Methods and systems for adaptive cropping
A video encoder is configured to encode a bitstream to be decoded by a compliant decoder receiving the bitstream. The bitstream including a first coded picture having a first resolution and a second coded picture having a second resolution, wherein the first coded picture is an intra-coded picture, parameters defining a cropping window. The decoder decodes the first coded picture and stores the first picture as a reference picture, determines a scaling factor from at least one parameter in the bitstream defining the first cropping window, determines a predictor for the second picture from the reference picture and the scaling factor, decodes the second coded picture using the predictor, and outputs for display the first picture as cropped in accordance with the parameters defining the cropping window.
1. An encoder comprising circuitry to encode a bitstream for decoding by a compliant decoder:
the bitstream including a first coded picture having a first resolution and a second coded picture having a second resolution, a sequence parameter set associated with both the first and second coded pictures, a first picture parameter set associated with the first picture, and a second picture parameter set associated with the second picture, the sequence parameter set including a first set of parameters defining a first cropping window, the first set of parameters including, a top offset, a bottom offset, a left offset and a right offset;
the decoder being configured to:
receive the bitstream,
decode the first coded picture and store the first picture as a reference picture;
determine a vertical scaling factor as a function of the top offset and bottom offset parameters in the sequence parameter set
determine a horizontal scaling factor as a function of the left offset and right offset parameters in the sequence parameter set;
determine a predictor for the second picture from the reference picture and the vertical scaling factor and horizontal scaling factor;
decode the second coded picture using the predictor, and
output for display the first picture as cropped in accordance with the first set of parameters defining the first cropping window in the sequence parameter set.
2. The encoder of claim 1 , wherein:
the second picture parameter set includes a second set of parameters different from the first set of parameters and defining a second cropping window, the second set of parameters including a second top offset, a second bottom offset, a second left offset and a second right offset;
the second picture is decoded and stored as a second reference picture;
a second vertical scaling factor is determined as a function of the second top offset and second bottom offset;
a second horizontal scaling factor is determined as a function of the second left offset and second right offset; and
a second predictor is determined from the second reference picture, the second horizontal scaling factor and the second vertical scaling factor.
3. The encoder of claim 1 , wherein the first resolution is smaller than the second resolution.
4. The encoder of claim 1 , wherein the second resolution is smaller than the first resolution.
5. An encoder comprising circuitry to encode a bitstream for decoding by a compliant decoder:
the bitstream including:
a first coded picture having a first resolution and a second coded picture having a second resolution,
a sequence parameter set associated with both the first and second coded pictures, the sequence parameter set including a first set of parameters defining a first cropping window,
a first picture parameter set associated with the first picture, and
a second picture parameter set associated with the second picture;
the decoder being configured to:
receive a bitstream,
decode the first coded picture and store the first picture as a reference picture;
determine a scaling factor from at least one parameter in the sequence parameter set defining the first cropping window;
determine a predictor for the second picture from the reference picture and the scaling factor;
decode the second coded picture using the predictor; and
output for display the first picture as cropped in accordance with the first set of parameters defining the first cropping window in the sequence parameter set.
6. The encoder of claim 5 , wherein:
the second picture parameter set includes a second set of parameters different from the first set of parameters and defining a second cropping window;
the second picture is decoded and stored as a second reference picture;
a second scaling factor is determined from at least one parameter in the second set of parameters; and
a second predictor is determined from the second reference picture and the second scaling factor.
7. The encoder of claim 6 , wherein the first set of parameters comprise a plurality of values from which four corners of a rectangular cropping window can be determined.
8. The encoder of claim 6 , wherein the first set of parameters defining a first cropping window comprise a top offset, a bottom offset, a left offset and a right offset.
9. The encoder of claim 5 , wherein the first resolution is smaller than the second resolution.
10. The encoder of claim 5 , wherein the second resolution is smaller than the first resolution.