Rate control system
In a rate control system, an MMU temporarily stores in a mass storage an input bit stream including compressed and encoded data which is compressed and encoded according to the JPEG2000 standard. The MMU then reads out data from the mass storage and outputs it to a multiplexer according to readout control signals. The multiplexer multiplexes the data and outputs the result as an output bit stream. A bit truncation controller comprises an image quality controller for selecting a target to be coded according to target image quality; and a rate controller for controlling a rate according to a target rate. A layer splitting controller outputs to the MMU the readout control signal for generating an output bit stream which is divided into a plurality of layers.
1. A rate control system including a processor for controlling a rate of compressed image data, comprising:
an image quality controller configured to, in compressed image data compressed by recursively dividing an image signal into high- and low-pass components using a wavelet transform to calculate transform coefficients in a plurality of bandpass components and entropy coding said transform coefficients, bit shift each of said plurality of bandpass components by a number of bits corresponding to a priority set based on a norm of 2-D synthesis filter coefficients of a predetermined bandpass component among said plurality of bandpass components and according to a number of recursive divisions, and select a target scanning area to be coded, based on a target image quality parameter, from said plurality of bandpass components that have been bit shifted, prior to generating a coded bit stream using the transform coefficients.
2. The rate control system according to claim 1 , wherein said image quality controller is configured to use said priority to which weighting in consideration of human visual characteristics is applied.
3. The rate control system according to claim 1 , wherein
said image quality controller is configured to determine said target scanning area to be coded on a bit-plane-by-bit-plane basis.
4. The rate control system according to claim 1 , wherein said image quality controller is configured to determine said target scanning area to be coded on a coding-pass-by-coding-pass basis.
5. The rate control system according to claim 1 , further comprising:
a layer splitting controller configured to bit shift each of said plurality of bandpass components in said compressed image data by the number of bits corresponding to the priority set according to the number of recursive divisions into said low-pass components, and to divide said plurality of bandpass components that have been bit shifted into a plurality of layers.
6. The rate control system according to claim 5 , wherein said layer splitting controller is configured to use said priority to which weighting in consideration of human visual characteristics is applied.
7. A rate control system including a processor for controlling a rate of compressed image data, comprising:
a rate controller configured to, in compressed image data compressed by recursively dividing an image signal into high- and low-pass components using a wavelet transform to generate transform coefficients in the plurality of bandpass components and entropy coding said transform coefficients, (1) bit shift each of said plurality of bandpass components by a number of bits corresponding to a priority set based on a norm of 2-D synthesis filter coefficients of a predetermined bandpass component among said plurality of bandpass components and according to a number of recursive divisions into said low-pass components; and (2) calculate a truncation point appropriate to a target rate from a code sequence generated by sorting coded data of said plurality of bandpass components that have been bit shifted, in a predetermined order of scanning, so that a part of said code sequence before said truncation point is outputted.
8. The rate control system according to claim 7 , wherein said rate controller is configured to generate said code sequence by sorting said coded data in descending order of said priority and, if said priority is the same, then in said predetermined order of scanning, sorting from high pass to low pass.
9. The rate control system according to claim 7 , further comprising:
a layer splitting controller configured to bit shift each of said plurality of bandpass components in said compressed image data by the number of bits corresponding to the priority set according to the number of recursive divisions into said low-pass components, and to divide said plurality of bandpass components that have been bit shifted into a plurality of layers.
10. The rate control system according to claim 9 , wherein said layer splitting controller is configured to use said priority to which weighting in consideration of human visual characteristics is applied.
11. A computer readable medium storing a program for controlling a rate of compressed image data, said program, when executed on a microprocessor, causes the microprocessor to perform the steps of:
in compressed image data compressed by recursively dividing an image signal into high- and low-pass components using a wavelet transform to generate transform coefficients in a plurality of bandpass components and entropy coding said transform coefficients, bit shifting each of said plurality of bandpass components by a number of bits corresponding to a priority set based on a norm of 2-D synthesis filter coefficients of a predetermined bandpass component among said plurality of bandpass components and according to a number of recursive divisions into said low-pass components; and
selecting a target scanning area to be coded based on a target image quality parameter, from said plurality of bandpass components that have been bit shifted.
12. The computer readable medium according to claim 11 , wherein the program causes said microprocessor to perform the step of using said priority to which weighting in consideration of human visual characteristics is applied.
13. The computer readable medium according to claim 11 , wherein the program causes said microprocessor to perform the step of determining said target to be coded on a bit-plane-by-bit-plane basis.
14. The computer readable medium according to claim 11 , wherein the program causes said microprocessor to perform the step of determining said target to be coded on a coding-pass-by-coding-pass basis.
15. The computer readable medium according to claim 11 , wherein the program causes said microprocessor to perform the step of:
bit shifting each of said plurality of bandpass components in said compressed image data by the number of bits corresponding to the priority set according to the number of recursive divisions into said low-pass components; and
dividing said plurality of bandpass components that have been bit shifted into a plurality of layers.
16. The computer readable medium according to claim 15 , wherein the program causes said microprocessor to perform the step of using said priority to which weighting in consideration of human visual characteristics is applied.
17. A computer readable medium storing a program for controlling a rate of compressed image data, said program, when executed on a microprocessor causes the microprocessor to perform the steps of:
in compressed image data of the target to be coded, determined in the selecting step, compressed by recursively dividing an image signal into high- and low-pass components using a wavelet transform to generate transform coefficients in the plurality of bandpass components and entropy coding said transform coefficients, bit shifting each of said plurality of bandpass components by a number of bits corresponding to a priority set based on a norm of 2-D synthesis filter coefficients of a predetermined bandpass component among said plurality of bandpass components and according to a number of recursive divisions into said low-pass components; and
calculating a truncation point appropriate to a target rate from a code sequence generated by sorting coded data of said plurality of bandpass components that have been bit shifted, in a predetermined order of scanning, so that a part of said code sequence before said truncation point is outputted.
18. The computer readable medium according to claim 17 , wherein the program causes said microprocessor to perform the step of generating said code sequence by sorting said coded data in descending order of said priority and, if said priority is the same, then in said predetermined order of scanning from high pass to low pass.
19. The computer readable medium according to claim 17 , wherein the program causes said microprocessor to perform the steps of:
bit shifting each of said plurality of bandpass components in said compressed image data by the number of bits corresponding to the priority set according to the number of recursive divisions into said low-pass components; and
dividing said plurality of bandpass components that have been bit shifted into a plurality of layers.
20. The computer readable medium according to claim 19 , wherein the program causes said microprocessor to perform the step of using said priority to which weighting in consideration of human visual characteristics is applied.