Image resolution

Image resolution is the detail an image holds. The term applies to raster digital images, film images, and other types of images. Higher resolution means more image detail.

Image resolution can be measured in various ways. Resolution quantifies how close lines can be to each other and still be visibly resolved. Resolution units can be tied to physical sizes (e.g. lines per mm, lines per inch), to the overall size of a picture (lines per picture height, also known simply as lines, TV lines, or TVL), or to angular subtense. Line pairs are often used instead of lines; a line pair comprises a dark line and an adjacent light line. A line is either a dark line or a light line. A resolution of 10 lines per millimeter means 5 dark lines alternating with 5 light lines, or 5 line pairs per millimeter (5 LP/mm). Photographic lens and film resolution are most often quoted in line pairs per millimeter.

Resolution of digital images

The resolution of digital cameras can be described in many different ways.

Pixel resolution

The term resolution is often considered equivalent to pixel count in digital imaging, though international standards in the digital camera field specify it should instead be called "Number of Total Pixels" in relation to image sensors, and as "Number of Recorded Pixels" for what is fully captured. Hence, CIPA DCG-001 calls for notation such as "Number of Recorded Pixels 1000 × 1500".[1][2] According to the same standards, the "Number of Effective Pixels" that an image sensor or digital camera has is the count of pixel sensors that contribute to the final image (including pixels not in said image but nevertheless support the image filtering process), as opposed to the number of total pixels, which includes unused or light-shielded pixels around the edges.

An image of N pixels height by M pixels wide can have any resolution less than N lines per picture height, or N TV lines. But when the pixel counts are referred to as "resolution", the convention is to describe the pixel resolution with the set of two positive integer numbers, where the first number is the number of pixel columns (width) and the second is the number of pixel rows (height), for example as 7680 × 6876. Another popular convention is to cite resolution as the total number of pixels in the image, typically given as number of megapixels, which can be calculated by multiplying pixel columns by pixel rows and dividing by one million. Other conventions include describing pixels per length unit or pixels per area unit, such as pixels per inch or per square inch. None of these pixel resolutions are true resolutions, but they are widely referred to as such; they serve as upper bounds on image resolution.

Below is an illustration of how the same image might appear at different pixel resolutions, if the pixels were poorly rendered as sharp squares (normally, a smooth image reconstruction from pixels would be preferred, but for illustration of pixels, the sharp squares make the point better).

Resolution illustration

Resolution illustration

An image that is 2048 pixels in width and 1536 pixels in height has a total of 2048×1536 = 3,145,728 pixels or 3.1 megapixels. One could refer to it as 2048 by 1536 or a 3.1-megapixel image. Or, you can think of it as a very low quality image (72ppi) if printed at about 28.5 inches wide, or a very good quality (300ppi) image if printed at about 7 inches wide.

Unfortunately, the count of pixels isn't a real measure of the resolution of digital camera images, because color image sensors are typically set up to alternate color filter types over the light sensitive individual pixel sensors. Digital images ultimately require a red, green, and blue value for each pixel to be displayed or printed, but one individual pixel in the image sensor will only supply one of those three pieces of information. The image has to be interpolated or demosaiced to produce all three colors for each output pixel.

Spatial resolution

The terms blurriness and sharpness are used for digital images but other descriptors are used to reference the hardware capturing and displaying the images.

Spatial resolution in radiology refers to the ability of the imaging modality to differentiate two objects. Low spatial resolution techniques will be unable to differentiate between two objects that are relatively close together.

Image at left has a higher pixel count than the one to the right, but is still of worse spatial resolution.

Matakis - blurred
MARTAKIS1

The measure of how closely lines can be resolved in an image is called spatial resolution, and it depends on properties of the system creating the image, not just the pixel resolution in pixels per inch (ppi). For practical purposes the clarity of the image is decided by its spatial resolution, not the number of pixels in an image. In effect, spatial resolution refers to the number of independent pixel values per unit length.

