Three-CCD camera

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A beam splitter prism assembly, with a white beam entering the front, exiting the three focal-plane faces, filtered to produce red, green and blue. Color Separation Prism.jpg
A beam splitter prism assembly, with a white beam entering the front, exiting the three focal-plane faces, filtered to produce red, green and blue.
A Philips type trichroic beam splitter prism schematic, with a different color separation order than the assembly shown in the photo. The red and blue beams each undergo one total internal reflection at the air gap and air/glass boundary respectively, while the other reflections are dichroic. This construction has the advantage over the above type that all 3 separated images are laterally inverted (as with a single sensor). In the first type, the blue image is not laterally inverted but the other two are. Dichroic-prism.svg
A Philips type trichroic beam splitter prism schematic, with a different color separation order than the assembly shown in the photo. The red and blue beams each undergo one total internal reflection at the air gap and air/glass boundary respectively, while the other reflections are dichroic. This construction has the advantage over the above type that all 3 separated images are laterally inverted (as with a single sensor). In the first type, the blue image is not laterally inverted but the other two are.
A 3CCD imaging block consisting of a color separation prism of Philips type on which 3 CCDs are mounted. A 3CCD imaging block.jpg
A 3CCD imaging block consisting of a color separation prism of Philips type on which 3 CCDs are mounted.

A three-CCD (3CCD) camera is a camera whose imaging system uses three separate charge-coupled devices (CCDs), each one receiving filtered red, green, or blue color ranges. Light coming in from the lens is split by a complex prism into three beams, which are then filtered to produce colored light in three color ranges or "bands". The system is employed by high quality still cameras, telecine systems, professional video cameras and some prosumer video cameras.

Camera type of camera for recording still images

A camera is an optical instrument to capture still images or to record moving images, which are stored in a physical medium such as in a digital system or on photographic film. A camera consists of a lens which focuses light from the scene, and a camera body which holds the image capture mechanism.

Image sensor device that converts an optical image into an electronic signal

An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves into signals, small bursts of current that convey the information. The waves can be light or other electromagnetic radiation. Image sensors are used in electronic imaging devices of both analog and digital types, which include digital cameras, camera modules, medical imaging equipment, night vision equipment such as thermal imaging devices, radar, sonar, and others. As technology changes, digital imaging tends to replace analog imaging.

Charge-coupled device device for the movement of electrical charge

A charge-coupled device (CCD) is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time. CCDs move charge between capacitive bins in the device, with the shift allowing for the transfer of charge between bins.

Contents

Overview

Compared to cameras with only one CCD, three-CCD cameras generally provide superior image quality by using full-frame dichroic filters to better separate the red, green and blue color bands, and better low-light performance. By separating red, green, and blue color ranges with a 1:1 pixel ratio (known as "4:4:4"), three-CCD cameras achieve much better precision than single-CCD cameras. [1]

Image quality can refer to the level of accuracy in which different imaging systems capture, process, store, compress, transmit and display the signals that form an image. Another definition refers to image quality as "the weighted combination of all of the visually significant attributes of an image". The difference between the two definitions is that one focus on the characteristics of signal processing in different imaging systems and the latter on the perceptual assessments that make an image pleasant for human viewers.

In contrast, almost all single-CCD cameras use a Bayer filter, using less accurate dye filters in front of each pixel to separate the colors. Because each pixel on a single CCD sensor is covered with its own tiny color filter, a frame is necessary to keep the dye filters from leaking into adjacent pixels. The result is less light absorbed compared to a CCD without a Bayer filter. Typically there is a 2:1 ratio of green and red/blue pixels, producing less color detail. [2]

Bayer filter color filter array for arranging RGB color filters on a square grid of photosensors

A Bayer filter mosaic is a color filter array (CFA) for arranging RGB color filters on a square grid of photosensors. Its particular arrangement of color filters is used in most single-chip digital image sensors used in digital cameras, camcorders, and scanners to create a color image. The filter pattern is 50% green, 25% red and 25% blue, hence is also called BGGR,RGBG, GRGB, or RGGB.

