SPRUJ28E November 2021 – September 2024 AM68 , AM68A , TDA4AL-Q1 , TDA4VE-Q1 , TDA4VL-Q1
The Lens Shading Correction (LSC) is implemented prior to NSF. This is not an optimal order of operation and therefore an adjustment factor is implemented to compensate for the order of operations. The LSCC (Lens Shading Correction Compensation) first approximates the gain of LSC and calculates both that gain and it’s inverse. Within the T_n calculation, the inverse gain is applied to the LL2 average, then the T_n is calculated. Last, the result is multiplied by the gain. In this way, the LSC is approximately reversed temporarily in order that T_n is calculated properly.
LSCC calculates the radius (distance) from the center of the image, then uses a programmable curve to look up the gain value.
While calculating the radius, the center on the frame is programmable. Also a correction gain (kh and kv) separately for X and Y are programmable which allows for elliptical shaped lenses. Because the SQRT is such an expensive function, the resulting radius is used in the SQR form and as such has a very large dynamic range. A programmable shift value effectively selects which portion of this dynamic range is to use for the curve lookup.
The curve lookup is a 16 segment curve. The SQR(Radius) is lookup on the X axis and the resulting gain is supplied on the Y axis.