Method of applying edge offset
An apparatus for post-processing a reconstructed image is discussed. The apparatus includes an inter prediction unit for generating a prediction block using a reference picture and a motion vector, wherein the prediction block generated by the inter prediction unit is added to a residual block to generate a reconstructed picture; an intra prediction unit for recovering an intra prediction mode for a current prediction unit and generating a prediction block using the intra prediction mode, wherein the prediction block generated by the intra prediction unit is added to a residual block to generate a reconstructed picture; and a post-processing unit for determining a boundary strength for an edge which is a prediction edge or a transform edge on the reconstructed picture, determining whether deblocking filtering is applied on the edge or not using the boundary strength, and filtering the edge in order of vertical edges and horizontal edges if the deblocking filtering is applied on the edge, and for generating an edge index of a current sample, and applying an edge offset corresponding to the edge index to the current sample.
1. An apparatus for post-processing a reconstructed image, the apparatus comprising:
an intra predictor to recover an intra prediction mode for a current prediction unit and generate a prediction block using the intra prediction mode, wherein the prediction block generated by the intra prediction unit is added to a residual block to generate a reconstructed picture; and
a post-processer to determine a boundary strength for an edge which is an edge of the prediction block or an edge of a transform block on the reconstructed picture, determine whether deblocking filtering is applied on the edge or not using the boundary strength, filter the edge in order of vertical edges and horizontal edges if the deblocking filtering is applied on the edge, generate an edge index of a current sample, and apply an edge offset corresponding to the edge index to the current sample,
wherein the boundary strength is determined for each of 4-sample edges lying on an 8×8 sample grid, which is the edge of the prediction block or the edge of the transform block, and
wherein the edge offset is set as negative or positive based on the edge index.
2. The apparatus of claim 1 , wherein the edge is filtered with a deblocking filter which is selected using a boundary quantization parameter.
3. The apparatus of claim 1 , wherein the boundary strength is set equal to zero if the edge is not the edge of the transform block and the edge is not the edge of the prediction block.
4. The apparatus of claim 1 , wherein the post-processor generates the edge index using the following equation:
edgeIdx=2+sign3(recPicture( x )−recPicture( x− 1))+sign3(recPicture( x )−recPicture( x+ 1)),
wherein the function sign3(y) is equal to 1 if the y is larger than 0, the function sign3(y) is equal to −1 if the y is smaller than 0, and the function sign3(y) is equal to 0 if the y is equal to 0, the variable recPicture(x) represents a current sample value, and the variables recPicture(x−1) and recPicture(x+1) represent two neighboring sample values.
5. The apparatus of claim 1 , wherein a boundary quantization parameter is used for determining whether the deblocking filter is applied when the boundary strength is not equal to zero.
6. The apparatus of claim 5 , wherein the boundary quantization parameter is an average of a quantization parameter of P block containing sample p0 and a quantization parameter of Q block containing sample q0,
the quantization parameter of the P block is generated by using a quantization parameter predictor and a differential quantization parameter of the P block, and
if two or more quantization parameters are available among a left quantization parameter, an above quantization parameter and a previous quantization parameter of the P block, the quantization parameter predictor of the P block is generated using two available quantization parameters which are determined according to a predetermined order.