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Topic: Aliasing

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Sampling frequency

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	Aliasing - Wikipedia, the free encyclopedia
		Aliasing is a major concern in the analog-to-digital conversion of video and audio signals: improper sampling of the analog signal will cause high-frequency components to be aliased with genuine low-frequency ones, and be incorrectly reconstructed as such during the subsequent digital-to-analog conversion.
		The aliasing distortion in the lower frequencies is increasingly obvious with higher fundamental frequencies, and while the bandlimited sawtooth is still clear at 1760 Hz, the aliased sawtooth is degraded and harsh with a buzzing audible at frequencies lower than the fundamental.
		Sawtooth aliasing demo {440 Hz bandlimited, 440 Hz aliased, 880 Hz bandlimited, 880 Hz aliased, 1760 Hz bandlimited, 1760 Hz aliased}
	en.wikipedia.org /wiki/Aliasing (2226 words)

	Anti-aliasing - Wikipedia, the free encyclopedia
		In signal acquisition, this is often done using an analog anti-aliasing filter to remove the out-of-band component of the input signal prior to sampling with an analog-to-digital converter.
		See the articles on signal processing and aliasing for more information about the theoretical justifications for anti-aliasing; the remainder of this article is dedicated to anti-aliasing methods in computer graphics.
		When the lower level aliasing is suppressed, to make the third image and then that is down-sampled once more, without anti-aliasing, to make the fifth image, the order on the scale of the third image appears as systematic aliasing in the fifth image.
	en.wikipedia.org /wiki/Anti-aliasing (2665 words)

	Aliasing
		Aliasing, in that sense, is an important consideration in both compiler and CPU design.
		Aliasing can also occur in spatial sampling; the "jaggies" seen in poorly-sampled raster images are a common spatial aliasing phenomenon.
		The term "aliasing" derives from the usage in radio engineering, where a radio signal could be picked up at two different positions on the radio dial in a superheterodyne radio: one where the local oscillator was above the radio frequency, and one where it was below.
	www.ebroadcast.com.au /lookup/encyclopedia/al/Aliasing.html (1543 words)

	Anti-Aliasing in Computer Graphics
		Generally, aliasing refers to the degradation of a sound, image, or other signal during the sampling process due to low-resolution sampling.
		Aliasing is common in computer graphics because screen or file resolutions are finite whereas the mathematical models describing an image have infinite resolution.
		The reason we do not notice aliasing is that high frequency image components beyond the Nyquist limit are perceived as noise which our brains have evolved to ignore.
	www-static.cc.gatech.edu /classes/AY2001/cs4451_spring/projects/Five (1033 words)

	NatBat :: Aliasing and Anti-aliasing :: (Site not responding. Last check: 2007-11-07)
		Aliasing is what is happening in the lower half of FIGURE 2, where valuable information is lost and the sampled wave pretends 'aliases' as a lower frequency.
		Aliasing, in its broadest sense; is the effect that happens when the sampling rate is not high enough to sample the full range of the frequency received in analogue form.
		An example of "aliasing" is jaggedness of curves and lines represented by pixels, this is because the colour to be represented by each individual pixel is recorded at either full or zero intensity.
	www.natbat.co.uk /uniProj/graphicsCW.php (1918 words)

	Aliasing - PanoTools
		Aliasing is a process that results in "jaggies" or Moire effects when an image is sampled or resampled.
		Slow periodic sampling of a signal causes high frequency components to be "aliased" into low frequency ones that corrupt the sampled signal.
		To avoid aliasing, a signal must not contain frequencies that are higher than one half the sample rate.
	www.panotools.info /mediawiki/index.php?title=Aliasing (302 words)

	The Geneva Convention On The Treatment of Object Aliasing
		While some aliasing problems may thus result from insufficient problem analysis, leading to situations in which roles accidentally conflict, perhaps they more typically arise out of class and method design and implementation decisions that either ignore the possibility of aliasing or intentionally disallow it without making this fact visible to clients.
		In any case, the fact that objects are referred to by variables describing their roles, but are actually manipulated in terms of their identities means aliasing is essentially always present, and aliasing problems are always possible within the object-based ([Weg87]) paradigm, whether or not constructs like inheritance, concurrency and persistence are supported.
		Aliasing prevention is not sufficient in itself because aliasing is not avoidable under the conventional object-oriented paradigm.
	gee.cs.oswego.edu /dl/aliasing/aliasing.html (3265 words)

