JP2006279340A - Video processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a video processing apparatus capable of properly executing black extension with a digital method for an input luminance signal with a special form. <P>SOLUTION: The video processing apparatus includes: a black extension setting circuit 21a for detecting a back region on the basis of the input luminance signal by one display image supplied as digital data and setting a valid display video image except the black region in the display video image to be a region that should be subjected to be black extension; and a black extension circuit 22a for applying black extension to the valid display video image. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a video processing apparatus that performs black expansion on an input luminance signal in a digital manner.

  A video signal input to a video processing device such as a television receiver is composed of a luminance signal, a color difference signal, a synchronization signal, and the like. A television receiver or the like is mounted with a black expansion circuit that performs black expansion for enhancing the contrast of an image. The luminance signal is displayed as black on the display device when the luminance level is low, and is displayed as white on the display device when the luminance level is high. Black stretching means processing for reducing the luminance level of an input luminance signal below a certain luminance level. As a black stretch circuit that employs an analog method, a method of performing black stretch according to an average video level (APL) is known (for example, see Patent Document 1).

  In recent years, with the development of digital technology, the black extension circuit has been digitized. In a black expansion circuit that employs a digital method, black expansion is performed in accordance with the ratio of the number of pixels having a black level to the total number of pixels in a display image. In addition, as a black expansion circuit that employs a digital method, a luminance histogram is generated, whether the display image is a natural image or a non-natural image is determined from the luminance histogram, and black expansion is performed for a non-natural image. A method that does not exist has been proposed (see, for example, Patent Document 2).

However, in both the method using the APL and the method using the luminance histogram, when the input luminance signal has a special format, that is, when a display panel includes a side panel or a letter box, an appropriate black extension is performed. Can not do. With respect to the analog or digital black expansion circuit, the side panel or letterbox that was originally displayed at the black level is further black expanded. In particular, in a digital black expansion circuit, the ratio of the number of pixels having a black level with respect to the total number of pixels in the display image is erroneously detected, so that black expansion cannot be performed properly. As described above, it is desired to realize a video processing apparatus capable of appropriately performing black expansion digitally on an input luminance signal having a special format.
JP 2000-261893 A JP 2004-261893 A

  The present invention provides a video processing apparatus capable of appropriately performing black expansion digitally on an input luminance signal having a special format.

  According to one aspect of the present invention, a black region is detected based on an input luminance signal for one display image supplied as digital data, and an effective display image excluding the black region in the display image is set as a region to be black expanded. The gist of the present invention is an image processing apparatus including a black expansion setting circuit that performs black expansion on an effective display image.

  ADVANTAGE OF THE INVENTION According to this invention, the video processing apparatus which can perform appropriately black expansion with a digital system with respect to the input luminance signal which has a special format can be provided.

  Next, first and second embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings in the first and second embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(First embodiment)
As shown in FIG. 1, the video processing apparatus according to the first embodiment of the present invention includes a video signal generation apparatus 1, an image quality correction circuit 2a, a small arithmetic unit (MPU) 24a, a matrix circuit 25, and a display apparatus 3. . The image quality correction circuit 2a includes a black expansion setting circuit 21a, a black expansion circuit 22a, and a control circuit 23a. The black stretch setting circuit 21a detects a black area based on an input luminance signal for one display video supplied as digital data, and sets an effective display video excluding the black area in the display video as a black stretch area. To do. Here, the “black region” means a non-video portion displayed in a black strip shape on the display device 3, such as a letterbox video or a side panel video. The black expansion circuit 22a performs black expansion on the effective display image. Further, the control circuit 23a controls the black expansion operation of the black expansion circuit 22a. As the display device 3, for example, a liquid crystal display panel (LCD), a plasma display panel (PDP), a surface-conduction electron-emitter display (SED) panel, or the like can be used. As the video signal generating device 1, a receiving device that receives a television broadcast can be used. The receiving device includes, for example, an antenna (not shown), a tuner device, an analog / digital (A / D) converter, a video generating device for generating a luminance signal Y and a color signal C, and converting the color signal C into two color difference signals. A color decoder or the like.

