Image data compression device and encoder
An image data compression device includes: a quantization section which quantizes image data based on a quantization parameter; a FIFO buffer section in which quantized data for at least N frames (N is an integer larger than one) is buffered; an encoded data generation section which reads the quantized data from the FIFO buffer section, and generates encoded data; a rate control section which changes a quantization step by using a data size of the encoded data; and a frame skip section which skips a quantization processing of the quantization section. The rate control section calculates the quantization parameter by using an average data size of the encoded data for previous N frames, and the frame skip section performs the skip processing when a frame in which the quantization parameter is greater than a threshold continues equal to or more than a number of times for a number threshold.
1. An image data compression device for compressing image data, the image data compression device comprising:
an image data processing section which includes a quantization section which quantizes image data by a quantization step which changes based on a quantization parameter;
a FIFO buffer section in which quantized data for at least N frames (N is an integer larger than one) quantized by the quantization section is buffered;
an encoded data generation section which reads the quantized data from the FIFO buffer section asynchronously from writing into the FIFO buffer section, and generates encoded data by encoding the quantized data;
a rate control section which calculates the quantization parameter by using a data size of the encoded data, and controls a data size of encoded data to be processed by changing the quantization step of the quantization section; and
a frame skip section which performs skip processing of causing the image data processing section to skip processing of image data in a frame processed by the image data processing section or image data in a frame subsequent to the processed frame,
wherein the rate control section calculates the quantization parameter by using an average data size obtained by averaging the data size of the encoded data for N frames before a frame of the image data quantized by the quantization section, and
wherein the frame skip section performs the skip processing when a frame in which the quantization parameter calculated for each frame is greater than a skip threshold continues a number of times equal to or greater than a number of times set as a skip continuous number threshold.
2. The image data compression device as defined in claim 1 ,
wherein the rate control section calculates the quantization parameter by using the average data size obtained by averaging a data size of the encoded data for N frames before the frame of the image data quantized by the quantization section so that the quantization parameter becomes equal to or less than an upper threshold of the quantization parameter.
3. The image data compression device as defined in claim 2 ,
wherein, when the quantized data read from the FIFO buffer section is data of an intra-frame-coded macroblock which is encoded within one frame, the rate control section calculates the data size of the encoded data obtained by encoding the quantized data as the average data size.
4. The image data compression device as defined in claim 2 ,
wherein the rate control section calculates the quantization parameter by using the average data size so that the quantization parameter becomes equal to or less than the upper threshold and becomes equal to or greater than a lower threshold of quantization parameter.
5. The image data compression device as defined in claim 2 ,
wherein the rate control section calculates the average data size after the quantization section has quantized image data for M frames (M≧N, M is an integer) by a predetermined quantization step.
6. The image data compression device as defined in claim 1 , comprising:
a quantization table which stores a quantization step value,
wherein the rate control section changes the quantization step by performing quantization by using a product of the quantization parameter and the quantization step value.
7. The image data compression device as defined in claim 1 , comprising a discrete cosine transform section which supplies the image data subjected to a discrete cosine transform to the quantization section in unit of a frame.
8. The image data compression device as defined in claim 1 , comprising:
a hardware processing section which processes image data of a moving image by hardware; and
a software processing section which generates encoded data by performing encode processing of quantized data read from the FIFO buffer section by software,
wherein the hardware processing section includes the image data processing section and the FIFO buffer section, and
wherein the software processing section includes the encoded data generation section, the rate control section, and the frame skip section.
9. The image data compression device as defined in claim 8 ,
wherein the hardware processing section outputs a difference between input image data in a current frame and previous image data in a frame one frame before the current frame as motion vector information, performs a discrete cosine transform of the motion vector information and outputs the transformed motion vector information to the quantization section as the image data, and generates the previous image data based on inverse-quantized data calculated by inverse-quantizing the quantized data by the quantization step.
10. The image data compression device as defined in claim 9 ,
wherein the software processing section encodes the quantized data read from the FIFO buffer section into a variable length code.
11. The image data compression device as defined in claim, 10
wherein the software processing section performs scan processing of rearranging the quantized data read from the FIFO buffer section, and encodes a result of the scan processing into a variable length code.
12. The image data compression device as defined in claim 11 ,
wherein the software processing section calculates a DC component and an AC component from the quantized data read from the FIFO buffer section, performs scan processing of rearranging the DC component and the AC component, and encodes a result of the scan processing into a variable length code.
13. An image data compression device for compressing image data, the image data compression device comprising:
an image data processing section which includes a quantization section which quantizes image data by a quantization step which changes based on a quantization parameter;
a FIFO buffer section in which quantized data for at least N frames (N is an integer larger than one) quantized by the quantization section is buffered;
an encoded data generation section which reads the quantized data from the FIFO buffer section asynchronously from writing into the FIFO buffer section, and generates encoded data by encoding the quantized data;
a rate control section which calculates the quantization parameter by using a data size of the encoded data, and controls a data size of encoded data to be processed by changing the quantization step of the quantization section; and
a frame skip section which performs skip processing of causing the image data processing section to skip processing of image data in a frame processed by the image data processing section or image data in a frame subsequent to the processed frame,
wherein the rate control section calculates the quantization parameter by using an average data size obtained by averaging the data size of the encoded data for N frames before a frame of the image data quantized by the quantization section, and
wherein the frame skip section performs the skip processing when complexity corresponding to a difference between image data quantized by the quantization section and image data in a frame before a frame of the quantized image data is equal to or greater than a complexity threshold.
