- NK Guy, PhotoNotes.org.
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Photon or Poisson Noise
At a simple level, we can say that pixels measure light by counting photons (small packets of light).
Photons hitting a photosite and releasing electrons
Differences between the two types of sensors lead to a number of pros and cons:
Photo courtesy DALSA
A CCD sensor ...
Photon:
A particle of light energy. It is the smallest quantity of radiant energy that can be transmitted between two systems.
Photoshop: ...
Photonotes: Dictionary of Film and Digital Photography
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When light (photons) strike the image sensor, electrons are produced. These "photoelectrons" give rise to analog signals which are then converted into digital pixels by an Analog to Digital (A/D) Converter.
Causes of Noise ...
The idea of the photon was first put forward by Albert Einstein in his theory of the photoelectric effect. Photosite A small area on the surface of an image sensor that captures the brightness for a single pixel in the image.
Image Attachment: PhotoNet_Aruna-Parth-Neptun.jpg
Great document, uncle Bob! Would it is sensible to assume that there is a difference in UV absorbance between film and digital?
Br- (in crystal) + photon - - - > Br(in crystal) + e- (mobile)
It is believed that latent image formation involves both the migration of silver ions within the grain and the trapping of photoelectrons.
Similar to an array of buckets collecting rain water, digital camera sensors consist of an array of "pixels" collecting photons, the minute energy packets of which light consists.
The quantum of light is called the photon. The quantum theory is used to explain X ray, radiation, and photoelectricity.
Each of the 4096 levels represents an equal number of photons. The human visual system's response to light isn't linear though. Humans are sensitive to percentage changes in light, not absolute changes.
The photo-sensitive material called photo-resist coated on the wafer goes into an exposed state by absorbing a single photon.
Photons (light particles) that enter the sensor knock loose charge carriers (electrons). Those are stored and read out after the exposure, thus getting a count of Photons that entered the sensor during a period of time (exposure time).
When a caesium atom within the chamber encounters a photon from the lamp, it jumps to a higher energy state and then re-emits a photon and falls to an indeterminate lower energy state.
Larger sensors perform better at lower light levels - larger pixels can gather more photons at any given light level - so allowing lower-light photography and generally reducing noise.
This converts the light's photons into electrons which are then accelerated by an electric field to increase their energy level.
It is not fully understood exactly what happens during exposure but the energy released when a photon of light strikes a silver halide crystal frees an electron from the bromide ion.
The electrical signal produced in response to photons is commingled with electrical variations in the operation of the capture device. Random noise patterns always change, even if exposure conditions are identical.
After converting the photons into electrons, a mini-computer, located inside of the camera, reads the stored electrical value in each photograph. Then a built-in analogy-to-digital converter turns the stored electrical value into a digital value.
In digital photography, this defines the relationship between the incoming signal (light/photons striking the pixels/sensor elements) and the background electronic noise generated by the sensor. SNR is inherent in any electronic system.
Pay Attention to Light: The etymology of the word Photography is from the Greek works Photon and Graph - or "to record light.
" The values recorded by each photosite though are essentially simple counts of the number of photons that strike each.
photon). Microlenses capture the light striking the top portion of the camera sensor's pixels and redirect it into the pixel for processing.
An electronic device capable of reacting to the impact of photons, converting them to an electrical current that is then passed on to the A-D Converter. Sensors come in various types: CCD, CMD, CMOS. CCD are the most commonly used in digital imaging.
The convenience, the cost, the ease of use coupled with huge technical advances in converting photons into pixels have combined to make digital photography popular among top pros, advanced amateurs and novices alike.
Often, blooming occurs in scenes that are intensely backlit. In such cases, the bright light in the back produces more photons than a camera's photodiode (the photon receptor) can take in.
You can e-mail shots directly from the Kodak Picture CD, or by Kodak Photonet Online, a secure Internet link where friends and family can view your pictures and even order prints, enlargements, or gifts based on your shots.
Electromagnetic energy spectrum: Range of wavelengths or frequencies of radiant energy including, in order of increasing wavelength, cosmic-ray photons, gamma rays, x-rays, ultraviolet radiation, microwaves, radiowaves, heat, ...
In a nutshell: you can white balance to correct colour casts in white light, but not for coloured light. There is no way of getting natural-looking colour in a scene lit by sodium streetlights: there simply aren't any blue or green photons to carry ...
You can usually find me hiking in the San Gabriel Mountains or the Mojave Desert, both located in the beautiful state of California. Read more of my articles on nature photography at my website, PhotoNaturalist.
 See also: Image, Camera, Light, Photograph, Digital
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