Three-CCD cameras are more expensive than single-CCD cameras because they use three sensors rather than one, and because they use a beam splitter to drive each of the three CCD chips. Additionally most 3CCD cameras use higher quality but more expensive dichroic filters to separate the color bands.

Dichroic filter

A dichroic filter, thin-film filter, or interference filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic reflectors tend to be characterized by the colors of light that they reflect, rather than the colors they pass.

The practice of cameras using three separate colors for color reproduction dates back to the advent of color photography, when three glass plates covered with photographic emulsion were used beginning in the late nineteenth century.

Now that (C)MOS (MOS = "metal oxide semiconductor") sensors are sufficiently advanced to compete with CCD technology, the catch-all term "three-chip" has arisen to cover all cameras that use beam splitters and three sensors for color reproduction. Previously, CCD sensors were superior to MOS in areas like image noise and sensitivity, and the ability to operate with global shutter.

Prior to CCD technology, color cameras used vacuum tube sensors for both color and monochrome. Because of mechanical tolerances and electrical changes as electronic components aged, 3-tube cameras had to be adjusted for image registration before each use. Each pixel in a CCD imager is fixed, so each of the three CCD elements on a 3CCD camera are registered in the factory, and permanently glued onto the optical block, thus eliminating any need for manual alignment (registration) by the end user.

Vacuum tube Device that controls electric current between electrodes in an evacuated container

In electronics, a vacuum tube, an electron tube, or valve or, colloquially, a tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.

Misconceptions

Those with an elementary understanding of optics often wrongly assume that the prism assembly in the optical block bends light by refraction into the different colors, as a dispersive prism does. In fact the type of prism used for 3-chip cameras is used only as a beam splitter. Each of the three resulting beams still contain all visible colors, just as complex prisms in binoculars and single-lens reflex cameras also pass the entire visible spectrum. Optical filters are what separate the full spectrum into three sub-spectra (not just primary colors) for color reproduction.

The notion that a larger single sensor is as good as a 3-chip system is less-than-true due to two main factors: The first is that current Bayer filter designs use absorptive dye filters, which are inferior to dichroic filters in terms of color purity. The second is that current Bayer filter designs collect significantly less red and blue information than green, resulting in 1/4 the color resolution of 3-chip sensors. These limitations could possibly be overcome by using many tiny dichroic filters, and by designing Bayer filter matrices with equal numbers of red, green and blue pixels. However none currently exist.

See also

Related Research Articles

Pixel a physical point in a raster image

In digital imaging, a pixel, pel, dots, or picture element is a physical point in a raster image, or the smallest addressable element in an all points addressable display device; so it is the smallest controllable element of a picture represented on the screen.

RGB color model additive color model based on combining red, green, and blue

The RGB color model is an additive color model in which red, green and blue light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additive primary colors, red, green, and blue.

Dichroism

In optics, a dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths (colours), or one in which light rays having different polarizations are absorbed by different amounts.

Digital camera camera that captures photographs or video in digital format

A digital camera or digicam is a camera that captures photographs in digital memory. Most cameras produced today are digital, and while there are still dedicated digital cameras, many more are now incorporated into devices ranging from mobile devices to vehicles. However, high-end, high-definition dedicated cameras are still commonly used by professionals.

LBCAST is a type of photo sensor which the manufacturer claims is simpler and thus smaller and faster than CMOS sensors. It was developed over ten years by Nikon, in parallel with other manufacturer's development of CMOS, and resulted in shipping product in 2003.

The Foveon X3 sensor is an image sensor for digital cameras, designed by Foveon, Inc. and manufactured by Dongbu Electronics. It uses an array of photosites, each of which consists of three vertically stacked photodiodes, organized in a two-dimensional grid. Each of the three stacked photodiodes responds to different wavelengths of light; that is, each has a different spectral sensitivity curve. This difference is because different wavelengths of light penetrate silicon to different depths. The signals from the three photodiodes are then processed, resulting in data that provides the amounts of three additive primary colors, red, green, and blue.

