Digital cameras

The invention of photographic emulsion in the 1850s revolutionized how we document history and society. The invention of the charge-coupled device (CCD) by Willard Boyle and George Smith in 1969 led to many advances in astronomy and other fields. Digital cameras based on CCDs have made photography easy to do and ubiquitous in society. How does a digital camera work? Read the text aloud
How the charge-coupled device (CCD) works in a digital camera
The light detector in a digital camera is the CCD. A detector is an instrument used to detect and measure radiation. Photons of visible light enter the camera and strike the silicon surface of the CCD, liberating electrons through the photoelectric effect. A CCD typically has millions of tiny pixels, each of which acts as both a detector and a storage bin. Each pixel is a p-n junction semiconductor device, which acts very similar to photovoltaic cells used in solar arrays. In a CCD, each pixel acts as a capacitor, where electric fields keep the electrons in place until it is time to read out the picture. Read the text aloud
Reading out a CCDThe accumulated charge in a pixel corresponds to the number of photons that were incident upon the pixel and liberated an electron. An amplifier converts the charge of the stored electrons into a voltage that is read and stored. If more photons strike a pixel, then it stores more electrons and results in a higher voltage when the pixel is read out. The CCD shifts the charge for the first row’s pixels one by one across the serial register to the amplifier where the voltage is read out. The CCD then shifts the remaining pixels down by a row and reads out the second row’s pixels one by one. In this way the CCD creates an image of the number of photons detected in each pixel. Read the text aloud Show CCD and CMOS
To create a color image with a CCD, alternating pixels have a red, green, or blue filter mounted in front of them, called a Bayer mask. In the digital image, adjacent RGB pixels are combined to create a color that you can see on a computer screen. Read the text aloud
What are the relative strengths of CCD and APS imager (CMOS) technology for a detector in a digital camera? Show

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