Abstract:
Image display method and apparatus are capable of displaying an input image signal in an optical condition on a display screen according to the brightness of the screen image. The image display apparatus for performing a specified process on an input image signal and displaying an image by the image signal on a display unit comprises a controller for adjusting a signal level detecting circuit for detecting brightness levels of an image by the input image signal by controlling the sharpness of an image by the image signal according to a detected signal level in such a way that as the detected signal level rises, the sharpness increases.

Description:
INCORPORATION BY REFERENCE  
       [0001]     The present application claims priority from Japanese application JP2004-047668 filed on Feb. 24, 2004, the content of which is hereby incorporated by reference into this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an image display method and apparatus that display a television signal or an image signal input from a personal computer or the like on a display unit, such as a PDP (plasma display panel) or a liquid crystal panel, for example.  
         [0004]     2. Description of the Related Art  
         [0005]     In recent years, image display apparatuses using fixed-pixel devices, such as PDPs and a liquid crystal panels, are spreading widely and their display screens are becoming progressively larger.  
         [0006]     Meanwhile, the above-mentioned image display apparatuses with fixed-pixel devices, such as PDPs and liquid crystal panels, are inferior in terms of contrast to conventional types of image display units using the cathode ray tubes. Therefore, to improve the contrast, improvements have been made to the drive system and the structure thereof that enhance the luminous efficiency of the phosphors. Technologies of prior art of this kind disclosed in JP-A-10-208637 and JP-A-8-138558, for example, are well known.  
       SUMMRY OF THE INVENTION  
       [0007]     As mentioned above, in the image display apparatuses having fixed pixel devices, such as PDPs and liquid crystal panels, it is possible to improve the contrast. Not only with those display apparatuses using fixed pixel devices such as a PDP or a liquid crystal panel, but, the image display apparatuses usually have a problem pointed out below.  
         [0008]     More specifically, generally, when a displayed image on a display apparatus is dark on the whole screen, noise signals or the like mixed in the image signal appear as white dots on the screen image, giving a rough effect to the picture quality. Moreover, when the screen image is bright in its entirety, the contours of features displayed becomes indistinct. This problem is particularly notable with the image display apparatuses using fixed pixel devices, such as PDPs and liquid crystal panels of high definition achieved by an enlarged display screen and the greatly increased number of display pixels.  
         [0009]     The present invention has been made with the above-mentioned problem in the prior art in mind. The present invention provides an image display method capable of displaying the input image signal in an optimal condition on the display screen regardless of the enlargement of the display screen size, and also provides apparatus for realizing the same image display method.  
         [0010]     The present invention provides an image display method for performing a specified process on an input image signal and displaying an image by the input image signal on a display unit, comprising a step of detecting brightness levels of an image by the input image signal and a step of adjusting the sharpness of the image by the image signal according to the signal level detected, and also provides apparatus therefor.  
         [0011]     According to the present invention, in the above-mentioned image display method and apparatus therefore, the above-mentioned signal level may be detected by detecting an average signal level of the input image signal for one frame of an image. Or, the signal level may be detected by detecting the gain of means for amplifying the input image signal. Also, the above-mentioned sharpness may be controlled by adjusting in such a way that as the signal level detected by the signal level detecting means rises, its sharpness increases. Moreover, the strength of removing noise from the input image signal may be controlled according to the signal level detected.  
         [0012]     According to the image display method and apparatus of the present invention, regardless of the enlargement of the display screen, the input image signal may be displayed in an optimum condition on the display screen in accordance with the brightness of the screen image.  
