US 5,631,644 AGranted

Image encoding apparatus

AssigneeSharp Kabushiki Kaisha

InventorsHiroyuki Katata, Hiroshi Kusao, Yohichi Fujiwara

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Abstract

In an image encoding apparatus, image information is quantized and variable-length encoding is performed thereon so that the data are stored in a buffer. Thereafter, the data in the buffer are transmitted to the outside at a fixed data rate. At this time, a controller monitors a number of occupied bits in the buffer, and when the number of occupied bits is not more than predetermined thresholds, the controller switches the output of the apparatus to a dummy data generator. At this time, a parameter which is used for rate control is initialized, and dummy data which can be eliminated at a decoding circuit are outputted from the dummy data generator. Furthermore, bit allocation is changed so that a sum of the number of occupied bits and the bit allocation to a frame, which is determined before encoding, does not exceed a fixed amount. Moreover, when the number of occupied bits exceeds the fixed value, a quantization step size is changed to a greater value. This efficiently prevents underflow and overflow of the buffer, and the image information can be encoded with excellent quality.

Claims18

Dependent claims

An image encoding apparatus comprising:

quantizing means for quantizing an input image;
variable-length encoding means for performing variable-length encoding on the quantized result of said quantizing means;
temporary storage means for temporarily storing encoded data from said variable-length encoding means, the stored encoded data thereafter being transmitted at a fixed data rate;
encoded data amount control means for calculating a quantization step size of quantizing information to be encoded based upon the encoded result of said variable-length encoding means to control an amount of data encoded by said variable-length encoding means;
dummy data generating means for generating dummy data, eliminatable when decoding the encoded data;
switching means for switching an output of said image encoding apparatus between the encoded data from said temporary storage means and the dummy data from said dummy data generating means;
and
control means for monitoring a number of occupied bits of encoded data in said temporary storage means to control switching of said switching means such that the output of the image encoding apparatus is the encoded data from said temporary storage means when the number of occupied bits of encoded data exceeds a predetermined threshold, and such that transmission of encoded data from said temporary storage means is suspended and the output of the image encoding apparatus is the dummy data generated from said dummy data generating means when the number of occupied bits of encoded data is not more than the predetermined threshold, wherein said control means outputs a switching signal to said encoded data amount control means when the number of occupied bits of encoded data is not more than the predetermined threshold, and
said encoded data amount control means initializes parameters which are used for calculation of the quantization step size when the switching signal is output.

6 more elements

An image encoding apparatus, comprising:

quantizing means for quantizing information of an input image;
variable-length encoding means for performing variable-length encoding on the quantized result of said quantizing means;
temporary storage means for temporary storing encoded data from said variable-length encoding means, the stored encoded data thereafter being transmitted at a fixed data rate;
and
encoded data amount control means for calculating bit allocation per frame of image information to be encoded based upon the encoded result of said variable-length encoding means, and calculating a quantization step size from the calculated bit allocation, and adjusting the quantization step size of quantization in said quantizing means according to the calculated bit allocation to control an amount of the encoded data of said variable-length encoding means,
wherein said encoded data amount control means includes bit allocation changing means for monitoring a number of occupied bits of encoded data in the temporary storage means and for changing the calculated bit allocation when a sum of a bit allocation of a frame, which has been calculated before encoding, and a number of occupied bits of encoded data in said temporary storage means, at the time of the calculation of the bit allocation, exceeds a predetermined threshold, the bit allocation being changed such that the sum does not exceed the predetermined threshold.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/362,148Filed 22 Dec 1994
Priority: JP 5-32506322 Dec 1993
Granted: 20 May 1997
Term ends: Not estimatedThe source records don’t support an estimate.

Classification13 codes

H04N 19/152
Data rate or code amount at the encoder output: by measuring the fullness of the transmission buffer
H04N 19/115
Characterised by the element, parameter or selection affected or controlled by the adaptive coding: selection of the code volume for a coding unit…
H04N 19/126
Quantisation: details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
H04N 19/14
Incoming video signal characteristics or properties: coding unit complexity, e.g. amount of activity or edge presence estimation