Dictionary

This is a device that analyzes a real-world object or environment to collect data on its shape and possibly color.
The collected data can then be used to construct digital, three dimensional models useful for a wide variety of applications.

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An electronic device that converts an analog quantity (such as a voltage) to a proportional digital value.

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In context of photography or machine vision, aperture refers to the diameter of the aperture stop of a photographic lens. T
he aperture stop can be adjusted to control the amount of light reaching the film or image sensor.

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A set of specifications allowing application software to communicate with the camera.

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Defines the sensor's area used to capture the image.
It can be customized by users in its position on the sensor and in number of included pixel lines and rows.
During acquisition, only the pixel information within the specified area is transmitted out of the camera.
This is recommended when the key information being sought can be found in a smaller portion of the image.
A smaller AOI leads in general to higher maximum frame rates, since resulting images are smaller than the maximum sensor resolution: they are handled and processed faster while data volumes are kept smaller.

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Area Scan cameras contain a rectangular sensor with more than one line of pixels, which are exposed simultaneously.

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The aspect ratio of an image is its displayed width divided by its height (usually expressed as "x:y").

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back illuminated sensorIn a sensor, the circuitry surrounding the pixel active area greatly reduce light sensitivity. With last fabrication technology, it’s possible to build a sensor flipped upside down: in this process, after the creation of the photodiodes, transistor and metal interconnections, the chip is flipped upside down and mechanically polished till the previous “bottom” of the silicon chip is exposed. In this way the pixel active area is on the top of the sensor and it’s no longer obstructed by the readout circuitry.

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A regular array of red, green and blue color filters covering a sensor's pixels.
Each pixel is covered by a color filter of one color: the closest neighbors are covered by other color filters, according to a precise layout.

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binningIt’s a camera feature that combines the readout of adjacent pixels on the sensor (in rows/columns or, more often, in 2 x 2 or 4 x 4 squares). Using this feature resolution decreases, but there are other benefits: in the case of 2x2 binning, for example, resolution is halved, (since the capacities of each potential well are summed), but sensitivity and dynamic range are increased by a factor of 4, readout time is halved (frame rate doubled) and noise is quartered.

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Inspecting an image for discrete blobs of connected pixels (e.g. a black hole in a grey object) as image landmarks.

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CCDs, Charged-coupled devices, are sensors based on an array of passive photodiodes which integrates charge during the exposure time of the camera.
The charge is then transferred to electronics which reads the accumulated charges of the different pixels and translates them in voltages.
CCD is a passive-pixel device (i.e. with no electronics at pixel level), so the quantum efficiency is very high: this is an advantage in applications where the light is quite poor.
Then, since the electronics is the same for all the pixels, it’s possible to achieve a high pixel uniformity. On the other hand, the charge transfer is quite slow, resulting in a low frame rate (typically <20fps) and they are quite expensive since construction technology is not standard.

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CMOS, Complementary metal-oxide semiconductor, is a typology are sensors based on an array of active pixel.
The pixel-level electronics (typically 3 or 4 transistors) translates the charge accumulated in the photodiode in a well-defined voltage; in this way, the output of each pixel needs only to be acquired and sampled.
Since the pixel output relies on voltage (rather than on charge), with CMOS sensors it’s possible to achieve higher frame rates thanks to the easier readout scheme and it’s possible to define region of interest (ROI) to be acquired.
This readout scheme has the disadvantage to exploit a higher noise, due to the readout transistors in each pixel and due to the so-called fixed pattern noise: a non-homogeneity in the image due to the mismatches across the different pixel circuitries.
CMOS sensors have made a path into machine vision based largely on their advantage in speed (frame rate) and resolution (number of pixels) compared to CCD imagers.

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A lens mount for screw in lenses. The thread has a nominal diameter of 24.5 mm (1 inch) and 32 turns per inch.
The lens mount employs a flange to image plane distance of 17.526 mm (0.69 inch).

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Identify parts, products and items using color, assess quality from color, and isolate features using color.

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Image sensors are capable of delivering only grey values. To obtain full color information, each pixel is covered by a color filter (Red, Green or Blue) following an assigned pattern (e.g. Bayer pattern), allowing the pixel to deliver the gray value for the color of related color filter.
If a value is not measured, it can be interpolated using the gray values delivered by the neighboring pixels.
As an alternative to this technique is using a different sensor for each primary color.

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"White light" is commonly described by its color temperature. A traditional incandescent light source's color temperature is determined by comparing its hue with a theoretical, heated black-body radiator.
The lamp's color temperature is the temperature in kelvins at which the heated black-body radiator matches the hue of the lamp.

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The study and application of methods which allow computers to "understand" image content.

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In visual perception, contrast is the difference in visual properties that makes an object (or its representation in an image) distinguishable from other objects and the background.

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This kind of noise is caused by electrons that can be randomly produced by thermal effect. The number of thermal electrons, as well as the related noise, grows with temperature and exposure time.

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A standard image sensor captures black-and-white images. Color images require the use of a color matrix.
The most frequently used matrix is the Bayer pattern, featured in a process known as Bayering: it involves the composition of a mosaic using the color pixels, although the color values for that mosaic are actually incomplete.
To produce a proper color image, those color values are reconstructed using a dedicated algorithm: this process is known as Debayering or Demosaicing.
Demosaicing can either be performed directly within the camera's firmware or afterward in post-production using the raw data.

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In optics, particularly photography and machine vision, the depth of field (DOF) is the distance in front of and behind the subject which appears to be in focus.