Dichroic prism

A dichroic prism is a prism that splits light into two beams of differing wavelength (colour). A trichroic prism assembly combines two dichroic prisms to split an image into 3 colours, typically as red, green and blue of the RGB colour model. They are usually constructed of one or more glass prisms with dichroic optical coatings that selectively reflect or transmit light depending on the light's wavelength. That is, certain surfaces within the prism act as dichroic filters. These are used as beam splitters in many optical instruments.

Super CCD camera parts, features and technologies

Super CCD is a proprietary charge-coupled device that has been developed by Fujifilm since 1999. The Super CCD uses octagonal, rather than rectangular, pixels. This allows a higher horizontal and vertical resolution to be achieved than a traditional sensor of an equivalent pixel count.

A demosaicing algorithm is a digital image process used to reconstruct a full color image from the incomplete color samples output from an image sensor overlaid with a color filter array (CFA). It is also known as CFA interpolation or color reconstruction.

Active pixel sensor an image sensor consisting of an integrated circuit

An active-pixel sensor (APS) is an image sensor where each picture element ("pixel") has a photodetector and an active amplifier. There are many types of integrated circuit active pixel sensors including the complementary metal–oxide–semiconductor (CMOS) APS used most commonly in cell phone cameras, web cameras, most digital pocket cameras since 2010, in most digital single-lens reflex cameras (DSLRs) and Mirrorless interchangeable-lens cameras (MILCs). Such an image sensor is produced using CMOS technology, and has emerged as an alternative to charge-coupled device (CCD) image sensors.

Color filter array

In photography, a color filter array (CFA), or color filter mosaic (CFM), is a mosaic of tiny color filters placed over the pixel sensors of an image sensor to capture color information.

RGBE filter

In digital photography, the RGBE filter is an alternative color filter array to the Bayer filter (GRGB). It similarly uses a mosaic of pixel filters, of red, green, blue and "emerald", and so also requires demosaicing to produce a full-color image. It was developed by Sony and so far is used only in the ICX456 8-megapixel CCD and in the Sony Cyber-shot DSC-F828 camera.

A scanning back is a type of digital camera back. Digital imaging devices typically use a matrix of light-sensitive photosensors, such as CCD or CMOS technologies. These sensors can be arranged in different ways, like a Bayer filter, where each row captures RGB components, or using one full-sized layer for each color, such as the Foveon X3 sensor.

Sigma SD14 digital camera model

The Sigma SD14 is a digital single-lens reflex camera produced by the Sigma Corporation of Japan. It is fitted with a Sigma SA mount which takes Sigma SA lenses.

Colour co-site sampling

Colour co-site sampling is a system of photographic colour sensing, wherein 4, 16 or 36 images are collected from the sensor and merged to form a single image. Each subsequent image physically moves the sensor by exactly one pixel, in order to collect R, G and B data for each pixel, known as microscanning. This is a viable alternative to the typical Bayer filter array of pixels which returns a lower quality images with interpolated pixel colours.

3LCD

3LCD is the name and brand of a major LCD projection color image generation technology used in modern digital projectors. 3LCD technology was developed and refined by Japanese imaging company Epson in the 1980s and was first licensed for use in projectors in 1988. In January 1989, Epson launched its first 3LCD projector, the VPJ-700.

References

  1. "3CCD colour advantages -AT". www.adept.net.au. Retrieved 11 April 2018.
  2. Cliff Wootton (2005). A Practical Guide to Video and Audio Compression: From Sprockets and Rasters to Macroblocks. Elsevier. p. 137. ISBN   978-0-240-80630-3.
3 monochrome sensors and color separation prism from Sony DCR-VX100E camera 3CCD sensors and separation prism.jpg
3 monochrome sensors and color separation prism from Sony DCR-VX100E camera