In the camera pickup tube, there are horizontal deflection coils and vertical deflection coils. They move the electron beam across the target as well as up and down (Figure 2.4). A series of grids inside.bmp)
the neck of the pickup tube focuses the electron beam and keepsthe beam perpendicular to the target. This keeps the aperture assmall as possible and, therefore, the image as sharp as possible.
In the television system that is used in the United States, the electronbeam will scan back and forth across the target 525 times in eachtelevision frame. Thus each frame in the television signal is composedof 525 scan lines. It does not matter what size the camerais or what size the pickup tube or monitor is. The total number oflines scanned from the top of the frame to the bottom of the framewill always be 525.
The image created in the video camera has now been turned intoan electronic signal of varying voltages. As an electronic signal, thetelevision image can be carried by cables, recorded on videotapemachines, or even transmitted through the air.
Displaying the Image
There is a peculiar problem that is caused by lenses. A right-side-up image coming through the face of a lens will be inverted, or turned upside down, as it comes out of that lens. In film, this is not a serious problem. Although the image is recorded upside down on thefilm, when it goes back through a lens during projection, it is once again inverted, and the image on the movie screen is displayed rightside up.
In video, the camera lens causes the image to be focused upside down on the face of the target (see Figure 2.1). There is no lens in front of a television monitor or receiver to flip the upside-down image right side up again. The television image is inverted by scanning the image in the camera from the bottom to the top, instead of from the top down. On the receiver, or monitor, the scan is from top to bottom. This way the image appears right side up on the monitor.
The varying voltages generated by the camera can be converted back into light. This electrical energy powers an electron gun in the television receiver or monitor. That gun sends a stream of electrons to the face of the picture tube in the receiver. Changing voltages in the video signal cause chemical phosphors on the inside face ofthe receiver tube to glow with intensity in direct proportion to the amount of voltage. The image that originated in the tube camera is thus recreated, line by line. Motion and detail are all reproduced.
CCD Cameras
The pickup tubes and the scanning yokes needed to drive the tube cameras have been eliminated and replaced by a light-sensitive chip (Figure 2.5). The chip is a charge-coupled device, or CCD, from which this type of camera gets its name. CCD cameras are also referred to as chip cameras.
A CCD is a chip that contains an area, or site, covered with thousands, and in some instances millions, of tiny capacitors or condensers (devices for storing electrical energy). Consumer digital still cameras have chips that can contain as many as five million sites, or five megapixels. This chip came out of the technology that was developed for EPROM (Erasable Programmable Read-Only Memory) chips.They are used for computer software where updates or changes can occur. When the information is burned onto an EPROM, it is meant to be semi-permanent. It is erasable only under high-intensity ultraviolet light.
the neck of the pickup tube focuses the electron beam and keepsthe beam perpendicular to the target. This keeps the aperture assmall as possible and, therefore, the image as sharp as possible.In the television system that is used in the United States, the electronbeam will scan back and forth across the target 525 times in eachtelevision frame. Thus each frame in the television signal is composedof 525 scan lines. It does not matter what size the camerais or what size the pickup tube or monitor is. The total number oflines scanned from the top of the frame to the bottom of the framewill always be 525.
The image created in the video camera has now been turned intoan electronic signal of varying voltages. As an electronic signal, thetelevision image can be carried by cables, recorded on videotapemachines, or even transmitted through the air.
Displaying the Image
There is a peculiar problem that is caused by lenses. A right-side-up image coming through the face of a lens will be inverted, or turned upside down, as it comes out of that lens. In film, this is not a serious problem. Although the image is recorded upside down on thefilm, when it goes back through a lens during projection, it is once again inverted, and the image on the movie screen is displayed rightside up.
In video, the camera lens causes the image to be focused upside down on the face of the target (see Figure 2.1). There is no lens in front of a television monitor or receiver to flip the upside-down image right side up again. The television image is inverted by scanning the image in the camera from the bottom to the top, instead of from the top down. On the receiver, or monitor, the scan is from top to bottom. This way the image appears right side up on the monitor.
The varying voltages generated by the camera can be converted back into light. This electrical energy powers an electron gun in the television receiver or monitor. That gun sends a stream of electrons to the face of the picture tube in the receiver. Changing voltages in the video signal cause chemical phosphors on the inside face ofthe receiver tube to glow with intensity in direct proportion to the amount of voltage. The image that originated in the tube camera is thus recreated, line by line. Motion and detail are all reproduced.
CCD Cameras
The pickup tubes and the scanning yokes needed to drive the tube cameras have been eliminated and replaced by a light-sensitive chip (Figure 2.5). The chip is a charge-coupled device, or CCD, from which this type of camera gets its name. CCD cameras are also referred to as chip cameras.
A CCD is a chip that contains an area, or site, covered with thousands, and in some instances millions, of tiny capacitors or condensers (devices for storing electrical energy). Consumer digital still cameras have chips that can contain as many as five million sites, or five megapixels. This chip came out of the technology that was developed for EPROM (Erasable Programmable Read-Only Memory) chips.They are used for computer software where updates or changes can occur. When the information is burned onto an EPROM, it is meant to be semi-permanent. It is erasable only under high-intensity ultraviolet light.
In a CCD camera, the light information that is converted to electrical energy is deposited on sites on the chip. Unlike an EPROM, however, it is easily removed or changed. The sites are tiny condensers that hold an electrical charge and are separated from each other by insulating material. This prevents the charge from leaking off. The chip is very efficient and can hold the information for extended periods of time. The charge can be released and then replaced by the next set of charges.
