SPRUJ28E November 2021 – September 2024 AM68 , AM68A , TDA4AL-Q1 , TDA4VE-Q1 , TDA4VL-Q1
The AF engine works by extracting each green (Gr or Gb) pixel from the video stream and subtracts a fixed offset of 128 or 512 (depending of whether A-Law is enabled or disabled) from the pixel value. The offset value is then passed through an IIR filter and the absolute value of the filter output is the focus value (FV). Both FV and FV2 are produced. The FV and FV2 values can be accumulated or the maximum for each line/column can be accumulated. The following sections describe this process in more detail.