JP2005351949A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To insure that more natural animation image display is performed by eliminating coloring of tailing. <P>SOLUTION: The image display device which performs display by causing the stimulation luminescence of phosphors of three colors R, G, and B is equipped with a signal conversion circuit comprised of a signal conversion section 1 and a frame memory section 2 for recording an image signal for one frame component. The signal conversion section 1 reads out the image signal relating to the frame just before the display frame accumulated in the frame memory section 2 according to the input of the image signal of a certain display frame, calculates the correction component of the afterglow by the proximate frame based on the read out image signal of the proximate frame, and outputs the obtained correction signal in superposition on the input signal of the display frame. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is an image that emits a plurality of primary colors such as red (R), green (G), and blue (B) for each pixel by using excitation of a phosphor, such as a plasma display or a field emission display. The present invention relates to a technique for improving image display quality in a display device.

  A conventional image display device states that “a basic processing circuit for a green signal corresponding to an afterglow phosphor is set to 0 or at least a bit from the last sub-scan (subframe) depending on a detected transition. It can be set to “1”. That is, a configuration has been proposed in which transitions of R, G, and B signals are detected between frames and a partial signal of a subframe is changed so that the influence of afterglow is reduced (see, for example, Patent Document 1). .

Japanese Patent Application Laid-Open No. 11-259044

  In an image display device that performs display by exciting a phosphor to emit light like a plasma display device, the phosphor causes light emission by afterglow after the excitation is completed, accompanying light emission at the time of excitation. For this reason, in moving image display, when an image moves on the screen, afterglow due to excitation in the previous frame becomes one of the causes of blurring of the moving image outline. This point is schematically shown in FIG. In FIG. 4, (a) shows an image signal to be displayed on a certain pixel, and p1 to p5 show the position of each pixel. In the case of this figure, the image signal A is the image signal B or the image signal so that the line segment connecting the pixels p1 to p3 in the frame n moves to the line segment P2 to P4 or the line segment P3 to P5 in the frame n + 1. Change to C. The difference between the image signal B and the image signal C is the difference in the number of pixels that move per frame, indicating that the image signal B is one pixel per frame and the image signal C is two pixels. Before the frame n, there is no signal (that is, black display), and the image signal A of the line segments p1 to p3 is input in the frame n, and the light emission at that time is shown in (b). Furthermore, moving image light emission of the frame n + 1 after movement is shown in (c) and (d). (C) is the image signal B, and (d) is the moving image light emission corresponding to the image signal C. For example, when the line segments p1 to p3 move to the line segments p2 to p4 in the next frame n + 1, the moving picture light emission (c) p4 emits light corresponding to the input signal, but the pixels p2 and p3 emit light of the frame n. It is shown that afterglows by p2 and p3 in (b) are superimposed. Further, although no image signal is input at p1 in (c), the afterglow is emitted by the emission of p1 in (b), which is one of the causes of blurring of the moving image outline. (D) shows light emission of a moving image when the moving speed is moved by two pixels per frame, and indicates that tailing due to afterglow occurs longer than the moving image when moved by one pixel per frame. . One pixel is composed of three primary colors, but only one color is schematically shown in order to avoid the complexity of the figure. The moving image blur of the plasma display device is not as remarkable as the moving image blur generated in the liquid crystal display device, but uses phosphors of a plurality of primary colors R, G, B3, and afterglow characteristics for each color. Is not constant, the moving image contour may be colored in the plasma display device.

For example, when considering the display of a moving image in which a white object moves on the screen against a black background, the most remaining behind the moving white object is due to the difference in the afterglow time of each phosphor of R, G, B. A phenomenon of dragging the shadow of a phosphor with a long light time is observed, and this phenomenon is called “tailing” or “color shift”. In the plasma display device, in general, Zn ₂ SiO ₄ : Mn is a green phosphor, (Y, Gd) BO ₃ : Eu is a red phosphor, BaMgAl ₁₀ O ₁₇ : Eu is a blue phosphor, Each is used. When this combination is used, the 1/10 decay time of the emission intensity of each color is 14 ms for green, 9 ms for red, and much shorter than 1 ms for blue. Therefore, the green tail is most easily observed. In particular, considering that the frame time of NTSC television is 16.7 ms, it will be understood that the image remains clear even when the next frame is reached. Moreover, since green has a higher luminance than red and blue, green tailing is regarded as a problem as one of the disturbing phenomena of television images.

