DIGITAL CAMERA

RAVI P. AGRAHARI (Science & Technology)

WHAT IS DIGITAL CAMERA?

• A Digicam is a camera that takes videos or still photos by recording images on an electronic image sensor.

• Many digital cameras are incorporated into many devices ranging from PDA’s and mobile phones.

• They share an optical system using lens with variable diaphragm to focus light on image pickup device.

• light reflected from an object enters the camera and passes through convex lens that captures the image.

• Early cameras used the PC serial port. USB is now most widely method though some has fire-wire port.

• The other cameras used wireless communication such as Bluetooth 802.11.

• Pressing the button of camera opens the shutter so the light from the object travels to the back of the camera instead.

• For most a conversion to digital is required to give enough space for electronics and allow a LCD to preview the image and replacing it with built digital unit.

HOW DIGITAL CAMERA WORKS?

• It converts analog information (represented by fluctuated wave) into digital information(represented by ones and zeros or bits)

• Once a picture is taken image pic must be converted into a form that computer can recognize (bits and bytes)

• A digicam has different lenses that helps to focus the light to create image of the scene

• Digicams uses CCDs (charged coupled devices) or CMOS.

• CCD sensors create high quality low noise images but CMOS sensors are more susceptible to noise.

• Lets have a look what is the real difference

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SIMPLE DIGITAL CAMERA• Captures images• Stores images in digital format

– No film– Multiple images stored in camera

• Number depends on amount of memory and bits used per image

• Downloads images to PC• Only recently possible

– Systems-on-a-chip• Multiple processors and memories on one IC

– High-capacity flash memory• Very simple description used for example

– Many more features with real digital camera• Variable size images, image deletion, digital stretching, zooming in and out, etc.

TYPES OF DIGITAL CAMERA

• Compact digital cameras• Mirror less interchangeable-lens camera• Line-scan camera systems• Bridge cameras

HOW DO DIGITAL CAMERASCAPTURE COLOR?

• To get full color of an image, most sensors use filtering to look at the light in its three primary colors

• All three colors get recorded and combined to create the full spectrum

• Beam splitter – directs light to different sensors and each sensor only responds to one of the primary colors

EXPOSURE AND FOCUS

• Digital camera has to control the amount of light that reaches the sensor.

• The two components it uses to do this, the aperture and shutter speed, and are also present on conventional cameras.

• Aperture: The size of the opening in the camera. The aperture is automatic in most digital cameras, but some allow manual adjustment to give professionals and hobbyists more control over the final image.

• Shutter speed: The amount of time that light can pass through the aperture. Unlike film, the light sensor in a digital camera can be reset electronically, so digital cameras have a digital shutter rather than a mechanical shutter

STORAGE

• Many camera phones and most separate digital cameras use memory cards having flash memory to store image data.

• The majority of cards for separate cameras are SD format; many are CompactFlash and the other formats are rare.

• Digital cameras have computers inside, hence have internal memory.

• A few cameras use some other form of removable storage such as Microdrive's (very small hard disk drives), CD single (185 MB), and 3.5" floppy disks. Other unusual formats include:

• Onboard flash memory — Cheap cameras and cameras secondary to the device's main use (such as a camera phone)

• PC Card hard drives — early professional cameras thermal printer — known only in one model of camera that printed images immediately rather than storing.

PIXEL RESOLUTION OF A DIGITAL CAMERA

• The clarity of the photos taken from a digital camera depends on the resolution of the camera.

• This resolution is always measured in the pixels.

• If the numbers of pixels are more, the resolution increases, thereby increasing the picture quality.

• There are many type of resolutions available for cameras. They differ mainly in the price.

TYPES OF PIXELS• 256×256 – This is the basic resolution a camera

has.• 640×480-These type of cameras are suitable for

posting pics and images in websites.• 1216×912 – This resolution is normally used in

studios for printing pictures. • 2240×1680 – This is commonly referred to as a

4 megapixel cameras.• There are even higher resolution cameras up to

20 million pixels or so.

