DFK 23G618 CCD Color Camera
- 1/4" Sony CCD, progressive scan
- 640x480 pixel, up to 120 images
- Trigger input and I/O
- Casing compatible to most analog computers
- Software included!
At the "input" of a camera, we have a CCD chip. It transforms photons into electrons. The spectral sensitivity of this transformation is an important characteristic of the "camera input".At the camera's output, we except an image data stream with a color format, such as "Y800" for monochrome cameras, or "UYVY" for color cameras.
The camera's spectral behavior is determined by the following four components:
- The CCD chip transforms photons into electrons (photoelectric effect). A Bayer filter inside the color CCDs is responsible for the creation of colors (please see CCD chips (color).
- In contrast to the human eye, CCD chips are also sensitive to near infrared light. In the case of color cameras this would lead to a predominance of red. An IR cut filter corrects this situation. However, cameras without IR cut filter provide more flexibility because they enable the users to apply their own filter depending on the particular requirements.
- If the object that is to be acquired shows fine and regular structures, moiré patterns may occur in the resulting image. An optical low pass filter (OLPF) reduces this effect.
- The camera electronics enhance the CCD chips' raw data. This enhancement can be controlled by adjusting different parameters (to learn more about this topic, please see the white paper Camera Parameters - Maximizing the Image Quality). In this white paper, the color formats created by the camera electronics are discussed.
CCD Chips Color:
CCD chips convert photons into electrons due to the photoelectric effect. Unfortunately, during this process important information gets lost: the photon's wavelength. Thus, CCDs are "color-blind". In 1976 Bryce E. Bayer obtained the US patent 3,971,065 for the solution of this problem. He equipped every second pixel with a green filter and distributed blue and red filters evenly to the remaining pixels. Because of this mosaic-like arrangement a Bayer filter is also called mosaic filter.Thus, with the aid of these filters, the pixels do not only provide luminance values but a pixel is more or less red, green or blue. The following spectral diagrams illustrate the meaning of "red", "green" and "blue" in case of the CCDs used by The Imaging Source.
The Imaging Source uses three Sony CCD chips for its color FireWire cameras. The spectral diagrams have been taken from the manufacturer's data sheet. Please note that the manufacturer does not specify deviations to the specified values.
IR Cut Filter:
In contrast to the human eye, CCD chips are also sensitive to near infrared light (NIR). Daylight as well as the light emitted by filament lamps show a significant amount of NIR. There are two main reasons to protect CCD chips from being influenced by the NIR:
- Lenses (or other optics) that are not IR-corrected "process" the NIR incorrectly, and thus, would decrease the image quality.
- In the case of color cameras the NIR would lead to a predominance of red. Correct white balance would not be possible.
For this reason many manufacturers equip their cameras with an IR cut filter.
Ideally, an IR cut filter should be completely transparent for the visible part of the spectrum, while blocking all IR light. The following diagram depicts the actual behavior of the IR cut filter used in The Imaging Source FireWire cameras:
Optical low pass filter (OLPF)
Fine and regular structures in the object that is to be acquired may lead to moiré effects in the resulting image. An OLPF reduces this effect, but causes slightly blurred images.
Moiré effects may also be reduced by slightly defocussing the lens. The basic advantage of an OLPF that is integrated in the camera is the easy handling. Independently of the lenses setting there is always a protection from moiré effects - but there are also always slightly blurred images. Thus, the use of any high quality optics makes almost no sense.
Color formats define the coding of the information "color" in a digital image data stream. Unfortunately, this coding lacks standards and thus there is a vast number of such formats. Often they only differ in their names.
The Imaging Source monochrome FireWire cameras use the format Y800. It provides 256 graylevels per pixel.
Cleaning CCD Chip in DMK, DBK, and DFK Camera Methods:
- Compressed air from air blower - Compressed air is usually sufficient to remove most foreign bodies from the surface of the CCD chip. We recommend using an air-blower, such as from Edmund Optics, and not compressed air from an aerosol. Compressed air from an aerosol may contain other chemicals (propellant, water, oil etc.) which could damage the surface of the CCD.
- Hama Lenspen MiniPro II - A company called Hama manufactures a product, which is ideally suited to the task: Lenspen MiniPro II. It is available online and from most well-stocked photography stores. One side of the pen has a brush on it, while the other, a small cleaning surface. The later is suited to efficiently removing dirt and fingerprints.
- Microfiber cleaning cloth - Although a microfiber cleaning cloth is a very viable option, it can be tricky to get the cloth onto the surface of the CCD chip through the camera's mount opening. A cotton swab (UK: Q-Tip) can help here.
- 90% pure alcohol - This can be purchased from most chemists. Never use Isopropanol, as it draws moisture from the air, which results in streaks on the surface of the CCD.
- Alcohol substitute - Instead of pure alcohol, Methanol or a liquid called Eclipse can be used (Eclipse is essentially Methanol). However, we do not recommend this approach, as Methanol is highly poisonous.
- Combination of all the above - Of course, all approaches can be combined! Do not worry about touching the glass in front of the CCD chip. It is pretty robust. Only by rubbing glass, sand or diamond on the surface can it be scratched.
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