The spatial resolution of consumer displays range from 50 to 800 pixel lines per inch. With scanners, optical resolution is sometimes used to distinguish spatial resolution from the number of pixels per inch.

In remote sensing, spatial resolution is typically limited by diffraction, as well as by aberrations, imperfect focus, and atmospheric distortion. The ground sample distance (GSD) of an image, the pixel spacing on the Earth's surface, is typically considerably smaller than the resolvable spot size.

In astronomy, one often measures spatial resolution in data points per arcsecond subtended at the point of observation, because the physical distance between objects in the image depends on their distance away and this varies widely with the object of interest. On the other hand, in electron microscopy, line or fringe resolution refers to the minimum separation detectable between adjacent parallel lines (e.g. between planes of atoms), whereas point resolution instead refers to the minimum separation between adjacent points that can be both detected and interpreted e.g. as adjacent columns of atoms, for instance. The former often helps one detect periodicity in specimens, whereas the latter (although more difficult to achieve) is key to visualizing how individual atoms interact.

In Stereoscopic 3D images, spatial resolution could be defined as the spatial information recorded or captured by two viewpoints of a stereo camera (left and right camera).

Spectral resolution

Pixel encoding limit the information stored in a digital image, and the term color profile is used for digital images but other descriptors are used to reference the hardware capturing and displaying the images.

Spectral resolution is the ability to resolve spectral features and bands into their separate components. Color images distinguish light of different spectra. Multispectral images can resolve even finer differences of spectrum or wavelength by measuring and storing more than the traditional 3 of common RGB color images.

Temporal resolution

Temporal resolution (TR) refers to the precision of a measurement with respect to time.

Movie cameras and high-speed cameras can resolve events at different points in time. The time resolution used for movies is usually 24 to 48 frames per second (frames/s), whereas high-speed cameras may resolve 50 to 300 frames/s, or even more.

Many cameras and displays offset the color components relative to each other or mix up temporal with spatial resolution:

Lcd display dead pixel

LCD (Triangular pixel geometry)

Shadow mask closeup cursor

CRT (shadow mask)

In the quantum physics there is a trade-off between temporal resolution of a measurement and its spatial resolution due to uncertainty principle, similarly a time/space trade-off is an inherent property of Fourier transform used to visualise audio.185.127.125.171

Radiometric resolution

Radiometric resolution determines how finely a system can represent or distinguish differences of intensity, and is usually expressed as a number of levels or a number of bits, for example 8 bits or 256 levels that is typical of computer image files. The higher the radiometric resolution, the better subtle differences of intensity or reflectivity can be represented, at least in theory. In practice, the effective radiometric resolution is typically limited by the noise level, rather than by the number of bits of representation.

Resolution in various media

This is a list of traditional, analog horizontal resolutions for various media. The list only includes popular formats, not rare formats, and all values are approximate, because the actual quality can vary machine-to-machine or tape-to-tape. For ease-of-comparison, all values are for the NTSC system. (For PAL systems, replace 480 with 576.) Analog formats usually had less chroma resolution.

