SPRUIL1D May 2019 – December 2024 DRA829J , DRA829J-Q1 , DRA829V , DRA829V-Q1 , TDA4VM , TDA4VM-Q1
Some sensors provide few optically masked pixels at the beginning/end of each line which allow user to determine the noise floor on any given frame of data. The optical black clamping function provides a means to average the optically black pixels and subtract that value from each input pixel as the first step in reducing the noise on the input pixels.
Figure 12-1190 Optical Black Averaging and Application for Raw Data ModeThe averaging circuit takes an average of masked (black) pixel values from the image sensor, averaging pixels at the start (in the VPFE_CLAMP[24-10] OBST bitfield) of each line (in the VPFE_CLAMP[30-28] OBSLEN bitfield) and for the number of indicated lines (VPFE_CLAMP[27-25] OBSLN bitfield), plus an optional gain adjustment (VPFE_CLAMP[4-0] OBGAIN bitfield). The resultant value is subtracted from the image data at the succeeding line. User can control the position of the black pixels, the number of pixels (1, 2, 4, 8, or 16) in each line that are averaged, and the number of lines (1, 2, 4, 8, or 16) that are averaged.
Alternately, user can disable black clamp averaging (VPFE_CLAMP[31] CLAMPEN bit) and select a constant black value for subtraction (VPFE_DCSUB[13-0] DCSUB bit) instead of using the calculated average value.
The corresponding data path is shown in the thicker lines in Figure 12-1191.
Figure 12-1191 Black Clamping and Black Level Compensation for Raw Data Mode