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DESIGNER’S PERSPECTIVE

• Two key tasks– Processing images and storing in memory

• When shutter pressed:– Image captured– Converted to digital form by charge-coupled device (CCD)– Compressed and archived in internal memory

– Uploading images to PC• Digital camera attached to PC• Special software commands camera to transmit archived

images serially

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CHARGE-COUPLED DEVICE (CCD)• Special sensor that captures an image• Light-sensitive silicon solid-state device composed of many cells

When exposed to light, each cell becomes electrically charged. This charge can then be converted to a 8-bit value where 0 represents no exposure while 255 represents very intense exposure of that cell to light.

Some of the columns are covered with a black strip of paint. The light-intensity of these pixels is used for zero-bias adjustments of all the cells.

The electromechanical shutter is activated to expose the cells to light for a brief moment.

The electronic circuitry, when commanded, discharges the cells, activates the electromechanical shutter, and then reads the 8-bit charge value of each cell. These values can be clocked out of the CCD by external logic through a standard parallel bus interface.

Lens area

Pixel columns

Covered columns

Electronic circuitry

Electro-mechanical shutter

Pixe

l ro

ws

• The light falling on a cell is converted into small amount of electric charge which is measured by electronics and stored as a number.

• On periphery screen is composed of electromechanical shutter. When activated screen opens momentarily and allows light to hit the light sensitive surface.

• In a digital device, the voltages are sampled, digitized, and usually stored in memory; in an analog device (such as an analog video camera)

• They are processed into a continuous analog signal (e.g. by feeding the output of the charge amplifier into a low-pass filter) which is then processed and fed out to other circuits for transmission, recording, or other processing.

WHAT’S THE REAL DIFFERENCE• Because each pixel on a CMOS

sensor has several transistors located next to it, the light sensitivity of a CMOS chip is lower. Many of the photons hit the transistors instead of the photodiode.

• CMOS sensors traditionally consume little power. CCDs, on the other hand, use a process that consumes lots of power. CCDs consume as much as 100 times more power than an equivalent CMOS sensor.

• CCD sensors create high-quality, low-noise images. CMOS sensors are generally more susceptible to noise.

• CCD sensors have been mass produced for a longer period of time, so they are more mature. They tend to have higher quality pixels, and more of them.

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ZERO-BIAS ERROR• Manufacturing errors cause cells to measure slightly above or below actual

light intensity• Error typically same across columns, but different across rows• Some of left most columns blocked by black paint to detect zero-bias error

– Reading of other than 0 in blocked cells is zero-bias error– Each row is corrected by subtracting the average error found in blocked cells for

that row

123 157 142 127 131 102 99 235134 135 157 112 109 106 108 136135 144 159 108 112 118 109 126176 183 161 111 186 130 132 133137 149 154 126 185 146 131 132121 130 127 146 205 150 130 126117 151 160 181 250 161 134 125168 170 171 178 183 179 112 124

136 170 155 140 144 115 112 248 12 14145 146 168 123 120 117 119 147 12 10144 153 168 117 121 127 118 135 9 9176 183 161 111 186 130 132 133 0 0144 156 161 133 192 153 138 139 7 7122 131 128 147 206 151 131 127 2 0121 155 164 185 254 165 138 129 4 4173 175 176 183 188 184 117 129 5 5

Covered cells

Before zero-bias adjustment After zero-bias adjustment

-13-11-90-7-1-4-5

Zero Bias

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COMPRESSION• Store more images• Transmit image to PC in less time• JPEG (Joint Photographic Experts Group)

– Popular standard format for representing digital images in a compressed form

– Provides for a number of different modes of operation– Mode used provides high compression ratios using DCT (discrete

cosine transform)– Image data divided into blocks of 8 x 8 pixels– 3 steps performed on each block

• DCT• Quantization• Huffman encoding

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DCT STEP• Transforms original 8 x 8 block into a cosine-

frequency domain– Upper-left corner values represent more of the essence of the image– Lower-right corner values represent finer details

• Can reduce precision of these values and retain reasonable image quality

• FDCT (Forward DCT) formula– C(h) = if (h == 0) then 1/sqrt(2) else 1.0

• Auxiliary function used in main function F(u,v)– F(u,v) = ¼ x C(u) x C(v) Σx=0..7 Σy=0..7 Dxy x cos(π(2u + 1)u/16) x cos(π(2y + 1)v/16)