         [0013]     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a diagram showing a basic structure of a sharpness adjusting circuit of an image display apparatus according to an embodiment of the present invention;  
         [0015]      FIG. 2  is a block diagram showing a general structure of the image display apparatus according to the embodiment of the present invention;  
         [0016]      FIG. 3  is a flowchart for explaining the operation of the sharpness adjusting circuit of the present invention;  
         [0017]      FIGS. 4A and 4B  are diagrams for explaining a method for obtaining a sharpness correction amount and a noise reducer correction amount in the above-mentioned sharpness adjusting circuit;  
         [0018]      FIG. 5  is a diagram showing an example of a concrete structure of a sharpness circuit which is practically applied in the above-mentioned sharpness adjusting circuit;  
         [0019]      FIG. 6  is a diagram showing a structure of the sharpness adjusting circuit according to another embodiment of the present invention; and  
         [0020]      FIG. 7  is a diagram for explaining a method for adjusting sharpness according to yet another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0021]     Embodiments of the present invention will be described in detail with reference to the accompanying drawings.  FIG. 2  is a block diagram showing a general structure of an image display apparatus according to an embodiment of the present invention. In  FIG. 2 , reference numeral  1  denotes a tuner unit for performing a specified process on an analog image signal input from outside and outputting digital image signals Rd, Gd and Bd to a display unit  2  (a fixed pixel device, such as a PDP or a liquid crystal panel). The image display apparatus of this embodiment includes a video amplifier  11  for amplifying an analog luminance signal Ya input from an input terminal T 1 , an A/D converter  12  for converting the amplified analog luminance signal Ya into a digital luminance signal, and a scan converter  13  for converting the input signal into a signal with a signal timing at which the display apparatus can display the signal.  
         [0022]     The above-mentioned tuner  1  includes an input terminal T 2 , and an A/D converter  14  which converts an analog color (color difference) signal Cb input from T 2  and an analog color (color difference) signal Cr into digital color (color difference) signals Cbd and Crd. The digital color (color difference) signals Cbd and Crd obtained by A/D conversion are both guided to the above-mentioned scan converter  13 . Further, the tuner  1  includes a color matrix circuit  31  which receives the above-mentioned digital luminance signal Yd and digital color (color difference) signals Cbd and Crd and converts them into digital image signals Rd, Gd and Bd to display red (R), green (G) and blue (B). The digital image signals Rd, Gd, and Bd output from the color matrix circuit  31  are supplied to the above-mentioned display unit  2  and displayed. In this embodiment, between the A/D converters  12 ,  14  and the scan converter  13 , there is provided a noise reducer  32  to remove noise from the above-mentioned digital luminance signal Yd and digital color (color difference) signals Cbd and Crd.  
         [0023]     In addition to the basic structure described above, the tuner  1  further includes noise-removing low pass filters LPF 151  and LPF 152  to remove noise from the digital luminance signal Yd obtained by the above-mentioned A/D conversion, an average luminance detecting circuit  16  for detecting an average luminance level for a predetermined time period (one frame or one field, for example) from an output signal (digital luminance signal) of the noise-removing LPF 151 , a maximum luminance detecting circuit  17  for detecting the maximum luminance level for a predetermined time period (one frame or one field, for example) from an output signal (digital luminance signal) of the noise-removing LPF 152 , an average luminance decision unit  18  for receiving the average luminance level information (signal) detected by the above-mentioned average luminance detecting circuit  16  and deciding a luminance area to which the average luminance level corresponds, and a maximum luminance decision unit  19  for receiving the maximum luminance level information (signal) detected by the above-mentioned maximum luminance level detecting circuit  17  and deciding a luminance area to which the maximum luminance level corresponds.  
         [0024]     Reference numeral  20  in  FIG. 2  denotes a gain controller for forming a control signal to control the gain or the like of the video amplifier  11  according to information about the fluminance area to which the average luminance level corresponds and the luminance area to which the maximum luminance level corresponds. This gain controller  20  is formed by a microcomputer, for example. In the image display apparatus according to the present invention, as shown in  FIG. 2 , between the above-mentioned scan converter  13  and the above-mentioned color matrix circuit  31 , there is provided the sharpness circuit  30  which will be described in detail later. Control of the sharpness of the digital luminance signal Yd by the sharpness circuit  30  is controlled by a signal sent from the gain controller  20 . In addition, the above-mentioned A/D converters  12 ,  14 , scan converter  13 , noise-removing LPFs  151 ,  152 , average luminance detecting circuit  16 , maximum luminance detecting circuit  17 , sharpness circuit  30 , and color matrix circuit  31  are fabricated as an LSI (large scale integrated circuit), for example.  
