JP2007047244A - Image display device and image display method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device and an image display method that can perform expansion processing corresponding to a deterioration position when an image deteriorates as a gray scale range is expanded. <P>SOLUTION: A third detection section 72c comprises an overexposed white area detection section 85, an overexposed white evaluated value calculation section 86, and a local overexposed white decision section 87. The overexposed white area detection section 85 detects an overexposed white area (pixel group) which is too low in density to have no gradation in a frame based upon a luminance signal Y input from an image processing section 70 and a critical luminance value I<SB>Limit</SB>calculated by a histogram analysis section 83. The overexposed white evaluated value calculation section 86 calculates overexposed white evaluated values corresponding to positions and areas of detected overexposed white areas by the detected overexposed white areas and the local overexposed white decision section 87 recognizes a scene change when a calculated an evaluated value exceeds a specified value and sets a flag F<SB>LSat</SB>true. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image display apparatus and an image display method for inputting an image signal and displaying an image corresponding to the image signal.

  As one form of an image display device, light emitted from a light source is modulated in accordance with an image signal by a light modulation device (liquid crystal light valve or the like), and the modulated light is enlarged and projected onto a screen or the like to display an image. It has been known. The light modulation device includes a plurality of pixels, and forms an image according to the image signal by controlling the light transmittance for each pixel according to the gradation information represented by the image signal.

  Furthermore, in order to extend the effective gradation range, the expansion means for correcting the gradation (transmittance) of each pixel, and the amount of light incident on each pixel of the light modulation device is reduced substantially uniformly in accordance with the correction. There has been proposed a projector provided with a light control means capable of performing the above. According to this, for example, when displaying a dark image, the number of effective gradations is increased (the dynamic range is expanded) by reducing the amount of light by the light control means and extending the gradation range by the expansion means. And a sense of contrast can be improved.

  In such a projector, if the expansion process or the light control process cannot follow the change in the image, the image is likely to deteriorate (whiteout, blackout, etc.) immediately after the scene is switched. For example, when a dark scene is suddenly switched to a bright scene, excessive expansion suitable for a dark scene is performed without following a change in luminance, and whiteout occurs. On the other hand, when expansion or dimming is performed following the brightness of an image that changes sequentially, overexposure or the like can be suppressed, but there is a problem that the screen flickers. For this reason, there has been proposed a projector capable of detecting a change in a scene and performing dimming and expansion according to the detection result (see, for example, Patent Document 1).

JP-A-2005-79994

  However, as in the video display device described in Patent Document 1, in the configuration in which the average luminance or the like in one frame is extracted and the change in the scene is detected based on the temporal change, the brightness tendency in the entire image However, there is a problem that light control and expansion cannot be performed in consideration of a position where deterioration occurs. For this reason, for example, even when a whiteout occurs in the center of an image that is likely to be watched by a viewer, if the range is small, the brightness does not change and is not detected as a scene change. There is a risk that the image will flicker in an attempt to suppress the whiteout that occurs at the periphery of the image that is rarely watched by the viewer.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image display device capable of performing an expansion process according to a deterioration position when an image deteriorates as the gradation range expands. And an image display method.

  The image display device of the present invention is an image display device that modulates incident light by a light modulation device and displays an image according to an input image signal, and the level represented by the image signal based on the image signal. A feature amount extraction unit that extracts a feature amount according to key information, a parameter determination unit that determines an extension parameter for extending the gradation range of the gradation information based on the feature amount, and the gradation range A decompression processing unit that corrects the gradation information using the decompression parameter, and a modulation driving unit that drives the light modulation device based on the gradation information corrected by the decompression processing unit, And the parameter determination unit detects a deteriorated area where the image deteriorates as the gradation range is extended, performs an evaluation according to the area and position of the deteriorated area, and based on the evaluation result. Z And determines the decompression parameters Te.

  According to this image display device, the parameter determination unit detects a deteriorated area where the image deteriorates as the gradation range extends, and determines a parameter for expansion according to the position of the deteriorated area. It is possible to perform extension processing according to the position where the deterioration occurs.

  In this image display device, the parameter determination unit divides the image into a plurality of small regions, weights each small region according to its position, and determines a degradation region in each small region. You may make it perform the said evaluation according to the area and the weight provided to each said small area | region.

  According to this image display device, since the degradation area is evaluated for each small area weighted according to the position, the position of the degradation area can be easily specified, and the evaluation according to the position can be easily performed. Is possible.

  In this image display device, the parameter determination unit divides the image into small regions having different areas according to weights according to positions, and determines the area of the degraded region in each small region relative to the area of each small region. The evaluation may be performed accordingly.

  According to this image display device, since the divided small regions are weighted according to the position according to the area, it is not necessary to consider the weight according to the position again when performing the evaluation.

  In this image display device, the parameter determination unit detects a whiteout region in which an image is whitened as the gradation range is expanded to a bright side, and the area and position of the whiteout region are determined. It is desirable to perform a corresponding evaluation and determine an expansion parameter for expanding the gradation range to the bright side based on the evaluation result.

  According to this image display device, the parameter determination unit detects a whiteout region where an image is overexpanded as the gradation range is expanded to the bright side (extended white side), and parameters for expansion are set. Since the determination is made according to the position of the whiteout area, it is possible to perform an expansion process according to the whiteout occurrence position.

