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Bias Frame
In digital photography, a bias frame is an image obtained from an opto-electronic image sensor, with no actual exposure time. The image so obtained only contains unwanted signal due to the electronics that elaborate the sensor data, and not unwanted signal from charge accumulation (e.g. from dark current) within the sensor itself. A bias frame is complementary to a dark frame, which has a charge integration time but in darkness. Since a dark frame contains unwanted signal including a fixed-pattern noise component, some of which corresponds to the bias frame, and some of which is due to dark current and is proportional to the exposure time, it is possible to obtain an image representing only the dark-current component by subtracting a bias frame from a dark frame. The resulting image allows obtaining an "artificial" dark frame when multiplied by a factor depending on exposure time and then added back to the bias frame. Although this technique is less accurate than shooting a dark ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Photography
Digital photography uses cameras containing arrays of electronic photodetectors interfaced to an analog-to-digital converter (ADC) to produce images focused by a lens, as opposed to an exposure on photographic film. The digitized image is stored as a computer file ready for further digital processing, viewing, electronic publishing, or digital printing. Digital photography spans a wide range of applications with a long history. In the space industry, where much of the technology originated, it pertains to highly customized, embedded systems combined with sophisticated remote telemetry. Any electronic image sensor can be digitized; this was achieved in 1951. The modern era in digital photography is dominated by the semiconductor industry, which evolved later. An early semiconductor milestone was the advent of the charge-coupled device (CCD) image sensor, first demonstrated in April 1970; the field has advanced rapidly and continuously ever since, paced by concurrent advances ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Image Sensor
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 (as they pass through or reflect off objects) 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, camera phones, optical mouse devices, medical imaging equipment, night vision equipment such as thermal imaging devices, radar, sonar, and others. As technology changes, electronic and digital imaging tends to replace chemical and analog imaging. The two main types of electronic image sensors are the charge-coupled device (CCD) and the active-pixel sensor (CMOS sensor). Both CCD and CMOS sensors are based on metal–oxide–semiconductor (MOS) technology, with CCDs based on MOS capacitors and CMOS sensors based on M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dark Current (physics)
In physics and in electronic engineering, dark current is the relatively small electric current that flows through photosensitive devices such as a photomultiplier tube, photodiode, or charge-coupled device even when no photons enter the device; it consists of the charges generated in the detector when no outside radiation is entering the detector. It is referred to as reverse bias leakage current in non-optical devices and is present in all diodes. Physically, dark current is due to the random generation of electrons and holes within the depletion region of the device. The charge generation rate is related to specific crystallographic defects within the depletion region. Dark-current spectroscopy can be used to determine the defects present by monitoring the peaks in the dark current histogram's evolution with temperature. Dark current is one of the main sources for noise in image sensors such as charge-coupled devices. The pattern of different dark currents can result in a fix ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dark Frame
Darkness, the direct opposite of lightness, is defined as a lack of lighting, illumination, an absence of visible spectrum, visible light, or a surface that absorbs light, such as black or brown. Human visual perception, vision is unable to distinguish colors in conditions of very low luminance. This is because the hue sensitive photoreceptor cells on the retina are inactive when light levels are insufficient, in the range of visual perception referred to as scotopic vision. The emotional response to darkness has generated metaphorical usages of the term in many cultures, often used to describe an unhappy or foreboding feeling. Referring to a time of day, night, complete darkness occurs when the Sun is more than 18° below the horizon, without the effects of twilight on the night sky. Scientific Perception The perception of darkness differs from the mere absence of light due to the effects of afterimage, after images on perception. In perceiving, the eye is active, and the p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fixed-pattern Noise
