Image analysis – Image compression or coding – Predictive coding
Reexamination Certificate
2000-09-21
2001-10-30
Couso, Jose L. (Department: 2624)
Image analysis
Image compression or coding
Predictive coding
C382S232000, C382S239000
Reexamination Certificate
active
06310980
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an encoding apparatus and method of efficiently encoding an image and a storage medium storing the method.
2. Related Background Art
Predictive encoding is available as one conventional encoding scheme used in an encoding apparatus. In the predictive encoding, when the value of a pixel to be encoded (target pixel) is encoded, a predictive value is generated on the basis of the values of pixels around the target pixel, and the difference (prediction error) between the value of the target pixel and the prediction value is entropy-encoded.
In improved predictive encoding, a plurality of so-called prediction schemes of generating a prediction value from neighboring pixels are prepared, and these prediction schemes are adaptively used to generate an optimal prediction value, thereby entropy-encoding the difference between the prediction value and the value of the target pixel.
In the above conventional predictive encoding scheme of generating the prediction value on the basis of a plurality of neighboring pixels, no technique has been available to suppress the amount of encoded data generated by this encoding to an amount near to a predetermined amount. Furthermore, there has been room for development of an effective technique of minimizing any deterioration in the quality of the image represented by the above encoded data.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above problems, and has as its object to provide an encoding technique of controlling the amount of encoded data to an amount as near to a predetermined amount as possible in an apparatus for entropy-encoding the difference (prediction error) between a prediction value and a target pixel. It is another object of the present invention to minimize any deterioration in image quality while limiting the amount of encoded data to a predetermined data amount.
In order to achieve the above objects, according to a preferred embodiment of the present invention, there is provided an encoding apparatus for encoding a target pixel, comprising prediction means for generating a prediction value by predicting a target pixel value representing the target pixel on the basis of pixels around the target pixel, difference generation means for generating a difference between the prediction value generated by the prediction means and the target pixel value, quantization means for generating a quantized value by quantizing the difference generated by the difference generation means, entropy encoding means for generating encoded data by entropy-encoding the quantized value generated by the quantization means, and quantization control means for selecting a quantization method for the quantization means in accordance with a code amount of the encoded data generated by the entropy encoding means.
It is still another object of the present invention to limit the deterioration in image quality to a predetermined degree in units of target pixels.
In order to achieve the above objects, according to another preferred embodiment of the present invention, there is provided an encoding apparatus for encoding a target pixel, comprising prediction means for generating a prediction value by predicting a target pixel value representing the target pixel on the basis of pixels around the target pixel, difference generation means for generating a difference between the prediction value generated by the prediction means and the target pixel value, quantization means for generating a quantized value by quantizing the difference generated by the difference generation means, entropy encoding means for generating encoded data by entropy-encoding the quantized value generated by the quantization means, and quantization control means for selecting one of k quantization methods which is to be used for the quantization means in accordance with a code amount of the encoded data generated by the entropy encoding means, wherein each of the k quantization methods is a method of performing quantization such that an error between the difference generated by the difference generation means and a quantized value obtained by quantizing the difference using the quantization means falls within a range of −N
m
to +N
m
(m=1 to k).
The above and other objects, features, and advantages of the present invention will be apparent from the following detailed description in conjunction with the accompanying drawings and the appended claims.
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Canon Kabushiki Kaisha
Couso Jose L.
Do Anh Hong
Fitzpatrick ,Cella, Harper & Scinto
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