Image decoder and image decoding method
AssigneeNEC Corporation
InventorToru Yamada
Life of this patent
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Abstract
The present invention performs an ordinary process for reducing resolution in a case where a DCT mode is a field DCT mode. On the other hand, in a case where the DCT made is a frame DCT mode, the present invention performs inverse discrete cosine transform by changing a basis function of discrete cosine transform to another basis function, so that image data whose data of each field is thinned out is output. Due to this process, thinning out in a vertical direction which would be performed after performing full scale IDCT becomes unnecessary. Therefore, according to the present invention, it is possible to prevent occurrence of distortion which might occur when decoding image data while reducing display resolution.
Claims14
An image decoder which applies a decoding process to image data comprising:
- means for applying a variable length decoding process to a first image data;
- means for applying an inverse quantizing process to said first image data;
- means for determining a mode of discrete cosine transform of said first image data;
- inverse discrete cosine transform means for obtaining a second image;
- and
- wherein said inverse discrete cosine transform means transform said first image data into said second image having a lower degree than said first image data when said mode is a field mode which performs said discrete cosine transform by each field, and transform said first image data into said second image with keeping field information when said mode is a frame mode which performs said discrete cosine transform by each frame.
An image decoding method for obtaining image data, comprising the following steps:
- applying a variable length decoding process to image data having first resolution;
- applying an inverse quantizing process to said image data;
- determining a mode of discrete cosine transform of said image data;
- obtaining image data having second resolution having an lower degree than said image data having first resolution when said mode is a field mode which performs said discrete cosine transform by each field;
- and obtaining image data having second resolution by applying inverse discrete cosine transform to said image data which has been subjected to said inverse quantizing process while keeping field information when said mode is a frame mode which performs said discrete cosine transform by each frame.
An image decoder which applies a decoding process to image data comprising:
- a first image data transformed into a second image data through a variable length decoding process, an inverse quantizing process, a discrete cosine transform mode selection process and an inverse discrete cosine transform process;
- and
- wherein said second image data transformed a lower resolution data than said first image data when a discrete cosine process is performed by each field and, said second image data having a same resolution with said first image data when said discrete cosine process is performed by each frame.
Dependencies are inferred from the claim text.