Fixed-pattern noise (FPN) is the term given to a particular noise pattern on digital imaging sensors often noticeable during longer exposure shots where particular pixels are susceptible to giving brighter intensities above the average intensity. Overview FPN is a general term that identifies a temporally constant lateral non-uniformity (forming a constant pattern) in an imaging system with multiple detector or picture elements (pixels). It is characterised by the same pattern of variation in pixel-brightness occurring in images taken under the same illumination conditions in an imaging array. This problem arises from small differences in the individual responsitivity of the sensor array (including any local postamplification stages) that might be caused by variations in the pixel size, material or interference with the local circuitry. It might be affected by changes in the environment like different temperatures, exposure times, etc. The term "fixed pattern noise" usually refers ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dark Frame Subtraction
In digital photography, dark-frame subtraction is a way to reduce image noise in photographs shot with long exposure times, at high ISO sensor sensitivity or at high temperatures. It takes advantage of two components of image noise that remain the same from one shot to the next, dark current and fixed-pattern noise. Noise from the image sensor include hot pixels, which light up more brightly than surrounding pixels. The technique works by taking a picture with the shutter closed and subtracting that electronically from the original photo exhibiting the noise. A dark frame is an image captured with the sensor in complete darkness (i.e. with a closed shutter or the lens and viewfinder capped). Such a dark frame is essentially an image of noise produced by the sensor. A dark frame, or an average of several dark frames, can then be subtracted from subsequent images to correct for fixed-pattern noise. It is important that dark frames are taken at the same ISO sensitivity and expos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flat-field Correction
Flat-field correction (FFC) is a technique used to improve quality in digital imaging. It cancels the effects of image artifacts caused by variations in the pixel-to-pixel sensitivity of the detector and by distortions in the optical path. It is a standard calibration procedure in everything from personal digital cameras to large telescopes. Overview Flat fielding refers to the process of compensating for different gains and dark currents in a detector. Once a detector has been appropriately flat-fielded, a uniform signal will create a uniform output (hence flat-field). This then means any further signal is due to the phenomenon being detected and not a systematic error. A flat-field image is acquired by imaging a uniformly-illuminated screen, thus producing an image of uniform color and brightness across the frame. For handheld cameras, the screen could be a piece of paper at arm's length, but a telescope will frequently image a clear patch of sky at twilight, when the illumi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dark-frame Subtraction
In digital photography, dark-frame subtraction is a way to reduce image noise in photographs shot with long exposure times, at high ISO sensor sensitivity or at high temperatures. It takes advantage of two components of image noise that remain the same from one shot to the next, dark current and fixed-pattern noise. Noise from the image sensor include hot pixels, which light up more brightly than surrounding pixels. The technique works by taking a picture with the shutter closed and subtracting that electronically from the original photo exhibiting the noise. A dark frame is an image captured with the sensor in complete darkness (i.e. with a closed shutter or the lens and viewfinder capped). Such a dark frame is essentially an image of noise produced by the sensor. A dark frame, or an average of several dark frames, can then be subtracted from subsequent images to correct for fixed-pattern noise. It is important that dark frames are taken at the same ISO sensitivity and exposu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photographic Techniques
Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed in many fields of science, manufacturing (e.g., photolithography), and business, as well as its more direct uses for art, film and video production, recreational purposes, hobby, and mass communication. Typically, a lens is used to focus the light reflected or emitted from objects into a real image on the light-sensitive surface inside a camera during a timed exposure. With an electronic image sensor, this produces an electrical charge at each pixel, which is electronically processed and stored in a digital image file for subsequent display or processing. The result with photographic emulsion is an invisible latent image, which is later chemically "developed" into a visible image, either negative or positive, depending on the purpose ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photogrammetry
Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant imagery and other phenomena. The term photogrammetry was coined by the Prussian architect Albrecht Meydenbauer, which appeared in his 1867 article "Die Photometrographie." There are many variants of photogrammetry. One example is the extraction of three-dimensional measurements from two-dimensional data (i.e. images); for example, the distance between two points that lie on a plane parallel to the photographic image plane can be determined by measuring their distance on the image, if the scale (map), scale of the image is known. Another is the extraction of accurate color ranges and values representing such quantities as albedo, specular reflection, Metallicity#Photometric colors, metallicity, or ambient occlusion from photographs of mater ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
