JP4117290B2 - Image quality improving method and image quality improving apparatus - Google Patents

Description

  The present invention relates to flare correction.

  In an image display device such as a television receiver or a video projector, it is known that image quality deteriorates due to the occurrence of flare. Flares are light edges that leak into bright areas due to reflection or scattering of light on the tube or projection tube of the picture tube or projection tube. This is a phenomenon where the boundary of the area is blurred.

  In order to correct such flare, image processing for emphasizing edges with a large luminance difference in the display image is performed. Referring to FIG. 3, a conventional example of an image quality improving apparatus that performs flare correction by image processing that emphasizes an edge (Japanese Patent Laid-Open No. 1-224694 (Patent Document 1) or Japanese Patent Laid-Open No. 1-224685 (Patent Document 2)). The block diagram showing the configuration of the reference) is shown. In FIG. 3, image processing for emphasizing the edge of the Y signal among the luminance (Y) color (C) signals is performed.

In FIG. 3, a Y input signal (Y _in ) is input to a delay compensation circuit 31 and a two-dimensional low-pass filter (LPF) circuit 32. The delay compensation circuit 31 is a circuit that delays an input signal by a time required for processing of the two-dimensional LPF circuit 32. The two-dimensional LPF circuit 32 is a filter that removes frequency components (edge components) higher than a predetermined frequency from an input signal. The two-dimensional LPF circuit 32 includes a unit delay circuit, a gain adjustment circuit, an addition circuit, and the like, and removes high-frequency components of the input signal by replacing the data of a certain pixel with the weighted average of the data of a plurality of neighboring pixels. (See Patent Document 2).

Since the high-frequency component of the Y input signal input to the two-dimensional LPF circuit 32 is removed, a signal with a rounded edge is output from the two-dimensional LPF circuit 32 (see the waveform shown in FIG. 3). ). The subtracting circuit 34 receives the Y input signal delayed by the processing time of the two-dimensional LPF circuit 32 by the delay compensation circuit 31 and the signal with a rounded edge output from the two-dimensional LPF circuit 32. The subtraction circuit 34 outputs a signal obtained by subtracting the latter signal from the former signal. Therefore, the subtraction circuit 34 outputs a signal obtained by extracting the high frequency component (edge component) removed by the two-dimensional LPF circuit 32 (see the waveform shown in FIG. 3). The gain adjustment circuit 35 multiplies the signal obtained by extracting the high frequency component output from the subtraction circuit 34 by a predetermined number and outputs it to the addition circuit 36 (see the waveform shown in FIG. 3). The adder circuit 36 adds a signal obtained by multiplying the Y input signal output from the delay compensation circuit 31 by a predetermined number of times, which is output from the gain adjustment circuit 35 and extracted from the high frequency component. As a result, the Y output signal (Y _out ) becomes a signal in which the edge component of the Y input signal is emphasized (see the waveform shown in FIG. 3). As described above, flare correction is performed. The C input signal (C _in ) is delayed by the delay compensation circuit 33 for the processing time of the two-dimensional LPF circuit 32, the subtraction circuit 34, the gain adjustment circuit 35, and the addition circuit 36. Then, it is output as it is as a C output signal (C _out ).

In the above description, flare correction is performed using only the Y signal. This is because flare correction with the Y signal is the most effective for improving image quality in the luminance color signal. However, flare correction may be performed not only with the Y signal but also with the C signal. Further, flare correction may be performed on RGB (Red, Green, Blue) signals. In this case, flare correction with the G signal is most effective for improving the image quality.
JP-A-1-246984 JP-A-1-246985

  In the image quality improving apparatus as described above, the largest burden is placed on the processing in the two-dimensional LPF circuit 32. Therefore, in order to smoothly improve the image quality, it is important to reduce the processing load on the two-dimensional LPF circuit 32. Therefore, in order to reduce the processing load on the two-dimensional LPF circuit 32, it is desirable to perform two-dimensional LPF processing after compressing the data of the input signal and reducing the number of data.

  However, if the data of the input signal is compressed and the number of data is reduced and then the two-dimensional LPF processing is performed, there arises a problem that the width of flare correction varies depending on the size of the input image. Referring to FIG. 4, a schematic diagram for explaining this problem is shown.

