (n) field. , SF1 and SF2 (luminance weight 1 + 2), and thereafter, the light emission subfields increase one by one from (m + 7) pixels (gradation value 255), and all subfields (SF1) in (m + 7) pixels (gradation value 255). ~ SF8) emit light (luminance weight 1 + 2 + 4 + 8 + 16 + 32 + 64 + 128).

  When this contour portion moves on the screen in the left direction at a speed of 7 pixels in one field period, the area where the gradation value increases to 1, 3, 7, 15, 31, 63, 127, 255 is shown in FIG. As shown in FIG. 6 (a), in the (n + 1) field, from (m−7) pixels to (m) pixels. The light emission subfield in the (n + 1) field also changes in the same manner. At this time, if the observer's viewpoint moves to the left in accordance with the moving speed of the contour portion as indicated by the broken-line arrow in FIG. 6B, the observer starts from SF1 of (m−1) pixels ( m-15) The non-light emitting subfield is continuously observed up to SF8 of the pixel, and the light emitting subfield is continuously observed from SF1 of the (m + 14) pixel to SF8 of the (m) pixel. Accordingly, as shown in FIG. 6C, the apparent contour width from the apparent luminance level 0 where the non-light emitting subfield is continuously observed to the apparent luminance level 255 where the light emitting subfield is continuously observed is The edge blur is about 14 pixels and the rising edge of the original contour portion is observed.

  On the other hand, when the processing for improving the edge blur according to Embodiment 1 of the present invention is performed, the gradation value of the contour portion is as follows. Here, description will be made assuming that the threshold A is 50, the threshold B is 20, the threshold C is 01000000 (SF7), and the constant in the subfield shift unit 106 is 2. Further, it is assumed that the contour portion moves to the left at a speed of 7 pixels in one field period from the (n-1) field to the (n) field.

  First, the gradation value increasing area detecting unit 102 determines an area where the one-field difference of gradation values is equal to or greater than the threshold value A (50) as a gradation value increasing area. Therefore, in the (n) field, the (m + 5) pixel to the (m + 13) pixel is determined as the gradation value increasing region, and in the (n + 1) field, the (m−2) pixel to the (m + 6) pixel is the gradation value. It is judged as an increase area.

  Next, the contour region detection unit 103 determines that the difference between the current pixel and the adjacent pixel is equal to or greater than the threshold B (20) as the contour region. Therefore, in the (n) field, (m + 5) pixels and (m + 6) pixels are determined as contour regions, and in the (n + 1) field, (m-2) pixels and (m−1) pixels are determined as contour regions. .

  Since the specific area detection unit 104 uses the area determined as the gradation value increasing area and the outline area as the specific area, (m + 5) pixels in the (n) field, (m + 6) pixels in the (n + 1) field, The (m-2) pixel and the (m-1) pixel are determined as specific areas, respectively.

  On the other hand, the subfield shift unit 106 compares the gradation value of each pixel with the threshold value C (01000000), and performs processing separately for subfield data that is greater than or equal to the threshold value C and subfield data that is less than the threshold value C. The gradation value where the threshold value C (01000000) or more is a light emission subfield is 64 or more, and the gradation value where the emission subfield is less than the threshold value C (01000000) is 63 or less. Therefore, the subfield data of the gradation values 0, 1, 3, 7, 15, 31, and 63 are multiplied by a constant (1/2), and 0, 0, 00000001, 00000011, 00000111, and 00001111, respectively. , 00011111, and subfield data of gradation values 127 and 255 are subjected to constant multiplication (double) and overflow prevention processing to become 11111111 and 11111111, respectively.

  In the selector 107, the (m) pixel in the (n) field, the (m + 6) pixel, the (m + 6) pixel in the (n + 1) field, (m−1) ) Subfield data that has passed through the subfield shift unit 106 is selected only for pixels. Accordingly, as shown in FIG. 7B, the subfield data is 00001111 for the (m + 5) pixel in the (n) field and the (m-2) pixel in the (n + 1) field, and the (m + 6) pixel in the (n) field. In (m + 1) pixels in the (n + 1) field, the subfield data is 11111111.