	Grain aliasing
		'Aliasing' is geek speak for spurious signals that are generated as the result of the interaction of two other signals, or as the side effect of digitising an analogue signal.
		Aliasing in CCD image sensors is a fairly well documented phenomenon, and is a cause of major concern to, and investigation by, CCD manufacturers.
		Kodak is one maker that seems to take the problem of aliasing seriously, and in fact they list suitability for scanning in the specifications of some of their films.
	www.photoscientia.co.uk /Grain.htm (5463 words)

	Video Artefacts - Aliasing (Site not responding. Last check: 2007-11-07)
		The typical image components that show aliasing are; venetian blinds, automobiles with lots of chrome, automobile grilles and finely detailed images of greenery.
		Aliasing does not show up until these elements are in motion, so it is typical to see a finely detailed image periodically shimmer whenever the camera pans, particularly in a diagonal direction.
		Aliasing is created by the conversion by the DVD player from this film format to the appropriate format for display on a TV or other display device.
	www.michaeldvd.com.au /Articles/VideoArtefacts/VideoArtefactsAliasing.html (576 words)

	Aliasing (Site not responding. Last check: 2007-11-07)
		Two variables are aliases if they denote (share) the same data object during a unit activation.
		Aliasing is another feature of imperative programming languages that makes programs harder to understand and harder to reason about.
		Another way in which aliasing can occur is when a data object may be a component of several data objects (referenced through pointer linkages).
	cs.wwc.edu /~aabyan/PLBook/book/node169.html (238 words)

	[No title] (Site not responding. Last check: 2007-11-07)
		The key to understanding aliasing and what we do about it is the Nyquist limit.
		Adjust the frequency of the sine wave to be sampled as well as the sampling frequency by using the sliders located under the topmost graphing window in the applet.
		Try setting the sampling rate to be low and then vary the frequency to see the low-frequency aliases of the input signal.
	www.cs.brown.edu /exploratories/freeSoftware/repository/edu/brown/cs/exploratories/applets/nyquist/nyquist_limit_guide.html (248 words)

	fractalus - Anti-aliasing and Fractals
		This is known as aliasing—where elements (the small squares) with frequencies too high to be shown in the sampling grid are misrepresented instead as elements of lower frequency that can be displayed (the bigger squares you see in the last checkerboard).
		Sometimes, the aliasing can be very distracting—as a fractal explorer, I know that a certain fractal has detail too fine to see, but that detail just becomes "mush" because there's no anti-aliasing.
		Aliased images are on the left, anti-aliased images are on the right.
	www.fractalus.com /info/antialias.htm (800 words)

	anti-aliasing - Hutchinson encyclopedia article about anti-aliasing (Site not responding. Last check: 2007-11-07)
		In computer graphics, a software technique for diminishing aliasing (‘jaggies’) – steplike lines that should be smooth.
		Jaggies occur because the output device, the monitor or printer, does not have a high enough resolution to represent a smooth line.
		This information should not be considered complete, up to date, and is not intended to be used in place of a visit, consultation, or advice of a legal, medical, or any other professional.
	encyclopedia.farlex.com /anti-aliasing (128 words)

	IP-Aliasing (Site not responding. Last check: 2007-11-07)
		Typical uses of IP aliasing are virtual hosting of Web and FTP servers and reorganizing servers without having to update any other machines (this last one is especially useful for nameservers).
		The term multi-homing used to denote IP aliasing is a mistake propagated from the Mac world and you would be wise not to follow in their footsteps.
		The /32 on the end of the aliased address indicates the length of the subnet mask (the number of 1's starting from the left of the netmask).
	www.defcon1.org /html/Networking_Articles/natdhowto-whisky/aps-filter/Sharity-Light/body_ip-aliasing.html (1121 words)

	Filter Basics: Anti-Aliasing - Maxim/Dallas
		Most of the time, aliasing in an undesirable side effect, so the "undersampled" higher frequencies are simply filtered out before the A/D stage.
		But sometimes, the undersampling is deliberate and the aliasing causes the A/D system to function as a mixer.
		It describes aliasing and the types of filters that can be used for anti-aliasing.
	www.maxim-ic.com /appnotes.cfm/appnote_number/928 (2481 words)

