Television – Image signal processing circuitry specific to television – Special effects
Reexamination Certificate
1998-07-29
2001-01-09
Hsia, Sherrie (Department: 2714)
Television
Image signal processing circuitry specific to television
Special effects
C348S587000, C348S591000, C348S593000
Reexamination Certificate
active
06172717
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image processing unit that applies an anti-aliasing processing to both an image signal and a key signal, when synthesizing a foreground image and a background image by using the key signal, and a method of the same.
2. Description of the Related Art
When one visual image (foreground image) is synthesized with another visual image (background image) in such a manner as the former hollows out the latter with an arbitrary shape, a key signal is used which represents a composite rate of a picture element of an image against a picture element of another image (hereafter, ‘picture element’ is abbreviated by ‘pixel’). Generally, the key signal is given a value such that a part to be erased as the background is made transparent and a part not to be erased is made opaque by extracting a blue-back (background color) from an input image, or the like.
When a synthesized image in which the foreground image is synthesized with the background image by using this key signal is presented on a raster scanning color display, for example, a stepped aliasing can obviously be observed by some chance especially on a slant line or a periphery of the image plane. This is a phenomenon called the aliasing error resulting from an insufficiency of the number of pixels, which will invite a deterioration of the quality of a synthesized image. Accordingly, the anti-aliasing processing is considered to be necessary which makes the edge parts of the aliasing obscure not to be obvious.
However, only executing a filter operation directly to the key signal for the sake of the anti-aliasing processing will spread the key values on the background area that should originally be made transparent, and there is a possibility that the background color can be observed while synthesizing video signals.
That is, when a simple three-tap filter operation
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is applied to an input key signal value Ki, for example, as shown in FIG.
13
(
a
) (drawn as i=0-9), the transparency is degraded as to the pixels of i=1, 8 to be originally the background area, as shown in FIG.
13
(
b
).
The anti-aliasing processing becomes necessary also to the foreground image signal to be synthesized. However, only applying a simple filter operation to the foreground image will mix the background color on the border area of the synthesized image, which should originally be removed by the key and should not be observed, which poses a problem.
That is, when a simple three-tap filter operation
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is applied to an input image signal value Pi, for example, as shown in FIG.
14
(
a
) (drawn as i=0-9), the foreground color is mixed in i=1, 8 to be originally the background area, and the background color is mixed in i=2, 7 to be the foreground color, as shown in FIG.
14
(
b
).
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing problems, and an object of the present invention is to provide an image processing unit that the application of the anti-aliasing processing to both an image signal and a key signal will not mix the foreground image with the background color thereof, and will not deteriorate the picture quality, and a method of the same.
In order to solve the foregoing problem, the image processing unit relating to the present invention synthesizes a foreground image and a background image using a key signal, and comprises: an image filter circuit that applies to the foreground image an anti-aliasing processing to make obscure an aliasing that displays a slant graphic border in a stepped indentation due to an insufficiency of the number of pixels; a key filter circuit that applies the anti-aliasing processing to the key signal; and a pixel detection circuit that detects a pixel having a possibility to generate a color mixture by an operation of the image filter circuit from the key signal and a size of the image filter circuit. In this construction, the image filter circuit applies an anti-aliasing processing using only the pixel that constitutes the foreground image and does not contain a background color to the pixel having a possibility to generate the color mixture that the pixel detection circuit detects.
Here, when the pixel detection circuit detects a border part between a foreground color and a background color of the foreground image from the key signal, the image filter circuit copies the foreground color of the foreground image onto a background color part as to the border part.
Further, when the pixel detection circuit detects an area where the key signal spreads to the background color of the foreground image from the size of the key filter circuit, the pixel detection circuit copies a border pixel of the nearest foreground onto the area.
The image processing method relating to the invention synthesizes a foreground image and a background image using a key signal, when applying to both the image signal and the key signal an anti-aliasing processing to make obscure an aliasing that displays a slant graphic border in a stepped indentation due to an insufficiency of the number of pixels. A pixel having a possibility to generate a color mixture is detected by an operation of the image filter from the size of the image filter that applies the anti-aliasing processing to the foreground image, and to the pixel is applied an anti-aliasing processing by the image filter, which uses only the pixel not containing a background color.
Here, a border part between a foreground color and a background color of the foreground image is detected from the key signal, and as to the border part, the foreground color of the foreground image is copied onto a background color part.
Further, an area in which the key signal spreads to the background color of the foreground image is detected from the size of a key filter circuit that applies the anti-aliasing processing to the key signal, and to the area is applied an anti-aliasing processing that copies a border pixel of the nearest foreground.
According to the invention, a pixel having a possibility to generate a color mixture by an operation of the image filter is detected from the size of the image filter, and as to the pixel, the image filter is switched so as to operate by using only the pixel not containing a background color.
Further, an area in which the key signal spreads to the background color is detected from the size of the key filter, and an anti-aliasing processing that copies a border pixel of the nearest foreground is executed to the area.
The image processing unit relating to the invention synthesizes a foreground image and a background image using a key signal, which comprises: an image filter circuit that applies to the foreground image an anti-aliasing processing to make obscure an aliasing that displays a slant graphic border in a stepped indentation due to an insufficiency of the number of pixels; a control circuit that, on the basis of an identification result of a foreground color/background color of pixels input to the image filter circuit, decides either select to instruct an operation system of the image filter circuit, or to copy the input pixels; and a key filter circuit that applies the anti-aliasing processing to the key signal. In this construction, when the control circuit detects a pixel having a possibility to generate a color mixture from the identification result of a foreground color/background color, the image filter circuit applies an anti-aliasing processing using only the pixel that constitutes the foreground image and does not contain a background color.
Here, when the control circuit detects a border part between a foreground color and a background color of the foreground image from the identification result of a foreground color/background color, as to the border part, the control circuit copies the foreground color of the foreground image onto a background color part.
Hsia Sherrie
Limbach & Limbach LLP
Sony Corporation
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