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Topic: Compression artifacts

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	Compression Artifact Encyclopedia Article, Definition, History, Biography (Site not responding. Last check: 2007-11-06)
		A compression artifact (or artefact) is the result of an agressive data compression scheme applied to an image, audio, or video that discards some data which is determined by an algorithm to be of lesser importance to the overall content but which is nonetheless discernible and objectionable to the user.
		Artifacts in time-dependent data such as audio or video are often a result of the latent error in lossy data compression.
		Technically speaking, a compression artifact is a particular class of data error that is usually the consequence of quantization in lossy data compression.
	www.alienartifacts.com /encyclopedia/Compression_artifact (1119 words)

	Lossy data compression - Wikipedia, the free encyclopedia
		A lossy data compression method is one where compressing data and then decompressing it retrieves data that may well be different to the original, but is "close enough" to be useful in some way.
		Depending on the design of the format lossy data compression often suffers from generation loss, that is compressing and decompressing multiple times will do more damage to the data than doing it once.
		Flaws caused by lossy compression that are noticeable to the human eye or ear are known as compression artifacts.
	en.wikipedia.org /wiki/Lossy_data_compression (617 words)

	Compression artifact -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-11-06)
		A compression artifact is a particular type of data error that is typically the result of (The act of dividing into quanta or expressing in terms of quantum theory) quantization in (Click link for more info and facts about lossy data compression) lossy data compression.
		Compression artifacts occur in many common media such as DVDs and also common computer file formats such as MP3 or MPG files.
		Compression artifacts are a result of the latent error in (Click link for more info and facts about lossy data compression) lossy data compression.
	www.absoluteastronomy.com /encyclopedia/c/co/compression_artifact.htm (695 words)

	Method and apparatus to reduce transform compression visual artifacts in medical images - Patent 4939645
		Digital image compression is employed to represent an image by using as few bits as possible consistent with a high degree of image fidelity, with the goals of reducing data processing and transmission time and reducing data storage space requirements.
		The compression ratio is the ratio of the number of data bits needed to represent the uncompressed image divided by the number of data bits needed to represent the same image in a compressed format.
		The compressed data and the parameter describing the mathematical model of the rejected spectral subimage data, consisting in the preferred embodiment of coded and quantized non-rejected spectral subimage data and the standard deviation of the rejected spectral subimage data, are stored on data storage device 40 of FIG.
	www.freepatentsonline.com /4939645.html (4406 words)

	S3 Texture Compression - Wikipedia, the free encyclopedia
		S3 Texture Compression (S3TC) (sometimes also called DXTn or DXTC) is a group of related image compression algorithms originally developed by S3 Graphics, Ltd. for use in their Savage 3D computer graphics accelerator.
		Unlike previous image compression algorithms, S3TC's fast random access to individual pixels made it uniquely suited for use in compressing textures in hardware accelerated 3D computer graphics.
		S3TC is a lossy compression algorithm, resulting in image quality degradation, but for most purposes the resulting images are more than adequate.
	www.wikipedia.org /wiki/S3TC (621 words)

	Systems and methods for reducing boundary artifacts in hybrid compression - Patent 6192155
		However, it should be appreciated that the compression method and system of this invention can be applied to any set of hybrid compression techniques, where one or both of the compression techniques compresses the image data on a block-by-block basis, such that there are boundary blocks containing more than one type of image data.
		Thus any set of compression techniques for these various data types can be used to form the hybrid compression technique, and the system and method of this invention can be used with any such set of compression techniques if one or more of those compress techniques compress the image data on a block-by-block basis.
		In the compression portion of the method and system of this invention, the recursive dilation processor 436 progressively assigns the value of its neighboring pixels to a boundary pixel positioned in the boundary block adjacent to the boundary between the image data portion and the blank portion.
	www.freepatentsonline.com /6192155.html (5267 words)

	JPG Image File Format
		The JPG file is wonderfully small, often compressed by 90%, or to only 1/10 of the size of the original data, which is very good when modems are involved.
		JPG compression has very high efficiency (relatively tiny files) because it is intentionally designed to be lossy, designed to give very small files without the requirement for full recoverability.
		JPG compression can be adjusted to be better quality in a larger file, or to be lesser quality in a smaller file.
	www.scantips.com /basics9j.html (2603 words)

