04-02-2013, 12:49 PM
Digital Camera Example
Digital Camera.ppt (Size: 279.5 KB / Downloads: 30)
Introduction
Putting it all together
General-purpose processor
Single-purpose processor
Custom
Standard
Memory
Interfacing
Knowledge applied to designing a simple digital camera
General-purpose vs. single-purpose processors
Partitioning of functionality among different processor types
Introduction to a 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.
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
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
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 in this chapter 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