Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1992-05-13
1993-08-31
Britton, Howard W.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358133, H04N 7133
Patent
active
052413837
ABSTRACT:
A method for coding frames of video wherein a coding circuit (14,16,18) includes a processor (30) for performing an orthogonal transform such as a discrete
cosine transform and a quantizer (32) for quantizing the resulting transform coefficients. The coding circuit codes the video frames using intra-frame, predictive or interpolative coding to generate code bits at a variable rate. The code bits are stored at a variable rate in a rate buffer (22), which transmits the code bits into a communication channel (24) at a pseudo-constant rate, i.e. a rate which is constant in every time interval of one frame. To maintain the contents of the rate buffer (22) within predetermined limits, the quantization parameters utilized by the quantizer (32) are periodically adjusted to increase or decrease the amount of code bits generated by the coding circuit. The quantization parameters are changed on a global SGOP level to avoid changes of quantization parameters and corresponding changes in decoded image quality within particular frames. The change in quantization parameters for coding the next SGOP is determined by a deviation measure between the actual number of code bits generated by the coding circuit (14,16,18) for the previous SGOP and an estimate of the number of code bits for the previous SGOP. The estimated number of code bits is determined based on the contents of the rate buffer (22) such that the rate buffer (22) will be emptied in a predetermined time period.
REFERENCES:
patent: 5038209 (1991-08-01), Hang
patent: 5134476 (1992-07-01), Aravind
patent: 5144425 (1992-09-01), Joseph
"Description of Reference Model 8 (RM8)," CCITT SGXV, Doc. 525, Working Party XV/4 Specialists Group on Coding for Visual Telephony, Jun. 1989.
"MPEG Video Simulation Model 3," ISO/MPEG, Doc. 90/041, International Organization For Standardization, Jul. 1990.
"Scene Adaptive Coder," W-H Chen et al., IEEE Trans. Comm., vol. Com-32, No. 3, pp. 225-232, Mar. 1984.
Chen Cheng-Tie
Wong Andria H.
Bell Communications Research Inc.
Britton Howard W.
Falk James W.
Suchyta Leonard Charles
Tung Bryan S.
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