  When the black stretch setting circuit 21a determines that no black area exists in the display video, the black stretch operation of the black stretch circuit 22a is executed according to the following procedures (1) to (4). (1) The number of pixels having a luminance level equal to or lower than the detection level in the display video is detected by comparing the luminance level of the input luminance signal Y with the detection level. As an example, in FIG. 2, the number of pixels below the detection level for the video period of the input luminance signal Y for one horizontal scanning line (1H) is zero. (2) The ratio of the number of pixels below the detection level to the total number of pixels in the display image (hereinafter referred to as “black pixel ratio”) is calculated. (3) The calculated black pixel ratio is compared with a preset reference ratio, and whether or not to perform black expansion and a black expansion amount (black expansion gain) are determined based on the comparison result. (4) Decrease the luminance level of the input luminance signal Y below the black expansion start level according to the determined black expansion amount. As a result, as indicated by the broken line in FIG. 2, the luminance level of a part of the luminance signal Y indicated by the solid line in FIG. 2 decreases.

  As an example, the detection level is set to about 0 to 3 [IRE]. The reference ratio is set to about 1% to 18% of all pixels in one display video, for example. The start level of black extension is set to about 25 to 55 [IRE]. The maximum gain of the black extension gain is, for example, about 1.5, that is, about 3 [dB].

  Further, as shown in FIG. 1, the black extension setting circuit 21a includes a comparator 211, a counter 212, a detection circuit 213, and a setting signal generation circuit 214. The input of the comparator 211 is connected to the respective outputs of the video signal generator 1 and the MPU 24a. The input of the counter 212 is connected to the output of the comparator 211. The input of the detection circuit 213 is connected to the output of the counter 212. An input of the setting signal generation circuit 214 is connected to an output of the detection circuit 213. The input of the control circuit 23a is connected to the output of the black expansion circuit 22a. The input of the black extension circuit 22a is connected to the respective outputs of the video signal generation device 1, the setting signal generation circuit 214, and the control circuit 23a. Specific operations of the comparator 211, the counter 212, the detection circuit 213, and the setting signal generation circuit 214 will be described later.

  The MPU 24a supplies each data of the detection level, the reference ratio, and the start level to the control circuit 23a. The MPU 24 a supplies determination level data to the comparator 211. The MPU 24a includes a table that stores a plurality of combinations of detection levels, reference ratios, and start levels. The control circuit 23a controls the black expansion circuit 22a based on the detection level, reference ratio, and start level data supplied from the MPU 24a. The determination level and the detection level are not limited to being set as separate data, and can be the same data. This is because both the determination level and the detection level are used for the purpose of detecting the black level.

  When the video signal generating device 1 displays a 9:16 cinema size video on the display device 3 having an aspect ratio of 3: 4, as shown in FIG. 3, both ends of the display video in the vertical direction are displayed. The part is a black region. That is, a so-called letterbox image in which the first several tens of H periods and the last several tens of H periods of one vertical scanning (1V) period are all black levels is inserted.

  Assuming that the luminance level of the effective display image shown in FIG. 3 is constant, the input luminance signal Y corresponding to the display image shown in FIG. 3 has a waveform as shown by the solid line in FIG. However, in the waveform diagram shown in FIG. 4, the horizontal blanking period and the vertical blanking period are not shown. The period from time t0 to t1 and time t2 to t3 in FIG. 4 corresponds to letterbox video.

  Further, when black expansion is performed on the entire display image shown in FIG. 3, the black pixel ratio in the 1V period of the input luminance signal Y shown by the solid line in FIG. It is judged that it is about 15%. When the reference ratio is 18%, as shown by the broken line in FIG. 4, the input luminance signal Y is black-stretched with a small black stretch amount (black stretch gain) in order to compensate the black pixel rate of 3%. . In addition, the entire luminance level of the input luminance signal Y in the period from time t0 to t4 is lowered.

  On the other hand, when the black extension setting circuit 21a designates an effective display image, the black pixel ratio in the 1V period of the input luminance signal Y shown by the solid line in FIG. 5 is the period of the effective display image excluding the letterbox image, that is, Since only the black level during the period from the time t1 to the time t2 is detected, it is determined to be about 0%. When the reference ratio is 18%, the input luminance signal Y is black-stretched with a large black stretch amount (black stretch gain) so as to compensate the black pixel rate for 18% as shown by the broken line in FIG. Further, the black expansion circuit 22a reduces only the luminance level of the input luminance signal Y during the period from time t1 to time t2.