Here, (a) shows the flow of processing until the flare-corrected image data is output to the video display device when the input image size is S (S is arbitrary). The left figure is a two-dimensional image (the shaded area indicates a portion with low luminance), and the right figure is a cross-sectional view of this image cut along a horizontal dotted line. (1) shows an input window image. (2) shows an image that has been subjected to two-dimensional LPF processing after the data of the input window image of (1) is horizontally compressed and the number of data is reduced (after the image size is reduced) (data compression). The rate is a fixed value). In (3), after the data of (2) is decompressed and restored to the original number of data (after restoring the image size), it is converted into a flare correction component, which is converted into an input window image. The added image is shown. (4) is an image obtained by scaling the image of (3) to the size of the video display device. The scaling rate is T ₂ / T ₁ times.

Similarly, (b) is similar to (a) in the input image, and the input image size is 5S / 4 (S is arbitrary and the input image size is 5/4 times (a)). The flow of processing until the flare-corrected image data is output to the video display device is shown. The left figure is a two-dimensional image (the shaded area indicates a portion with low luminance), and the right figure is a cross-sectional view cut along a horizontal dotted line. (1) shows an input window image. (2) shows an image that has been subjected to two-dimensional LPF processing after the data of the input window image of (1) is horizontally compressed and the number of data is reduced (after the image size is reduced) (data compression). The rate is a fixed value). In (3), after the data of (2) is decompressed and restored to the original number of data (after restoring the image size), it is converted into a flare correction component, which is converted into an input window image. The added image is shown. (4) is an image obtained by scaling the image of (3) to the size of the video display device. The scaling rate is 4T ₂ / 5T ₁ times.

In FIG. 4, the data compression rate is a fixed value (for example, 1/2 times). Therefore, in (2), the image sizes of (a) and (b) after data compression are different. However, since the cutoff frequencies of the two-dimensional LPF circuit are the same, the edge removal width is the same. Then, the data expansion ratio is a fixed value (e.g., if the data compression ratio is 1/2, the data expansion ratio is 2 times), (3), takes the width of the flare correction same by T ₁ It becomes. However, since the scaling rates are different as described above, in (4), the width of flare correction in the image output to the video display device is as follows: (a) is T ₁ × T ₂ / T ₁ = T ₂ , (b) is _{T 1 × 4T 2 / 5T 1} = 4T 2/5 , and becomes a mixed by the input image size.

  As described above, if the width of the flare correction varies depending on the input image size, the user who views the video display device may have a strange impression and may even halve the effect of the flare correction.

  Accordingly, an object of the present invention is to reduce the amount of flare correction applied to an image displayed on a video display device even when the input image size is different when data compression is performed in order to reduce the processing burden in the two-dimensional LPF circuit. It is an object of the present invention to provide an image quality improvement method and an image quality improvement apparatus that can be aligned.

  In order to achieve the above object, the present invention does not fix the data compression rate (and data expansion rate), but fixes the size of the image size after data compression. That is, the data compression rate is changed according to the input image size so that the image size after data compression becomes a predetermined value.

  As shown in FIG. 4, when the data compression rate is fixed in (2), the edge removal width by the two-dimensional LPF process becomes the same even though the image size after data compression is different. This is a cause of varying flare correction widths in images displayed on a video display device when the input image sizes are different.

  Therefore, in the present invention, the two-dimensional LPF processing is performed after unifying the size of the image size after data compression to a predetermined value. Since the product of the data expansion rate and the scaling rate is naturally the same even if the input image size is different, the width of the flare correction applied to the image displayed on the video display device can be made uniform even if the input image size is different.

  According to the present invention, it is necessary to determine the input image size. The input image size can be easily obtained by using a dot clock, a horizontal synchronizing signal, and a vertical synchronizing signal. That is, the number of data in the horizontal direction can be detected by counting the number of dot clocks between successive horizontal synchronization signals. Further, by counting the number of horizontal synchronization signals between successive vertical synchronization signals, the number of data in the vertical direction can be obtained. Thus, the input image size can be obtained.

  As described above, according to the present invention, the image size after data compression is unified to a predetermined value and the two-dimensional LPF processing is performed. There is an effect that the width of flare correction in the image displayed on the display device can be made uniform.

  Next, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  Referring to FIG. 1, there is shown a schematic diagram for explaining the image quality improving method of the present invention.

Here, (a) shows the flow of processing until the flare-corrected image data is output to the video display device when the input image size is S (S is arbitrary) (FIG. 4A). See also). The left figure is a two-dimensional image (the shaded area indicates a portion with low luminance), and the right figure is a cross-sectional view cut along a horizontal dotted line. (1) shows an input window image. (2) shows an image that has been subjected to two-dimensional LPF processing after the data of the input window image of (1) is horizontally compressed and the number of data is reduced (after the image size is reduced) (data compression). Later image size is a fixed value). For example, if the image size after data compression is S / 2, the data compression rate in the case of (a) is ½. In (3), after the data of (2) is decompressed and restored to the original number of data (after restoring the image size), it is converted into a flare correction component, which is converted into an input window image. The added image is shown. (4) is an image obtained by scaling the image of (3) to the size of the video display device. The scaling rate is T ₂ / T ₁ times.

