Image analysis – Image compression or coding – Predictive coding
Reexamination Certificate
2000-06-20
2003-09-02
Couso, Jose L. (Department: 2721)
Image analysis
Image compression or coding
Predictive coding
Reexamination Certificate
active
06614937
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image processing circuit. More specifically, the invention relates to a circuit for a quick compression processing of two-dimensional image data.
2. Description of Related Art
The two adjacent pixels in an image frame are strongly correlated with each other. When a large amount of image data produced by a scanner is transferred to a PC, the data processing of scanner is faster than the interface to the PC can handle; thus, the scanner has to stop scanning. To address this problem, a built-in compression technique for image data is necessary to reduce the amount of data and thereby increase the speed of scanning. Further, current scanner development is tending to low-cost and high-resolution. Using the Joint Photographic Experts Group (JPEG) compression technique requires a lot of memory and computation power in the scanner; thus, this technique is configured only in high-end scanners. Currently, the compression technique in low-end scanners will scan and compress the image data line by line. Using this technique does not require a lot of memory but has a low compression ratio. Hence, the scanning speed is not improved by this technique.
SUMMARY OF THE INVENTION
Accordingly, to solve the problem mentioned above, it is an object of the present invention to provide a simple configuration for quick compression of two-dimensional data. This configuration offers quick processing of two-dimensional image data from scanning.
It is another object of the present invention to provide a simple configuration for quick compression of two-dimensional data with a higher compression ratio as compared with the prior art.
The present invention achieves these objects based on the fact that there is a high correlation between the upper pixel and left pixel of a pixel to be predicted on a frame. According to this fact, a computation unit for receiving a pixel currently being scanned, a pixel from a line buffer, and a pixel from the register and divided-by-2 device performs a simple prediction computation using these received pixel data, hence obtaining a difference value between the pixels. Typically, the small difference value between the pixels represents the high correlation between the pixels. Therefore, the coding on a frame can be simplified when the correlation between the pixels is high. By utilizing the simple prediction computation and the conventional encoding process, not only the compression ratio is increased, but the compression processing time can also be reduced.
Based on the high correlation between the upper and left pixel of the pixel to be predicted on a frame, a scan line memory is used to store the values of previous scan line for computing the pixel difference. The three color components R, G, B used to form an image respectively require a scan line memory for storing the previous scan line values. A register is used to store the value of the left pixel of the pixel to be predicted on a frame. Therefore, the difference between the pixel to be predicted and the average of the upper pixel stored in the scan line memory and the left pixel stored in the register determines the correlation level. For example, a high correlation has a smaller difference.
When scanning image data, the value of the three color. components R, G, B will be read in at the same time. Because the correlation between the adjacent pixels of the image data is very high due to the similar color, the invention predicts a pixel value using two pixels located on upper and left of the pixel to be predicted. The more exact the prediction, the closer to zero the value of the pixel. For example, referring to
FIG. 1
, the pixels on a frame are illustrated. Assume that a
n,n
is a pixel to be predicted, and the equations are as follows:
a
n,n
=(
a
n−1,n
/2)+(
a
n,n−1
/2)+&Dgr;
a
n,n
(1)
&Dgr;
a
n,n
=a
n,n
−(
a
n−1,n
/2)−(
a
n,n−1
/2) (2)
Hence, the smaller the value &Dgr;a
n,n
, the higher compression ratio obtained by using a variable-length code.
In addition, the memory used for the line and image buffer, a computation device is used for computating the equation (2) mentioned above. The computation device comprises two divided-by-2 devices, a data read latch, a register and a three input computation unit. The divided-by-2 devices are used to output half the value of the input, i.e., the input value is divided by 2. The data read latch reads out the data positioned above the pixel to be predicted in the previous scan line from the memory line buffer. The register temporarily stores the value a
n,n
for the next process. The three input computation unit performs one addition and two subtractions as described in equation (2). As a result, the output value from the three input computation unit is the desired value &Dgr;a
n,n
. In the value &Dgr;a
n,n
, because a large amount of data are ignored and only the required information is kept for the image recovery, the image encoding process is quicker and the compression ratio is increased.
The present invention also provides a circuit for the quick compression processing of two-dimensional image data comprising: a memory; an address select device; a computation unit; a data write select device; and a control logic unit.
The memory includes a line buffer and an image buffer to store the pixels of a scan line and an image, respectively.
The address select device selects the address from the line buffer or image buffer for the computation. The computation unit calculates the difference between the scanned pixel and its adjacent pixel, based on the previously scanned pixel stored in the line buffer by the data write select device and the currently scanned pixel.
After the computation, the result is stored in an image buffer address which is selected by the address select device.
The control logic unit controls the access of the memory.
Accordingly, the circuit as mentioned above can perform the function of equations (1) and (2), thereby achieving the object of the present invention of quickly processing and efficiently compressing image data.
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Couso Jose L.
Ladas & Parry
Winbond Electronics Corp.
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