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Dynamic range is the ratio between maximum and minimum signal that a sensor can acquire.
It indicates the ability of a sensor to produce an image of an area that includes both very low light (shadowed) and full light situations simultaneously with minimum noise or interference.
It could be described even as the ratio of the largest signal to the smallest signal, that can be distinguished from noise, in an image.
Dynamic range is usually expressed by the logarithm of the min-max ratio, either in base-10 (decibel) or base-2 (doublings or stops).

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ED marks the points in a digital image at which the luminous intensity changes sharply. It also marks the points of luminous intensity changes of an object or spatial-taxon silhouette.

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Radio Frequency Interference (RFI) is electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals, as a by-product of their normal operation, and which causes unwanted signals (interference or noise) to be induced in other circuits.

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It’s the amount of time in which light is allowed to reach the sensor. Increasing exposure time allows you to get brighter images, but there are even some drawbacks: blur effects can appear when dealing with moving objects and noise always increases in longer exposure time.
With a longer exposure time, the object will be impressed on a number of different pixels, causing the well-known ‘motion blur’ effect.
Furthermore, long exposure times can lead to overexposure – namely, when a number of pixels reach maximum capacity and thus appear to be white, even if the light intensity on each pixel is actually different.

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The field of view (FOV) is the part which can be seen by the machine vision system at one moment.
Field of view depends from the lens of the system and from the working distance between object and camera.

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An FPGA is a is an integrated circuit designed to be configured by a customer or a designer after manufacturing.
Many FPGAs can be reprogrammed to implement different logic functions, allowing flexible reconfigurable computing as performed in computer software.

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A non-homogeneity in the image due to the mismatches across the different pixel circuitries.

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A bayonet type lens mount introduced by Nikon. The lens mount employs a flange to image plane distance of 46.5 mm (1.83 inch).

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An image, or image point or region, is said to be in focus if light from object points is converged about as well as possible in the image; conversely, it is out of focus if light is not well converged.
The border between these conditions is sometimes defined via a circle of confusion criterion.

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Frame Per Second. This is the unit of the frame rate. Frame rate, measured in fps, describes the number of frames that are captured within a time unit.

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Frame rate, measured in fps, describes the number of frames that are captured within a time unit.
Higher frame rates are recommended in case you have to capture fast movements without blur, thus providing a continuously high image quality. Frame rate must be adjusted in every application.

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This index refers to the largest charge that a pixel can hold before overflowing to adjacent pixels, causing the so-called blooming.
Both, full well capacity and dark noise are decisive for the dynamic range of a sensor or camera.

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Gain is a measure of the ability to increase the amplitude of a signal from the input to the output port.
In a digital camera represents a way to increase the amount of signal collected by image sensor. Increasing gain value gives brighter images, thus increasing image noise as well.

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This kind of noise is caused by the difference in behavior of different pixels (in terms of sensitivity and gain). This is an example of ‘constant noise’ that can be measured and eliminated.

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In computer graphics and photography, a color histogram is a representation of the distribution of colors in an image, derived by counting the number of pixels of each of given set of color ranges in a typically two-dimensional (2D) or three-dimensional (3D) color space.
A histogram is a standard statistical description of a distribution in terms of occurrence frequencies of different event classes; for color, the event classes are regions in color space.

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Line Scan cameras have an image sensor consisting of 1 to 2 pixel lines.

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Metrology is the science of measurement. There are lots of applications for machine vision in metrology.

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micro lensesEspecially on CMOS sensors, each pixel active area is surrounded and surmounted by circuitry and metal connections responsible for the image readout: this reduces the amount of light which can be successfully detected.
If the light rays are not perpendicular to the sensor surface, they could even be reflected by near interconnections on the metal layers of the sensor chip.
Almost all modern image sensors are coated with an array of micro-lenses. These lenses gather incident light and focus it on the sensitive area of the pixel, thus increasing sensitivity.

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microlens shiftMicro-lenses are usually centered over each pixel active area, regardless of their relative position on the sensor surface.
However some sensors can be equipped with micro-lenses: these can be gradually shifted as we go from the center to the corner of the sensor: this helps to obtain better sensitivity uniformity over the sensor.

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Image noise is random variation of brightness or color information in images, and is usually an aspect of electronic noise.
They can be caused by either geometric, physical and electronic factors, and they can be randomly distributed as well as constant.

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Original Equipment Manufacturer (OEM): it manufactures products or components then purchased by a company and retailed under that purchasing company's brand name.
OEM refers to the company that originally manufactured the product.

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Describes the ability of a system to distinguish, detect, and/or record physical details by electromagnetic means.
The system may be imaging (e.g., a camera) or non-imaging (e.g., a quad-cell laser detector).

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A pixel is one of the many tiny dots that make up the representation of a picture in a computer's memory or screen.

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Pixel defects can be of three kinds: hot, warm and dead pixels.
Hot pixels are elements that always saturate (give maximum signal, e.g. full white) whichever the light intensity is.
Dead pixels behave the opposite, always giving zero (black) signal.
Warm pixels produce random signal. These kinds of defects are independent of the intensity and exposure time, so they can be easily removed – e.g. by digitally substituting them with the average value of the surrounding pixels.

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This kind of noise is related to conversion of continuous value of analog voltage value to discrete value of digital voltage.

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The percentage of photons effectively converted into electrons at a given wavelength.

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Defines the sensor's area used to capture the image.
It can be customized by users in its position on the sensor and in number of included pixel lines and rows.
During acquisition, only the pixel information within the specified area is transmitted out of the camera.
This is recommended when the key information being sought can be found in a smaller portion of the image.
A smaller ROI leads in general to higher maximum frame rates, since resulting images are smaller than the maximum sensor resolution: they are handled and processed faster while data volumes are kept smaller.

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The RGB color model utilizes the additive model in which red, green, and blue light are combined in various ways to create other colors.

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