• Gives encoded pixel at row u, column v• Dxy is original pixel value at row x, column y

• IDCT (Inverse DCT)– Reverses process to obtain original block (not needed for this design)

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QUANTIZATION STEP• Achieve high compression ratio by reducing image

quality– Reduce bit precision of encoded data

• Fewer bits needed for encoding• One way is to divide all values by a factor of 2

– Simple right shifts can do this

– Dequantization would reverse process for decompression1150 39 -43 -10 26 -83 11 41

-81 -3 115 -73 -6 -2 22 -514 -11 1 -42 26 -3 17 -382 -61 -13 -12 36 -23 -18 5

44 13 37 -4 10 -21 7 -836 -11 -9 -4 20 -28 -21 14

-19 -7 21 -6 3 3 12 -21-5 -13 -11 -17 -4 -1 7 -4

144 5 -5 -1 3 -10 1 5-10 0 14 -9 -1 0 3 -1

2 -1 0 -5 3 0 2 -50 -8 -2 -2 5 -3 -2 16 2 5 -1 1 -3 1 -15 -1 -1 -1 3 -4 -3 2

-2 -1 3 -1 0 0 2 -3-1 -2 -1 -2 -1 0 1 -1

After being decoded using DCT After quantization

Divide each cell’s value by 8

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• Serialize 8 x 8 block of pixels– Values are converted into single list using zigzag pattern

• Perform Huffman encoding– More frequently occurring pixels assigned short binary code– Longer binary codes left for less frequently occurring pixels

• Each pixel in serial list converted to Huffman encoded values– Much shorter list, thus compression

HUFFMAN ENCODING STEP

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HUFFMAN ENCODING EXAMPLE• Pixel frequencies on left

– Pixel value –1 occurs 15 times– Pixel value 14 occurs 1 time

• Build Huffman tree from bottom up– Create one leaf node for each pixel value and assign frequency as node’s

value– Create an internal node by joining any two nodes whose sum is a minimal

value• This sum is internal nodes value

– Repeat until complete binary tree• Traverse tree from root to leaf to obtain binary code for leaf’s

pixel value– Append 0 for left traversal, 1 for right traversal

• Huffman encoding is reversible– No code is a prefix of another code

144

5 3 2

1 0 -2

-1

-10 -5 -3

-4 -8 -96141 1

2

1 1

2

1

22

4

3

5

4

65

9

5

10

5

11

5

14

6

17

8

18

15

29

35

64

1

-1 15x 0 8x-2 6x1 5x2 5x3 5x5 5x-3 4x-5 3x

-10 2x144 1x-9 1x-8 1x-4 1x6 1x

14 1x

-1 00

0 100

-2 110

1 010

2 1110

3 1010

5 0110

-3 11110

-5 10110

-10 01110

144 111111

-9 111110

-8 101111

-4 101110

6 011111

14 011110

Pixel frequencies Huffman treeHuffman codes

COMPONENTS OF CAMERA1. Battery compartment: This camera takes two 1.5-volt batteries, so it runs on a total voltage of 3 volts (3 V).2. Flash capacitor: The capacitor charges up for several seconds to store enough energy to fire the flash.3. Flash lamp: Operated by the capacitor. It takes a fair bit of energy to fire a xenon flash like this, which is why a lot of indoor flash photography quickly uses up your batteries.4. LED: A small red LED (light-emitting diode) indicates when the self-timer is operating, so you can take photos of yourself more easily.5. Lens: The lens catches light from the object you're

photographing and focuses it on the CCD.6. Focusing mechanism: This camera has a simple switch-operated focus that toggles the lens between two positions for taking either close-ups or distant shots.

7. CCD: This is the light-detecting microchip in a digital camera. You can't actually see the CCD in this photo, because it's directly underneath the lens. But you can see what it looks like in our article on how CCDs work.8. USB connector: Attach a USB cable here and connect it to your computer to download the photos you've taken. To your computer, your camera looks like just another memory device (like a hard drive or a flash memory).9. SD (secure digital) card slot: You can slide a flash memory card in here for storing more photos. The camera has a very small internal memory that will store photos too.10. Processor chip: The camera's main digital "brain". This controls all the camera's functions. It's an example of an integrated circuit.11. Wrist connector: The strap that keeps the camera securely tied to your wrist attaches here.12. Top case: Simply screws on top of the bottom case shown here.

