High precision encoding and decoding of video images
Methods, systems, and computer programs for improved quality video compression. Image quality from MPEG-style video coding may be improved by preserving a higher number of bits during intermediate encoding and decoding processing steps. Problems of inverse discrete cosine transform (IDCT) mismatch can be eliminated by exactly matching the IDCT function numerical algorithm of the decoder to the IDCT function numerical algorithm used for the decoding portion of the encoder. Also included is an application of high precision compression to wide dynamic range images by extending the range of the “quantization parameter” or “QP”. The extension of QP may be accomplished either by increasing the range of QP directly, or indirectly through a non-linear transformation. Also included is an application of extended intermediate processing precision and an extended QP range to reduced contrast regions of an image to extend the precision with which the low-contrast portions are compression coded.
1. A method for increasing the average compression ratio during compression of a sequence of digitized video images, the method comprising:
receiving, at an encoder, a sequence of digitized video images, the digitized video images including a sequence of frames, wherein the digitized video images comprise a first number of bits of precision;
encoding, at the encoder, the sequence of digitized video images by applying an inverse discrete cosine transform numerical algorithm that matches an inverse discrete cosine transform numerical algorithm applied during a subsequent decoding process by a decoder, wherein the inverse discrete cosine transform numerical algorithm applied by the encoder preserves a second number of bits of precision, the second number of bits of precision being greater than the first number of bits of precision, and wherein the second number of bits of precision matches a number of bits of precision of the inverse discrete cosine transform numerical algorithm applied by the decoder; and
generating a compressed bitstream having increased spacing between Intra frames.
2. The method of claim 1 , further including decoding the compressed bitstream by the decoder, including applying an inverse discrete cosine transform numerical algorithm that matches the inverse discrete cosine transform numerical algorithm applied during encoding.
3. A computer program, stored on a non-transitory computer-readable medium, for increasing the average compression ratio during compression of a sequence of digitized video images, the computer program comprising instructions for causing a first computer to:
receive, at the first computer, a sequence of digitized video images, the digitized video images including a sequence of frames, wherein the digitized video images comprise a first number of bits of precision; and
encode, at the first computer, the sequence of digitized video images by applying an inverse discrete cosine transform numerical algorithm that matches an inverse discrete cosine transform numerical algorithm applied during a subsequent decoding process by a second computer, wherein the inverse discrete cosine transform numerical algorithm applied by the first computer preserves a second number of bits of precision, the second number of bits of precision being greater than the first number of bits of precision, and wherein the second number of bits of precision matches a number of bits of precision of the inverse discrete cosine transform numerical algorithm applied by the second computer; and
generate a compressed bitstream having increased spacing between Intra frames.
4. The computer program of claim 3 , further including instructions for causing the second computer to decode the compressed bitstream, including instructions for causing the second computer to apply an inverse discrete cosine transform numerical algorithm that matches the inverse discrete cosine transform numerical algorithm applied during encoding.
5. An encoder for increasing the average compression ratio during compression of a sequence of digitized video images, the encoder comprising:
one or more processors;
one or more memories operatively coupled to the one or more processors, the one or more memories having instructions stored therein to cause the one or more processors to perform operations comprising:
receiving, at the encoder, a sequence of digitized video images, the digitized video images including a sequence of frames, wherein the digitized video images comprise a first number of bits of precision;
encoding, at the encoder, the sequence of digitized video images by applying an inverse discrete cosine transform numerical algorithm that matches an inverse discrete cosine transform numerical algorithm applied during a subsequent decoding process by a decoder, wherein the inverse discrete cosine transform numerical algorithm applied by the encoder preserves a second number of bits of precision, the second number of bits of precision being greater than the first number of bits of precision, and wherein the second number of bits of precision matches a number of bits of precision of the inverse discrete cosine transform numerical algorithm applied by the decoder; and
generating a compressed bitstream having increased spacing between Intra frames.
6. The encoder of claim 5 , wherein the operations further comprise decoding the compressed bitstream, including applying an inverse discrete cosine transform numerical algorithm that matches the inverse discrete cosine transform numerical algorithm applied during encoding.
7. A method for decoding a coded bitstream by a decoder, the method comprising:
receiving, at a decoder, a coded bitstream;
dequantizing, at the decoder, the coded bitstream to generate a dequantized bitstream;
processing, at the decoder, the dequantized bitstream using an inverse transform function to generate output transform data, wherein a first number of bits of precision of the inverse transform function of the decoder matches a number of bits of precision of an inverse transform function of an encoder that encoded the coded bitstream; and
decoding the output transform data to generate a sequence of digitized video images, wherein the digitized video images comprise a second number of bits of precision, the second number of bits of precision being less than the first number of bits of precision.
8. The method of claim 7 , wherein the dequantized bitstream and the output transform data have the same number of bits of precision.
9. The method of claim 7 , wherein the inverse transform function of the decoder comprises an inverse DCT (IDCT) function.
10. The method of claim 7 , wherein the first number of bits of precision is 16 bits.
11. The method of claim 10 , wherein the second number of bits of precision is one selected from the group consisting of 8-bits, 10-bits, or 12-bits.