Decoding texels from a block of encoded texture data

A method of decoding a plurality of texels of a p by q sub-block of texels from a block of texture data encoded according to the Adaptive Scalable Texture Compression (ASTC) format, the block of texture data representing an n by m block of texels, where p≤n and q≤m, the method comprising:

• determining a position of a first texel of the p by q sub-block of texels with respect to the rows and/or columns of a weight grid, the weight grid comprising a first plurality of weights in a first plane;
• determining a position of a second texel of the p by q sub-block of texels with respect to the rows and/or columns of the weight grid;
• comparing the positions of the first and second texels with respect to the rows and/or columns of the weight grid;
• extracting fewer than (p+1)(q+1) weights of the first plurality of weights in response to determining that the positions of the first and second texels with respect to the rows and/or columns of the weight grid are between:
• the upper-most and lower-most rows of a predetermined number of adjacent rows of the weight grid;
• and/or
• the left-most and right-most columns of a predetermined number of adjacent columns of the weight grid;
• and
• decoding the plurality of texels in dependence on the extracted weights.

A non-transitory computer readable storage medium having stored thereon an integrated circuit definition dataset that, when processed in an integrated circuit manufacturing system, configures the integrated circuit manufacturing system to manufacture a decoder configured to decode a plurality of texels of a p by q sub-block of texels from a block of texture data encoded according to the Adaptive Scalable Texture Compression (ASTC) format, the block of texture data representing an n by m block of texels, where p≤n and q≤m, the decoder being configured to:

• determine a position of a first texel of the p by q sub-block of texels with respect to the rows and/or columns of a weight grid, the weight grid comprising a first plurality of weights in a first plane;
• determine a position of a second texel of the p by q sub-block of texels with respect to the rows and/or columns of the weight grid;
• compare the positions of the first and second texels with respect to the rows and/or columns of the weight grid;
• extract fewer than (p+1)(q+1) weights of the first plurality of weights in response to determining that the positions of the first and second texels with respect to the rows and/or columns of the weight grid are between:
• the upper-most and lower-most rows of a predetermined number of adjacent rows of the weight grid;
• and/or
• the left-most and right-most columns of a predetermined number of adjacent columns of the weight grid;
• and
• decode the plurality of texels in dependence on the extracted weights.