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Camera ISP Functional Description
The HS, VS, and FLD signals can be set as inputs or outputs. The polarity of the HS, VS, and FLD signals
can be set as positive or negative. If the HS, VS, and FLD signals are output, the signal length can be set.
6.4.6.1.3.2 Camera ISP CCDC Input Sampling and Formatting
•
Data is latched by the pixel clock.
•
Pixel-clock polarity can be either rising- or falling-edge. This is set through
[4]
PAR_CLK_POL.
•
Data can be interpreted as normal or inverted (
[6] DATAPOL).
•
For RAW data:
–
Data is clipped to the number of LSBs specified in the
[10:8] DATSIZ field.
This also sets the maximum data size allowed in subsequent clipping/limiting operations and is the
output data alignment if data is written to memory.
•
For YUV data (BT656 or SYNC mode):
–
The MSB of the chroma signal can also be inverted (
[13] MSBINVI). It adds 128 to
chrominance signals, to be compatible with several sensors.
•
BT656 decoder: Separates data and synchronization signals. This module outputs HS, VS, and FIELD
signals.
6.4.6.1.3.3 Camera ISP CCDC Initial Processing
Optical Clamp
The optical black clamping function provides a means of averaging the optically black pixels and
subtracting that value from each input pixel as a first step. The goal is to remove an offset caused by the
sensor technology.
The averaging circuit takes an average of masked (black) pixel values from the image sensor, averaging
pixels at the start (
[24:10] OBST) of each line (
[30:28] OBSLEN) and for
the number of indicated lines (
[27:25] OBSLN), plus an optional gain adjustment
(
[4:0] OBGAIN), and subtracting this value from the image data at the succeeding line.
Users can control the position of the black pixels, the number of pixels (1, 2, 4, 8, or 16) in each line
averaged, and the averaged number of lines (1, 2, 4, 8, or 16).
Alternately, users can disable black clamp averaging (
[31] CLAMPEN) and select a
constant black value for subtraction (
[13:0] DCSUB), instead of using the calculated
average value.
NOTE:
For YUV data, this operation subtracts a fixed value (
[13:0] DCSUB) from
the luminance sample. To disable this operation, set the subtraction value to zero. This
function does not clip negative results to 0 for YUV 8 bit input or REC656 input modes
(
[13:12] INPMOD == 2 ||
[0] REC656ON == 1).
This function does not clip negative results to 0 for YUV 8 bit input or REC656 input modes
(
[13:12] INPMOD == 2 ||
[0] REC656ON == 1).
shows an optical clamp representation.
1195
SWPU177N – December 2009 – Revised November 2010
Camera Image Signal Processor
Copyright © 2009–2010, Texas Instruments Incorporated