  In this image display device, it is preferable that the parameter determination unit determines an expansion parameter that can suppress the deterioration as the deterioration region is located at the center of the image.

  According to this image display device, it is possible to suppress deterioration in the central portion of an image that is likely to be watched by the viewer, so that it is not necessary for the viewer to be aware of the deterioration. If the degradation area occurs in the peripheral part of the image that the viewer is less likely to watch, by determining the extension parameter that emphasizes the prevention of flickering rather than the degradation suppression, It is possible to prevent the image from flickering.

  In this image display device, the parameter determination unit determines the gradation range as the most extensible parameter within a range in which the deterioration does not occur when the deterioration region is located at the center of the image. Is desirable.

  According to this image display apparatus, in order to suppress the occurrence of deterioration at the center of the image that the viewer tends to watch, it is possible to prevent the viewer from paying attention to the deterioration and to expand the gradation range that can be expanded most. Since the parameter is determined, it is possible to improve the contrast of the image.

  In this image display device, a dimming unit capable of adjusting at least one light amount of light incident on the light modulation device and light modulated by the light modulation device, and a dimming drive unit that drives the dimming unit The parameter determining unit determines a dimming parameter for determining the dimming amount by the dimming unit based on the evaluation result, and the dimming driving unit uses the dimming parameter. The dimming means may be driven.

  According to this image display apparatus, since the light control means is provided, it is possible to suppress a change in luminance due to expansion of the gradation range by light control by the light control means.

  According to the image display method of the present invention, a feature amount extraction step of extracting a feature amount according to the tone information represented by the image signal based on the input image signal, and the tone information of the tone information based on the feature amount. A parameter determining step for determining an expansion parameter for extending the gradation range, an expansion processing step for correcting the gradation information using the expansion parameter to extend the gradation range, and the expansion processing step And a modulation step of modulating incident light by a light modulation device based on the gradation information corrected in step (b), and in the parameter determination step, a deteriorated area where an image deteriorates as the gradation information is expanded is detected. In addition, the degradation region is evaluated according to its area and position, and the extension parameter is determined based on the evaluation result.

  According to this image display method, in the parameter determination step, the deterioration area where the image deteriorates with the extension of the gradation range is detected, and the parameter for extension is determined according to the position of the deterioration area. It is possible to perform extension processing according to the position where the deterioration occurs.

  Further, when the image display device and the image display method described above are constructed using a computer provided in the image display device, the present invention provides a program for realizing the function, or the program as described above. It is also possible to configure in the form of a recording medium recorded so as to be readable by a computer. As recording media, flexible disks, CD-ROMs, magneto-optical disks, IC cards, ROM cartridges, punch cards, printed matter on which codes such as barcodes are printed, projector internal storage devices (memory such as RAM and ROM), Various media that can be read by the computer, such as an external storage device, can be used.

Hereinafter, as an image display apparatus according to an embodiment of the present invention, a projector that modulates light emitted from a light source in accordance with an image signal and enlarges and projects the modulated light onto a screen or the like will be described.
FIG. 1 is a configuration diagram showing a schematic configuration of the projector according to the present embodiment, and shows an optical path from the light emitted from the light source to the screen.
As shown in FIG. 1, the projector 1 includes an illumination optical system 10, a color light separation optical system 20, a relay optical system 30, three liquid crystal light valves 40R, 40G, and 40B as light modulation devices, and a cross dichroic prism. 50 and a projection lens 60.

  The illumination optical system 10 includes a light source 11 including a discharge type light source lamp such as an ultrahigh pressure mercury lamp and a metal halide lamp, a first lens array 12, a second lens array 13, a polarization conversion element 14, and a superimposing lens 15. And a light control element 16. The light bundle emitted from the light source 11 is divided into a number of minute light bundles by the first lens array 12 in which minute lenses 12a are arranged in a matrix. The second lens array 13 and the superimposing lens 15 are provided so that each of the divided light bundles irradiates the entire three liquid crystal light valves 40R, 40G, and 40B that are illumination targets. For this reason, each light bundle is superimposed by the liquid crystal light valves 40R, 40G, and 40B, and the entire liquid crystal light valves 40R, 40G, and 40B are illuminated almost uniformly.

  Here, a dimming element 16 is provided in the optical path between the first and second lens arrays 12 and 13. The light control element 16 can narrow the light emitted from the first lens array 12 by the rotation of the louver 16a, and blocks a part of the light beam divided by the first lens array 12. be able to. For this reason, the amount of light that illuminates the liquid crystal light valves 40R, 40G, and 40B is substantially uniformly limited in accordance with the aperture amount of the light control element 16.

  The polarization conversion element 14 has a function of aligning with polarized light having a specific polarization direction so that the light from the light source 11 can be efficiently used by the liquid crystal light valves 40R, 40G, and 40B. The polarized light emitted from the illumination optical system 10 enters the color light separation optical system 20.

  The color light separation optical system 20 includes a first dichroic mirror 21, a first reflection mirror 22, and a second dichroic mirror 23, and the light emitted from the illumination optical system 10 has a different wavelength range. Separate into three colors of light. The first dichroic mirror 21 transmits substantially red light and reflects light having a shorter wavelength than the transmitted light. The red light R that has passed through the first dichroic mirror 21 is reflected by the first reflecting mirror 22 to illuminate the liquid crystal light valve 40R for red light.