  In recent years, green phosphors whose afterglow time has been shortened to about 8 ms have been manufactured by methods such as increasing the amount of Mn activation of the green phosphor. The use of phosphors with short afterglow characteristics can be said to be effective as a countermeasure against the tailing phenomenon, but on the other hand, the luminous efficiency of the green phosphors is sacrificed, so there is a trade-off relationship with luminance. Is a problem.

  Patent Document 1 discloses a method of reducing afterglow by focusing on a green signal with long afterglow, detecting transition between frames, and shortening light emission time before transition. Here, since the plasma display apparatus performs gradation expression by the number of light emission pulses within one frame time, normally, one frame is divided into about 8 to 15 subframes (also synonymous with subfields). It is composed. In the prior art of Patent Document 1, when tailing occurs, the order of frames preceding this forcibly turns off the subsequent subframe, thereby reducing the green light emission intensity and the remaining frame for the next frame. The light component is reduced. By this method, it can be said that the tailing can be surely weakened, but on the other hand, by turning off some subframes, the brightness of the image becomes so low that it cannot be ignored, and R, G, Since the color balance of B changes, the image itself is disturbed.

  Furthermore, as described in Patent Document 1, it means that a phosphor with a long afterglow delays the rise of light emission at the same time, so at the head of the moving direction of a bright moving image with a black background, Conversely, the long afterglow color is weak. This point is not as noticeable as “tailing”, but is seen as a slight disturbance. Since this phenomenon can be handled in the same manner as the “tailing” described above, this phenomenon will be considered to be included in the “tailing” below.

  The present invention has been made to overcome the above-described problems in an image display apparatus that displays by exciting and emitting phosphors corresponding to the three primary colors. It is to realize a more natural moving image display by eliminating the coloring.

  An image display device according to the subject of the present invention is an image display device that performs display by exciting and emitting phosphors corresponding to three primary colors, a frame memory unit that records an image signal for one frame, and a signal conversion unit The signal conversion unit receives an image signal related to a frame immediately before the display frame stored in the frame memory unit in response to an input of the image signal of a certain display frame. Based on the read previous frame image signal, the afterglow correction component of the previous frame is calculated, and the obtained correction signal is superimposed on the input image signal of the display frame.

  Hereinafter, various embodiments of the subject of the present invention will be described in detail along with the effects and advantages thereof with reference to the accompanying drawings.

  According to the subject matter of the present invention, the trailing in the moving image has the same hue as that of the original moving image, and at least the color shift of the trailing is eliminated, thereby realizing a more natural moving image display.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a signal conversion circuit of the image display apparatus according to the present embodiment. In FIG. 1, the signal conversion circuit includes a signal conversion unit 1 and a frame memory unit 2. That is, the signal conversion unit 1 reads out an image signal related to a frame immediately before the display frame stored in the frame memory unit 2 in response to an input of an image signal of a certain display frame, and reads out the immediately preceding frame image signal. Then, after calculating the afterglow correction component of the previous frame, the obtained correction signal is superimposed on the input image signal of the display frame. In other words, the signal conversion circuit refers to the input digital image signal with reference to the image data of the previous frame stored in the frame memory unit 2 and a plurality of primary colors R, G, The signal conversion unit 1 corrects the image data based on the coefficient prepared for each B, and outputs the corrected image data. Specific processing of image data in the signal conversion circuit will be described below.

  Following the black screen frame, the light emission intensity of the image display device during one frame period (LR, LG, LB) in the frame in which the data (R, G, B) corresponding to each pixel of the image display device is input. ). If the coefficients (Sr, Sg, Sb) are used, the light emission intensity is expressed as follows.