  • Analog and early digital[3]
  • Digital
    • 500×480 : Digital8
    • 720×480 : D-VHS, DVD, miniDV, Digital Betacam (NTSC)
    • 720×480 : Widescreen DVD (anamorphic) (NTSC)
    • 720×576 : D-VHS, DVD, miniDV, Digital8, Digital Betacam (PAL/SECAM)
    • 720×576 : Widescreen DVD (anamorphic) (PAL/SECAM)
    • 1280×720 : D-VHS, HD DVD, Blu-ray, HDV (miniDV)
    • 1440×1080 : HDV (miniDV)
    • 1920×1080 : HDV (miniDV), AVCHD, HD DVD, Blu-ray, HDCAM SR
    • 1998×1080 : 2K Flat (1.85:1)
    • 2048×1080 : 2K Digital Cinema
    • 3840×2160 : 4K UHDTV, Ultra HD Blu-ray
    • 4096×2160 : 4K Digital Cinema
    • 7680×4320 : 8K UHDTV
    • 15360×8640 : 16K Digital Cinema
    • 61440×34560 : 64K Digital Cinema
    • Sequences from newer films are scanned at 2,000, 4,000, or even 8,000 columns, called 2K, 4K, and 8K, for quality visual-effects editing on computers.
    • IMAX, including IMAX HD and OMNIMAX: approximately 10,000×7,000 (7,000 lines) resolution. It is about 70 Mpix, which is currently highest-resolution single-sensor digital cinema camera (as of January 2012).
  • Film
    • 35 mm film is scanned for release on DVD at 1080 or 2000 lines as of 2005.
    • The actual resolution of 35 mm camera original negatives is the subject of much debate. Measured resolutions of negative film have ranged from 25-200 lp/mm, which equates to a range of 325 lines for 2-perf, to (theoretically) over 2300 lines for 4-perf shot on T-Max 100.[4][5][6] Kodak states that 35mm film has the equivalent of 6K resolution according to a Senior Vice President of IMAX.[7]
  • Print
PPI Pixels cm
800 1000 3.18
300 1000 8.47
200 1000 12.7
72 1000 35.28
PPI Pixels cm
800 3150 10
300 1181 10
200 787 10
72 283 10
PPI Pixels mm Paper size
300 9921×14008 840×1186 A0
300 7016×9921 594×840 A1
300 4961×7016 420×594 A2
300 3508×4961 297×420 A3
300 2480×3508 210×297 A4
300 1748×2480 148×210 A5
300 1240×1748 105×148 A6
300 874×1240 74×105 A7
300 614×874 52×74 A8
  • Modern digital camera resolutions
    • Digital medium format camera - single, not combined one large digital sensor - 80 Mpix(starting from 2011, current as of 2013) - 10320 × 7752 or 10380 × 7816(81.1Mpix).[8][9][10][11]
    • Mobile phone - Nokia 808 PureView - 41 Mpix (7728 × 5368), Nokia Lumia 1020 - also 41 Mpix (7712 × 5360)
    • Digital still camera - Canon EOS 5DS - 51 Mpix (8688 × 5792)

See also

References

  1. ^ [1] Guideline for Noting Digital Camera Specifications in Catalogs. "The term 'Resolution' shall not be used for the number of recorded pixels"
  2. ^ ANSI/I3A IT10.7000-2004 Photography - Digital Still Cameras - Guidelines for Reporting Pixel-Related Specifications
  3. ^ http://www.derose.net/steve/resources/video-resolution.html
  4. ^ "Archived copy" (PDF). Archived from the original (PDF) on 2011-09-11. Retrieved 2011-08-31.CS1 maint: Archived copy as title (link) Kodak 500t Film spec sheet
  5. ^ [2] An analysis of film resolution
  6. ^ [3] Explanation of MTF
  7. ^ "/Film Interview: IMAX Executives Talk 'The Hunger Games: Catching Fire' and IMAX Misconceptions". Slash Film. December 2, 2013. Retrieved December 17, 2013.
  8. ^ http://www.phaseone.com/en/camera-systems/iq-series.aspx
  9. ^ "Leaf Aptus Medium Format Digital Backs". www.mamiyaleaf.com.
  10. ^ DxO. "Phase One IQ180 Digital Back : Tests and Reviews - DxOMark". www.dxomark.com.
  11. ^ Forret, Peter. "Megapixel calculator - toolstudio". web.forret.com.
Angular resolution

Angular resolution or spatial resolution describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object, thereby making it a major determinant of image resolution. In physics and geosciences, the term spatial resolution refers to the precision of a measurement with respect to space.

