SPRUJ28E November 2021 – September 2024 AM68 , AM68A , TDA4AL-Q1 , TDA4VE-Q1 , TDA4VL-Q1
Offset table defines a (x, y) vector for a regular grid of output points. Each grid will define 2 offset vectors one each for EVEN and ODD line(s), defining how far output pixel needs to be moved in either direction. Final pixel location in input source image is used to compute the output pixel. Offset table can have precise definition and can capture rapidly changing offset tables. However it will require a large amount of memory. Since most offset tables are not expected to change rapidly in a small spatial region, CAC uses a subsampled offset table. Grid is down sampled with down-sampling factor in the range of 8 to 128 with increments of 4 in both horizontal and vertical directions. Subsampling factor is set in the register; BLOCKSZ.SIZE This enables reducing the amount of memory required to describe the offset vectors, but requires hardware to interpolate the missing offset vectors. CAC supports bilinear interpolation to interpolate missing offset vectors.
The mapping procedure is described by the following series of equations. Given an output pixel at location (x0,y0), we compute the input image pixel location (x1,y1).
Clip new index to Offset grid boundaries.
Clip to Horizontally to -8.0 to +8.0 pixel range (-64 to +64 with Q3 precision).
Clip to Vertically to -4.0 to +4.0 pixel range (-32 to +32 with Q3 precision).
The input coordinate (x1,y1) refers to final input frame co-ordinates.