JP2008294539A - Digital broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent flickering due to picture quality enhancement processing even when a digital broadcast of a hierarchical transmission system is received and the frame rate of a video signal is changed by hierarchical switching. <P>SOLUTION: An output control unit 110 makes a γcorrection unit 109 update its correction characteristics in the timing when a scene detection unit 115 detects switching of a video scene while an output selection unit 108 is outputting a video signal of a strong hierarchical layer with a low frame rate. When the output selection unit 108 outputs a video signal of a weak hierarchical layer with a high frame rate, correction characteristics of the γ correction unit 109 are updated for each frame of the video signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a digital broadcast receiving apparatus, and more particularly to a digital broadcast receiving apparatus that suitably receives a hierarchically transmitted broadcast.

  In digital broadcasting, hierarchical transmission in which one transport stream is transmitted using a plurality of encoding methods is used. In digital terrestrial broadcasting, it is possible to simultaneously transmit up to 3 hierarchies composed of one or more segments. Weak / middle hierarchies in order from the highest required CN ratio due to differences in transmission coding schemes / It is called the strong hierarchy. In other words, high-quality data can be transmitted in the weak layer but reception stability is low, and high-quality data cannot be transmitted in the strong layer, but reception stability is high.

  By using this feature and transmitting broadcasts with the same content in the weak and strong layers, high-definition video signals with high image quality in areas with strong electric fields, and more stable strong signals in wide areas with weak electric fields. Hierarchical video signals can be received. Digital broadcast receivers can continue to watch by switching to a strong layer with high reception stability if the reception level of the broadcast signal decreases while viewing the video and audio of the weak layer and viewing becomes difficult. it can. Patent Document 1 discloses a digital broadcast receiving apparatus that switches an output hierarchy based on an electric field strength or a reproduction state of a received broadcast signal.

  On the other hand, the video display device employs a γ correction circuit that expands bright gradations and dark gradations in response to the level of the average luminance level (APL) of the input video signal, thereby improving the contrast of the display image. Image quality improvement processing is known. For example, Patent Document 2 discloses a liquid crystal display device that detects luminance characteristics with respect to gradation of input video data, corrects gradation according to the luminance characteristics, and displays the corrected gradation on a liquid crystal panel. ing. Patent Document 2 also describes that the luminance characteristic is detected for each of one or more frames of the input video data.

JP 2003-274302 A JP 2001-343957 A

  The inventor receives a hierarchical transmission system digital broadcast, switches the output hierarchy as shown in Patent Document 1, for example, and performs high-quality processing such as γ correction as shown in Patent Document 2, for example. When displaying an image, the present inventors have found that the display image quality may rather deteriorate due to human visual characteristics.

  The reason is estimated as follows. In the hierarchical transmission method, the video signal of the weak layer and the strong layer have different frame rates. Usually, transmission is performed at 60 Hz in the weak layer and 15 Hz in the strong layer. When the frame rate is 60 Hz, the frame is updated at a speed sufficiently higher than the response speed of the eyes. Therefore, flicker is not felt even when the image quality enhancement process is performed on a frame basis. However, when the frame rate is 15 Hz, the frame update speed approaches the eye response speed, so flicker is felt when image quality enhancement processing is performed in the frame period. As a result, for example, the brightness of the background screen in the same scene should originally be constant, but the brightness of the background screen changes due to the movement of a person or the like on the screen, which gives viewers discomfort. .

  An object of the present invention is to provide a digital broadcast receiving apparatus that prevents occurrence of flicker due to high image quality processing even when a frame rate of a video signal is switched by layer switching when receiving a digital transmission of a layer transmission system. is there.

  The digital broadcast receiving apparatus of the present invention detects a luminance level of a video signal from a received broadcast signal, detects a scene change from the change, and a strong hierarchy with a low frame rate from the received broadcast signal. Output selection unit that switches and outputs a video signal of a weak layer with a high frame rate, a γ correction unit that performs γ correction on the video signal output from the output selection unit, and an output that controls the γ correction unit And a control unit. The output control unit controls the timing at which the correction characteristic is updated for the γ correction unit depending on which level of the video signal is output by the output selection unit.