Compound eye

A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which distinguish brightness and color. The image perceived by the arthropod is a combination of inputs from the numerous ommatidia, which are oriented to point in slightly different directions. Compared with single-aperture eyes, compound eyes have poor image resolution; however, they possess a very large view angle and the ability to detect fast movement and, in some cases, the polarization of light.

Diffraction-limited system

The resolution of an optical imaging system – a microscope, telescope, or camera – can be limited by factors such as imperfections in the lenses or misalignment. However, there is a principal limit to the resolution of any optical system, due to the physics of diffraction. An optical system with resolution performance at the instrument's theoretical limit is said to be diffraction-limited.The diffraction-limited angular resolution of a telescopic instrument is proportional to the wavelength of the light being observed, and inversely proportional to the diameter of its objective's entrance aperture. For telescopes with circular apertures, the size of the smallest feature in an image that is diffraction limited is the size of the Airy disk. As one decreases the size of the aperture of a telescopic lens, diffraction proportionately increases. At small apertures, such as f/22, most modern lenses are limited only by diffraction and not by aberrations or other imperfections in the construction.

For microscopic instruments, the diffraction-limited spatial resolution is proportional to the light wavelength, and to the numerical aperture of either the objective or the object illumination source, whichever is smaller.

In astronomy, a diffraction-limited observation is one that achieves the resolution of a theoretically ideal objective in the size of instrument used. However, most observations from Earth are seeing-limited due to atmospheric effects. Optical telescopes on the Earth work at a much lower resolution than the diffraction limit because of the distortion introduced by the passage of light through several kilometres of turbulent atmosphere. Some advanced observatories have recently started using adaptive optics technology, resulting in greater image resolution for faint targets, but it is still difficult to reach the diffraction limit using adaptive optics.

Radiotelescopes are frequently diffraction-limited, because the wavelengths they use (from millimeters to meters) are so long that the atmospheric distortion is negligible. Space-based telescopes (such as Hubble, or a number of non-optical telescopes) always work at their diffraction limit, if their design is free of optical aberration.

The beam from a laser with near-ideal beam propagation properties may be described as being diffraction-limited. A diffraction-limited laser beam, passed through diffraction-limited optics, will remain diffraction-limited, and will have a spatial or angular extent essentially equal to the resolution of the optics at the wavelength of the laser.

Digital image

A digital image is a numeric representation, normally binary, of a two-dimensional image. Depending on whether the image resolution is fixed, it may be of vector or raster type. By itself, the term "digital image" usually refers to raster images or bitmapped images (as opposed to vector images).

Dykstraflex

The Dykstraflex was the first digital motion control photography camera system, named after its primary developer John Dykstra. Numerous people actually created the camera, with the critical electronics being created by Alvah J. Miller and Jerry Jeffress.

The camera was developed in 1976 specifically for complex special effects shots in Star Wars. Using old VistaVision cameras (for their high image resolution), created by engineers at Paramount Pictures in 1954, and hand wire wrapped TTL chips, the all-digitally controlled system allowed for 7 axes of motion: roll, pan, tilt, swing, boom, traverse, track, lens focus, motor drive, shutter control, and their duplication in multiple takes.

Dykstra's development of this first digital motion control camera system earned himself, Al Miller, and Jerry Jeffress Academy Awards in 1978.

GoPro

GoPro, Inc. (marketed as GoPro and sometimes stylised as GoPRO) is an American technology company founded in 2002 by Nick Woodman. It manufactures eponymous action cameras and develops its own mobile apps and video-editing software. Founded as Woodman Labs, Inc, the company eventually focused on the connected sports genre, developing its line of action cameras and, later, video editing software.

It developed a quadcopter drone, Karma, released in October 2016. In January 2018, Karma was discontinued and the company hired JPMorgan Chase to pursue options of selling the company. However, a month later, the CEO denied this. GoPro has continued its business in manufacturing action cameras.