Similarly, (b) is similar to (a) in the input image, and the input image size is 5S / 4 (S is arbitrary and the input image size is 5/4 times (a)). The flow of processing until the flare-corrected image data is output to the video display device is shown (see also FIG. 4B). The left figure is a two-dimensional image (the shaded area indicates a portion with low luminance), and the right figure is a cross-sectional view of this image cut along a horizontal dotted line. (1) shows an input window image. (2) shows an image that has been subjected to two-dimensional LPF processing after the data of the input window image of (1) is horizontally compressed and the number of data is reduced (after the image size is reduced) (data compression). Later image size is a fixed value). For example, if the image size after data compression is S / 2, the data compression rate in the case of (b) is 2/5. This is a different value from the case of (a). In (3), after the data of (2) is decompressed and restored to the original number of data (after restoring the image size), it is converted into a flare correction component, which is converted into an input window image. The added image is shown. (4) is an image obtained by scaling the image of (3) to the size of the video display device. The scaling rate is 4T ₂ / 5T ₁ times.

In FIG. 4, the image size after data compression is a fixed value (for example, S / 2). Therefore, in (2), the image sizes of (a) and (b) after data compression are the same. Since the cutoff frequency of the two-dimensional LPF circuit is the same, the edge removal width is the same. The product of the data expansion rate (reciprocal of the data compression rate) and the scaling rate is naturally the same. In the above example, in the case of (a), the product of the data expansion rate and the scaling rate is 2 × (T ₂ / T ₁ ) = 2T ₂ / T ₁ , and in the case of (b), (5 / 2) × (4T ₂ / 5T ₁ ) = 2T ₂ / T _1, which is the same value. Therefore, in (4) takes the width of the flare correction in the image to be displayed on the video display device is the same in T _2.

  In this way, by unifying the image size when performing the two-dimensional LPF processing, the edge removal width is unified, and the width of the flare correction applied to the image displayed on the video display device that depends on the edge removal width is input. It prevents being mixed depending on the image size.

  In FIG. 1, compression is performed only in the horizontal direction, but compression may be performed in the vertical direction in the same manner.

  According to the present invention, it is necessary to determine the input image size. The input image size can be easily obtained by using a dot clock, a horizontal synchronizing signal, and a vertical synchronizing signal. That is, the number of data in the horizontal direction can be detected by counting the number of dot clocks between successive horizontal synchronization signals. Further, by counting the number of horizontal synchronization signals between successive vertical synchronization signals, the number of data in the vertical direction can be obtained. Thus, the input image size can be obtained.

  Referring to FIG. 2, a diagram showing the configuration of the image quality improvement apparatus of the present invention is shown. The image quality detection circuit 114 is provided as a feature compared with the conventional image quality improvement apparatus, and the input image size data obtained by the above method is converted into the horizontal compression circuit 103, the vertical compression circuit 104, and the vertical direction. The output is to the expansion circuit 107 and the horizontal expansion circuit 108. The horizontal direction compression circuit 103, the vertical direction compression circuit 104, the vertical direction expansion circuit 107, and the horizontal direction expansion circuit 108 are based on the input image size data so that the data size after data compression becomes a predetermined value. Determine the compression rate or data decompression rate.

  The delay compensation circuit 102 corresponds to the delay compensation circuit 31 in FIG. The horizontal LPF circuit 105 and the vertical LPF circuit 106 correspond to the two-dimensional LPF circuit 32. The subtraction circuit 109, the gain adjustment circuit 110, the addition circuit 111, and the delay compensation circuit 116 correspond to the subtraction circuit 34, the gain adjustment circuit 35, the addition circuit 36, and the delay compensation circuit 33 in FIG.

  The horizontal direction compression circuit 103, the vertical direction compression circuit 104, the vertical direction expansion circuit 107, and the horizontal direction expansion circuit 108 perform two-dimensional LPF processing after data compression, and then are necessary for data expansion to the original size. It is a circuit. The scaling circuits 112 and 117 are circuits necessary for scaling an image to the size of the video display device. Although not shown in FIG. 3, the A / D conversion circuits 101 and 115 and the D / A conversion circuits 113 and 118 convert an analog input signal into a digital signal and perform flare correction. Thus, the circuit is necessary for output.