  Here, when the output selection unit is outputting a high-level video signal, the output control unit causes the γ correction unit to update the correction characteristic at the timing when the scene detection unit detects the switching of the video scene, and outputs When the selection unit outputs a video signal of a weak hierarchy, the correction characteristic of the γ correction unit is updated for each frame of the video signal.

  According to the present invention, it is possible to provide a good video without causing discomfort due to the occurrence of flicker, regardless of whether a weak hierarchical video or a strong hierarchical video is selected and displayed.

  FIG. 1 is a block diagram showing an embodiment of a digital broadcast receiving apparatus according to the present invention. The digital broadcast receiving apparatus 100 is configured as follows. The input terminal 101 receives a signal in which several video / audio / data are multiplexed, modulated, and hierarchically transmitted. Here, it is assumed that a weak layer signal with a frame rate of 60 Hz and a strong layer signal with a frame rate of 15 Hz are input. The receiving unit 102 corrects errors generated during demodulation and transmission of the input signal, and the packet separation unit 103 selectively extracts a desired video / audio / data signal from the multiplexed signal. The strong layer buffer unit 104 stores (buffers) the strong layer signal, and the strong layer decoding unit 105 decodes the encoded strong layer signal. The weak layer buffer unit 106 stores weak layer signals, and the weak layer decoding unit 107 decodes the encoded weak layer signals.

  The scene detection unit A115 obtains a luminance level from the video signal decoded by the strong hierarchy decoding unit 105, and detects a scene change. The scene detection unit B116 obtains a luminance level from the video signal decoded by the weak hierarchy decoding unit 107, and detects a scene change. The video output selection unit 108 selects one of the video signals of the strong layer decoding unit 105 and the weak layer decoding unit 107. The γ correction unit 109 performs γ correction as a high image quality process on the output video signal of the video output selection unit 108. The video output terminal 111 outputs the video signal output from the γ correction unit 109. The audio output selection unit 112 selects one of the strong hierarchy decoding unit 105 and the weak hierarchy decoding unit 107. The audio output terminal 113 outputs the audio signal selected by the audio output selection unit 112.

  The output control unit 110 controls the selection of the video output selection unit 108 and the audio output selection unit 112, and based on information from the scene detection unit A115 and the scene detection unit B116, the strong hierarchy buffer unit 104 and the weak hierarchy buffer unit 106. The buffer capacity of the γ correction unit 109 is controlled. The real time clock 114 manages time information used by the receiving apparatus 100.

Next, the operation of the digital broadcast receiving apparatus of this embodiment will be described.
The digital signal transmitted hierarchically input to the input terminal 101 is demodulated by the receiving unit 102. The strong layer video / audio signal extracted by the packet separation unit 103 is stored in the strong layer buffer unit 104, and the extracted weak layer video / audio signal is stored in the weak layer buffer unit 106. When the buffer capacity of the strong layer buffer unit 104 is filled with accumulated signals, the strong layer video / audio signals are sent to the strong layer decoding unit 105 and decoded. Similarly, when the buffer capacity of the weak layer buffer unit 106 is filled with the accumulated signal, the video / audio signal of the weak layer is sent to the weak layer decoding unit 107 and decoded.

  For the video signal decoded by the strong hierarchy decoding unit 105, the scene detection unit A115 calculates the average luminance level of the screen for each frame, and the scene change is detected from the change in the luminance level between frames. Similarly, for the video signal decoded by the weak hierarchy decoding unit 107, an average luminance level of the screen is calculated for each frame by the scene detection unit B116, and a scene change is detected from a change in luminance level between frames. The These scene change detection signals are sent to the output control unit 110.