  Of the light reflected by the first dichroic mirror 21, green light G is reflected by the second dichroic mirror 23 and illuminates the liquid crystal light valve 40G for green light. Further, the blue light B passes through the second dichroic mirror 23, passes through the relay optical system 30, and illuminates the liquid crystal light valve 40B for blue light.

  In addition, since the path | route of blue light B becomes long compared with the path | route of other color lights, in order to suppress that the illumination efficiency to liquid crystal light valve 40B falls by the divergence of a light beam, blue light B The relay optical system 30 is provided in the path. The relay optical system 30 includes an incident side lens 31, a second reflection mirror 32, a relay lens 33, a third reflection mirror 34, and an emission side lens 35. The blue light B emitted from the color light separation optical system 20 converges in the vicinity of the relay lens 33 by the incident side lens 31 and diverges toward the emission side lens 35.

  Each of the liquid crystal light valves 40R, 40G, and 40B includes a liquid crystal panel 41 in which liquid crystal is sealed between a pair of transparent substrates, and the liquid crystal panel 41 has an inner surface for each minute region (pixel) with respect to the liquid crystal. Transparent electrodes (pixel electrodes) to which a driving voltage can be applied are formed in a matrix. An incident-side polarizing plate 42 and an emitting-side polarizing plate 43 are attached to the incident-side surface and the emitting-side surface of the liquid crystal panel 41, respectively. The incident side polarizing plate 42 and the exit side polarizing plate 43 can transmit only polarized light in a specific polarization direction, respectively, and the incident side polarizing plate 42 transmits polarized light in the polarization direction aligned by the polarization conversion element 14. It is possible. Therefore, most of each color light incident on each of the liquid crystal light valves 40R, 40G, and 40B is transmitted through the incident-side polarizing plate 42 and is incident on the liquid crystal panel 41.

  Here, when a driving voltage corresponding to an image signal is applied to each pixel of the liquid crystal panel 41, light incident on the liquid crystal panel 41 is modulated according to the driving voltage and has a different polarization direction for each pixel. It becomes polarized light. Of this polarized light, only the polarization component that can be transmitted through the exit-side polarizing plate 43 is emitted from the liquid crystal light valves 40R, 40G, and 40B. That is, the liquid crystal light valves 40R, 40G, and 40B transmit incident light with different transmittances for each pixel according to the image signal, so that an optical image having a gradation is formed for each color light. An optical image composed of each color light emitted from the liquid crystal light valves 40R, 40G, and 40B enters the cross dichroic prism 50.

  The cross dichroic prism 50 combines the optical images of the respective colors emitted from the liquid crystal light valves 40R, 40G, and 40B for each pixel to form an optical image representing a color image. The optical image synthesized by the cross dichroic prism 50 is enlarged and projected on the screen SC by the projection lens 60 and displayed as an image.

FIG. 2 is a block diagram for explaining the circuit configuration of the projector 1.
As shown in FIG. 2, in addition to the components shown in FIG. 1, the projector 1 includes an image signal processing unit 70, a feature amount extraction unit 71, a scene change detection unit 72, an expansion coefficient calculation unit 73, and a dimming coefficient calculation. A unit 74, a coefficient switching unit 75, an extension processing unit 76, a dimming drive unit 77, a light valve drive unit 78 as a modulation drive unit, and the like. When displaying a dark image, the projector 1 expands the gradation range to the bright side by the expansion processing unit 76, and performs light control (reduction of the amount of light) by the light control element 16, thereby obtaining an effective number of gradations. Increase the contrast (enlarge the dynamic range) and improve the contrast. Specifically, the projector 1 includes a computer including a CPU, a ROM, a RAM, and the like, and the units 70 to 76 are realized by the CPU operating according to a control program stored in the ROM. Has been.

  The image signal processing unit 70 can input various types of image signals from the outside, and R (red), G (green), B (blue), and gradations of each color based on the input image signal. A digital image signal RGB and a luminance signal Y represented by 10-bit luminance values (0 to 1023) are generated. The luminance signal Y is composed of a 10-bit luminance value representing the luminance when the respective colors are combined. Based on the image signal RGB, Y = 0.299R + 0.587G + 0.144B (R, G, B are the colors of the respective colors). (Luminance value) can also be calculated. The generated image signal RGB is output to the expansion processing unit 76, and the luminance signal Y is output to the feature amount extraction unit 71 and the scene change detection unit 72.

  The feature amount extraction unit 71 extracts various feature amounts based on the brightness (luminance value) of the image from the input luminance signal Y for each frame (one screen). As the feature amount, the maximum luminance value (white peak value) in one frame and the APL (Average Picture Level) representing the average luminance in one frame represent the frequency distribution of each luminance value in one frame. A histogram or the like is extracted or derived. In this embodiment, the white peak value and the histogram are output to the scene change detection unit 72, and the white peak value and the APL are output to the expansion coefficient calculation unit 73 and the dimming coefficient calculation unit 74.

  The expansion coefficient calculation unit 73 uses an LUT (Look Up Table) or the like based on the input white peak value and APL, and generates an expansion coefficient for deriving a magnification (expansion rate) for expanding each luminance value of the image signal RGB. G is derived. Here, the expansion coefficient G is expressed by an 8-bit numerical value (0 to 255), and by defining the expansion rate as 1 + G / 256, each luminance value is expanded in the range of 1 to about 2 times. Can do.

