Iterative IDCT with adaptive non-linear filtering

An apparatus for decoding an image block, comprising:

• a memory;
• and
• a processor, the processor configured to execute instructions stored in the memory to:
• receive a quantized transform block,
• wherein an encoder used quantization data and a transform type in generating the quantized transform block;
• inverse-quantizing the quantized transform block to obtain a decoded block;
• apply an edge-preserving filter to the decoded block to obtain an edge-filtered decoded block;
• obtain a transformed edge-preserved block by applying the transform type and the quantization data to the edge-filtered decoded block;
• clamp a value of the transformed edge-preserved block to a corresponding value of the quantized transform block to obtain a smoothed transform block;
• and
• after the clamping, inverse transform, using the transform type and the quantization data, the smoothed transform block to obtain an edge-preserved smoothed block.

An apparatus that decodes an image block, the apparatus:

• receives a quantized transform block,
• wherein an encoder used quantization data and a transform type in generating the quantized transform block;
• inverse-quantizing the quantized transform block to obtain a decoded block;
• applies an edge-preserving filter to the decoded block to obtain an edge-filtered decoded;
• obtains a transformed edge-preserved block using the transform type and the quantization data to the edge-filtered decoded block;
• clamps a value of the transformed edge-preserved block to a corresponding value of the quantized transform block to obtain a smoothed transform block;
• and
• after the clamping, inverse transforms, using the transform type and the quantization data, the smoothed transform block to obtain an edge-preserved smoothed block.