  One of the video signals from the strong layer decoding unit 105 and the weak layer decoding unit 107 is selected by the video output selection unit 108 and sent to the γ correction unit 109 for γ correction. The γ correction unit 109 performs expansion correction (γ correction) of bright gradations or dark gradations according to the level of the average luminance level of the video signal calculated by the scene detection unit A115 or the scene detection unit B116. Thus, the contrast can be improved. The γ-corrected video signal is output from the video output terminal 111 to a display device (not shown) or the like. On the other hand, either one of the audio signals from the strong layer decoding unit 105 and the weak layer decoding unit 107 is selected in accordance with the video by the audio output selection unit 112, and is output from the audio output terminal 113 to a display device (speaker) or the like. Is done.

  The output control unit 110 controls the timing of updating the correction process (switching of correction characteristics) of the γ correction unit 109. That is, when the video output selection unit 108 selects the video signal from the strong hierarchy decoding unit 105, the correction of the correction process is permitted every time the scene detection unit A115 detects a scene change. Prohibits updating in the middle of a scene. On the other hand, when the video signal from the weak hierarchy decoding unit 107 is selected, the correction process is permitted to be updated every time the frame is switched. As a result, when the frame rate is low as in the case of a strong hierarchical signal, it is possible to avoid updating the γ correction processing in the same scene and prevent the occurrence of flicker.

  Further, the output control unit 110 has a function of adjusting a difference in output timing between video and audio signals of the strong layer and the weak layer by controlling the buffer capacity of the strong layer buffer unit 104 and the weak layer buffer unit 106. For example, when the weak layer video / audio signal is delayed by a certain time from the strong layer video / audio signal, the buffer capacity of the strong layer buffer unit 104 is delayed from the buffer capacity of the weak layer buffer unit 104. By setting as much as the time, the video and audio signals in the strong hierarchy are delayed to synchronize the two. On the contrary, when the video / audio signal of the strong hierarchy is delayed from the video / audio signal of the weak hierarchy, the signals of both are synchronized by setting a larger buffer capacity of the weak hierarchy buffer unit 106. . The difference between the output timings of the video / audio signals of both can be obtained, for example, by detecting the timing of scene switching between the scene detection unit A115 and the scene detection unit B116 and the difference between them. In this way, even when switching between the strong layer and the weak layer and outputting, it is possible to smoothly switch the video and audio signals in synchronization.

Hereinafter, the operation of each unit will be described in detail.
First, a method for detecting scene switching from a video signal will be described.
FIG. 2 shows a configuration example of the display memory 200 that stores the decoded video signal in the strong layer decoding unit 105 and the weak layer decoding unit 107. The display memory 200 stores pixel information 201 corresponding to the number of pixels in the vertical direction and the horizontal direction, and the pixel information 201 includes luminance signal information Y and color difference signal information Cb and Cr for the corresponding pixel of the video, thereby the pixels Represents the brightness and color. Each decoding unit 105, 107 converts the pixel information of the display memory 200 into a video signal and outputs it.

  FIG. 3 shows an example of a table that stores the average value of the luminance signal in the video signal for each screen area in the scene detection unit A115 and the scene detection unit B116. (A) is a case where the entire screen is divided into 4 × 4 areas as an example of the divided screen 301. The scene detection units 115 and 116 calculate the average value Y of the pixels existing in each divided region for the luminance signal in the video signal sent from the decoding units 105 and 107. (B) is an example of the brightness value table 302 storing the calculated brightness average value, and the brightness average value Y of each divided region is stored in the corresponding address of the table 302. For example, the average luminance value Y11 of the divided area (x1, y1) is stored in the address (x1, y1) of the table 302. Similarly, the average luminance values Y12 to Y44 for the divided area (x4, y4) are obtained from the divided area (x1, y2), and are sequentially stored in the table 302 at addresses (x1, y2) to (x4, y4). In this way, the luminance average value Y is stored every time a new frame is input. Then, the difference between the luminance average value Y ′ of the previous frame and the luminance average value Y of the current frame is obtained and set as difference values ΔY11 to ΔY44.

  In this embodiment, the screen is divided into 4 × 4 and the average value is calculated. However, the number of divisions is not limited to this. Increasing the number of divisions can increase the accuracy of scene change detection, but the amount of necessary memory resources and arithmetic processing increases accordingly. Therefore, it can be appropriately changed depending on the balance between the detection accuracy and the processing load.