  The dimming coefficient calculation unit 74 derives a dimming coefficient L for guiding the dimming amount (aperture amount) of the dimming element 16 using an LUT or the like based on the input white peak value and APL. The dimming coefficient L is also expressed by an 8-bit numerical value (0 to 255), and the smaller the numerical value, the larger the aperture amount (the light amount that illuminates the liquid crystal light valves 40R, 40G, and 40B decreases). The dimming amount (aperture amount) to be set changes according to the derived expansion rate (the larger the expansion rate, the more the light amount needs to be reduced). The dimming coefficient L may be derived based on this.

In the present embodiment, the expansion coefficient calculation unit 73 and the dimming coefficient calculation unit 74 each have two types of expansion factors G ₀ and G _New and two types according to the input feature amount (white peak value or APL). The dimming coefficients L ₀ and L _New can be derived.

The expansion coefficient G ₀ and the dimming coefficient L ₀ are ideal coefficients for expanding the dynamic range in one frame to be processed, and are coefficients derived from the white peak value and APL of the frame. When the expansion process and the dimming process are performed using the expansion coefficient G ₀ and the dimming coefficient L ₀ , it is possible to obtain a high contrast feeling in each frame, but the flicker accompanying the temporal luminance change of the image Is conspicuous. On the other hand, the expansion coefficient G _New and the dimming coefficient L _New are leveled coefficients and are determined in consideration of coefficients used in the past (one frame before to several frames before). When the extension process and the dimming process are performed using the extension coefficient G _New and the dimming coefficient L _New , flickering can be made inconspicuous because the leveled extension and dimming process is performed. It is difficult to follow the temporal luminance change of the image, and whiteout is likely to occur.

  It should be noted that the smaller the input white peak value is, the greater the luminance value can be expanded without causing overexposure, so that the expansion coefficient calculation unit 73 and the dimming coefficient calculation unit 74 derive each coefficient. For this reason, it is desirable to increase the expansion coefficient G (the dimming coefficient L is small) as the white peak value is small. Further, the smaller the input APL value is, and the farther the white peak value is, the more pixels are subject to whiteout due to expansion processing. Therefore, the smaller the APL is, the larger the expansion coefficient G is (the dimming coefficient L is small) It is desirable to take this into account.

The two expansion coefficients G ₀ and G _New derived by the expansion coefficient calculation unit 73 are output to the scene change detection unit 72 and the coefficient switching unit 75, and the two dimming coefficients L derived by the dimming coefficient calculation unit 74. ₀ and L _New are output to the coefficient switching unit 75.

Based on the control signal from the scene change detecting unit 72, the coefficient switching unit 75 selects the expansion coefficient G ₀ and the two dimming coefficients L ₀ and L _New from the input two expansion coefficients G ₀ and G _New. The dimming coefficient L ₀ or any combination of the expansion coefficient G _New and the dimming coefficient L _New is output to the expansion processing unit 76 and the dimming driving unit 77, respectively.

The expansion processing unit 76 applies the expansion rate (1 + G / G) corresponding to the expansion coefficient G (G ₀ or G _New ) input from the coefficient switching unit 75 to each luminance value of the image signal RGB input from the image signal processing unit 70. 256) to expand (correct). As a result of multiplication by the expansion ratio, 1023 is set as the luminance value for a pixel exceeding the maximum luminance value (1023). The expanded luminance value is output to the light valve driving unit 78, and the light valve driving unit 78 drives the liquid crystal light valves 40R, 40G, and 40B according to the expanded luminance value.

The dimming drive unit 77 drives the louver 16a of the dimming element 16 so that the aperture amount of the dimming element 16 becomes a value corresponding to the input dimming coefficient L (L ₀ or L _New ).

The scene change detection unit 72 can detect a scene change that switches from a dark image to a bright image based on the white peak value and histogram in one frame input from the feature amount extraction unit 71 for each frame. A control signal corresponding to the detection result is output to the coefficient switching unit 75. More specifically, the scene change detection unit 72 generates a control signal that selects coefficients (extension coefficient G _New and dimming coefficient L _New ) that can suppress flicker during a period in which no scene change is detected. When output to the switching unit 75 and a scene change is detected, whiteout is suppressed by selecting ideal coefficients (expansion coefficient G ₀ and dimming coefficient L ₀ ). Note that the expansion process and the dimming process using the ideal coefficient are not accompanied by temporal leveling and follow sensitively to changes in the luminance of the image. Therefore, this process is also referred to as a speed-up process.

When detecting the following three states, the scene change detection unit 72 of the present embodiment recognizes it as a scene change and outputs a control signal to be accelerated.
(1) When the screen is suddenly switched from a black screen (entirely black or dark screen) often inserted intentionally at a scene change to a bright screen.
(2) When whitening is likely to occur in many (global) pixels as a whole by performing expansion processing using the expansion coefficient G _New .
(3) When a predetermined amount of whiteout is likely to occur in the central portion (local area) of the image that is viewed by the viewer by performing expansion processing using the expansion coefficient G _New .

Details of the scene change detection unit 72 will be described in detail with reference to the drawings.
FIG. 3 is a block diagram showing a detailed configuration of the scene change detection unit 72.
As shown in FIG. 3, the scene change detection unit 72 includes a first detection unit 72a that detects a scene change based on an increase in luminance from a black screen, and a first detection unit that detects a scene change based on global whiteout. 2 detection unit 72b, a third detection unit 72c that detects a scene change based on local whiteout, an OR circuit 72d, and a memory (not shown) that stores various setting values and the like. is doing.