  Further, data of frame n to be processed is expressed as (Rn, Gn, Bn), and data of frame n-1 one frame before is expressed as (Rn-1, Gn-1, Bn-1). When the afterglow intensity generated in frame n due to the light emission of frame n-1 is represented by (LRn *, LGn *, LBn *), the afterglow intensity is expressed as follows using coefficients (Kr, Kg, Kb). Is done.

  At this time, the emission intensity of frame n when the image data is output without performing correction processing in the signal conversion circuit is as follows.

  Generally, since the values of the coefficients Kr, Kg, and Kb are different, the afterglow color is different from the color of the previous frame. That is, the afterglow emission color by (LRn *, LGn *, LBn *) is different from the color of (LRn, LGn, LBn) or (Rn, Gn, Bn) due to the difference in afterglow characteristics of each phosphor. become. For example, in a general phosphor of a plasma display, Kg> Kr >> Kb≈0.

The values of the coefficients Kr, Kg, and Kb can be measured using an optical filter corresponding to the wavelength region of each emission color and a sensor such as a photomultiplier having sensitivity in the wavelength region. If the decay time constant is known, the decay curve can be easily predicted.
Strictly speaking, a very small amount of G color afterglow remains on the screen two frames ahead, but the 1/10 decay time of a normal phosphor is equal to or less than one frame time (16.7 ms). Since it is short, the influence on the image quality is small, and the G color afterglow for the screen two frames ahead may be ignored.

  In order to make the afterglow hue the same as that of the previous frame, it is necessary to perform the following processing. Here, the output signal (corrected image data) of the signal converter 1 is expressed as <Rn>, <Gn>, <Bn>, and the correction coefficients are (Fr, Fg, Fb) as follows. Define.

  For example, Fb · Bn−1 represents a blue correction amount calculated from the signal data Bn−1 of the frame n−1.

  The operation of the signal conversion circuit in FIG. 1 will be described. The signal conversion unit 1 calls the signal data of the frame n−1 stored in the frame memory unit 2 for each pixel, inputs the signal data to the signal conversion unit 1, and An operation using the input signal of n and the above equation is performed, and output from the signal conversion unit 1 as a display signal.

  In the calculation of correction in the signal conversion unit 1, a method of determining a constant afterglow luminance with respect to the luminance of the previous frame n-1 is the simplest. FIG. 2 schematically shows a moving image corrected in such a manner. 2A and 2B, (a) shows an image signal of a frame n to be displayed on a certain pixel, and p1 to p5 show the positions of the respective pixels. Before the frame n, there is no signal (ie, black display), and the image signal A of the line segments p1 to p3 is input in the frame n. Image signal B is input. (B) shows an image signal that is corrected in the frame n + 1 and actually input to the pixel. (C) shows light emission by the image signal A of frame n in (a), and (d) shows light emission by the image signal B of frame n + 1 in (b). Since the correction components to be superimposed on the image signal in p1 to p3 in (b) are calculated for each of the three primary colors from the image signal in frame n, the moving image displayed in frame n + 1 in the result (d) The color of the tail will be natural. In this figure, the case where the moving speed is 1 pixel per frame has been described, but even when the moving speed is 2 pixels per frame, a natural moving image display can be obtained by the same correction.

  By this correction, the color of the tail portion becomes close to that of the moving image, and a natural image can be realized.

Next, a method for determining the correction coefficient F in Equation 4 will be described. Before and frame n-1 is completed and the time frame n starts and t = 0, afterglow intensity Iz at time t in the frame n, the frame n-1 at the end emission intensity I ₀ and the following formula There is a relationship.

  In the equation (1), c is a constant and has a relationship of the following equation with the 1/10 decay time τ that is often used as the afterglow time of the phosphor.

  The afterglow luminance Lz in one frame period is obtained by integrating equation (1) from t = 0 to 16.67 ms.

  For example, when τ is 14 ms, the afterglow luminance from light emission with luminance 1 is 0.34 on average for the entire subsequent frame. When τ is 10 ms, the afterglow luminance is 0.25. This corresponds to the coefficient K described above in Equation 2.