FIG. 4 is a flowchart showing a scene change detection process performed by the scene detection unit A115 and the scene detection unit B116.
In step S401, it waits for a new video frame to be input from the decoding units 105 and 107.
In step S <b> 402, when a new frame is input, the scene detection units 115 and 116 calculate the average value Y of the luminance signal in each divided area of the divided screen 301 and store it in the current frame column of the luminance value table 302. These values are stored in a FIFO (First In First Out) method, and the value Y ′ stored in the current frame column is moved to the previous frame column.

  In step S403, a difference value ΔY between the current frame value Y and the previous frame value Y ′ is obtained for each divided region with respect to the average value of the luminance signal stored in the luminance value table 302. Then, the number N of regions in which the difference value ΔY has changed by a predetermined value ΔY0 or more is counted. For example, when the luminance signal Y changes from 0 to 255, the predetermined value ΔY0 is preferably set to a value of about 10 to 30. If ΔY0 is a small value, it is easy to detect a scene change, but on the other hand, the possibility of including false detection increases, so it is desirable to set appropriately depending on the type of video.

  In step S404, it is determined whether or not the number N of regions where the difference value ΔY has changed by a predetermined value ΔY0 or more exceeds the predetermined number N0. For example, when the number of divided areas is 16, the predetermined number N0 is preferably set to a value of about 3 to 10. Also in this case, if N0 is a small value, it becomes easy to detect a scene change, but on the other hand, the possibility of including erroneous detection increases.

  If it is determined that the number of areas N exceeds the predetermined number N0 (Yes in step S404), it is determined in step S405 that the video scene has been switched, and the output controller 110 detects the scene switching. It is signaled that it was done. If the number N of areas does not exceed the predetermined number N0 (No in step S404), the process returns to step S401.

  By performing such processing for each frame of the video, the output control unit 110 can sequentially know the scene switching timing of the input video signal. Then, the output control unit 110 can use this scene switching timing information to control the update timing of the correction processing of the γ correction unit 109, and to match the output timing shift between the strong layer and the weak layer. .

Next, the γ correction processing method in this embodiment will be described.
FIG. 5 is a diagram illustrating an example of an internal configuration of the γ correction unit 109. The feature information detection unit 121 detects feature information of the video signal output from the video output selection unit 108. As the feature information, an average value Yav in the frame of the luminance signal of the video signal is used. The γ control unit 123 determines the γ correction characteristic from the feature information (frame luminance average value Yav) of the video signal detected by the feature information detection unit 121, and sets it in the modulation unit 122. At that time, with reference to the control signal 110 s of the video output selection unit 108 output from the output control unit 110 and the scene switching signal 115 s output from the scene detection unit A 115, the γ correction characteristic set in the modulation unit 122. Control the update timing. The modulation unit 122 modulates the video signal input from the video output selection unit 108 based on the correction characteristic set by the γ control unit 123 and outputs the modulated video signal to the video output terminal 111. Here, the color signal is omitted because it is not particularly modulated.

FIG. 6 is a flowchart showing the correction characteristic update process of the γ control unit 123.
In step S <b> 601, an initial condition of a predetermined gamma correction characteristic is set in the modulation unit 122. The initial condition is, for example, a condition for performing an optimal γ correction on a standard video (luminance signal distribution).
In step S602, it is determined based on the polarity of the control signal 110s of the video output selection unit 108 whether the selected video signal is a strong hierarchy or a weak hierarchy. If it is a strong hierarchical signal, the process proceeds to step S604, and if it is a weak hierarchical signal, the process proceeds to step S603.

In step S603 (when the weak layer is selected), the process waits until reception of the current frame is completed. When frame reception is completed, the process proceeds to step S605.
In step S604 (when the strong hierarchy is selected), the process waits until the scene switching signal 115s is output from the scene detection unit A115. When the scene is switched, the process proceeds to step S605.

