2. Basics
Camera: Device that records and stores
images.
Still Images:
Videos or movies:
3. Basics
But essentially, what defines a camera device?
Recording medium
Lens
Light
Lens Recording Medium
Light
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.)
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. Image sensor pixel arrays
Foveon:
100% Red
100% Green
100% Blue
Bayer:
25% Red
50% Green
25% Blue
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 charge-
to-voltage converter.
YUV 4:2:2 8-bits.
Represent pairs of horizontally contiguous pixels. 8-
bits 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. 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. Image sensor core
Typical block diagram of an image sensor core
components:
Column
Sample/hold
Digital gain
Row select
Black level
calibration
Image 10-bit
array
AMP
ADC ...
Gain
control
11. Image sensor core functions
Analog gain: Amplifies constant voltage per-
pixel 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. 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. 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. 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. 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.
Horizontal Blanking
D[9:0]
Image data Sensor
PCLK
Master IC
HSYNC
VSYNC
Vertical Blanking
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 (+/-) Master IC
DAT2 (+/-)
DAT3 (+/-)
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. 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.
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.
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. 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 Signaling method CLK, or
(sustain data rate) STROBE
(+/-)
Class 0 <208 Mbit/s Data/Clock
Class 1 208 Mbit/s to 416 Mbit/s Data/Strobe Sensor DAT (+/-) Master IC
Class 2 416 Mbit/s to 650 Mbit/s Data/Strobe