Image analysis – Image compression or coding
Reexamination Certificate
1998-06-05
2001-07-24
Chang, Jon (Department: 2623)
Image analysis
Image compression or coding
C348S441000, C382S304000
Reexamination Certificate
active
06266446
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to converting a format of image data, for example from block data to raster data. In particular, this invention is related to converting an order of pixel data supplied in a predetermined format.
2. Description of the Related Art
A conventional compression method that utilizes a Discrete Cosine Transform (DCT), such as JPEG, has been used for compressing and decompressing digital image data. In compression, it is usually necessary to convert raster form image data into block form image data. In decompression, it is usually necessary to convert block form image data into raster form image data.
FIG. 7
explains the operation of such a conventional compression/decompression method. In
FIG. 7
, image capturing of extracting part
601
comprises optical lenses, image pick-up elements, signal processing circuits and so on. DRAM
602
stores image data. The image data stored in DRAM
602
is used by image display part
603
, such as CRT and LCD, for displaying an image. Therefore, the image data is stored in a raster display form for image display part
603
. Buffer memory
604
is used for converting raster form image data into block form image data or for converting block form image data into raster form image data. Compressor/decompressor
605
performs compression/decompression using a method such as DCT. The image data compressed by compressor/decompressor
605
is stored in storage medium
606
.
When image data stored in storage medium
606
is decompressed, the compressed image data is read out from storage medium
606
, supplied to compressor/decompressor
605
, and expanded. The decompressed image data is output to and written into buffer memory
604
.
Consider a case where a number of pixels in a horizontal direction of uncompressed image data (i.e., original image data) is H. It is necessary for buffer memory
604
to have a holding capacity for data for at least 8×H pixels, assuming that the block form data has 8 rows. During decompression, the image data is written into buffer memory
604
from compressor/decompressor
605
in units of blocks. When the image data is read out of buffer memory
604
and supplied to DRAM
602
, the block form image data is converted to raster form image data. As a result, the decompressed image data shown in
FIG. 8
is written into DRAM
602
and an image is displayed on image display part
603
, as shown in FIG.
8
.
On the other hand, when image data from image capturing part
601
is compressed, the image data is written in DRAM
602
in raster form. The image data in DRAM
602
is divided into groups of 8 rows by H pixels of image data and transferred to buffer memory
604
. Thus, 8×H pixels of image data are written into buffer memory
604
.
Compressor/decompressor
605
reads out the image data from buffer memory
604
in units of, for example, 8×8 pixel blocks and compresses them. In this way, the image data compressed by compressor/decompressor
605
is stored in storage medium
606
.
However, according to the above conventional method, the maximum value for it is given by the following equation:
H
=
the
capacity
of
buffer
memory
604
8
(
rows
)
×
m
(
bits
)
Here, m is the number of bits which represents one pixel.
Therefore, a maximum horizontal size of an image that can be processed by compressor/decompressor
605
depends on the capacity of buffer memory
604
.
SUMMARY OF THE INVENTION
An object of the invention is to address the above-mentioned shortcomings. In particular, an object of the invention is to convert raster image data into block image data or to convert block image data into raster image data using a buffer memory having a capacity which is smaller than image data for 8×H pixels, where 8 is a number of rows for blocks processed by a compression/decompression method and H is a number of pixels in a horizontal direction of an uncompressed image.
In one aspect, the present invention is an image processing apparatus which converts image data between a raster form and a block form. The apparatus comprises obtaining means for obtaining a number of pixels of given image data in a raster direction, dividing means for dividing the image data into plural process units in accordance with the number of pixels and in accordance with a capacity of a memory to which the image data is written temporarily, and transferring means for transferring the image data written in the memory to a different device in units of the process units.
Preferably, the capacity of said memory is smaller than a predetermined amount of image data determined based on the number obtained by said obtaining means.
The amount of image data is determined based on a size of a block used for compressing the image data.
The memory stores the image data of a plurality of rows.
In another aspect, the present invention is an image processing apparatus which converts block form image data into raster form image data by using buffer memory. The apparatus comprises obtaining means for obtaining a number of pixels of given image data in a raster direction, the given image data representing an original image, calculating means for calculating an amount of image data which is temporarily stored in said buffer memory by comparing an amount of image data based on the number of pixels and a capacity of said buffer memory, storage control means for dividing the image data based on the amount calculated by said calculating means and storing the divided image data into said buffer memory, and converting means for generating raster form image data by connecting the divided image data read out from said buffer memory based on the number of pixels of the divided image data in the horizontal direction and the number of pixels of the original image in the raster direction.
Preferably, the apparatus further comprises image memory for storing the converted image data, first memory means for storing the number of pixels of the original image in the raster direction, second memory means for storing a number of pixels of the divided image data in the horizontal direction, counting means for counting a number of pixels read out from said buffer memory, and control means for storing the image data of next rows read out from said buffer memory into said image memory by using the number stored in said first memory means as an offset address of said image memory when the counted pixel number coincides with the number stored in said second memory means.
This summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the followed detailed description of the preferred embodiments thereof in connection with the attached Figures.
REFERENCES:
patent: 3810174 (1974-05-01), Heard et al.
patent: 4386367 (1983-05-01), Peterson et al.
patent: 5339108 (1994-08-01), Coleman et al.
patent: 5359694 (1994-10-01), Concordel
patent: 5446560 (1995-08-01), Schwartz
patent: 5694489 (1997-12-01), Kishi
Canon Kabushiki Kaisha
Chang Jon
Fitzpatrick ,Cella, Harper & Scinto
Johnson Timothy M.
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