The first detection unit 72a includes a black screen detection unit 81 and an acceleration processing start determination unit 82. The black screen detection unit 81 determines whether or not the target frame (hereinafter also referred to as the current frame) is in a black screen state, and sets the flag F _Black to true when the frame is a black screen. When the flag F _Black is true, that is, when the black screen state was present before the current frame, the acceleration processing start determination unit 82 determines whether or not the screen has suddenly switched to a bright screen. If it is, it is recognized as a scene change and the flag F _BStart is _set to true.

FIG. 4 is a flowchart for explaining the operation of the first detection unit 72a.
As shown in FIG. 4, in step S101, the black screen detection unit 81 determines whether or not the flag F _Black is true (TRUE), that is, whether or not a black screen has been detected in a past frame. Judging. When the flag F _Black is false (FALSE), the process proceeds to step S102, and when the flag F _Black is true, the process proceeds to step S104.

When the flag F _Black is false and the process proceeds to step S102, the black screen detection unit 81 determines whether or not the current frame is a black screen. Specifically, the white peak value input from the feature amount extraction unit 71 is compared with the threshold value Th _Black stored in the memory in advance, and when the white peak value is less than the threshold value Th _Black , to decide. If it is determined that the screen is a black screen, the process proceeds to step S103. If it is not determined that the screen is a black screen, the processing in the current frame is terminated.
If it is determined that the screen is a black screen and the process proceeds to step S103, the black screen detection unit 81 sets the flag F _Black to true and ends the processing in the current frame.

When the flag F _Black is true and the process proceeds to step S104, the high-speed processing start determination unit 82 determines whether or not the screen is suddenly switched from the black screen state to the bright screen. Specifically, first, a difference G _New -G ₀ between the two expansion coefficients G ₀ and G _New input from the expansion coefficient calculation unit 73 is calculated. Here, the expansion coefficient G _New is a coefficient considering the luminance state in the past frame, and the expansion coefficient G ₀ is a coefficient depending on the luminance state of only the current frame. G _New > G ₀ , and the difference G _New −G ₀ increases as the change in luminance increases. Therefore, high-speed processing start determination unit 82, the difference G _New -G ₀ calculated is compared with the threshold value Th _Start stored beforehand in the memory, the difference G _New -G ₀ is a threshold value Th _Start If it exceeds, it will be judged that it has brightened suddenly from the black screen. If it is determined that the black screen suddenly becomes bright, that is, if the difference G _New -G ₀ exceeds the threshold Th _Start , the process proceeds to step S105, where the difference G _New -G ₀ is equal to or less than the threshold Th _Start. In that case, the process in the current frame is terminated.
If it is determined that the brightness has suddenly increased from the black screen and the process proceeds to step S105, the speed-up process start determination unit 82 sets the flag _FBStart to true and ends the process in the current frame.

Returning to FIG. 3, the second detection unit 72 b includes a histogram analysis unit 83 and a global whiteout determination unit 84. The histogram analysis unit 83 estimates the number of pixels P _{Sat at} which _whiteout may occur due to the expansion process, from the histogram input from the feature amount extraction unit 71 and the expansion coefficient G _New input from the expansion coefficient calculation unit 73. The global whiteout determination unit 84 obtains the ratio of the number of _whiteout pixels P _Sat to the total number of pixels constituting the image, recognizes that the scene change has occurred when this ratio exceeds a predetermined value, and _sets the flag F _GSat to true.

FIG. 5 is a flowchart for explaining the operation of the second detection unit 72b.
As shown in FIG. 5, in step S201, the histogram analysis unit 83 calculates a critical luminance value I _Limit . The critical luminance value I _Limit is a luminance value that becomes the maximum luminance value (1023) when multiplied by the expansion ratio (1 + G _New / 256), and can be obtained by I _Limit = 1023 / (1 + G _New / 256).

In step S202, the histogram analysis unit 83, based on the histogram input from the feature amount extraction unit 71, a pixel that is over-exposed by the expansion process using the expansion coefficient G _New , that is, the luminance value is greater than or equal to the critical luminance value I _Limit. In addition, the number of pixels equal to or less than 1022 (the number of pixels P _Sat ) is counted, and the count result is output to the global whiteout determination unit 84. It should be noted that a pixel whose luminance value before expansion is the maximum value (1023) is likely to be the maximum luminance intended by the image producer, and is excluded from the count in order to distinguish it from overexposure due to expansion. Yes.

In step S203, the global overexposure determination unit 84, an image to calculate the ratio of the overexposed pixel number P _Sat for the pixel number P _Max of all the pixels constituting the threshold Th _GSAT this ratio is stored in advance in the memory It is determined whether or not it exceeds. As a result, only when the threshold Th _GSat is exceeded, the flag F _GSat is _set to true (step S204), and the processing in the current frame is terminated.

Returning to FIG. 3, the third detection unit 72 c includes a whiteout region detection unit 85, a whiteout evaluation value calculation unit 86, and a local whiteout determination unit 87. Based on the luminance signal Y input from the image signal processing unit 70 and the critical luminance value I _Limit calculated by the histogram analysis unit 83, the whiteout region detection unit 85 has a whiteout region (pixel) in which whiteout may occur in the frame. Group). The whiteout evaluation value calculation unit 86 calculates a _whiteout evaluation value corresponding to the position and area of each detected _{whiteout region,} and then _derives a maximum value (maximum evaluation value V _LSat ) from the _whiteout evaluation value. When the maximum evaluation value V _LSat exceeds a predetermined value, the jump determination unit 87 recognizes it as a scene change and _{sets the} flag F _LSat to true.