  In step S605, the latest frame feature information (frame luminance average value Yav) is acquired from the feature information detection unit 121, the γ correction characteristic is determined according to the feature information, and is set (updated) in the modulation unit 122. Thereafter, the process returns to step S602, and the process is repeated in the same manner for the next frame.

  By operating as described above, the γ control unit 123 updates the correction characteristics in units of frames when outputting a weak hierarchical signal, but updates the correction characteristics when switching scenes instead of in units of frames when outputting a strong hierarchical signal. To control.

  FIG. 7 is a diagram illustrating an example of γ correction characteristics determined by the γ control unit 123. The feature information detection unit 121 detects the average value Yav of the luminance signal for each frame of the input video signal, and the γ control unit 123 determines the correction characteristic according to the level of the luminance average value Yav. For this purpose, the γ control unit 123 classifies the level of the luminance average value Yav into a plurality of ranks, and determines correction characteristics to be applied in each rank. Here, a case is shown in which seven correction characteristics (a) to (g) are applied by dividing into seven ranks by the low luminance side reference value Yref1 and the high luminance side reference value Yref2. In each correction characteristic, the horizontal axis represents the input luminance level Yin (minimum level 0 to maximum level 255), and the vertical axis represents the corrected output luminance level Yout. The broken line is the case without correction. For example, the low luminance side reference value Yref1 = 100 and the high luminance side reference value Yref2 = 150.

  First, the case where the input video is a dark screen and the luminance average value Yav is smaller than the low luminance side reference value Yref1 (= 100) will be described. (A) is a case where Yav is slightly smaller than Yref1 (example: Yav = 90). At this time, the correction curve has a peak that slightly increases the output luminance level Yout near the center of the input luminance level Yin. (B) enlarges the peak of the correction curve when Yav is even smaller (example: Yav = 50). (C) is a case where Yav is extremely small (example: Yav = 10), and the correction curve has a larger peak. As described above, when the input video is a dark screen, by correcting the steep slope of the output luminance level Yout with respect to the input luminance level Yin in the low luminance region according to the average value Yav of the luminance signal, the dark portion of the image is displayed. The contrast can be improved and the image can be corrected to be easy to see.

  Next, a case where the input video is a bright screen and the luminance average value Yav is larger than the high luminance side reference value Yref2 (= 150) will be described. (D) is a case where Yav is slightly larger than Yref1 (example: Yav = 160). A correction curve having an inverse peak that slightly decreases the output luminance level Yout near the center of the input luminance level Yin. (E) enlarges the reverse peak of the correction curve when Yav is even larger (example: Yav = 200). In (f), when Yav is extremely large (example: Yav = 240), the correction curve has a larger inverse peak. In this way, when the input video is a bright screen, by correcting the steep slope of the output luminance level Yout with respect to the input luminance level Yin in the high luminance region according to the average value Yav of the luminance signal, the bright portion of the image is displayed. The contrast can be improved and the image can be corrected to be easy to see.

  Further, when the input video is a screen having an intermediate brightness and the average luminance value Yav is larger than the low luminance side reference value Yref1 (= 100) and smaller than the high luminance side reference value Yref2 (= 150), (g ), The output luminance level Yout is made equal to the input luminance level Yin and no correction is performed.

  Note that the correction characteristic shown in FIG. 7 is an example, and it goes without saying that the method of dividing the luminance level and the method of giving the correction curve thereto can be set as appropriate.

  FIG. 8 is a diagram illustrating a time change of the luminance signal by the γ correction processing in the present embodiment. Schematic representation of the update timing of the γ control unit 1093 and how the luminance level of the output video signal changes due to γ correction when the input weak layer and strong layer video signals are switched and output by the video output selection unit 108. Is shown.

  (A) shows the input weak hierarchical video signal (frame rate 60 Hz), the horizontal axis is time, and the frame update timing has a period of 1/60 seconds. The vertical axis represents the average luminance level of pixels in a specific area in the screen, for example, pixels in the center of the screen. In scene 1, the average luminance level of each frame is represented by 11A, 12A... 1 mA, and the average luminance level decreases with time. In the scene 2, the average luminance level of each frame is represented by 21A, 22A... 2nA, and the average luminance level increases with time.

