Charge Coupled Devices Converts analogue signal of the light image into digital signals and then transfer to the camera’s memory system and store as an electronic data. CCDs are not inherently color sensitive. Three different ways are commonly employed to produce colour images with CCD camera systems in order to capture the visual appearance. three-chip design frame-sequential method Bayer's pattern (most common)

1. INDIAN INSTITUTE OF TECHNOLOGY ROORKEE
CCD colour capture
Aditya Chauhan
Master of Technology
Packaging Technology

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Content
• Introduction
• Image sensor
• Charge Coupled Devices
• Composition and working of CCDs
• Colored image using CCDs
• Methods of producing colored image with CCD
• Advantages and Disadvantages of CCD Sensors

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Introduction
• In the past we used to place a piece of film behind lens.
• But now we have purely electronic imager to do all the work

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Image Sensor
• It is the image sensor that decides
the image resolution. So, it is like
the heart of the camera.
• In the early days, the film used to
do this job. Now, it got replaced by
CCD and CMOS sensors.
• They are responsible for acquiring
each of the pixels in an image. An
image sensor is quantified based
on its size and number of
megapixels.

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CCD (Charge Coupled Devices)
• Converts analogue signal of light image into digital
signals
• These digital signals are then transfers to camera’s
memory system and stored as a electronic data
• CCDs are about ten times more light-sensitive than film

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Formation of CCD
• CCD is made from light sensitive silicon slab.
• Channel stops are the insulating section to make each pixel in
the slab
• Surface is covered with a thin layer of insulating silicon dioxide.
• Perpendicular to channel stops, thin aluminum strips are placed.
• This will divided silicon into a geometrically regular array of
thousands or millions of light-sensitive regions (pixels) that
capture and store image information in the form of localized
electrical charge.

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Working of CCDs
• Sensor is exposed to light rays
• Photons will hit sensor and charge is build up proportional
to the light’s intensity
• Charge will amplify and then it will convert into voltage
signal
• Later these signals will get converted into digital numbers
and stored in memory
Photons
(light)
Electrons Voltage
Digital
numbers

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Colored Image
• CCDs are not inherently
color sensitive
• For the acquisition of color
images with a CCD camera
requires that red, green, and
blue wavelengths be
isolated by color filters,
acquired separately, and
subsequently combined into
a composite color image.

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Cont.
• Monochrome Chips have exact same pixel array
• They capture single black and white exposure

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Ways to produce colored image
Three different ways are commonly employed to produce color
images with CCD camera systems in order to capture the
visual appearance.
• three-chip design
• frame-sequential method
• Bayer's pattern (most common)

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Three-chip design
• The image is divided with a beam-splitting prism and color
filters into three (RGB) components, which are captured
with separate CCDs, and their outputs recombined into a
color image.
• Light intensity delivered to each CCD is substantially
reduced, the combined color image is much dimmer than a
monochrome single-chip image.

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Frame-sequential method
• Frame-sequential are equipped with a motorized filter to
sequentially expose red, green, and blue component
images onto a single CCD.
• Same sensor is used for separate red, green, and blue
images, the resolution of the chip is maintained, and image
registration is automatically obtained.
• Acquisition of three frames in succession slows the process
of image acquisition.

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Bayer’s Matrix
• Easiest way is to use Single filter with red, blue and green
pixel size sections.

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Cont.
• Each four-pixel sensor units include one red, one blue, and
two green filters. Green is emphasized in the distribution
pattern to better conform to human visual sensitivity.

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Cont.
• for e.g. if green filter covered a pixel we would need to
estimate red and blue pixel
• To do that adjacent pixels will average out the color
intensity of the pixel in question
• It works because significant details of image are much large
than each pixel

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Advantages and Disadvantages of CCD Sensors
Advantages of CCD sensors include
• lower noise and higher sensitivity
• fewer defective pixels due to their simple structure
• better image homogeneity.
Disadvantages include
• higher energy consumption
• slower readout
• increased complexity of image sensing systems
• higher cost.
Due to the these disadvantages, CMOS sensors are increasingly replacing CCD
sensors for certain applications, but CCD sensors still find use in medical and
scientific research.

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Thank You