Camera Chips
Inside the chip camera, light coming through the lens is focused on a chip (Figure 2.5). In the case of cameras that use multiple chips, light entering the camera goes through a beam splitter and is then focused onto the chips, rather than passing through a pickup tube or tubes. A beam splitter is an optical device that takes the light coming in through the lens and divides or splits it. It directs the light through filters that filter out all but one color for each of the chips. One chip sees only red light, one only blue, and one only green. The filters are called dichroic because they filter out two of the three colors. These chips are photosensitive, integrated circuits..bmp)
When light strikes the chip, it charges the chip’s sites with electrical energy in proportion to the amount of light that strikes the chip.
In other words, the image that is focused on the chip is captured by the photosensitive surface as an electrical charge. This electrical charge is then read off the chip, site by site. The technology behind these chips allows them to shoot bright light without overloading.
However, if the light is bright enough, the charge can spill over from one site to the next. This can cause the edges of an object within an image to smear or lag.
To prevent this, an optical grid or black screen is laid over the face of the chip so that between the light-sensitive sites there is both insulation and light absorbing material. The same process is usedin a video monitor where a shadow mask is used to prevent excess light from spilling over between adjacent phosphor groups on the screen, which would cause a blurring of the image.
To capture the information stored on the chip, the chip is scanned from site to site, and the energy is discharged as this happens. A numerical value is assigned as each site is scanned, according to the amount of electrical energy present. This numerical information is converted to electrical energy at the output of the camera. This is part of the digitizing process, as the numerical value is converted tocomputer data for storage and transmission.
Lower-end consumer cameras typically have one CCD chip, while most professional or prosumer cameras have three. In consumer cameras, chips resemble the construction of TV receiver tubes. All three colors (red, green, and blue) are present on the one chip. There is no need for three chips and a beam splitter. Typically, the largerthe size of the CCD or CCDs in the camera, the better the image quality. For example, a camera with a 2/3-inch chip will capture a better quality image than a camera with a 1/2-inch chip.
On professional cameras, there is one chip for each color: red, green, and blue (Figure 2.6). The resolution in these cameras is much greater; that is, the chips are better able to reproduce details in an image (resolution), which is determined by the number of sites on the chip. The more sites a chip has, the more detailed the stored video information will be. The chip will also be more expensive. Also, through
Camera Chips
Inside the chip camera, light coming through the lens is focused on a chip (Figure 2.5). In the case of cameras that use multiple chips, light entering the camera goes through a beam splitter and is then focused onto the chips, rather than passing through a pickup tube or tubes. A beam splitter is an optical device that takes the light coming in through the lens and divides or splits it. It directs the light through filters that filter out all but one color for each of the chips. One chip sees only red light, one only blue, and one only green. The filters are called dichroic because they filter out two of the three colors. These chips are photosensitive, integrated circuits.
When light strikes the chip, it charges the chip’s sites with electrical energy in proportion to the amount of light that strikes the chip.In other words, the image that is focused on the chip is captured by the photosensitive surface as an electrical charge. This electrical charge is then read off the chip, site by site. The technology behind these chips allows them to shoot bright light without overloading.
However, if the light is bright enough, the charge can spill over from one site to the next. This can cause the edges of an object within an image to smear or lag.
To prevent this, an optical grid or black screen is laid over the face of the chip so that between the light-sensitive sites there is both insulation and light absorbing material. The same process is usedin a video monitor where a shadow mask is used to prevent excess light from spilling over between adjacent phosphor groups on the screen, which would cause a blurring of the image.
To capture the information stored on the chip, the chip is scanned from site to site, and the energy is discharged as this happens. A numerical value is assigned as each site is scanned, according to the amount of electrical energy present. This numerical information is converted to electrical energy at the output of the camera. This is part of the digitizing process, as the numerical value is converted tocomputer data for storage and transmission.
Lower-end consumer cameras typically have one CCD chip, while most professional or prosumer cameras have three. In consumer cameras, chips resemble the construction of TV receiver tubes. All three colors (red, green, and blue) are present on the one chip. There is no need for three chips and a beam splitter. Typically, the largerthe size of the CCD or CCDs in the camera, the better the image quality. For example, a camera with a 2/3-inch chip will capture a better quality image than a camera with a 1/2-inch chip.
On professional cameras, there is one chip for each color: red, green, and blue (Figure 2.6). The resolution in these cameras is much greater; that is, the chips are better able to reproduce details in an image (resolution), which is determined by the number of sites on the chip. The more sites a chip has, the more detailed the stored video information will be. The chip will also be more expensive. Also, through
the camera’s electronic processing ability, the video image can be altered in several ways. For example, the resolution of an image can be increased without actually having more sites on the chip. An image can be enlarged digitally within the camera, beyond the optical ability of the lens. This same processing can also eliminate noise, or spurious information, and enhance the image. During the digitizing process, certain artifacts can occur in the video that can be a problem. Through image processing in the camera, these artifacts can be blended to make them less noticeable.
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Sometimes these problems can also be overcome by changing a camera angle or altering the lighting.Because of their small size and minimal weight, chip cameras have become very useful in field production, news work, documentaries, and even low-budget films. With their resistance to smearing and lagging, and their ability to work in low-light situations, they have also found a use in studios.
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