  In FIG. 2, when the input signal is a luminance color difference signal or luminance color signal, flare correction is applied to the Y signal, and the color difference signal or C signal is only subjected to delay compensation. When the input signal is an RGB signal, flare correction is applied to the G signal, and the R signal and the B signal are only subjected to delay compensation. Of course, flare correction may be applied to the color difference signal or C signal, R signal, and B signal.

  Further, the horizontal direction compression circuit 103, the vertical direction compression circuit 104, the vertical direction expansion circuit 107, and the horizontal direction expansion circuit 108 may not be in this order. The vertical direction compression circuit, the horizontal direction compression circuit, the horizontal direction expansion circuit, It may be in the order of the vertical extension circuit. Also, compression and expansion may be performed only in either the horizontal or vertical direction. Similarly, the horizontal LPF circuit 105 and the vertical LPF circuit 106 may not be in this order, and may be in the order of the vertical LPF circuit and the horizontal LPF circuit.

  As described above, the image size detection circuit 114 appropriately obtains the input image size for the input images of different sizes, and the horizontal direction compression circuit 103 and the vertical direction compression circuit 104 perform the post-compression according to the input image size. By compressing the image so that the image size becomes a predetermined fixed value, it is possible to prevent the flare correction width in the image displayed on the video display device from varying depending on the input image size.

It is a schematic diagram for demonstrating the image quality improvement method of this invention. It is the figure which showed the structure of the image quality improvement apparatus of this invention. It is the figure which showed the structure of the conventional image quality improvement apparatus. It is a schematic diagram for demonstrating the conventional image quality improvement method.

Explanation of symbols

101 A / D conversion circuit 102 Delay compensation circuit 103 Horizontal compression circuit 104 Vertical compression circuit 105 Horizontal low-pass filter (LPF) circuit 106 Vertical low-pass filter (LPF) circuit 107 Vertical expansion circuit 108 Horizontal expansion circuit 109 Subtraction Circuit 110 Gain adjustment circuit 111 Addition circuit 112 Scaling circuit 113 D / A conversion circuit 114 Image size detection circuit 115 A / D conversion circuit 116 Delay compensation circuit 117 Scaling circuit 118 D / A conversion circuit 31 Delay compensation circuit 32 Two-dimensional low-pass filter (LPF) circuit 33 delay compensation circuit 34 subtraction circuit 35 gain adjustment circuit 36 addition circuit

Claims (6)

Even if the size of the input image is different, it is an image quality improvement method in which the applied width of flare correction in the image after scaling to the display size of the video display device is the same,
A first step for determining the size of the input image;
A second step of determining a data compression rate according to the size of the input image so that the image after data compression has a predetermined size, and performing data compression of the input image based on the data compression rate;
A third step of performing a two-dimensional low-pass filter process for flare correction on the image compressed to the predetermined size;
A fourth step of performing data expansion to the size of the input image at a data expansion rate that is the reciprocal of the data compression rate for the two-dimensional low-pass filtered image;
A fifth step of performing flare correction of the input image based on the image subjected to the data decompression;
An image quality improvement method comprising a sixth step of scaling the flare-corrected image to a display size of the video display device.   The image quality improvement method according to claim 1, wherein in the first step, the size of the input image is obtained based on a dot clock of the input image and a horizontal synchronization signal and / or a vertical synchronization signal.   The image quality improvement method according to claim 1 or 2, wherein the data compression in the second step and the data expansion in the fourth step are performed in both a horizontal direction and a vertical direction of the input image. An image quality improvement device in which the width of flare correction in the image after scaling to the display size of the video display device is the same even if the size of the input image is different,
A first means for determining the size of the input image;
A second means for determining a data compression rate according to the size of the input image so that the image after data compression has a predetermined size, and compressing the data of the input image based on the data compression rate;
A third means for performing a two-dimensional low-pass filter process for flare correction on the image compressed to the predetermined size;
A fourth means for performing data decompression to the size of the input image at a data decompression rate that is a reciprocal of the data compression rate for the two-dimensional low-pass filtered image;
A fifth means for performing flare correction of the input image based on the image subjected to the data decompression;
An image quality improving apparatus comprising sixth means for scaling the flare corrected image to a display size of the video display apparatus.   The image quality improvement apparatus according to claim 4, wherein the first means obtains the size of the input image based on a dot clock of the input image and a horizontal synchronization signal and / or a vertical synchronization signal.   The image quality improvement apparatus according to claim 4 or 5, wherein the second means and the fourth means respectively perform the data compression and the data expansion in both a horizontal direction and a vertical direction of the input image.

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