Ground sample distance

In remote sensing, ground sample distance (GSD) in a digital photo (such as an orthophoto) of the ground from air or space is the distance between pixel centers measured on the ground. For example, in an image with a one-meter GSD, adjacent pixels image locations are 1 meter apart on the ground. GSD is a measure of one limitation to image resolution, that is, the limitation due to sampling.GSD is also referred to as ground-projected sample interval (GSI) or ground-projected instantaneous field of view (GIFOV).

High-definition television

High-definition television (HDTV) is a television system providing an image resolution that is of substantially higher resolution than that of standard-definition television. This can be either analog or digital. HDTV is the current standard video format used in most broadcasts: terrestrial broadcast television, cable television, satellite television, Blu-rays, and streaming video.

HDTV may be transmitted in various formats:

720p (HD ready): 1280×720p: 923,600 pixels (~0.92 MP) per frame

1080i (full HD) : 1920×1080i: 1,036,800 pixels (~1.04 MP) per field or 2,073,600 pixels (~2.07 MP) per frame

1080p (full HD): 1920×1080p: 2,073,600 pixels (~2.07 megapixels) per frame

Some countries also use a non-standard CEA resolution, such as 1440×1080i: 777,600 pixels (~0.78 MP) per field or 1,555,200 pixels (~1.56 MP) per frameThe letter "p" here stands for progressive scan, while "i" indicates interlaced.

When transmitted at two megapixels per frame, HDTV provides about five times as many pixels as SD (standard-definition television). The increased resolution provides for a clearer, more detailed picture. In addition, progressive scan and higher frame rates result in a picture with less flicker and better rendering of fast motion. HDTV as is known today first started official broadcasting in 1989 in Japan, under the MUSE/Hi-Vision analog system. HDTV was widely adopted worldwide in the late 2000s.

High-resolution computed tomography

High-resolution computed tomography (HRCT) is a type of computed tomography (CT) with specific techniques to enhance image resolution. It is used in the diagnosis of various health problems, though most commonly for lung disease, by assessing the lung parenchyma.

ISO/IEC 19794-5

ISO/IEC 19794 Information technology — Biometric data interchange formats — Part 5: Face image data, or ISO/IEC 19794-5 for short, is the fifth of 8 parts of the ISO standard ISO/IEC 19794, published in 2005, which describes interchange formats for several types of biometric data. ISO/IEC 19794-5 defines specifically a standard scheme for codifying data describing human faces within a CBEFF-compliant data structure, for use in facial recognition systems. Modern biometric passport photos should comply with this standard. Many organizations and have already started enforcing its directives, and several software applications have been created to automatically test compliance to the specifications.The standard is intended to allow computer analysis of face images for automated face identification (one-to-many searching) and authentication (one-to-one matching), as well as human identification of distinctive features such as moles and scars that might be used to verify identity, and human verification of computer identification results.

In order to enable applications that run on a variety of devices, including those with limited resources (such as embedded systems), and to improve face recognition accuracy, the specification describes not only the data format, but also additional requirements, namely: scene constraints (lighting, pose, expression, etc.); photographic properties (positioning, camera focus etc.); and digital image attributes (image resolution, image size, etc.).

Four face image types are introduced to define categories that satisfy the needs of different applications, and the requirements above are specified for each image type:

Basic: the fundamental Face Image Type that specifies a record format including header and image data. All the remaining Face Image Types inherit the properties of this type. No mandatory scene, photographic and digital requirements are specified for this image type.

Frontal: consists of an extension to the Basic Face Image Type to conform to requirements appropriate for frontal face recognition. Two variants of the Frontal Face Image Type are defined:

Full Frontal: A Face Image Type that specifies frontal images with sufficient resolution for human examination as well as reliable computer face recognition. This type of Face Image Type includes the full head with all hair in most cases, as well as neck and shoulders. This image type is suitable for permanent storage of the face information, and it is applicable to ID portraits for passport, driver's license, and mug shot images.

Token Frontal: specifies frontal images with a specific geometric size and eye positioning based on the width and height of the image. It requires less detail, which makes it suitable for less demanding applications.