	Photoshop: Fixing CCD Color Aliasing (Site not responding. Last check: 2007-11-07)
		One of the main drawbacks of a single CCD digital camera is the presence of color aliasing in areas of high-contrast and fine detail.
		Color aliasing is caused by the color filters on a single CCD camera.
		Fortunately color aliasing is most noticeable in large areas that are the same color.
	tedfelix.com /ColorAliasing (534 words)

	Aliasing Problem
		Finally, if the aliased counter predicts an execution correctly (incorrectly) and the corresponding un-aliased counter would have predicted it correctly (incorrectly) too, it is called Harmless aliasing since the aliasing does not change the prediction accuracy.
		For example, 23% aliasing rate means that 23% of prediction is made by using aliased counters.
		For all schemes, 25% of total aliasing is destructive aliasing and this portion of aliasing cause the performance decrease.
	www.umiacs.umd.edu /users/hismail/818K/node8.html (673 words)

	Analog Devices : Virtual Design Center : Interactive Design Tools : Analog-to-Digital Converters: Aliasing Suppression ...
		Aliasing suppression in oversampled systems is achieved through a combination of analog and digital filtering, but digital filtering cannot replace a high-quality analog filter because it cannot remove aliasing noise after it's been folded into the passband by the sampling process.
		For simplicity, the additional aliasing noise that results from downsampling the sampled signal is not shown.
		Combined aliasing noise is shown in dark blue with the first three contributing folds in light blue.
	www.analog.com /Analog_Root/static/techSupport/designTools/interactiveTools/adc/adcalias.html (666 words)

	Sampling Rate (Site not responding. Last check: 2007-11-07)
		The next figure illustrates how aliasing would occur when the sampling rate is much too low for the frequency of an input signal.
		Obviously, aliasing has the effect of producing sounds of lower frequency from sounds that are higher in frequency than the Nyquist frequency.
		Once aliasing has occurred, it is absolutely impossible to distinguish a component generated by aliasing from one that was actually present in the input signal.
	www.asel.udel.edu /speech/tutorials/instrument/sam_rat.html (293 words)

	Relationships between Pixel Count, Aliasing, and Limiting Resolution in Digital Motion Picture Systems (Site not responding. Last check: 2007-11-07)
		This paper focuses on the aliasing artifact identified in the ISO 12233 standard and identified as Type A aliasing in the prior paper.
		A relationship termed “Type A aliasing equation” is presented, which predicts aliasing as measured by the ISO 12233 standard.
		Finally, the equation is used to compute the minimum number of pixels required for a given aliasing level and limiting resolution, and data is presented to determine the pixel count required to render a given limiting resolution.
	www.electronicipc.com /journalez/detail.cfm?code=45390011120705 (216 words)

	Temporal aliasing: Facts and details from Encyclopedia Topic (Site not responding. Last check: 2007-11-07)
		Temporal aliasing is the technical term for a phenomenon phenomenon quick summary:
		It is a particular example of a range of phenomena called aliasing aliasing quick summary:
		The reason it is called "aliasing" is that in electrical engineering, EHandler: no quick summary.
	www.absoluteastronomy.com /encyclopedia/t/te/temporal_aliasing.htm (828 words)

	Anti-aliasing in Fractal Domains (Site not responding. Last check: 2007-11-07)
		Aliasing occurs when a discrete grid (such as the pixel resolution of your display or printer) is superimposed on a continuous image which contains sharp edges or fine detail.
		The "jaggies" you see when a straight line or images with sharp discontinuities are displayed on a computer monitor are examples of artifacts caused by aliasing.
		These artifacts can be minimized by sampling the continuous image at a higher resolution than the final image desired, then applying an anti-aliasing filter that removes the high-frequency components that produce the artifacts before sampling down to the desired resolution.
	www.fractaldomains.com /anti-alias/anti-alias.html (386 words)

	Introduction to DSP - basics: aliasing
		This is called 'aliasing' because one frequency looks like another.
		Note that the problem of aliasing is that we cannot tell which frequency we have - a high frequency looks like a low one so we cannot tell the two apart.
		But sometimes we may have some a priori knowledge of the signal, or be able to make some assumptions about how the signal behaves in between samples, that will allow us to tell unambiguously what we have.
	www.bores.com /courses/intro/basics/1_alias.htm (395 words)

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