Image encoding apparatus adaptively determining a scan pattern according to an intra prediction mode
View Patent ↗Provided is an image encoding apparatus that generates a prediction block according to an intra prediction mode, generates a residual block, transforms the residual block to generate a transform block, quantizes the transform block to generate a quantized transform block, scans the quantized transform block to generate one-dimensional (1D) quantized coefficients, and entropy-codes the 1D quantized coefficients. When a size of the transform block is 8×8, the quantized transform block is divided into a plurality of sub-blocks, the plurality of sub-blocks are scanned are coefficients of each sub-block are scanned using a same scan pattern determined according to the intra prediction mode. The quantized coefficients of each sub-block are scanned in a reverse direction from a last non-zero coefficient according the scan pattern.
1. An image encoding apparatus, comprising:
an intra predictor configured to generate a prediction block corresponding to a current prediction block according to an intra prediction mode selected out of a plurality of intra prediction modes;
a subtracter configured to generate a residual block by calculating a difference between the prediction block and an original block;
a transformer configured to transform the residual block to generate a transform block;
a quantizer configured to quantize the transform block using a quantization step size to generate a quantized transform block;
a scanner configured to scan the quantized transform block to generate one-dimensional (1D) quantized coefficients; and
an entropy coder configured to entropy-code the 1D quantized coefficients,
wherein, when a size of the transform block is 8 × 8 , the quantized transform block is divided into a plurality of sub-blocks after the quantization of the transform block,
wherein the scanner scans the plurality of sub-blocks using a first scan pattern determined according to the selected intra prediction mode and scans coefficients of each sub-block using a second scan pattern determined according to the selected intra prediction mode,
wherein the first scan pattern is a scan order applied to the plurality of sub-blocks, and the second scan pattern is a scan order applied to the coefficients of each sub-block,
wherein the first scan pattern is the same as the second scan pattern;
wherein the quantized coefficients of each sub-block are scanned in a reverse direction from a last non-zero coefficient according to the second scan pattern, and
wherein the intra predictor includes:
a reference pixel generator configured to generate reference pixels using available reference pixels of the current prediction block when reference pixels do not exist;
a reference pixel filter configured to adaptively filter reference pixels adjacent to the current prediction block based on the selected intra prediction mode and size information of the current prediction block; and
a prediction block generator configured to generate the prediction block corresponding to the current prediction block according to the selected intra prediction mode.
2. The apparatus of claim 1 , wherein, when the selected intra prediction mode is a horizontal mode, the scan pattern is a vertical scan, and when the selected intra prediction mode is a vertical mode, the scan pattern is a horizontal scan.
3. The apparatus of claim 1 , wherein, when the selected intra prediction mode is one out of a predetermined number of intra prediction modes adjacent to a horizontal mode, the first scan pattern is a vertical scan.
4. The apparatus of claim 1 , wherein the plurality of sub-blocks are scanned in a reverse direction.
5. The apparatus of claim 1 , wherein the quantization step size is determined per coding unit of a predetermined size.