22-02-2011, 02:42 PM
[attachment=8955]
Digital Camera
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
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
Digital Camera
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
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
