Image analysis – Image compression or coding – Transform coding
Reexamination Certificate
1999-03-02
2001-10-02
Boudreau, Leo (Department: 2621)
Image analysis
Image compression or coding
Transform coding
C358S438000, C375S240240
Reexamination Certificate
active
06298168
ABSTRACT:
This application is based on applications Nos. 10-50453 and 10-50438/1998 filed in Japan, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image coding apparatus for compressing multi-level image data.
2. Description of Prior Art
A block truncation coding is used in the field of compression of the multi-level image data. In the block truncation coding, an image is divided into a plurality of pixel blocks. For each block, a quantity on an average value of the multi-level image data and a quantity on gradation level distribution thereof are calculated, and a pixel data is quantized in accordance with the quantities to determine code data of a smaller number of gradation levels. Then, the quantities on the average value and the gradation level distribution and the code data of each pixel are used as encoded data of the block.
However, when the pixel data is divided into a plurality of pixel blocks and compressed block by block, a great difference between the decoded image data arises at boundaries between the blocks, or a so-called block noise is produced to deteriorate image quality. It is therefore desirable that the block noise is reduced.
For the block truncation coding on image data comprising a plurality of colors for each color plane, it is proposed to shift coding blocks of the plurality of colors. However, this makes the circuit structure complicated because the adjustment is carried out based on correlation in each color.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image coding apparatus which reduces block noises at the boundaries between the blocks in the block truncation coding of the multi-level image data, so as to reproduce an image of good quality on decoding.
In one aspect of the present invention, in an image coding apparatus which encodes multi-level image data on image density at pixels, a block extractor extracts a first block and a second block based on image data, the first block comprising a plurality of pixels to be encoded, the second block including the plurality of pixels in the first blocks. A calculator which calculates feature quantities based on image data of all the pixels included in the second block extracted by said block extractor. An encoder which encodes image data of the pixels in the first block according to correlation of the image data in the first block with the feature quantities calculated on the second block by said calculator.
In a different aspect of the invention, the block extractor extracts the first blocks over an entire image area by shifting the first block sequentially in the entire image area. When one of the second blocks includes pixels not existing in the image area, it adds image data derived from image data of pixels existing in the image area to the pixels not existing in the image area.
An advantage of the present invention is that block noises are reduced.
Another advantage of the present invention is that in the block truncation coding, deterioration of the image quality of the decoded image can be reduced at an end of the image.
REFERENCES:
patent: 4319267 (1982-03-01), Mitsuya et al.
patent: 5060285 (1991-10-01), Dixit et al.
patent: 5576845 (1996-11-01), Komatsu
patent: 5805303 (1998-09-01), Imaizumi et al.
patent: 5828467 (1998-10-01), Suzuki
patent: 5987175 (1999-11-01), Imaizumi et al.
patent: 6026194 (2000-02-01), Torikai et al.
patent: 6195128 (2001-02-01), Streater
patent: 253745 (1996-06-01), None
Imaizumi Shoji
Morita Ken-ichi
Nishigaki Junji
Boudreau Leo
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
Sherali Ishrat
LandOfFree
Image coding apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image coding apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image coding apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2570938