FIG. 6 is a flowchart for explaining the operation of the third detection unit 72c.
As shown in FIG. 6, in step S <b> 301, the whiteout region detection unit 85 performs image processing based on the luminance signal Y input from the image signal processing unit 70 and the critical luminance value I _Limit calculated by the histogram analysis unit 83. Are extracted from the all pixels constituting the pixel having a luminance value not less than the critical luminance value I _{Limit and not} more than 1022. At this time, by considering the positional relationship of each pixel to be extracted, a whiteout region including pixels that may cause whiteout due to the decompression process is extracted. Further, the whiteout area detection unit 85 obtains the area of each extracted whiteout area, that is, the number of pixels constituting each whiteout area.

In step S302, the whiteout evaluation value calculation unit 86 calculates an evaluation value by multiplying each extracted whiteout area by the area and a weight corresponding to the position. In step S303, each whiteout area is calculated. The maximum evaluation value V _LSat is derived from the evaluation values and is output to the local _whiteout determination unit 87.

FIG. 7 is an explanatory diagram for explaining the operation of the whiteout evaluation value calculation unit 86 and shows two whiteout areas extracted from an image (frame image) represented by the current frame.
As shown in FIG. 7, the frame image A is divided into a central part Ai and a peripheral part Ao, and weights Wi and Wo are given respectively. In the present embodiment, the weight of the central portion Ai that is easy for the viewer to watch is increased (Wi> Wo). Since the whiteout region B1 (area: S1) is extracted from the central portion Ai, the whiteout evaluation value is S1 × Wi, and the whiteout region B2 (area: S2) is from the peripheral portion Ao. Since it has been extracted, the whiteout evaluation value is S2 × Wo. For example, when the areas of the whiteout areas B1 and B2 are S1 = 100 and S2 = 200, respectively, and the weights of the central part Ai and the peripheral part Ao are Wi = 3 and Wo = 1, respectively, the whiteout areas The evaluation values V1 and V2 of the regions B1 and B2 are 300 and 200, respectively, and the evaluation value V1 (300) of the _whiteout region B1 is derived as the maximum evaluation value _VLSat .

Returning to FIG. 6, in step S304, the local _whiteout determination unit 87 compares the input maximum evaluation value V _LSat with the threshold value Th _LSat stored in the memory in advance, and the maximum evaluation value V _LSat is obtained. It is determined whether or not the threshold Th _LSat is exceeded. As a result, only when the threshold value Th _LSat is exceeded, the flag F _LSat is _set to true (step S305), and the processing in the current frame is terminated.

Returning to FIG. 3, the flags F _BStart , F _GSat , and F _LSat output from the first to third detection units ₇₂ a to _{72 c} are input to the 3-input OR circuit _{72 d} . For this reason, when at least one of the first to third detection units 72a to 72c detects a scene change and sets the flag to true, the OR circuit 72d sets the output (acceleration processing flag) to true and sets the first If all of the third detection units 72a to 72c detect no scene change and set the flag to false, the OR circuit 72d sets the acceleration processing flag to false. The acceleration processing flag is output as a control signal to the coefficient switching unit 75 (see FIG. 2), and the coefficient switching unit 75 sets the expansion coefficient G _New and the adjustment signal when the signal is false (when no scene change is detected). The combination of the light coefficients L _New is continuously output to the expansion processing unit 76 and the dimming driving unit 77, and when the signal is true (when a scene change is detected), the expansion coefficient G ₀ and the dimming coefficient L ₀ are set. Shift to high-speed processing that outputs combinations.

On the other hand, if the difference between the expansion coefficient G ₀ calculated for each frame and the expansion coefficient G _New is sufficiently small during the high-speed processing, the expansion coefficient G _New and the dimming coefficient L _New Therefore, it is assumed that there is a low possibility of occurrence of a malfunction, so that the normal state in which the expansion coefficient G _New and the dimming coefficient L _New are output is restored. At this time, the flags F _Black , F _BStart , F _GSat , and F _LSat are returned to false. Note that the return condition is not limited to this.

Through the above operation, flickering can be normally suppressed by performing expansion processing and dimming processing using the expansion coefficient G _New and the dimming coefficient L _New (except at the time of a scene change). At the time of a scene change to a bright image, it is possible to suppress whiteout due to the expansion processing by performing expansion processing and light control processing using the expansion coefficient G ₀ and the light control coefficient L ₀ .

  The scene change detection unit 72, the expansion coefficient calculation unit 73, and the coefficient switching unit 75 detect a deterioration region (out-of-white region) where the image deteriorates as the gradation range extends, and the deterioration region Since the evaluation according to the area and position is performed and the expansion coefficient (expansion parameter) and the dimming coefficient (dimming parameter) are determined based on the evaluation result, this corresponds to the parameter determination unit of the present invention.