  In this way, by performing black expansion only on the effective display image, the black level in the letterbox image is not detected by the black expansion circuit 22a, and only the luminance level in the effective display image is reduced. It is possible to operate the expansion circuit 22a effectively.

  For example, regarding letterbox video, when black expansion is performed on the entire display video, it is assumed that the display video after black expansion is a video as shown in FIG. On the other hand, when the black extension is executed only for the effective display picture of the display picture, the display picture after the black extension becomes a picture as shown in FIG. The display video shown in FIG. 6B has a sufficiently lower luminance level than the display video shown in FIG.

  Further, when a 3 to 4 image is displayed on the display device 3 having an aspect ratio of 9 to 16, both end portions in the horizontal direction of the display image are black areas. That is, a so-called side panel format is adopted in which the first tens of pixels and the last tens of pixels in each 1H period for one display video are all black level.

  For example, regarding the side panel image, when black expansion is performed on the entire display image, the display image after black expansion is an image as shown in FIG. On the other hand, when the black extension is executed only for the effective display picture excluding the side panel picture of the display picture, the display picture after the black extension becomes a picture as shown in FIG. The brightness level of the display image shown in FIG. 7B is sufficiently lower than that of the display image shown in FIG.

  Next, the operation of the video processing apparatus according to the first embodiment will be described with reference to the flowchart shown in FIG.

  (A) In step S11, the MPU 24a shown in FIG. 1 sets a determination level for the comparator 211, and sets a detection level, a start level, and a reference ratio for the control circuit 23a. For example, the determination level is set to about 0 to 3 [IRE].

  (B) In step S12, the comparator 211 compares the luminance level of the input luminance signal Y with the determination level, and detects the input luminance signal Y below the determination level in units of pixels. However, the MPU 24a controls so that the comparator 211 does not detect the input luminance signal Y below the determination level for the input luminance signal Y in the horizontal blanking period and the vertical blanking period.

  (C) In step S13, the counter 212 counts the input luminance signal Y that is equal to or lower than the determination level detected by the comparator 211. The counter 212 counts up the input luminance signal Y below the determination level and transmits the count value to the detection circuit 213. For example, the counter 212 resets the count value at the timing when the input luminance signal Y below the determination level is interrupted and at the switching timing of the 1H period.

  (D) In step S14, the detection circuit 213 determines whether or not a black region is included in the display video based on the count value of the counter 212. Specifically, when the counter 212 is counted up during the first several tens of H periods and the last several tens of H periods of the 1V period, a letterbox video is detected. When the first several tens pixels and the last several tens of pixels in each 1H period for one display video are counted up by the counter 212, the side panel video is detected. If it is determined that a black area is included in the display video, the process proceeds to step S15. When it is determined that the black area is not included in the display video, the process proceeds to step S16.

  (E) In step S15, the setting signal generation circuit 214 supplies a range setting signal indicating the range of the effective display image to the black expansion circuit 22a. When the detection circuit 213 detects a letterbox image, the setting signal generation circuit 214 reduces the vertical range setting signal S1 as compared with FIG. 6A, as shown in FIG. 6B. On the other hand, when the detection circuit 213 detects a side panel image, the setting signal generation circuit 214 reduces the horizontal range setting signal S2 as compared with FIG. 7A, as shown in FIG. 7B. .

  (F) In step S16, the black expansion circuit 22a performs black expansion only on the effective display video based on the range setting signals S1 and S2 supplied from the setting signal generation circuit 214.

  As described above, according to the first embodiment, it is possible to calculate the black pixel ratio by excluding the letterbox image and the side panel image by executing the black expansion only on the effective display image. Furthermore, the luminance level below the start level of black expansion can be reduced for the effective display image. Therefore, it is possible to provide a video processing apparatus that can appropriately perform black expansion digitally even when a black region is included.

(Second Embodiment)
As shown in FIG. 9, the video processing apparatus according to the second embodiment of the present invention is different from FIG. 1 in that the black stretch setting circuit 21 b includes a histogram creation circuit 26. Based on the input luminance signal Y, the histogram creation circuit 26 creates a luminance histogram indicating the distribution of luminance levels of all the pixels in the display video, and detects a black region according to the luminance histogram. The black expansion circuit 22b performs black expansion on the effective display image excluding the black area.

