Cameratrainingsergiopublic 120904235733-phpapp02(2)

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Cameratrainingsergiopublic 120904235733-phpapp02(2)

  1. 1. Introduction to Camera By: Sergio Aguirre <sergio.a.aguirre@gmail.com>
  2. 2. Basics  Camera: Device that records and stores images.  Still Images:  Videos or movies:
  3. 3. Basics  But essentially, what defines a camera device?  Recording medium  Lens  Light Lens Light Recording Medium
  4. 4. Basics  Now, what about a typical digital camera?  Image sensor (CCD or CMOS)  Lens  Flash  ISP: Image Signal Processor  Image and video Encoders (To save space)  Storage Media (SD Cards, USB drives, Etc.)
  5. 5. Image sensors
  6. 6. Image sensor technology  CCD: Charge Coupled device.   Moves electrical charges to an area where it can be manipulated. CMOS: Complementary metal-oxide semiconductor.  Array of pixel sensors, each one containing a photodetector and an active amplifier.
  7. 7. Image sensor pixel arrays  Foveon:   100% Green   100% Red 100% Blue Bayer:  25% Red  50% Green  25% Blue
  8. 8. Image sensor formats (Most typical)  RAW 10-bits.   10-bit digital value obtained thru an ADC (Analog to Digital Converter) of the analog voltage coming from each pixel's associated photodetector chargeto-voltage converter. YUV 4:2:2 8-bits.  Represent pairs of horizontally contiguous pixels. 8bits per component (Y: Luminance, UV: Chrominance). Order is usually YUYV, or UYVY. Croma components (UV) are subsampled at half the sample rate than luma (Y).
  9. 9. Image sensor formats (Most typical)  YUV 4:2:0 8-bits.   Similar to 4:2:2, but the difference being that the UV components are also vertically subsampled by 2. This format contains interleaved data, which means, odd lines contain only Y elements, and even lines contain packed UYVY elements, similarly to 4:2:2 subsampling. NV12 (YUV 4:2:0 8-bits, planar)  Exact same subsampling as above format, but the difference being that one array contains only Y components, and a second array contains packed UV components, 2x2 subsampled.
  10. 10. Image sensor core Typical block diagram of an image sensor core components: AMP Gain control 10-bit ADC Digital gain Image array Black level calibration Column Sample/hold Row select  ...
  11. 11. Image sensor core functions      Analog gain: Amplifies constant voltage perpixel for entire array. Done before ADC. Black level: Level of pixel voltage at the darkest (black) part of the incoming image. Digital gain: Adds a constant number to the digitally converted pixel value, after going through the ADC. Skipping: Certain pixels rows/columns are avoided (skipped) on sampling. Binning: Averaging groups of neighborhood pixel charges.
  12. 12. Image sensor interfaces  Overall, there's at least 2 communication links:   Control: Typically I2C, but not necessarly the case. This is used by a master IC to initialize/program the sensor for desired operation and data output configuration. Data: This can be Parallel or Serial. Sensor Data Master IC Control
  13. 13. Image sensor interfaces - Control  I2C: Inter-Integrated Circuit   Multi-master serial single-ended computer bus, used to attach low-speed peripherals to a host IC. Uses 2 open-drain lines, w/pull-up resistors:   SCL (Serial CLock). SDA (Serial DAta).
  14. 14. Image sensor interfaces - I2C  I2C: Inter-Integrated Circuit    START and STOP conditions to claim/release bus control. First byte: 7-bit device address space, 1 bit used to indicate Read (HI) or Write (LOW). ACK bit pulled low by slave after each byte sent, used to handshake transmission between master and slave ICs. If ACK bit is high, master should stop transmission.
  15. 15. Image sensor interfaces - Parallel Parallel interface (a.k.a. Digital Video Port)  Data signals: 1 digital output pin per bit.  Sync signals:    PCLK: Pixel Clock. HSYNC: Horizontal Sync. VSYNC: Vertical Sync. Image data Vertical Blanking Horizontal Blanking  D[9:0] Sensor PCLK HSYNC VSYNC Master IC
  16. 16. Image sensor interfaces - CSI2  MIPI CSI2 (Camera Serial Interface 2).  Data signals: Up to 4 differential lanes (+/- signals).  Clock signals: 1 differential lane (+/- signals).  Speeds up to 1 Gbit/s per lane (500 MHz) CLK (+/-) DAT0 (+/-) Sensor DAT1 (+/-) DAT2 (+/-) DAT3 (+/-) Master IC
  17. 17. Image sensor interfaces - CSI2  CSI2 Receiver components:
  18. 18. Image sensor interfaces - CSI2  D-PHY layer:
  19. 19. Image sensor interfaces - CSI2  CSI2 Protocol Layer:
  20. 20. Image sensor interfaces - CSI2  Data Lane Merger
  21. 21. Lens
  22. 22. Lens   Could be either a simple convex lens, or a compound lens made up of a number of lens elements, used to correct optical aberrations, and keep good image sharpness on a specific object distance from the camera. There are fixed-focus lens, and lens whose position can be adjusted by a VCM (voice coil motor).
  23. 23. Lens   For moving lens, position can be either controlled as part of the image sensor registers, or as a separate I2C device in the bus. This is usually done as a result of the Auto Focus algorithm, after analyzing the captured images. It can also be due to manual control, if desired.
  24. 24. Flash
  25. 25. Flash    Used in photography to compensate natural ambient light, and illuminate a dark scene. Syncronized with start of capture image command, with adjusted flashing duration, and intensity. Usually triggered with GPIOs and configured with I2C commands.
  26. 26. Thanks!
  27. 27. Extra slides
  28. 28. Image sensor interfaces - Data  MIPI CSI (Camera Serial Interface).  Data signals: 1 differential lane (+/- signals).  Clock signals: 1 differential lane (+/- signals).  Speeds between 1->208 Mbps CLK (+/-) Sensor DAT (+/-) Master IC
  29. 29. Image sensor interfaces - Data  SMIA CCP2 (Compact Camera Port 2).  Data signals: 1 differential lane (+/- signals).  Clock signals: 1 differential lane (+/- signals). Class Data transfer capacity (sustain data rate) Class 0 <208 Mbit/s Data/Clock Class 1 208 Mbit/s to 416 Mbit/s Data/Strobe Class 2 416 Mbit/s to 650 Mbit/s Data/Strobe CLK, or STROBE (+/-) Signaling method Sensor DAT (+/-) Master IC

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