As described above, according to the projector 1 of the present embodiment, the following effects can be obtained.
According to the projector 1 of the present embodiment, the third detection unit 72c detects a whiteout area in which an image is whiteout as the gradation range is expanded, and whiteout evaluation is performed according to the position of the whiteout area. A value is calculated, and when there is a _whiteout region in which this _whiteout evaluation value is higher than a predetermined value (threshold Th _LSat ), an expansion coefficient (G ₀ ) capable of suppressing _whiteout is selected. Yes. Here, the whiteout area is weighted so that the whiteout evaluation value becomes higher as it is in the center of the image, so when the whiteout is likely to occur in the center of the image that is easy for the viewer to watch. Compared with the case where it occurs in the peripheral portion, whiteout is more easily suppressed, and it is not necessary for the viewer to be aware of the occurrence of whiteout. On the other hand, when the whiteout region occurs in the peripheral portion of the image that is rarely watched by the viewer, the expansion coefficient (G _New ) that emphasizes the prevention of flickering is selected. It is possible to prevent the image from flickering.

(Modification)
In addition, you may change embodiment of this invention as follows.
In the above embodiment, when the whiteout areas B1 and B2 are distributed over the central part Ai and the peripheral part Ao, the weights on the more distributed side may be adopted, or the distribution Accordingly, a value between the weight of the peripheral portion Ao and the weight of the central portion Ai may be adopted.

  In the above embodiment, the frame image A is divided into the central part Ai and the peripheral part Ao in order to perform weighting according to the positions of the whiteout areas B1 and B2. Is not limited to two and may be three or more. Alternatively, weighting according to the distance between the reference point (center point, etc.) of the frame image A and the reference point (center of gravity, etc.) of the whiteout regions B1, B2 may be performed without dividing the frame image A. .

In the embodiment, the whiteout areas B1 and B2 in the frame image A are detected and the whiteout evaluation value is derived for each of the whiteout areas B1 and B2. However, as shown in FIG. Image A is divided into a plurality of small areas (for example, 16 equal parts of Ai1 to Ai4 and Ao1 to Ao12), the area of the whiteout area included in each small area, and the weight according to the position of each small area Depending on, a whiteout evaluation value may be derived for each small area. For example, the weight of the small areas Ai1 to Ai4 in the central portion is Wi, the weight of the small areas Ao1 to Ao12 in the peripheral portion is Wo (Wi> Wo), and the area of the whiteout area included in each small area is After calculating the _whiteout evaluation value multiplied by the weight (Wi or Wo), the flag _FLSat is _set to true when the maximum evaluation value exceeds the threshold value among the _whiteout evaluation values. This makes it possible to easily specify the position of the whiteout area.

  Alternatively, each small region may have a different area depending on the weight according to the position, and the area ratio of the whiteout region to each small region may be used as the whiteout evaluation value. For example, as shown in FIG. 9, by making the area of the small area (Ai1 to Ai16) in the central part where the weight is to be increased smaller than the small area (Ao1 to Ao12) in the peripheral part, Even in B3 and B4, the whiteout evaluation value can be high in the central portion and low in the peripheral portion. For this reason, it is possible to change the expansion coefficient and dimming coefficient to be used depending on whether the whiteout regions B3 and B4 are in the central portion or the peripheral portion. In other words, in this case, weighting according to the position is performed according to the area of the small region, so that it is not necessary to perform calculation by multiplying the weight again.

  In the above embodiment, the weight of the central portion Ai of the frame image A is increased, but the present invention is not limited to this. For example, when captions are displayed in a region other than a black belt, The weight may be increased.

  In the above-described embodiment, one of the two coefficients calculated by the expansion coefficient calculation unit 73 and the dimming coefficient calculation unit 74 is employed, but two coefficients are calculated. However, one of three or more may be adopted.

  In the embodiment, the white peak value and the APL are used as the feature amount for deriving the expansion coefficient and the dimming coefficient, and the white peak value and the histogram are used as the feature amount for detecting the scene change. However, the feature amount to be used is not limited to the above. For example, various statistical values such as a minimum luminance value (black peak value), a mode luminance value, and a variance in one frame can be used.

  In the above-described embodiment, the gradation range is expanded to the white side (bright side), and the configuration that can suppress overexposure as the image degradation caused by the expansion processing has been described. The image may be expanded to the (dark side) to suppress black crushing associated with the expansion processing, or may be configured to be expandable to both sides of black and white. Suppression of black crushing can be realized by causing the scene change detection unit 72 to detect a scene change that switches from a bright image to a dark image based on, for example, a black peak value. When only the black side is expanded, there is no need for dimming by the dimmer 16.

  In the above embodiment, a discharge type light source lamp such as an ultra-high pressure mercury lamp or a metal halide lamp is used as the light source 11, but other light sources such as an LED light source composed of an LED (light emitting diode) may be used.

  In the above-described embodiment, a projector that projects an image on an external screen or the like is described as an example of the image display device. However, a rear screen that integrally includes a transmissive screen and projects an image on the back side thereof. It can also be applied to a projector. The present invention can also be applied to a liquid crystal display device that modulates light of a backlight or the like.

  In the above-described embodiment, the dimming element 16 that reduces the amount of light by the louver 16a is used for dimming the light of the light source 11, but other diaphragm mechanisms such as diaphragm blades, or light emission of the light source and the backlight A control circuit capable of controlling the amount of light can also be used. Further, a liquid crystal element or electrochromic glass whose light transmittance can be changed according to the applied voltage is used, in the middle of the optical path from the light source 11 to the transmissive screen SC, or when the screen SC is transmissive. May be provided on the front surface thereof.