  At this time, if the observer's viewpoint moves to the left in accordance with the moving speed of the contour portion as indicated by the broken-line arrow in FIG. 7B, the observer starts from SF1 of (m−1) pixels ( m-15) The non-light emitting subfield is continuously observed up to SF8 of the pixel, and the light emitting subfield is continuously observed from SF1 of the (m + 13) pixel to SF8 of the (m−1) pixel. Therefore, as shown by the solid line in FIG. 7C, the apparent contour width from the apparent luminance level 0 in which the non-light emitting subfield is continuously observed to the apparent luminance level 255 in which the light emitting subfield is continuously observed. Is about 13 pixels. That is, by performing the above-described processing, the apparent contour width can be made smaller by one pixel than the conventional apparent contour width indicated by a broken line in FIG.

  The apparent contour width is narrowed only for one pixel, but this is because the steep rise is made through the subfield shift unit 106 only in the steep portion where the gradation value changes more than the threshold value B. is there. In this way, by preventing the subfield shift unit 106 from passing through the gentle part where the gradation value changes below the threshold B, the edge blur is more effectively reduced while suppressing the uncomfortable appearance and unnaturalness. In addition, a moving image display in which the contour portion is tightened is realized.

  As described above, in the first embodiment of the present invention, a specific region that is a gradation value increasing region and a contour region is detected, and only the specific region is switched to the subfield data that has passed through the subfield shift unit 106. In addition, edge blurring can be suppressed and image quality degradation during video display can be improved.

(Embodiment 2)
FIG. 8 is a block diagram of a video signal processing circuit according to Embodiment 2 of the present invention.

  The video signal processing circuit 2 according to the second embodiment of the present invention shown in FIG. 8 differs from the video signal processing circuit 2 shown in FIG. This is a point provided with a conversion unit 206. Other than that, the configuration is almost the same and the same operation is performed. Therefore, here, the description will focus on differences from the first embodiment.

  As shown in FIG. 8, the video signal processing circuit 2 according to the second embodiment of the present invention includes a field memory 101, a gradation value increasing region detecting unit 102, a contour region detecting unit 103, a specific region detecting unit 104, a subfield conversion. Unit 105, gradation value conversion unit 206, and selector 107.

  The field memory 101, the gradation value increasing region detecting unit 102, the contour region detecting unit 103, and the specific region detecting unit 104 have the same configuration as that of the first embodiment and perform the same operation.

  The gradation value conversion unit 206 first compares each gradation value of the video signal with the threshold value C. If the gradation value is greater than or equal to the threshold value C, the gradation value is multiplied by a constant. If the gradation value is less than the threshold value C, the gradation value is multiplied by a constant. When the maximum gradation value set by multiplying the gradation value by a constant is exceeded, the maximum gradation value is substituted for the gradation value.

  The selector 107 selects the video signal that has passed through the gradation value conversion unit 206 in the region detected as the specific region by the specific region detection unit 104, and the video that has not passed through the gradation value conversion unit 206 in other regions. A signal is selected and output to the subfield conversion unit 105.

  The subfield conversion unit 105 creates subfield data from the video signal by the same operation as in the first embodiment, and outputs it to the subfield processing circuit 3 in the subsequent stage.

  In the second embodiment of the present invention, as described above, edge blur is reduced by the process of converting gradation values instead of subfield data, and the image quality at the time of moving image display is improved.

  FIG. 9 is a diagram showing how the contour portion looks when signal processing is performed in the second embodiment of the present invention. 9A, 9B, 9C are the same as FIGS. 6A, 6B, 7A, 7B, 7C in the first embodiment. Each gradation value, moving speed, threshold A, threshold B, constants in the subfield shift unit 106, and the like are also the same as those in FIGS. Therefore, the gradation value increasing area detection unit 102, the contour area detection unit 103, and the specific area detection unit 104 operate in the same manner as in the first embodiment. Therefore, in the (n) field, (m + 5) pixels, as in the first embodiment. , (M + 6) pixels, (m-2) pixels and (m-1) pixels are determined as specific areas in the (n + 1) field, respectively.

  Here, the threshold C is 64. Therefore, the gradation value conversion unit 206 compares the gradation value of each pixel with the threshold value C (64), and divides it into a video signal that is equal to or higher than the threshold value C (64) and a video signal that is less than the threshold value C (less than 63). Process each. As a result, the gradation values 0, 1, 3, 7, 15, 31, and 63 are each multiplied by a constant (1/2), and the gradation values 0, 0, 1, 3, 7, The gradation values 127 and 255 are subjected to constant multiplication (twice) and overflow prevention processing, respectively, and become gradation values 255 and 255, respectively.