14. The image data compression device as defined in claim 13 ,
wherein the rate control section calculates the quantization parameter by using the average data size obtained by averaging a data size of the encoded data for N frames before the frame of the image data quantized by the quantization section so that the quantization parameter becomes equal to or less than an upper threshold of the quantization parameter.
15. The image data compression device as defined in claim 14 ,
wherein, when the quantized data read from the FIFO buffer section is data of an intra-frame-coded macroblock which is encoded within one frame, the rate control section calculates the data size of the encoded data obtained by encoding the quantized data as the average data size.
16. The image data compression device as defined in claim 14 ,
wherein the rate control section calculates the quantization parameter by using the average data size so that the quantization parameter becomes equal to or less than the upper threshold and becomes equal to or greater than a lower threshold of quantization parameter.
17. The image data compression device as defined in claim 14 ,
wherein the rate control section calculates the average data size after the quantization section has quantized image data for M frames (M≧N, M is an integer) by a predetermined quantization step.
18. The image data compression device as defined in claim 13 , comprising:
a quantization table which stores a quantization step value,
wherein the rate control section changes the quantization step by performing quantization by using a product of the quantization parameter and the quantization step value.
19. The image data compression device as defined in claim 13 , comprising a discrete cosine transform section which supplies the image data subjected to a discrete cosine transform to the quantization section in unit of a frame.
20. The image data compression device as defined in claim 13 , comprising:
a hardware processing section which processes image data of a moving image by hardware; and
a software processing section which generates encoded data by performing encode processing of quantized data read from the FIFO buffer section by software,
wherein the hardware processing section includes the image data processing section and the FIFO buffer section, and
wherein the software processing section includes the encoded data generation section, the rate control section, and the frame skip section.
21. The image data compression device as defined in claim 20 ,
wherein the hardware processing section outputs a difference between input image data in a current frame and previous image data in a frame one frame before the current frame as motion vector information, performs a discrete cosine transform of the motion vector information and outputs the transformed motion vector information to the quantization section as the image data, and generates the previous image data based on inverse-quantized data calculated by inverse-quantizing the quantized data by the quantization step.
22. The image data compression device as defined in claim 21 ,
wherein the software processing section encodes the quantized data read from the FIFO buffer section into a variable length code.
23. The image data compression device as defined in claim 22 ,
wherein the software processing section performs scan processing of rearranging the quantized data read from the FIFO buffer section, and encodes a result of the scan processing into a variable length code.
24. The image data compression device as defined in claim 23 ,
wherein the software processing section calculates a DC component and an AC component from the quantized data read from the FIFO buffer section, performs scan processing of rearranging the DC component and the AC component, and encodes a result of the scan processing into a variable length code.
25. An encoder which performs compression processing of image data, the encoder comprising:
an image input interface which performs interface processing for inputting image data;
an image data processing section which includes a quantization section which quantizes the image data by a quantization step which changes based on a quantization parameter;
a FIFO buffer section in which quantized data for at least N frames (N is an integer larger than one) quantized by the quantization section is buffered;
a host interface which performs interface processing with a host which reads quantized data stored in the FIFO buffer section asynchronously from writing into the FIFO buffer section; and
a software start flag register for allowing the host to start the compression processing,
wherein the host calculates the quantization parameter by using an average data size obtained by averaging a data size of encoded data for N frames before a frame of the image data quantized by the quantization section, and sets the software start flag register on condition that a frame in which the quantization parameter is greater than a skip threshold does not continue a number of times equal to or greater than a number of times set as a skip continuous number threshold, and
wherein the image data processing section starts the compression processing when the software start flag register has been set.
26. An encoder which performs compression processing of image data, the encoder comprising:
an image input interface which performs interface processing for inputting image data;
an image data processing section which includes a quantization section which quantizes the image data by a quantization step which changes based on a quantization parameter;
a FIFO buffer section in which quantized data for at least N frames (N is an integer larger than one) quantized by the quantization section is buffered;
a host interface which performs interface processing with a host which reads quantized data stored in the FIFO buffer section asynchronously from writing into the FIFO buffer section; and
a software start flag register for allowing the host to start the compression processing,
wherein the host calculates the quantization parameter by using an average data size obtained by averaging a data size of encoded data for N frames before a frame of the image data quantized by the quantization section, and sets the software start flag register on condition that difference information between image data quantized by the quantization section and image data in a frame before a frame of the quantized image data is less than a complexity threshold, and
wherein the image data processing section starts the compression processing when the software start flag register has been set.