Television – Format conversion – Line doublers type
Reexamination Certificate
2001-12-19
2004-09-21
Hsia, Sherrie (Department: 2614)
Television
Format conversion
Line doublers type
Reexamination Certificate
active
06795123
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an interpolation apparatus that generates interpolation pixel values necessary for converting input video data of interlace scanning into video data of progressive scanning, and to a video signal processing apparatus including the interpolation apparatus. In particular, the present invention relates to improvements in interpolation processing.
(2) Related Art
Scan line conversion techniques for converting an input video signal of interlace scanning into a video signal of progressive scanning can be roughly categorized into two types: “inter-field interpolation” and “intra-field interpolation”. Inter-field interpolation generates an interpolation scan line using a video signal of a preceding field, whereas intra-field interpolation generates an interpolation scan line using a video signal within a present field. Intra-field interpolation is employed more frequently due to its simple interpolation processing.
An I/P conversion circuit, one example of which is shown in
FIG. 1
, is conventionally known as a technique to realize intra-field interpolation.
As the figure shows, the I/P conversion circuit
110
includes an input terminal
100
, a line memory
101
, a pixel difference detection circuit
102
, a correlation direction detection circuit
103
, an interpolation pixel generation circuit
104
, and a time axis conversion circuit
105
.
An interlaced video signal (X
1
) is inputted into the input terminal
100
. The input video signal (X
1
) is transmitted to the line memory
101
, the pixel difference detection circuit
102
, and the interpolation pixel generation circuit
104
.
The line memory
101
delays the video signal (X
1
) transmitted from the input terminal
100
for a time period corresponding to one scan line (1-line), and outputs the delayed video signal as a 1-line delay signal (X
2
), to the pixel difference detection circuit
102
and the time axis conversion circuit
105
.
The processing described above enables adjacent two lines within one field of the interlaced video signal to be inputted into the pixel difference detection circuit
102
.
The pixel difference detection circuit
102
selects, from pixels on the adjacent two lines, a plurality of pixel pairs each including two pixels that are respectively on the adjacent two lines and that are symmetric with respect to a position of a pixel that is going to be interpolated (hereafter, a “pixel that is going to be interpolated” is referred to as an “interpolation pixel”). The pixel difference detection circuit
102
calculates a difference in luminance between two pixels (hereafter referred to as a “luminance difference”) in each selected pixel pair. The pixel difference detection circuit
102
then outputs each calculated luminance difference as a pixel difference detection signal (X
3
) for the interpolation pixel.
The correlation direction detection circuit
103
selects a pixel pair with the smallest luminance difference, using the pixel difference detection signal outputted from the pixel difference detection circuit
102
. The correlation direction detection circuit
103
then detects a direction of a straight line that links the two pixels in the selected pair, and outputs a signal indicating the detected direction as a correlation direction signal (X
4
).
The interpolation pixel generation circuit
104
determines the two pixels that are respectively on the two lines and that are in the direction with the smallest luminance difference, using the video signal (X
1
), the 1-line delay signal (X
2
), and the correlation direction signal (X
4
). The interpolation pixel generation circuit
104
averages the luminance of the determined two pixels, and sets the averaged value as an interpolation value for the interpolation pixel.
The interpolation value being generated by averaging the luminance of the two pixels positioned in such a direction that has the smallest luminance difference is due to the following reason.
A sequence of pixels with similar luminance is most likely to extend in the direction of the straight line that links the two pixels with the smallest luminance difference. Being positioned on the straight line that links the two pixels, i.e., positioned on the sequence of the pixels with similar luminance, the interpolation pixel must have the highest correlation with the two pixels with the smallest luminance difference. Therefore, it is considered most appropriate to generate an interpolation value based on the luminance of these two pixels. The direction in which a pixel pair with the smallest luminance difference is positioned with respect to the interpolation pixel is hereafter referred to as the “correlation direction”.
The pixel difference detection circuit
102
, the correlation direction detection circuit
103
, and the interpolation pixel generation circuit
104
sequentially execute the above described processing on each pixel to be interpolated, and outputs an interpolation signal (X
5
) that indicates the generated interpolation values of the interpolation pixels.
The time axis conversion circuit
105
receives the 1-line delay signal (X
2
) and the interpolation signal (X
5
), and sequentially subjects the 1-line delay signal (X
2
) and the interpolation signal (X
5
) to the time compressed integration process, to output a progressive scanned video signal (X
6
).
The processing describe above enables the interpolation signal (X
5
) to be generated using the video signal (X
1
) and the 1-line delay signal (X
5
), and the interpolation line to be inserted at the interpolation line position.
With the interpolation described above, an interpolation pixel can be generated based on pixels positioned in such a direction that has the highest correlation with the interpolation pixel, thereby improving an image quality, compared with when an interpolation pixel is generated based on pixels that are not correlated with the interpolation pixel.
This interpolation, however, may be flawed because a direction with the smallest luminance difference is always set as the correlation direction. The problem may arise, for example, when the luminance of one pixel in the direction detected as the correlation direction with the smallest luminance difference is being influenced by noise. In this case, a completely wrong direction may be set as the correlation direction. If this happens, an interpolation pixel is generated based on pixels that are not correlated with the interpolation pixel, resulting in the interpolation contrarily deteriorating the image quality.
Further, in the case of a still image area, an interpolation line can be actually reconstructed using an input video signal of a field preceding the present field that includes interpolation pixels. Despite this fact, however, the above interpolation has conventionally been performed regardless of whether an interpolation pixel is in a still image area or in a moving image area with high motion. This creates unnecessary possibility of deteriorating the image quality due to the interpolation performed with being influenced by noise, even when an interpolation pixel is in a still image area.
SUMMARY OF THE INVENTION
In view of the above problem, a first object of the present invention is to provide an interpolation apparatus that can minimize image quality deterioration caused by noise influence on interpolation.
A second object of the present invention is to provide a video signal processing apparatus that can minimize image quality deterioration caused by noise influence on interpolation in a moving image area, and can nearly eliminate image quality deterioration caused by noise influence on interpolation in a still image area, by incorporating the interpolation apparatus therein.
The first object of the present invention can be achieved by an interpolation apparatus that generates interpolation pixel values necessary for converting input video data of interlace scanning into video data of progressive scanning, the interpolation apparatus including: a sele
Gotanda Chikara
Ishikawa Yuichi
Nakahigashi Hideto
Hsia Sherrie
Matsushita Electric - Industrial Co., Ltd.
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