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DIGITAL CAMERA A CASE STUDY

Rockey SuseelanM-Tech (S2)

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CONTENTS

Introduction. Introduction to a simple digital camera Designer’s perspective Functional block diagram of a digital

camera Digital Camera Block Diagram Specifications Requirements Applications. Hardware architecture Software architecture Conclusion References

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Embedded System Design Life Cycle

ConceptConceptSpecificationSpecification

HW/SWHW/SWPartitioningPartitioning

Hardware ComponentsHardware Components

Software ComponentsSoftware Components

Estimation -Estimation -ExplorationExploration

HardwareHardware

SoftwareSoftware

DesignDesign

(Synthesis, Layout, …)

(Synthesis, Layout, …)

DesignDesign(Compilation, …)

(Compilation, …)

Evaluation (area, power, performance, reliability, security, …)Evaluation (area, power, performance, reliability, security, …)

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Introduction to a simple digital camera

Captures imagesStores images in digital format

No filmMultiple images stored in camera

Number depends on amount of memory and bits used per image

Downloads images to PCOnly recently possible

Systems-on-a-chipMultiple processors and memories on one IC

High-capacity flash memoryVery simple description used for example

Many more features with real digital cameraVariable size images, image deletion, digital stretching, zooming in and out, etc.

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Two key tasksProcessing images and storing in memory

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

Uploading images to PCDigital camera attached to PCSpecial software commands camera to transmit archived images serially

Designer’s perspective

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Functional block diagram of a digital camera

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The CCD module is used to simulate the actions that an actual CCD would perform. Most notably it simulates the capture of an image and the transmission of pixels from the CCD.

The CCDPP module is responsible for performing the zero-bias adjustment on each pixel as they are being sent by the CCD module.

The CODEC module applies the Huffman encoding algorithm to the image by performing the DCT and quantization functions.

The CNTRL module serves as the controller of the system, instructing each module what function to perform next.

The UART models the serial transfer capability by sending the image byte by byte to an output file

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Block diagram of the executable model of the digital camera

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Digital Camera Block Diagram

Digital Camera Block Diagram

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1. Specifications

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CCD Array

Camera records the pictures using a charge coupled devices (CCD) array.

The array consisting of large number of horizontal rows and vertical columns of CCD cells for the picture

In each row of cells, a number of CCD cell unexposed to the picture but used for off-set

corrections in the each-row output from thepicture cells.

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Camera Picture resolution

2592 × 1944 pixels, there are 2592 × 1944 = 5038848 set of cells.

Each set of pixel has three cells, for the red, green and blue components in a pixel.

Each cell gets exposed to a picture when shutter of camera opens on a usercommand.

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2. Requirements

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Purpose

Digital recording and display of pictures

Processing to get the pictures of required brightness, contrast and color.

Permanent saving of picture in file in a standard format at a flash-memory stick or Card

Transfer files to a computer and printer through a USB port

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INPUT

Intensity and color values for each picture horizontal and vertical rows and columns of pixels in a picture frame.

Intensity and color values for unexposed (dark) area in each horizontal rows and columns of pixels.

User control inputs

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OUTPUT

Encoded file for a picture

Permanent store of the picture at a file on flash memory stick

Screen display of picture from the file after decoding

File output to an interfaced computer and printer

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Functions of the system

A color LCD dot matrix displays the picture before shooting─ enables manual adjustment of view of the picture.

For shooting a shutter button pressed─ a charge-coupled device (CCD) array placed at the focus generates a byte stream in output after operations by ADC on analog output of each CCD cell.

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Functions of the system

A file creates after encoding (compression) and pixel co-processing.

The byte stream is preprocessed and then encoded in a standard format using a CODEC.

The encoded picture file saved for permanent record. A memory stick saves the file.

The file is used for display of recorded picture using a display processor and can be copied or transferred to a memory stick and to computer or printer connected through USB port.

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Functions of the system…

The LCD displays picture file after it is decoded (decompressed) using the CODEC. Text such as picture-title, shooting date and time and serial number are also displayed.

USB port is used for transferring and storing pictures on a computer. Alternatively, Bluetooth or IR port can be used for interfacing the computer.

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Design metrics

Power Dissipation: Battery operation. Battery recharging after 400 pictures (assumed).

Resolution: High-resolution pictures with options of 2592 × 1944 pixels = 5038848 pixels, 2592 × 1728 = 3.2 M, 2048 × 1536 = 3 M and 1280 x 960 = 1M.

Performance: Shooting a 4M pixels still picture in 0.5 s. 25 pictures per m [Assumed]

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Design metrics…

Process Deadlines: Exposing camera process maximum 0.1 s. Flash synchronous with shutter opening and closing. Picture display latency maximum 0.5 s.

User Interfaces: Graphic at LCD or touch screen display on LCD and commands by camera user through fingers on touch screen and switches and buttons.

Engineering Cost: US$ 50000 (assumed).

Manufacturing Cost: US$ 50 (assumed).

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Test and validation conditions

All user commands must function correctly

All graphic displays and menus should appear as per the program.

Each task should be tested with test inputs

Tested for 30 pictures per m

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Camera tasks

Camera tasks are modeled by four class diagrams are divided

Picture_FileCreation,Picture_FileDisplay,Picture_FileTransfer andController_tasks

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3. Hardware architecture

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4. Software architecture

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Several implementations

Microcontroller: too slow

Microcontroller and coprocessor: better, but still too slow

Fixed-point arithmetic: almost fast enough

Additional coprocessor for compression: fast enough, but expensive and hard to design.

Tradeoffs between hw/sw

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Conclusion

The embedded systems contain programmed instruction running via processor chips. As the result of case studies, many differences were discovered among their current status, which is more helpful to meet proposed dead line and overcome the design challenges.

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References

[1] Embedded System Design – By Frank Vahid.

[2] Embedded Systems Architecture, Designing and Programming – By Rajkamal.

[3] Embedded Systems Programming and Designing – By Michael Barr.

[4] www.embedded.com.

[5] www.nptel.iitm.ac.in