         [0025]     The accompanying drawing  FIG. 1  shows a basic structure of the sharpness adjusting circuit for adjusting the sharpness. As is clear from this drawing, the sharpness adjusting circuit is made up of the A/D converter  4  (corresponding to  12  in  FIG. 2 ), the signal level detecting circuit  5  (corresponding to  16  in  FIG. 2 ), the noise reducer (corresponding to  32  in  FIG. 2 ), the sharpness circuit  6  (corresponding to  30  in  FIG. 2 ), and the microcomputer (corresponding to  20  in  FIG. 2 ) in the tuner  1  mentioned above.  
         [0026]     The image display apparatus whose structure has been described above, especially, the operation of the sharpness adjusting circuit will be described in detail with reference to the flowchart in the accompanying drawing  FIG. 3 . When a sequence of processes shown in  FIG. 3  is started, an average luminance level (APL) is detected from the signal level detecting circuit  5  (Step S 1 ). Note that an average luminance level (APL) to be detected is, as described above, a luminance level averaged for a predetermined time period, such as one frame or field, for example. From the detected average luminance level (APL), a sharpness correction amount is obtained (Step  2 ). By the way, an example of a method of obtaining a sharpness correction amount at this time is shown in the accompanying drawing  FIG. 4A .  
         [0027]     More specifically, as shown in  FIG. 4A , an APL value (correction APL center) is previously set which corresponds to a sharpness value (user adjust value) set by the user, and if a detected average luminance level (APL) from the signal level detecting circuit  5  is lower than the correction APL center, a correction amount is obtained which decreases the sharpness, or if the detected APL level is higher than the correction APL center, a correction amount is obtained which raises the sharpness. After this, the sharpness correction amount obtained at this time is applied to the above-mentioned sharpness circuit  6  (Step S 3 ).  
         [0028]     Next, from the average luminance level (APL) obtained as described above, a noise reducer correction amount is calculated (Step S 4 ). A method for calculating a noise reducer correction amount at this time is shown in the accompanying drawing  FIG. 4B . In other words, just as in the sharpness correction amount described above, an APL value (correction APL center) is set which corresponds to a noise reducer strength value (user adjust value) set in advance by the user. If an average luminance level (APL) detected by the signal level detecting circuit  5  is lower than the correction APL center, a correction amount to reduce the noise reducer strength is obtained. On the other hand, if the detected APL is higher than the correction APL center, a correction amount to raise the noise reducer strength is obtained. After this, this obtained noise reducer correction amount is applied to the above-mentioned noise reducer  8  (Step S 5 ). Further, a sharpness correction amount and a noise reducer correction amount mentioned above may be calculated by the above-mentioned microcomputer  7  based on a function set in advance or by using a table containing a specified function. After the above processes have been executed, the whole process is finished. Note that the above processes are executed repeatedly at predetermined intervals.  
         [0029]     According to the operation of the sharpness adjusting circuit described in detail above, when the whole screen image on the display unit  2  is dark (in other words, the detected average luminance level (APL) is lower than the correction APL center, the obtained sharpness is less than a user adjust value by an applied sharpness correction amount. On the other hand, when the whole screen image is light (in other words, the detected average luminance level (APL) is higher than the correction APL center), contrary to the above case, the obtained sharpness is more than a user adjust value by an applied sharpness correction amount. Put in other ways, the phenomenon that noise signal or the like mixed in the image signal appears as white dots on the displayed image is reduced, and on the other hand, even when the whole area of the screen is light, the contours of the features on the displayed image are prevented from becoming indistinct. Thus, it is possible to display the input image signal in optimum condition on the display screen at all times.  
         [0030]     Furthermore, according to the above-mentioned sharpness adjusting circuit, at the same time, the strength of noise removal by the above-mentioned noise reducer  8  is increased or decreased according to the brightness of the whole displayed image (in other words, whether or not a detected average luminance level (APL) is higher than the correction APL center). Therefore, the noise signal particularly when the whole screen is dark is reduced, thereby improving picture quality. It ought to be noted that those effects are conspicuous above all in image display apparatuses using fixed pixel devices, such as PDPs or liquid crystal panels of high definition image based on the enlarged screen size and greatly increased number of display pixels.  