  (B) shows the input strong hierarchical video signal (frame rate 15 Hz), and the frame update timing is a period of 1/15 seconds. The average luminance level of each frame in the scene 1 is represented by 11B, 12B... 1 pB, and the average luminance level of each frame in the scene 2 is represented by 21B, 22B. These time changes naturally show the same tendency as the weak hierarchical signal of (a).

  (C) shows a control signal (hierarchy selection signal) 110s from the output control unit 110. The video output selection unit 108 selects the weak hierarchy at the low level and the strong hierarchy at the high level according to the polarity of the control signal 110s. In this example, the video signal of the weak hierarchy is selected in the scene 1 and the video signal of the strong hierarchy is selected in the scene 2 and input to the γ correction unit 109.

  (D) shows a video signal output from the modulation unit 122 of the γ correction unit 109. The output luminance level of each frame is obtained by adding a γ correction component to the input luminance level.

  In scene 1, since a weak hierarchy video signal is input, the γ correction characteristics are updated and set for each frame. As a result, in each frame, an optimal correction amount (11C, 12C... 1 mC) is added according to the respective average luminance level (11A, 12A... 1 mA). At this time, since the correction characteristic is updated at a fine time interval of 1/60 seconds, the change in the correction amount between adjacent frames is miniaturized and is not perceived as flicker by human eyes. Then, by applying an optimal γ correction to the input video signal, it is possible to display an image with good contrast.

  Next, in scene 2, since a strong hierarchy video signal is input, the γ correction characteristic is updated after a scene change. That is, the correction characteristic (correction amount 21C) set for the luminance level 21B of the first frame of the scene 2 is held constant throughout the duration of the scene 2. Then, the correction characteristics are updated at the scene switching timing (when the scene 2 ends). As a result, correction and updating are not performed at a large time interval of 1/15 seconds that is easily perceived by human eyes, and flicker is prevented. Note that although the brightness of the entire screen changes by performing the correction update at the time of the scene switching, since the scene switching itself is accompanied by a large change in brightness, there is no sense of incongruity. In addition, since the correlation of the average value of the luminance signal is high between the previous and next frames in the same scene, the contrast characteristic is not deteriorated even if the correction characteristic is constant.

  (E) shows a video signal output by conventional γ correction for comparison. In the conventional method, the correction characteristics are updated and set for each frame in the scene 2 to which the video signal of the strong hierarchy is input as in the case of the scene 1 to which the weak hierarchy signal is input. As a result, the correction amount (21C, 22C... 2qC) of each frame changes significantly at the time of frame switching, and the human eye feels uncomfortable as flicker.

  As described above, the digital broadcast receiving apparatus according to the present embodiment suitably switches the update timing of the γ correction characteristic according to the hierarchy of the video signal being displayed, so that the weak hierarchy video display and the strong hierarchy video display are performed. Good image display is possible in both cases.

  In the above-described embodiment, an example in which the weak layer signal is 60 Hz and the strong layer signal is 15 Hz has been described regarding the frame rate, but the present invention is not limited to this. On the contrary, if the weak layer is 15 Hz and the strong layer is 60 Hz, the correction characteristics of the weak layer may be updated when the scene is switched, and the correction characteristics of the strong layer may be updated for each frame. In short, for video signals with a frame rate higher than a predetermined value, the correction characteristics may be updated for each frame, and for video signals with a frame rate lower than a predetermined value, the correction characteristics may be updated at scene switching. . Further, the frame rate value is not limited to the above frequency, and can be applied to a case where the weak layer signal is 30 Hz and the strong layer signal is 10 Hz, for example, in accordance with human visual characteristics.