  In the selector 107, the (m) pixel in the (n) field, the (m + 6) pixel, the (m + 6) pixel in the (n + 1) field, (m−1) ) Select a video signal that has passed through the gradation value conversion unit 206 only when it is a pixel. Therefore, as shown in FIG. 9B, the gradation value is 31 for the (m + 5) pixel in the (n) field and the (m-2) pixel in the (n + 1) field, and the (m + 6) pixel in the (n) field is The gradation value is 255 for (m−1) pixels in the (n + 1) field.

  Then, as shown in FIG. 9B, light emission and non-light emission of each subfield are determined in accordance with the gradation value. At this time, if the observer's viewpoint moves to the left in accordance with the moving speed of the contour portion as indicated by the broken-line arrow in FIG. 9B, the observer starts from SF1 of (m−1) pixels ( m-15) The non-light emitting subfield is continuously observed up to SF8 of the pixel, and the light emitting subfield is continuously observed from SF1 of the (m + 13) pixel to SF8 of the (m−1) pixel. Therefore, as shown by the solid line in FIG. 9C, the apparent contour width from the apparent luminance level 0 that continuously observes the non-light emitting subfield to the apparent luminance level 255 that continuously observes the light emitting subfield. Is about 13 pixels, and it is possible to obtain an effect similar to that shown in the first embodiment.

  As described above, in the first embodiment of the present invention, a specific region that is a gradation value increasing region and a contour region is detected, and only the specific region is switched to a video signal that has passed through the gradation value conversion unit 206. In addition, edge blurring can be suppressed and image quality degradation during video display can be improved.

  In the second embodiment of the present invention, the threshold value C is set between the gradation value corresponding to the subfield having the fourth largest weighting and the gradation value corresponding to the subfield having the fourth largest weighting. It is desirable to do. For example, if one field is divided into eight subfields (SF1, SF2,..., SF8) having luminance weights of (1, 2, 4, 8, 16, 32, 64, 128). , 16 to 128 is desirable. However, since this value differs optimally depending on the number of subfields, the weight of each subfield, the number of pixels, discharge characteristics, etc., it is desirable to optimize for each model.

  In the above-described embodiment, the configuration has been described in which the subfield data is multiplied by a constant when the subfield data is equal to or greater than the threshold C, and when the subfield data is less than the threshold C, the subfield data is multiplied by a constant. However, the present invention is not limited to this configuration. For example, when the subfield data is equal to or greater than the threshold value C, the subfield data may be simply multiplied by a constant. The data may only be multiplied by a constant. Alternatively, when the subfield data is greater than or equal to the threshold C, the subfield data is multiplied by four, and when the subfield data is less than the threshold C, the subfield data is multiplied by half. The constant of time may be a different value.

  In the above-described embodiment, the PDP has been described as an example. However, if the image display method is a subfield method in which an image of one field is divided into a plurality of subfield images to perform multi-gradation display, The invention can be similarly applied, and the same effects as described above can be obtained.

  The image display method according to the present invention detects a specific region that is a gradation value increasing region and a contour region and makes a sharper rise, thereby effectively suppressing edge blurring while suppressing discomfort and unnaturalness of appearance. Since image quality degradation during moving image display can be improved by suppressing the image, it is useful as an image display method for performing multi-gradation display by dividing an image of one field into a plurality of subfield images, such as PDP and DMD.

The perspective view which shows the structure of PDP of the plasma display apparatus in Embodiment 1 of this invention. Electrode arrangement of the PDP The figure which shows the drive voltage waveform of each electrode of the PDP 1 is a block diagram showing a configuration of a plasma display device in Embodiment 1 of the present invention. 1 is a block diagram of a video signal processing circuit according to Embodiment 1 of the present invention. The figure which showed how it looks when the outline part moves to the left direction on the screen of PDP The figure which showed the appearance of the outline part at the time of performing the signal processing in Embodiment 1 of this invention Block diagram of a video signal processing circuit in Embodiment 2 of the present invention The figure which showed the appearance of the outline part at the time of performing the signal processing in Embodiment 2 of this invention The figure which showed an example of the structure of the subfield in the conventional PDP The figure which showed the case where the image pattern X moves to the horizontal direction on the screen of PDP Image pattern X expanded into subfields The figure which showed the brightness level of appearance when the outline part is still on the screen of PDP The figure which showed the luminance level of appearance when an outline part moves rightward on the screen of PDP A diagram showing the apparent luminance level when the contour portion moves to the left on the screen of the PDP