  Therefore, in the case of a system in which the decay time of G is 14 ms, the decay time of R is 10 ms, and the decay time of B is 0 ms, G having the longest K is not corrected and Fg is set as follows. .

  For R having the next longest K, Fr is set as follows using the difference in afterglow.

  For B with no afterglow, Fb may be set as follows.

  A correction component can be calculated from the correction coefficient F obtained as described above and the image signal of frame n−1 to obtain an image signal of frame n. In this method, the influence of afterglow two frames before (frame n-2) is ignored in frame n.

  The signal conversion process described above spans multiple frames measured in a still image, with a conversion coefficient between signal input and electric energy input to the display device (corresponding to the number of display discharge pulses in the case of a plasma display). It can be considered that the definition based on the light emission output in the steady state is replaced with a definition roughly divided into the light emission output within one frame time and the afterglow output within the next frame time.

  In moving image expression, it is desirable to use a display device that does not have afterglow, but since there is actually afterglow due to restrictions on the light emitting material, it is necessary to use display signal correction based on the assumption that afterglow occurs. This is useful when considering the tailing of the video. As described above, according to the present embodiment, the trailing edge of the moving image outline has the same color as the original moving image, and the coloring of the trailing edge can be eliminated to achieve a more natural moving image display. .

(Embodiment 2)
The feature of the present embodiment is that “the signal conversion unit 1 does not perform the calculation of the correction signal described in the first embodiment for pixels whose luminance of the image signal does not exceed the threshold value”.

  In general, as the human visual characteristics become weaker, the ability to recognize colors decreases. For example, what is visible in the dark is about the contour, and even a colored object is perceived as gray or a little bluish with no hue.

  In addition, the afterglow of a dark image is negligible, and even if the correction signal F is calculated, it may not be actually corrected due to gradation limitations.

  Therefore, for a dark image, it is effective to provide a threshold value for stopping the correction processing. That is, in order to reduce the amount of calculation, the above processing may be stopped when the luminance Ln-1 of the frame n-1 is lower than the threshold Lth.

  Thereby, a cheaper arithmetic circuit can be used.

  The luminance of the pixel is calculated from the three primary colors, but since the luminance of blue is low, it may be obtained from Gn-1 and Rn-1 or only from Gn-1 having a high luminance.

  Further, when the image display device has a moving image detection circuit, the above correction processing may be performed only on the moving image portion using the result of the moving image detection circuit, thereby reducing the amount of calculation. An effect is obtained. As described above, according to the present embodiment, the signal conversion unit 1 does not calculate the correction signal for pixels whose luminance of the image signal does not exceed the threshold value, and therefore, a cheaper calculation circuit can be used. I can do it.

(Embodiment 3)
In the above example, Kr, Kg, Kb, and Fr, Fg, Fb are used as constant values.

  However, in a binary display type device such as a plasma display, gradation display is performed by time-dividing one frame called a subframe method (or subfield method) into a plurality of subframes having different output levels. In this case, the time from light emission to the next frame differs depending on which subframe emits light. Therefore, strictly speaking, the values of Kr, Kg, and Kb change depending on which subframe is turned on.

  In order to perform processing in consideration of this point, since it is known in which subframe the light is emitted depending on the gradation, conversion coefficients Fr, Fg, and Fb are obtained in advance for each gradation, and these conversion coefficients are converted into signal conversion. Stored in a lookup table (LUT) unit 2 (for example, the LUT unit 2 is composed of a storage device or a logic circuit) provided in the unit 1, and according to each gradation of Rn-1, Gn-1, and Bn-1 Corresponding Kr, Kg, Kb may be used.

  FIG. 3 is a functional block diagram showing the configuration of the signal conversion circuit according to the present embodiment. The signal conversion unit 1 further includes the LUT unit 3 described above. The operation of the signal conversion circuit in FIG. 3 differs from the signal conversion circuit in FIG. 1 only in that the correction coefficients Fr, Fg, and Fb are calculated by the signal conversion unit 1 for each pixel. That is, in calculating the correction coefficients Fr, Fg, and Fb in the signal conversion unit 1, first, Kr, Kg, and Kb values are look-up table units corresponding to the values of Rn-1, Gn-1, and Bn-1. 3. Then, correction coefficients Fr, Fg, and Fb are calculated from the difference between them.