  In the above embodiment, an example in which the average value of the luminance signal is used as the feature information has been described. However, the present invention is not limited to this, and a histogram of the luminance signal may be used. In addition, the scene change is detected from the strong hierarchy signal by the scene detection unit. However, a separate scene detection unit may be provided and the output thereof may be used. Further, the input video signal may be other than a broadcast wave, for example, a signal reproduced from various storage media. In that case, the update timing of the γ correction characteristic may be controlled in accordance with the frame rate of the target video signal.

The block diagram which shows one Example of the digital broadcast receiver by this invention. 2 is a configuration example of a display memory 200 that stores a decoded video signal. An example of the table which memorize | stores the average value of the luminance signal in a video signal for every screen area | region. The flowchart which shows a scene change detection process. The figure which shows an example of an internal structure of the (gamma) correction | amendment part 109. FIG. 7 is a flowchart showing correction characteristic update processing of the γ control unit 123. The figure which shows the example of the (gamma) correction characteristic which the (gamma) control part 123 determines. The figure which shows the time change of the luminance signal by (gamma) correction processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Digital broadcast receiver 102 ... Reception part 103 ... Packet separation part 104 ... Strong hierarchy buffer part 105 ... Strong hierarchy decoding part 106 ... Weak hierarchy buffer part 107 ... Weak hierarchy decoding part 108 ... Video output selection part 109 ... γ correction part 110: Output control unit 112 ... Audio output selection unit 115 ... Scene detection unit A
116: Scene detection unit B
121: Feature information detection unit 122 ... Modulation unit 123 ... γ control unit 200 ... Display memory 302 ... Luminance value table

Claims (5)

In a digital broadcast receiver that receives a digital broadcast of a hierarchical transmission method,
A scene detection unit that detects a luminance level of the video signal from the received broadcast signal and detects a change of the video scene from the change;
An output selection unit for switching and outputting a strong layer video signal with a low frame rate and a weak layer video signal with a high frame rate from the received broadcast signal;
A γ correction unit that performs γ correction on the video signal output from the output selection unit;
An output control unit for controlling the γ correction unit,
The digital broadcast receiving apparatus according to claim 1, wherein the output control unit controls the timing at which the correction characteristic is updated for the γ correction unit depending on which level of the video signal is output by the output selection unit. The digital broadcast receiver according to claim 1,
The output control unit causes the correction characteristics of the γ correction unit to be updated at a timing when the scene detection unit detects a change of a video scene when the output selection unit is outputting a high-level video signal. The digital broadcast receiving apparatus, wherein when the output selection unit outputs a video signal of a weak hierarchy, the correction characteristic of the γ correction unit is updated for each frame of the video signal. The digital broadcast receiver according to claim 1,
The scene detection unit divides the display screen, obtains a difference value ΔY of luminance levels between frames in each divided region, and the number N of divided regions where the difference value ΔY is equal to or greater than a predetermined value ΔY0 is a predetermined number N0. A digital broadcast receiver characterized by determining that the video scene has been switched if it exceeds. The digital broadcast receiver according to claim 1,
The γ correction unit refers to the average value Yav of the luminance level for each frame detected by the scene detection unit. When the average value Yav is smaller than the reference value Yref, the output luminance with respect to the input luminance level in the low luminance region A digital broadcast receiving apparatus characterized in that a level gradient is made steep, and when the average value Yav is larger than a reference value Yref, a correction is made to make the output luminance level gradient steep with respect to the input luminance level in the high luminance region. . In a digital broadcast receiver that receives a digital broadcast including a plurality of video signals having different frame rates,
A scene detection unit that detects a luminance level of the video signal from the received broadcast signal and detects a change of the video scene from the change;
An output selection unit for selecting and outputting one video signal from the received broadcast signal;
A γ correction unit that performs γ correction on the video signal output from the output selection unit;
An output control unit for controlling the γ correction unit,
When the output selection unit outputs a video signal having a frame rate lower than a predetermined value, the output control unit corrects the correction characteristics of the γ correction unit at the timing when the scene detection unit detects a change of the video scene. When the output selection unit outputs a video signal having a frame rate higher than a predetermined value, the correction characteristic of the γ correction unit is updated for each frame of the video signal. A digital broadcast receiver characterized by the above.

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