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AD converter 2 Video signal processing circuit 3 Subfield processing circuit 4 Data electrode drive circuit 5 Scan electrode drive circuit 6 Sustain electrode drive circuit 10 Plasma display panel (PDP)
20 Front plate 22 (made of glass) 22 Scan electrode 23 Sustain electrode 24 Dielectric layer 25 Protective layer 30 Back plate 32 Data electrode 33 Dielectric layer 34 Partition 35 Phosphor layer 101 Field memory 102 Gradation value increasing region detector 103 Outline Area detection unit 104 Specific area detection unit 105 Subfield conversion unit 106 Subfield shift unit 107 Selector 206 Tone value conversion unit

Claims (3)

An image display method in which one field is composed of a plurality of subfields having different luminance weights, and each subfield is controlled to emit or not emit light, thereby performing multi-gradation display.
A region that is a contour region in the image of the current field and has a gradation value larger than that of the previous field is detected, and the contour region is detected with a gradation value that is greater than that of adjacent pixels that are adjacent pixels in the horizontal direction. By detecting pixels that increase more than the value,
In the detected area, a pixel in which a subfield having a luminance weight equal to or higher than a predetermined luminance weight is lit, is combined with a light emission subfield that emits light with a luminance brighter than the luminance that should be emitted. In the combination, the luminance subfield for displaying the luminance to be originally emitted is shifted to the subfield having the larger luminance weight, so that the luminance is higher than that of the emission subfield for displaying the luminance to be originally emitted. A combination obtained by making a subfield having a large weight as a light emitting subfield,
In the detected area, a combination of light emission subfields that emit light with a luminance lower than the luminance that should originally be emitted in pixels other than the pixel in which the subfield having a luminance weight equal to or greater than the predetermined luminance weight is lit, The combination of light emission subfields is a light emission subfield for displaying the luminance to be originally emitted by shifting the combination of light emission subfields for displaying the luminance to be originally emitted to a subfield having a smaller luminance weight. An image display method characterized by being a combination obtained by making a subfield having a luminance weight smaller than that of a field into a light emission subfield. An image display method in which one field is composed of a plurality of subfields having different luminance weights, and each subfield is controlled to emit or not emit light, thereby performing multi-gradation display.
By detecting a pixel in which the gradation value of the video signal is increased by a first threshold or more than the previous field and is increased by a second threshold or more than adjacent pixels that are adjacent pixels adjacent in the horizontal direction , Detect an area that is a contour area in the image of the current field and has a larger gradation value than the previous field,
In the detected area, if the subfield data created from the video signal and representing the light emission / non-light emission of each subfield as numerical information is greater than or equal to the third threshold value, the subfield data is multiplied by a constant to obtain the luminance that should be originally emitted. If the subfield data is less than the third threshold value, it is multiplied by a constant to emit light with a brightness lower than the brightness that should originally be emitted. The combination of light emission subfields
In the detected area, each subfield is controlled to emit or not emit light based on the subfield data multiplied by the constant or the subfield data multiplied by a constant, and in areas other than the detected area Controls the emission or non-emission of each subfield based on the subfield data created from the video signal, the luminance weight of each of the subfields is a power of 2 and the constant is a power of 2 images displayed how to said <br/>. An image display method in which one field is composed of a plurality of subfields having different luminance weights, and each subfield is controlled to emit or not emit light, thereby performing multi-gradation display.
By detecting a pixel in which the gradation value of the video signal is increased by a first threshold or more than the previous field and is increased by a second threshold or more than adjacent pixels that are adjacent pixels adjacent in the horizontal direction , Detect an area that is a contour area in the image of the current field and has a larger gradation value than the previous field,
In the detected area, if the gradation value of the video signal is greater than or equal to the third threshold value, it should be multiplied by a constant, and subfield data should be generated based on the gradation value multiplied by the constant, so that light should be emitted originally. If the gradation value of the video signal is less than the third threshold value, it is multiplied by a constant and multiplied by the constant. By creating subfield data based on the key value, a combination of light emission subfields that emit light with a luminance lower than the luminance that should originally be emitted,
In the detected area, each subfield is controlled to emit or not emit light based on the subfield data created from the gradation value multiplied by the constant or the gradation value multiplied by the constant, and the detection is performed. In each of the areas other than the area that has been set, each subfield is controlled to emit or not emit light based on the subfield data created from the video signal, and the luminance weight of each of the subfields is a power of power of 2, and the constant images displayed how to said <br/> that is a power of two.

Images