  In the above-described embodiment, the transmissive liquid crystal light valves 40R, 40G, and 40B are used as the light modulator, but it is also possible to use a liquid crystal on silicon (LCOS) that is a reflective light modulator. is there. Also, a DMD (registered trademark of Texas Instruments) (digital micromirror device) that modulates the light emitted from the light source by controlling the emission direction of the incident light for each micromirror can be used. .

1 is a configuration diagram showing a schematic configuration of a projector according to an embodiment. The block diagram for demonstrating the circuit structure of a projector. The block diagram which shows the detailed structure of a scene change detection part. The flowchart explaining operation | movement of the 1st detection part 72a. The flowchart explaining operation | movement of the 2nd detection part 72b. The flowchart explaining operation | movement of the 3rd detection part 72c. Explanatory drawing explaining operation | movement of a whiteout evaluation value calculation part. The 1st explanatory view explaining the modification of the derivation method of a whiteout evaluation value. The 2nd explanatory view explaining the modification of the derivation method of a whiteout evaluation value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Projector, 10 ... Illumination optical system, 11 ... Light source, 12 ... 1st lens array, 12a ... Lens, 13 ... 2nd lens array, 14 ... Polarization conversion element, 15 ... Superimposition lens, 16 ... Light control element , 16a ... Louver, 20 ... Color light separation optical system, 21 ... First dichroic mirror, 22 ... First reflection mirror, 23 ... Second dichroic mirror, 30 ... Relay optical system, 31 ... Incident side lens, 32 ... Second reflection mirror, 33 ... Relay lens, 34 ... Third reflection mirror, 35 ... Emission side lens, 40R, 40G, 40B ... Liquid crystal light valve, 41 ... Liquid crystal panel, 42 ... Incident side polarizing plate, 43 ... Emission Side polarizing plate, 50 ... cross dichroic prism, 60 ... projection lens, 70 ... image signal processing unit, 71 ... feature amount extraction unit, 72 ... scene change detection unit, 72a ... first Detection unit, 72b ... second detection unit, 72c ... third detection unit, 72d ... OR circuit, 73 ... expansion coefficient calculation unit, 74 ... light control coefficient calculation unit, 75 ... coefficient switching unit, 76 ... extension processing , 77 ... Dimming drive part, 78 ... Light valve drive part, 81 ... Black screen detection part, 82 ... High-speed processing start determination part, 83 ... Histogram analysis part, 84 ... Global whiteout determination part, 85 ... Whiteout Area detection unit, 86... Whiteout evaluation value calculation unit, 87... Local whiteout determination unit.

Claims (8)

An image display device that modulates incident light by a light modulation device and displays an image according to an input image signal,
A feature amount extraction unit that extracts a feature amount according to gradation information represented by the image signal based on the image signal;
A parameter determining unit that determines an expansion parameter for extending a gradation range of the gradation information based on the feature amount;
An extension processing unit that corrects the gradation information using the extension parameter to extend the gradation range;
A modulation driving unit that drives the light modulation device based on the gradation information corrected by the extension processing unit;
With
The parameter determination unit detects a deteriorated area where an image deteriorates as the gradation range is extended, performs an evaluation according to the area and position of the deteriorated area, and performs the extension based on the evaluation result An image display device characterized by determining a parameter.   2. The image display device according to claim 1, wherein the parameter determination unit divides the image into a plurality of small regions, weights the small regions according to their positions, An image display device characterized in that the evaluation is performed according to an area of a deteriorated region in a small region and a weight assigned to each small region.   The image display device according to claim 1, wherein the parameter determination unit divides the image into small regions having different areas according to weights according to positions, and each of the small regions with respect to an area of each of the small regions. An image display device characterized in that the evaluation is performed in accordance with the area of the deteriorated region.   The image display device according to claim 1, wherein the parameter determination unit detects a whiteout region in which an image is whitened as the gradation range is expanded to a brighter side. And performing an evaluation according to the area and position of the whiteout region, and determining an expansion parameter for extending the gradation range to the bright side based on the evaluation result. Display device.   5. The image display device according to claim 1, wherein the parameter determination unit determines an expansion parameter that can suppress the deterioration as the deterioration region is located at a center of the image. An image display device characterized by that.   The image display device according to claim 5, wherein the parameter determination unit can expand the gradation range most in a range in which the deterioration is not caused when the deterioration region is located at a center of the image. An image display device characterized in that the expansion parameter is determined. The image display device according to any one of claims 1 to 6,
A light control means capable of adjusting a light amount of at least one of light incident on the light modulation device and light modulated by the light modulation device;
A dimming drive unit for driving the dimming means;
With
The parameter determining unit determines a dimming parameter for determining a dimming amount by the dimming unit based on the evaluation result, and the dimming driving unit uses the dimming parameter to adjust the dimming unit. An image display device characterized by driving. A feature amount extraction step of extracting a feature amount according to gradation information represented by the image signal based on the input image signal;
A parameter determining step for determining an expansion parameter for expanding a gradation range of the gradation information based on the feature amount;
An expansion process step of correcting the gradation information using the expansion parameter to expand the gradation range;
A modulation step of modulating incident light by a light modulation device based on the gradation information corrected in the extension processing step;
With
In the parameter determining step, a deteriorated area where an image deteriorates as the gradation information is expanded is detected, and the deteriorated area is evaluated according to its area and position, and the expansion is performed based on the evaluation result. An image display method characterized by determining a parameter.

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