ImageShack

ImageShack is a subscription-based image hosting website headquartered at Los Gatos, California.

Although ImageShack previously had a subscription service, the majority of its revenue was produced from advertising related to its free image hosting. In January 2014, ImageShack announced that it was switching to a subscription based service and would no longer offer free uploads.Images stored in free accounts were still available until January 31, 2016, and free accounts not converted to paid accounts were deleted after that date. The new website interface does not allow direct free web-based access to the original image resolution, but images can be bulk-downloaded at original resolution using their SkyPath application.

Image compression

Image compression is a type of data compression applied to digital images, to reduce their cost for storage or transmission. Algorithms may take advantage of visual perception and the statistical properties of image data to provide superior results compared with generic data compression methods which are used for other digital data.

PAL

Phase Alternating Line (PAL) is a colour encoding system for analogue television used in broadcast television systems in most countries broadcasting at 625-line / 50 field (25 frame) per second (576i). Other common colour encoding systems are NTSC and SECAM.

All the countries using PAL are currently in process of conversion or have already converted standards to DVB, ISDB or DTMB.

This page primarily discusses the PAL colour encoding system. The articles on broadcast television systems and analogue television further describe frame rates, image resolution and audio modulation.

Panasonic Lumix DMC-FZ28

The Panasonic Lumix DMC-FZ28 is a superzoom bridge digital camera, replacing the similar Panasonic Lumix DMC-FZ18. It was announced in 2008 and released for sale in the United Kingdom in August of that year. Like the FZ18 it has a Leica lens with an 18x optical zoom ratio. It has a slightly larger sensor than the FZ18, a 10.1-megapixel image resolution, and the newer Venus IV image processing engine.

Raster graphics

In computer graphics, a raster graphics or bitmap image is a dot matrix data structure that represents a generally rectangular grid of pixels (points of color), viewable via a monitor, paper, or other display medium. Raster images are stored in image files with varying formats.

A bitmap is a rectangular grid of pixels, with each pixel's color being specified by a number of bits. A bitmap might be created for storage in the display's video memory or as a device-independent bitmap file. A raster is technically characterized by the width and height of the image in pixels and by the number of bits per pixel (or color depth, which determines the number of colors it can represent).The printing and prepress industries know raster graphics as contones (from "continuous tones"). The opposite to contones is "line work", usually implemented as vector graphics in digital systems. Vector images can be rasterized (converted into pixels), and raster images vectorized (raster images converted into vector graphics), by software. In both cases some information is lost, although vectorizing can also restore some information back to machine readability, as happens in optical character recognition.

Specialist (computer)

The Specialist (Russian: Специалист) is a DIY computer designed in Soviet Union. Its description was published in Modelist-Konstructor (Russian: Моделист-Конструктор), a magazine for scale model builders in 1987. It was the first such publication in a magazine not oriented on electronics. The original construction was developed by a professional technical school teacher two years earlier. It was much more advanced than previous DIY computers, because it had a higher graphical image resolution (384x256) and a "transparent" video system, which did not slow down the CPU when both the CPU and the video system tried to access the RAM simultaneously. It gained limited popularity with hobbyists, though some factories produced DIY kits (Lik for example).

Traffic camera

A traffic camera is a video camera which observes vehicular traffic on a road. Typically, these are put along major roads such as highways, freeways, motorways, autoroutes and expressways, as well as arterial roads, and are connected with optical fibers buried alongside or even under the road, with electrical power either provided by mains power in urban areas, or via solar panels or another alternate power source which provides consistent imagery without the threat of a power outage during inclement conditions.

A monitoring center receives the live video in real time, and serves as a dispatcher if there is a traffic collision or some other disruptive incident or road safety issue.