  In recent years, green phosphors having an afterglow time of about 8 ms are sometimes used in PDP, and the problem of tailing is being reduced. Furthermore, the tailing is reduced by arranging a subframe having a large weight such as MSB (maximum bit) in the first half of the frame. In the present embodiment, sub-frames with a small weight such as LSB (minimum bit) are continuously arranged in the first few sub-frames, so that the coloring of the tail of the sequential erasure driving method can be improved.

  However, in the case of the sequential erase driving method in which each discharge cell is erased only once in one frame, the subframes must be arranged in ascending order from the smaller subframe. The pull becomes more noticeable.

  In the correction method according to the present embodiment, it is appropriate to perform the correction in the first half of the frame where the afterglow is strong in order to match the corrected light emission and the afterglow in time. In that sense, it is effective to arrange a small subframe used for correction at the beginning of the frame. That is, a small weighting subframe such as LSB (minimum bit) may be continuously arranged in the first few subframes. Therefore, the present invention is particularly advantageous when applied to the above-described sequential erasure driving method in order to improve the tail coloring of the driving method.

  By using the above-described method, the afterglow color can be appropriately corrected to the color of the original image, so that the afterglow color is natural and close to that of the moving image. That is, the color of the tailing becomes natural and the quality of the moving image is improved.

  As for the phenomenon in which coloring or luminance reduction occurs at the beginning of the moving direction of a moving image, assuming that the rise time constant is the same as the decay time constant, the luminance reduction is not improved by performing the above afterglow correction. However, the hue is improved in almost the same way as the tailing. Therefore, the hue is compensated at both the head and tail in the moving direction of the moving image, and the quality of the moving image is improved.

  Although an example of a plasma display is described in the description of the technical background, the present invention can be used for all other display elements that excite and emit phosphors, and is not 4 primary colors of R, G, and B. It goes without saying that the present invention can also be used in a display device that displays using multiple primary colors that are higher than the primary colors.

(Appendix)
While the embodiments of the present invention have been disclosed and described in detail above, the above description exemplifies aspects to which the present invention can be applied, and the present invention is not limited thereto. In other words, various modifications and variations to the described aspects can be considered without departing from the scope of the present invention.

  The present invention can be applied to an image display device including R, G, and B3 color phosphors such as a plasma display device.

It is a block diagram which shows the structure of a signal conversion circuit. It is a schematic diagram which shows the mode of the correct | amended signal. It is a functional block diagram which has LUT. It is a schematic diagram which shows the mode of the afterglow in a moving image.

Explanation of symbols

1 signal conversion unit, 2 frame memory unit, 3 LUT unit.

Claims (4)

An image display device that performs display by exciting and emitting phosphors corresponding to a plurality of primary colors,
A signal conversion circuit comprising a frame memory unit for recording an image signal for one frame and a signal conversion unit;
The signal conversion unit reads an image signal related to a frame immediately before the display frame stored in the frame memory unit in response to an input of an image signal of a certain display frame, and based on the read previous frame image signal , Calculating a correction component of afterglow by the immediately preceding frame, and superimposing the obtained correction component on the input image signal of the display frame,
Image display device. The image display device according to claim 1,
The signal conversion unit does not perform the calculation of the correction component for pixels whose luminance of the image signal does not exceed a threshold value,
Image display device. The image display device according to claim 1 or 2,
The signal conversion unit stores in advance a conversion coefficient for each gradation in a look-up table, and uses the conversion coefficient corresponding to the gradation of the image signal to calculate an afterglow correction component for the immediately preceding frame. It is characterized by
Image display device. An image display device according to any one of claims 1 to 3,
The signal conversion unit corrects afterglow of a subframe with a large weight arranged in the second half of the frame with a subframe with a small weight arranged in the first half of the next frame,
Image display device.

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