BLOCK DIAGRAM

WHY PREFER ARM CORTEX M3?

• With high performance and low dynamic power consumption the Cortex-M3 processor delivers leading power efficiency 12.5 DMIPS / mW based on 90nmG.

• The processor executes Thumb®-2 instruction set for optimal performance and code size.

• It including hardware division, single cycle multiply, and bit-field manipulation.

• The Cortex-M3 NVIC is highly configurable at design time to deliver up to 240 system interrupts.

FEATURES OF ARM CORTEXTMPM365FYXBG

• Operating voltage:2.7 to 3.6V (Single supply 3.0 to 3.45V when USB is used)

• Maximum Operating frequency: 48 MHz

• On-chip debug circuit: JTAG, SWD, SWV or 4-bit trace interface

• Power saving operationClock gear (for dividing clock to 1/1, 1/2, 1/4, 1/8 or 1/16)Standby modes (IDLE, STOP1)

• ARM cortex M is a group of 32 bit RISC processor cores licensed by Arm holdings intended for microcontroller applications

• 3 stage pipeline is used.

BUILT-IN FUNCTIONS

• USB(Full-Speed) : 1 channel• 12-bit AD converter :

1µsec conversion time(@fsys=40MHz) 12 channels

• DMA controller : 2 channels• I/O ports : 74 pins• 16-bit timer : 10 channels• SIO/UART : 2 channels• I2C(100kHz,400kHz)/SIO : 2 channels

JOINT TEST ACTION GROUP (JTAG)

• It is the common name for the IEEE 1149.1 Standard Test Access Port and Boundary-Scan Architecture.

• Today JTAG is also widely used for IC debug ports.• On most systems, JTAG-based debugging is

available from the very first instruction after CPU reset, letting it assist with development of early boot software which runs before anything is set up.

16-BIT TIMER

• The TIMERS are divided into two 8-bit SFR called Timer LOW (TL0, TL1) & Timer HIGH (TH0, TH1) these registers contain the latest count of the TIMER.

• The TIMER action is controlled by two more SFR's called Timer Mode Control Register(TMOD) & Timer/Counter Control Register (TCON).

• TMOD is dedicated to the two Timers & controls the mode of operation of both the Timers.

• It can be considered as two duplicate 4 bit register, where the high 4 bits controls Timer 1 & the lower 4 bits controls Timer 0.

THE PHYSICAL I2C BUS• This is just two wires, called SCL and SDA. SCL is the clock line. It is

used to synchronize all data transfers over the I2C bus. • SDA is the data line. The SCL & SDA lines are connected to all

devices on the I2C bus.• There needs to be a third wire which is just the ground or 0 volts.

There may also be a 5volt wire is power is being distributed to the devices. Both SCL and SDA lines are "open drain" drivers. What this means is that the chip can drive its output low, but it cannot drive it high.

• For the line to be able to go high you must provide pull-up resistors to the 5v supply. There should be a resistor from the SCL line to the 5v line and another from the SDA line to the 5v line.

• You only need one set of pull-up resistors for the whole I2C bus, not for each device, as illustrated below:

SOFTWARE USED

Keil u vision (IDE).

• Tools:Real View MDK-ARM, ULINK2 - USB-JTAG Debugger.Real View Real-Time Library (RL-ARM).

• Types of Target Debugging, Serial Wire Debugger for Cortex

CortexM3 – Core sight Debugger

ULINK2 - USB-JTAG Debug Adaptor

Future of Digital camera

• Smart camera- Application enhanced cameras along with the ability to access various apps, internet, compact like Galaxy camera

• Not only it gives a full interactive photographic capabilities but also keeps you connected via internet.

• You can directly post the pictures taken to Facebook etc. along with interactive media . Its just like a merged up high end smart phone with a smart camera

• iris-cameras is at a developing stage everyone has seen the glimpse of it in Mission impossible 4

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