Traffic cameras are a major part of most intelligent transportation systems. They are especially valuable in tunnels, where safety equipment can be activated remotely based upon information provided by the cameras and other sensors. On surface roads, they are typically mounted on high poles or masts, sometimes along with street lights. On arterial roads, they are often mounted on traffic light poles at intersections, where problems are most likely to occur. In remote areas without easy reach of the main electrical grid, they are usually powered by another means such as solar power, which also provides a backup source to urban camera infrastructure.

Traffic cameras are distinct from road safety cameras, which are put in specific places to enforce rules of the road. Those cameras take still photos in a much higher image resolution upon a trigger, whereas traffic cameras are simply for observation and constantly take lower-resolution video, often in full motion, though they are remotely controllable in order to focus on an ongoing traffic incident farther along a road that may not be in the camera's usual field of view or even along a frontage road or other roadway within its field of vision. Many transmit in the legacy analog NTSC and PAL formats, depending on location, though many are being converted to high definition video as equipment is replaced. Some have a compass built in which displays the cardinal direction at which the camera is aimed, though many providers also provide a reference image of a shot with the cardinal direction.

Many transportation departments have linked their camera networks to the Internet on online websites, thus making them webcams which allow commuters to view current traffic conditions. They may show either streaming video or still imagery which refreshes at a set interval of seconds or minutes, helping travelers determine whether an alternate route should be taken. In the United States and Canada, these often are displayed on state or municipally-run 5-1-1 websites (511 being a telephone number designed to relay current traffic information). These traffic images are also combined with road sensors which measure traffic timing to provide a full picture of traffic conditions.

Many states and provinces consider this information public domain, thus many television stations air live traffic camera imagery during their own traffic reports on their local news broadcasts, or simply as an augmenting moving visual background during newscasts. Some cable TV systems provide these pictures full-time on a governmental access channel, and some broadcast stations set aside a full digital subchannel solely for traffic information and camera imagery, such as Philadelphia's WPHL-DT4 in the past and WMVT-DT3 in Milwaukee and WFMZ-DT2 in Allentown, Pennsylvania currently. However, in some cases for toll roads and other private road authorities, such as the Illinois State Toll Highway Authority, these images are claimed to be the property of the toll agency (or private company which runs a toll road), and the images are held under an exclusivity agreement for one station (in the ISTHA's case, they only air on WMAQ-TV).

Yantar-4K2M

Yantar-4K2M (Russian: Янтарь meaning amber), also known as Kobalt-M, is a type of Russian reconnaissance satellite and is the current operational member of the Yantar series of satellites. In common with most Yantar satellites the Kobalt-M uses film rather than digital cameras. This allows a better quality of photographs. The drawback is film cannot be sent to Earth so easily, so Yantar satellites require special way of delivery.

The Kobalt-M is an improved version of the Kobalt satellite and the first one was launched as Kosmos 2410 in 2004. It returns three sets of film during its mission. The first two land in film return canisters (called SpK - Spuskayemaya Kapsula) and a final set of film returns in the satellite's special equipment module. Image resolution is reportedly 30 cm.Ten satellites of this series were launched, the last one in 2015; no further orders are planned. Further reconnaissance missions are carried out by the Persona-class satellites.

Zoom lens

A zoom lens is a mechanical assembly of lens elements for which the focal length (and thus angle of view) can be varied, as opposed to a fixed focal length (FFL) lens (see prime lens).

A true zoom lens, also called a parfocal lens, is one that maintains focus when its focal length changes. A lens that loses focus during zooming is more properly called a varifocal lens. Despite being marketed as zoom lenses, virtually all consumer lenses with variable focal lengths use varifocal design.

The convenience of variable focal length comes at the cost of complexity - and some compromises on image quality, weight, dimensions, aperture, autofocus performance, and cost. For example, all zoom lenses suffer from at least slight, if not considerable, loss of image resolution at their maximum aperture, especially at the extremes of their focal length range. This effect is evident in the corners of the image, when displayed in a large format or high resolution. The greater the range of focal length a zoom lens offers, the more exaggerated these compromises must become.

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