Signal processing device and moving image capturing device

1. A signal processing device for compressing image data of a plurality of frames to generate a stream, comprising:

an encoder configured to encode input image data;

an image processor configured to obtain spatial frequency information of an image within one frame of the image data and to obtain image movement information indicating an amount of a movement of a same image between two frames;

an encoding determination unit configured to compare the image movement information with an encoding determination threshold, thereby determining whether or not encoding is to be performed, wherein the encoding determination unit determines whether or not encoding is to be performed, after temporarily changing the encoding determination threshold so as to cause a frame skipping control if encoding is not to be performed to be less strict when the spatial frequency information of an image within one frame indicates a high spatial frequency, or without changing the encoding determination threshold when the spatial frequency information of an image within one frame indicates a low spatial frequency;

a frame skipping controller configured to perform a frame skipping control when the encoding determination unit determines that encoding is not to be performed; and

a threshold correction unit configured to correct the encoding determination threshold of the encoding determination unit,

wherein the encoder selectively performs the encoding in accordance with a result of determination obtained by the encoding determination unit, and the threshold correction unit corrects the encoding determination threshold of the encoding determination unit based on the number of bits allocated for encoding and a quantization parameter value in a frame encoded by the encoder, or a motion vector value or the number of intra-macroblocks in a frame encoded by the encoder.

2. The signal processing device of claim 1 , further comprising:

a pixel movement calculation unit,

wherein the image movement information used in the encoding determination unit is pixel movement information obtained by a representative point matching scheme performed by the pixel movement calculation unit.

3. The signal processing device of claim 1 , further comprising:

a lens controller,

wherein the image movement information used in the encoding determination unit is angular velocity sensor information obtained from the lens controller.

4. The signal processing device of claim 1 , further comprising:

at least one of a pixel movement calculation unit and a lens controller,

wherein the image movement information is a combination of at least one of pixel movement information obtained by a representative point matching scheme performed by the pixel movement calculation unit and angular velocity sensor information obtained from the lens controller, and the spatial frequency information obtained from the image processor.

5. The signal processing device of claim 1 , wherein

the encoding determination unit has a still image threshold as the encoding determination threshold, and determines that encoding is not to be performed on a frame which is lower than the still image threshold.

6. The signal processing device of claim 1 , wherein

the encoding determination unit has a moving image threshold as the encoding determination threshold, and determines that encoding is not to be performed on a frame which is higher than the moving image threshold.

7. The signal processing device of claim 1 , wherein

the encoding determination unit has a still image threshold and a moving image threshold as the encoding determination threshold, and determines that encoding is not to be performed on a frame which is lower than the still image threshold and a frame which is higher than the moving image threshold.

8. The signal processing device of claim 1 , wherein

when the encoding determination unit determines that encoding is not to be performed, the encoder does not perform encoding, and the frame skipping controller inserts a dummy frame including only skipped macroblocks.

9. The signal processing device of claim 1 , wherein

the encoding determination unit performed an encoding determination process based on a picture type of the stream at a time of encoding determination.

10. The signal processing device of claim 1 , wherein

the encoding determination threshold used in the encoding determination unit is changed based on a bit rate, a frame rate, or an image resolution of the stream to be generated.

11. The signal processing device of claim 1 , wherein

when the encoding determination unit determines that a motion is small or that a motion is large, frame skipping is performed at predetermined intervals for a first frame for which the determination is performed and a plurality of frames succeeding the first frame.

12. The signal processing device of claim 1 , wherein

the encoding determination unit has a plurality of encoding determination thresholds so that the number of frames which are to be continuously skipped is changed.

13. The signal processing device of claim 1 , wherein

the encoding determination unit determines whether or not encoding is to be performed, by using, instead of the image movement information, any of the number of intra-macroblocks in a frame obtained from the encoder, the motion vector value in a frame obtained from the encoder, and the number of bits allocated for encoding and a quantization parameter value obtained from the encoder.