DIGITAL CAMERA A CASE STUDY
Rockey Suseelan M-Tech (S2) 1
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
Hardware Components
Concept
Hardware
HW/SW Partitioning
Specification
Estimation
Exploration Software Components
Evaluation
Software
(area, power, pow er, perfor mance, reliability ility,, security, se curity, «)
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n ro u c o n o a s m p e camera
g a
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 s imple description used for exam ple Very sim Many more features with real digital camera Variable size images, image deletion, digital stretching, zooming in and out, etc. 4
Designer¶s
perspective
Two
key tasks Processing images and storing in memory When shutter pressed: Image captured Converted to digital form by charge-cou pled 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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Funct
on a oc agram o 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 res ponsible for performing the zero-bias adjustment adjustment on each e ach 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 ca pability by sending the image byte by byte to an out put file
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B
oc agram o t e executa e 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
ctur ure e ce cellls ls.. pict
in the each-row output from the 11
Camera Picture resolution pixels, there are 2592 × 1944 = 5038848 set of cells. 2592 × 1944
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 user command.
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2. Requirements
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Purpose Digital
recor cording and displ splay of pictu ctures
Processing to get the pictures of required brig bright htne ness ss,, cont contra rast st and and colo colorr.
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 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 sys syste tem
color LCD dot matrix displays the picture bef before shooting enables manual adjustment of view of the picture. A
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 sys syste tem
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 c omputer or printer connected through USB port. 1
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Functions
of the sys syste tem«
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
Powerr Di Powe Diss ssipa ipattio ion: n: Ba Batt tter ery y oper operat atio ion n. Battery rech rechar argi ging ng afte afterr 400 pic ictu ture res s (ass (assum umed ed). ). Resolution:
High-resolution pic icttures 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] 20
Design metrics« Proc Proces ess s Dead Deadli line nes: s: Expo Exposi sing ng ca came mera ra process maximum 0.1 s. Flash synchronous with shutter opening and closing. Picture display late la tenc ncy y maxi maximu mum m 0.5 s. U ser
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:
U S$ S$
Manu Manufa fact ctur urin in Cost Cost::
50000 (assumed).
U S
50 assumed
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Test and validation conditions All
user commands com mands 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 divid vided Picture_FileCreation, Picture_FileDisplay,
Pictu cture_ re_Fil FileTr eTrans ansfer fer Pi
and
Controller_tasks
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3.
Hardware architecture
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4.
Software architecture
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Several implementations Microcontroller:
Microcontroller Microcontroller
too slow
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 Vahi ahid. [2] Embedded Systems Archi rchite tect ctur ure, e, Desi Design gnin ing g and Programming ± By Rajkamal. [3] Embedded Systems Programming Designing ± By Michael Barr.
and
[4] www.embedded.com www.embedded.com.. [5] www.nptel.iitm.ac.in 31