  The histogram creation circuit 26 has inputs connected to the outputs of the video signal generator 1 and the MPU 24b, and outputs connected to the inputs of the black stretch circuit 22b and the control circuit 23b. The histogram creation circuit 26 includes, for example, a plurality of comparators (not shown) and a counter connected to each of the plurality of comparators. Other configurations are the same as those in FIG.

  Further, the MPU 24b sets a plurality of division points of the luminance histogram as shown in FIG. In the example shown in FIG. 10, 0, 3, 20, 40, 60, 80, and 100 [IRE] are set as segment points. As a result, the first class that is 0 [IRE] or more and less than 3 [IRE], the second class that is 3 [IRE] or more and less than 20 [IRE], 20 [IRE] or more, and 40 [IRE]. 3rd class, less than 40 [IRE], and 4th class, less than 60 [IRE], 5th class, 60 [IRE] and more, and less than 80 [IRE], 80 [IRE] and more, and A total of six classes of the sixth class that is less than 100 [IRE] are set.

  As shown in FIG. 10, the histogram creation circuit 26 calculates the ratio of the number of pixels belonging to each class to the total number of pixels in the display video for each of the first to sixth classes based on the input luminance signal Y. To do. In the example shown in FIG. 10, the first class is 15%, the second class is 25%, the third class is 30%, the fourth class is 20%, the fifth class is 10%, and the sixth class is 0%. Is calculated. The black expansion circuit 22b performs black expansion on a class including the minimum value (0 [IRE]), that is, other classes excluding the first class. For example, in FIG. 10, black expansion is executed only for the second class.

  Further, the histogram creation circuit 26 starts and stops the black expansion from the dividing points that classify the second to sixth classes excluding the first class, that is, 3, 20, 40, 60, 80, and 100 [IRE]. The level is set in the black expansion circuit 22b. In FIG. 10, 20 [IRE] is set as the black stretch start level, and 3 [IRE] is set as the black stretch stop level. That is, the black expansion circuit 22b does not decrease the luminance level for the input luminance signal Y (pixel) less than 3 [IRE]. As a result, for example, in FIG. 5 or FIG. 6, the luminance level is maintained for the input luminance signal Y in the period of time t0 to t1 and time t2 to t3.

  Further, the MPU 24b designates one or more of the classes set in the histogram creation circuit 26, and sets the reference ratio in the control circuit 23b. In FIG. 10, it is assumed that the second class is designated and the reference ratio is 30%. In this case, the black expansion circuit 22b compares the ratio of the number of pixels belonging to the second class to the total number of pixels in the display video with the reference ratio, and determines the black expansion amount (black expansion gain) according to the comparison result. . As a result, since the black pixel ratio of the second class is 25%, the black expansion amount (black expansion gain) is controlled so as to compensate for the black pixel ratio of 5%.

  Therefore, by not using the pixels belonging to the first class for the calculation of the black pixel ratio, even if the display video includes letterbox video or side panel video, the effective display video excluding the letterbox video or side panel video. Black stretch can only be performed on.

  Next, the operation of the video processing apparatus according to the second embodiment will be described with reference to the flowchart shown in FIG. However, the overlapping description of the operation overlapping with the operation of the video processing apparatus according to the first embodiment will be omitted.

  (A) In step S 21, the MPU 24 b shown in FIG. 9 sets a plurality of division points of the luminance histogram for the histogram creation circuit 26. In addition, the MPU 24b sets a reference ratio for at least one class among a plurality of classes determined by a plurality of division points.

  (B) In step S22, the histogram creating circuit 26 sets the black stretching start level and stop level in the black stretching circuit 22b from the dividing points that classify other classes excluding the class including the minimum value.

  (C) In step S23, the histogram creating circuit 26 creates a luminance histogram indicating the distribution of luminance levels of the input luminance signal Y.

  (D) In step S23, the black stretch circuit 22b refers to the brightness histogram to determine the black stretch amount, and lowers the brightness level of the input brightness signal Y between the start level and the stop level.

  As described above, according to the second embodiment, since the pixel group having the black level is not subjected to black expansion, the black expansion can be executed by eliminating the letterbox image and the side panel image. Therefore, it is possible to provide a video processing apparatus that can appropriately perform black expansion digitally even when a black region is included.