         [0031]     Next, the accompanying  FIG. 5  shows an example of a concrete circuit structure of the sharpness circuit  6  which is practically applied in the sharpness adjusting circuit. In other words, the sharpness circuit  6  is formed by connecting a path of the luminance signal (Yd) from the above-mentioned noise reducer  8  to the display unit  2  in parallel with a series connection of a quadratic differentiation circuit  50  and a gain adjusting circuit  51 . The gain of the gain adjusting circuit  51  is adjusted by the microcomputer  7  and output of the gain adjusting circuit  51  is added to the luminance signal (Yd) by an adder  60  in  FIG. 5  and a combined signal is output to the display unit  2 .  
         [0032]     According to the sharpness circuit  6  structured as described, as is clear also from waveform patterns in  FIG. 5 , part of the luminance signal (Yd) from the noise reducer  8  is subjected to a waveform process by the above-mentioned quadratic differentiation circuit  50 . Subsequently, after the gain of the amplitude of the signal from the differentiation circuit  50  is adjusted by the gain adjusting circuit  51 , output of the gain adjusting circuit  51  is added to the luminance signal (Yd) by the adder  60  mentioned above. Thus, changes of the waveform are accentuated to make the waveform&#39;s edges sharp as indicated by Y′d in  FIG. 5 .  
         [0033]     In the embodiment described above, with regard to the structure of the image display apparatus that forms the tuner  1  shown in  FIG. 2 , description has been made on the assumption that the noise reducer  32  is used. However, the present invention is not limited to the above-described structure, it is possible to adopt a structure which excludes the noise reducer  32 , for example. Or, in the structure of the image display apparatus, it will be possible to omit the maximum luminance detecting circuit  17  and the noise removing LPF  152  of the preceding stage.  
         [0034]     Particularly with respect to the sharpness adjusting circuit shown in  FIG. 1 , the present invention is not limited to such a structure as shown. For example, it is possible to configure such a structure without the noise reducer  8  that only the sharpness is adjusted but the noise reducer is not adjusted.  
         [0035]     In another embodiment of the present invention, the accompanying  FIG. 6  shows a structure of the sharpness adjusting circuit which adjusts the sharpness and also the gain of the video amplifier  3  (refer to  11  in  FIG. 2 ). In other words, in this other embodiment, the above-mentioned signal level detecting circuit  5  is formed by using a noise removing LPF 152  and a maximum luminance detecting circuit  17  in addition to the noise removing LPF 151  and an average luminance detecting circuit  16  in  FIG. 2  mentioned above. In this embodiment, the above-mentioned microcomputer  7  is used not only to adjust the sharpness circuit but also to adjust the gain of the video amplifier  11  that amplifies an input analog luminance signal Ya.  
         [0036]     More specifically, the microcomputer  7  detects an average luminance level (APL) and also detects a maximum luminance level (MAX) of the digital luminance signal from the signal level detecting circuit  5 . The sharpness is adjusted by a detected average luminance level (APL) and also, the gain of the video amplifier  3  is adjusted according to the detected maximum luminance level (MAX). By this method, a screen image with improved picture quality can be obtained.  
         [0037]     In the above embodiment, description has been made about the case where an average luminance level (APL) obtainable from the average luminance detecting circuit  16  is used to detect brightness levels of an image displayed on the display unit  2 . However, the present invention is not limited to this method. To cite an example, instead of an average luminance level (APL) described above, brightness levels can be detected by detecting, for example, gain of the video amplifier  11  for amplifying an input analog luminance signal Ya mentioned above. In this case, as shown in the accompanying  FIG. 7 , for example, a correction start point is set in advance, which corresponds to a luminance adjust value set by the user, for example, and when a video amp gain exceeds this correction start point, the sharpness is adjusted as indicated by a characteristic curve of  FIG. 7 . Note that this can obviously be realized in a similar way as described above, because the amp gain of the video amplifier  11  is controlled by the microcomputer  7  as shown in the structure of  FIG. 2 .  
         [0038]     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.