Buyers of video cameras will find two types of image sensors used to produce the digital images during recording: CCD and CMOS. These each utilize different technology, and some users find there can be a significant difference between them. The factors that are most affected by the image sensor are the price of the camera, the efficiency of its image processing, artifacts, and the quality of the images produced. Understanding how each of the two types of sensors work and the strengths and weaknesses of each will help buyers determine which technology is more suitable for their video camera needs.
CCD (Charged Coupled Device)
In a CCD video camera, light hitting the image sensor is converted to an electrical signal. This electron packet must then be transferred one pixel at a time through an output node to an image processor, at which point it is converted to voltage. The voltage is then buffered and sent out from the chip as an analog signal.
This process involves an extra step over CMOS sensors and therefore requires more time and energy to process imagery. However, because each pixel is devoted to capturing light, CCD sensors have a high output uniformity that results in cleaner, higher-quality images.
CCD sensors are also distinct from CMOS for their use of global shutters instead of rolling shutters. Global shutters process an entire image at once by exposing the full frame for a predetermined amount of time. This means the entire sensor gathers an equal amount of light at once. Global shutters are free of the image distortion related to rapid movement or flashes of light.
CMOS (Complementary Metal Oxide Semiconductor)
Unlike CCDs, CMOS sensors have circuitry at the pixel level. This means that every pixel on the sensor is read and transmitted simultaneously, preparing voltage for the chip. The chip then uses additional technology, such as amplifiers, noise correction, and digitization, to convert the voltage to digital data. This means that CMOS sensors do not require a separate image processor. Because CMOS sensors are able to convert visual information to digital data more quickly than CCDs, they require less power, which preserves battery life. However, the extra technology on the sensor crowds the pixels, limiting their ability to capture light and resulting in generally poorer visual clarity in the final image.
CMOS sensors are commonly designed with rolling shutters, especially on commercial applications. This means that the image frame is exposed from one side to the other, instead of all at once as on CCD sensors. For example, a video camera using a CMOS sensor may record data in a "rolling" sweep from left to right, or top to bottom. This results in the potential for a few types of distortion not found on CCD sensors.
Sensor Artifacts
Sensor artifacts refer to the alteration of digital imagery in a frame as a result of the video process. The types of artifacts produced by CCD and CMOS sensors vary due to their different shutter types. Keep in mind that there is no physical shutter on digital cameras as there would be on a film camera. The "shutter" instead indicates the sensor’s designed exposure method. Remember that CCDs use a global shutter, while CMOS sensors in commercial products use a rolling shutter. There are four primary types of artifacts. The first three are applicable only to rolling shutters (CMOS cameras), while the fourth, smear, affects global shutters (CCD cameras).
Skew
Skew only occurs on CMOS cameras, as it is a result of the rolling shutter. This artifact occurs when the camera or subject is moving swiftly during exposure. Because the rolling shutter records data from one side to the other, an object that has moved position between the start and end of exposure will appear to occupy multiple places within the image. For example, a person running across the frame of a camera that records from top to bottom may appear to have his lower body stretched out in front of his head and upper body, as the camera recorded the lower body in a moment after the upper body.
Wobble
Wobble is similar to skew, and results from instances in which the video camera is shaken or affected by other sudden motion. It is a common artifact in videos from handheld cameras. Images affected by wobble may appear to be stretched or sometimes duplicated. This is also commonly referred to as the Jello effect.
Partial Exposure
Partial exposure occurs when a flash of light, such as a camera flash or lightning bolt, is caught in the shot. The rolling shutter may only capture the light produced in part of the image, leaving the remainder dark. This can result in images that appear split, with a portion of the image lit more clearly than the other and divided by a sharp line. Like skew, wobble, and partial exposure only occur on CMOS cameras that use a rolling shutter.
Smear
Smear is a type of CCD artifact that occurs as a result of a bright spot within an image. The intense light causes a column of pixels to appear white or washed out on the exposed image. These columns, or streaks of light, often appear in images of headlights or any direct video of a light source.
Choosing Between CCD and CMOS
CCD technology was traditionally the dominant sensor since the development of the two forms in the late 1960s and early 1970s. This was mostly due to CCD’s ability to produce better image quality than CMOS with the manufacturing abilities of the time. However, developments in lithography in the 1990s allowed designers to produce CMOS sensors in a way that provided quality images at a lower cost than CCD. It was these developments that led to the inclusion of CMOS sensors in digital cameras, ultimately making the products affordable for the general public.
Although CCDs have set the benchmarks for image sensor performance, developments in CMOS have greatly reduced the differences in image quality between them. Meanwhile, developers of CCD sensors have worked to lower the cost of the technology. Contradictory to past perceptions of the sensors, modern forms of CCDs have become inexpensive enough to be used in applications like cell phone cameras, while some high-performance cameras in professional and industrial applications use CMOS technology.
In general, CCD cameras can produce higher resolution images with less noise. They are also more sensitive to light, which means that they produce higher-quality images in low-light settings. CMOS cameras are more energy efficient, which means the battery life is longer. They are also generally less expensive. However, many of these differences have already become negligible in modern products. For example, a high-end CMOS camera may produce clearer images than a mid-range CCD camera.
Ultimately, buyers of commercial video camera products may find that the sensor technology used in a video camera is less relevant than the manufacturer and specific camera. Modern developments in each type of sensor technology have made them quite comparable in terms of the amount of power used, their price, and their image quality.
Shop for CCD and CMOS Video Cameras on eBay
To shop for digital video cameras, head to the eBay homepage. Begin by opening the All Categories tab and selecting the option for Cameras & Photography, followed by camcorders. You may narrow item listings further by brand, camera type, media type, and optical zoom. To search for CCD and CMOS cameras from this page, use the search field. Type either "ccd" or "cmos" in the Search field to see all item listings within the Camcorders category related to those terms.
Read item listings for video cameras carefully before making a purchase. Check the price of the item and include any applicable shipping charges. Also, look to see which payment methods a seller accepts to be sure you can pay promptly for your purchase. Look over all available photos of the item, especially if you are purchasing a used video camera. Contact the seller if you want additional information or photos.
Research seller profiles before purchasing a CCD or CMOS video camera. Look at positive feedback ratings and read comments left by other buyers. The number of transactions a seller has completed can also be used to assess the user’s reliability. Once you have received your purchase, return to eBay to leave feedback about the transaction. Do this by clicking on the My eBay tab on the homepage and selecting Purchase History. From there, you will be shown a list of all your previous transactions and given the option to leave feedback for each. Contact the seller to see if a resolution can be reached if you are dissatisfied with your video camera transaction.
Conclusion
CCD and CMOS are two types of image sensors used in digital video cameras. The technology of each varies, and some users find there is a noticeable difference between their image qualities. Pixels in CCD sensors are committed to capturing light. This produces higher-quality images, though it also causes a camera to be less efficient. CMOS sensors cut out a step by integrating technology into the chip that converts visual information to digital data as it is processed to the chip. This makes these sensors highly efficient, though the extra tasks of the pixels can result in increased noise in the final image.
CCDs use a global shutter, while CMOS sensors use a rolling shutter. These are each prone to artifacts. CCDs suffer from smear, while CMOS can be affected by skew, wobble, and partial exposure. Despite inherent differences in their technology and performance, the benefits and drawbacks of the two sensor types may not be as pronounced as they have been in the past. Buyers are likely to find that image quality and camera performance is affected more by the manufacturer of a video camera than the type of sensor used. Read product reviews and research sellers to find the best products at reasonable prices, and choose video cameras that produce high-quality footage.