(Modification of the second embodiment)
As a modification of the second embodiment of the present invention, as shown in FIG. 12, the black expansion circuit 22b shown in FIG. 9 has a class including the minimum value (0 [IRE]), that is, other than the first class. Black stretching may be performed for all classes. In the example shown in FIG. 12, a black extension amount (black extension gain) is preset in advance for each of the second to sixth classes. In this case, the setting of the reference ratio and the setting of the black stretch start level are unnecessary. Therefore, the black expansion circuit 22b can have the characteristics as shown in FIG. 13, and image quality correction control with more sharpness can be performed.

(Other embodiments)
As described above, the present invention has been described according to the first and second embodiments. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the above-described first and second embodiments, the video signal generating device 1 has been described as an example of a receiving device that receives a television broadcast. However, the video signal generating device 1 is an optical disc playback device or a magnetic playback device (video). Tape recorders), terrestrial digital broadcasts, terrestrial analog broadcasts, satellite digital broadcasts, satellite analog broadcasts, cable TV digital broadcasts, receivers for receiving cable TV analog broadcasts, etc. can be used.

  Furthermore, the image quality correction circuits 2a and 2b shown in FIG. 1 and FIG. 9 can be monolithically integrated on a single semiconductor chip, or mounted as a multi-chip and formed into a single package to constitute a semiconductor integrated circuit.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

It is a block diagram which shows the structural example of the video processing apparatus which concerns on 1st Embodiment of this invention. It is a wave form diagram for demonstrating the black expansion | extension operation | movement at the normal time in the video processing apparatus which concerns on 1st Embodiment of this invention. It is a schematic diagram of a display image for explaining the function of the black extension setting circuit according to the first embodiment of the present invention. It is a wave form diagram which shows the comparative example for demonstrating operation | movement of the black expansion circuit which concerns on 1st Embodiment of this invention. It is a wave form diagram for demonstrating operation | movement of the black expansion circuit which concerns on 1st Embodiment of this invention. FIG. 6A is a schematic diagram showing an example in which black expansion is performed on the entire display image having a letter box, and FIG. 6B is an effective display image of the display image having the letter box. It is a schematic diagram which shows an example at the time of performing only black extension. FIG. 7A is a schematic diagram illustrating an example in which black expansion is performed on the entire display image having the side panel, and FIG. 7B illustrates an effective display image of the display image having the side panel. It is a schematic diagram which shows an example at the time of performing only black extension. It is a flowchart which shows operation | movement of the video processing apparatus which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structural example of the video processing apparatus which concerns on 2nd Embodiment of this invention. It is a figure explaining the function of the histogram preparation circuit which concerns on 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the video processing apparatus which concerns on 2nd Embodiment of this invention. It is a figure explaining the function of the histogram preparation circuit which concerns on the modification of 2nd Embodiment of this invention. It is a wave form diagram which shows the operation | movement of the black expansion circuit which concerns on the modification of 2nd Embodiment of this invention.

Explanation of symbols

21a, 21b ... Black stretch setting circuit 22a, 22b ... Black stretch circuit 26 ... Histogram creation circuit

Claims (5)

A black stretch setting circuit that detects a black region based on an input luminance signal for one display image supplied as digital data and sets an effective display image excluding the black region in the display image as a region to be black stretched When,
And a black expansion circuit for performing the black expansion on the effective display image.   The black extension setting circuit counts the number of pixels having a luminance level equal to or lower than a determination level based on the input luminance signal, and based on the count value, the black region is present at both ends of the display image in the vertical or horizontal direction. The video processing apparatus according to claim 1, wherein it is determined whether or not it exists.   The black stretch setting circuit creates a luminance histogram indicating a luminance level distribution of all pixels in the display video based on the input luminance signal, and detects the black region according to the luminance histogram. The video processing apparatus according to claim 1.   The video processing apparatus according to claim 3, wherein the black stretch setting circuit detects pixels belonging to a predetermined class in a plurality of classes of the luminance histogram as the black area.   The black stretch circuit calculates a ratio of the number of pixels having a luminance level equal to or lower than the detection level in the effective display image to the total number of pixels in the display image, compares the ratio with a reference ratio, 5. The video processing apparatus according to claim 1, wherein a black extension amount of the black extension is determined in response.