Video camera with rate control video compression
Embodiments provide a video camera that can be configured to compress video data in a manner that achieves a targeted output size in a computationally efficient manner. The video compression systems and methods can be used with DCT-based compression standards to include a rate control aspect. The rate controlled video compression methods can be configured to compress video data in real time and/or using a single pass. During compression of video data, the video compression systems and methods can modify compression parameters to achieve a targeted file size while maintaining relatively high visual quality of the compressed images.
1. An electronic device configured to compress a plurality of video image frames, the electronic device comprising:
a housing;
an image sensor within the housing and configured to convert light incident on the image sensor into video data, the video data having a frame rate and comprising a plurality of video frames including a first video frame and a second video frame, the first video frame comprising a two-dimensional array of pixel values; and
one or more hardware processors programmed to:
compress a first section of the first video frame using a discrete cosine transformation and a quantization table to thereby obtain a compressed first section, the first section comprising a first plurality of slices,
modify the quantization table based at least on a comparison of a size of the compressed first section and a first threshold to thereby obtain a modified quantization table,
compress a second section of the first video frame using the discrete cosine transformation and the modified quantization table to thereby obtain a compressed second section, the second section comprising a second plurality of slices and being different from the first section, and
store the compressed first section and the compressed second section to a memory device.
2. The electronic device of claim 1 , wherein the one or more hardware processors is programmed to compress the first section by compressing each slice of the first plurality of slices using the discrete cosine transformation and the quantization table to thereby obtain a plurality of compressed slices, the plurality of compressed slices together forming the compressed first section.
3. The electronic device of claim 2 , wherein each slice of the first plurality of slices is divided into macroblocks, the macroblocks each comprising a different 16×16 array of pixel values of the first video frame.
4. The electronic device of claim 1 , wherein the one or more hardware processors is programmed to:
adjust the quantization table based at least on a comparison of (i) a size of the compressed first section and the compressed second section and (ii) a second threshold, to thereby obtain an adjusted quantization table,
compress a third section of the first video frame using the discrete cosine transformation and the adjusted quantization table to thereby obtain a compressed third section, the third section being different from the first section and the second section, and
store the compressed third section to the memory device.
5. The electronic device of claim 1 , wherein the first threshold comprises an expected size of the first section with compression.
6. The electronic device of claim 1 , wherein the first threshold comprises a set percentage of a maximum size of the first video frame with compression.
7. The electronic device of claim 1 , wherein the one or more hardware processors is programmed to generate the quantization table by multiplication of a standard quantization table and an entropy index.
8. The electronic device of claim 1 , wherein the first section comprises a first set of pixel values that extend across an entirety of the first video frame, and the second section comprises a second set of pixel values that extend across the entirety of the first video frame.
9. The electronic device of claim 1 , wherein the one or more hardware processors is programmed to compress the first section a single time rather than a plurality of times.
10. The electronic device of claim 1 , wherein the two-dimensional array of pixel values comprises between 1920 pixels and 4000 pixels in one dimension.
11. The electronic device of claim 1 , wherein the two-dimensional array of pixel values comprises at least 4000 pixels in one dimension.
12. The electronic device of claim 1 , wherein the one or more hardware processors is programmed to compress the first video frame at a rate that is at least as fast as the frame rate.
13. The electronic device of claim 1 , wherein the one or more hardware processors is programmed to decompress the compressed first section and the compressed second section for output and presentation on a display.
14. The electronic device of claim 1 , further comprising a lens assembly supported by the housing, the one or more hardware processors being positioned within the housing.
15. A method of compressing a plurality of video image frames, the method comprising:
converting light incident on an image sensor into video data, the video data having a frame rate and comprising a plurality of video frames including a first video frame and a second video frame, the first video frame comprising a two-dimensional array of pixel values;
compressing, with one or more hardware processors, a first section of the first video frame using a discrete cosine transformation and a quantization table to thereby obtain a compressed first section, the first section comprising a first plurality of slices;
modifying, with the one or more hardware processors, the quantization table based at least on a comparison of a size of the compressed first section and a first threshold to thereby obtain a modified quantization table;
compressing, with the one or more hardware processors, a second section of the first video frame using the discrete cosine transformation and the modified quantization table to thereby obtain a compressed second section, the second section comprising a second plurality of slices and being different from the first section; and
storing the compressed first section and the compressed second section to a memory device.
16. The method of claim 15 , wherein said compressing the first section comprises compressing each slice of the first plurality of slices using the discrete cosine transformation and the quantization table to thereby obtain a plurality of compressed slices, the plurality of compressed slices together forming the compressed first section.
17. The method of claim 15 , wherein the first threshold comprises (i) an expected size of the first section with compression or (ii) a set percentage of a maximum size of the first video frame with compression.
18. The method of claim 15 , further comprising:
adjusting the quantization table based at least on a comparison of (i) a size of the compressed first section and the compressed second section and (ii) a second threshold, to thereby obtain an adjusted quantization table;
compressing a third section of the first video frame using the discrete cosine transformation and the adjusted quantization table to thereby obtain a compressed third section, the third section being different from the first section and the second section; and
storing the compressed third section to the memory device.
19. The method of claim 15 , wherein the first section comprises a first set of pixel values that extend across an entirety of the first video frame, and the second section comprises a second set of pixel values that extend across the entirety of the first video frame.
20. The method claim 15 , wherein said compressing the first section comprises compressing the first section a single time rather than a plurality of times.