	DVD Quality Reviews at The Internet Movie Database (Site not responding. Last check: 2007-11-06)
		Compression artifacts are due to the data reduction of the MPEG algorithm that removes high frequency content from the differences between individual frames as they are compared and encoded.
		Whether compression artifacts are visible or not depends on the quality of the compression software, the experience of the compressionist using it, the bit rates used and the characteristics of the master.
		Whether the artifacts are visible/distracting or not depends on the sophistication of the noise removal algorithm, the experience of the people using it, and the speed and detail of moving image parts.
	amazon-uk.imdb.com /Sections/DVDs/dvd-review (5866 words)

	Compression artifact (Site not responding. Last check: 2007-11-06)
		Where transform coding is used, they are typically in the form of one of the basis functions of the transform coder's transform space.
		Where the DCT image transform is used, for example, they are often 8x8 pixel squares, containing a stripe or "checkerboard" pattern.
		To stop the build-up of compression artifacts, most compression systems occasionally send an entire compressed frame without prediction or differencing.
	www.termsdefined.net /co/compression-artifact.html (429 words)

	ECE Colloquium - February 25, 2000 (Site not responding. Last check: 2007-11-06)
		However, in progressive transmission applications, all lower-rate decoded images have compression artifacts which are visible, and therefore in the supra-threshold regime.
		An extensive psychophysical experiment with 150 observers was performed to quantify human sensitivity to supra-threshold compression artifacts in wavelet-compressed images.
		Incorporation of these insights into several compression algorithms produces images of improved visual quality in the supra-threshold regime, demonstrating that compression gains can be achieved even at low bit rates by considering HVS characteristics.
	www-ece.rice.edu /ece/colloq/99-00/Feb25.html (232 words)

	Video Artifacts in Direct Broadcast Satellite (DBS) and Broadcasting (Site not responding. Last check: 2007-11-06)
		The term artifact is commonly applied to digital video impairments, essentially any unintended aspect not present in the original image, and usually as a result of the image coding, decoding, storage or transmission processes.
		Blocking is the most common artifact identified by DBS viewers only happens when the transmission system is over-stressed.
		This paucity of data per pixel is why video compression is often referred to as entropy coding and why it is important that each and every bit transmitted can be perfectly decoded by the receiver.
	www.heiconsulting.com /mpeg2g.html (715 words)

	Digital television - Wikipedia, the free encyclopedia
		The digital signal eliminates common analog broadcasting artifacts such as "ghosting", "snow", and static noises in audio.
		It can replace them with new MPEG compression artifacts, such as "blocking", when transmitted at too low a data rate, and may fail to work entirely in situations where analog television would have produced an impaired but watchable picture.
		Depending on the sophistication and level of the error correction defined by the standard and chosen by the broadcaster, DTV may either work perfectly or not work at all.
	en.wikipedia.org /wiki/Digital_television (1655 words)

	Thesis
		When this compressed data is stored as a file and then re-opened, the image exhibits error, or JPEG artifacts(1).
		Since these artifact blocks are skewed, or shifted, relative to the 8 x 8 blocking DCT that is applied to this shifted image, additional artifacts result from the second compression.
		This was the case when attempting to characterize the shift effect--though the phenomenon appears to be unavoidable, the severity/visibility of the artifacts due to shift tend to be dependent upon factors other than QF and shift.
	www.cis.rit.edu /research/thesis/bs/1998/jacoby/thesis.html (4819 words)

	JPEG and JPEG2k Artifacts (Site not responding. Last check: 2007-11-06)
		A particularly good example of ringing artifacts is compression of images with sharp edges, especially text, diagrams and line drawings.
		There are custom methods for compression of such data, such as JBIG and DjVu, but they are not supported by most image viewing applications.
		The same image was compressed with JPEG and JPEG2000 to approximately 27600 bytes, a larger size than PNG, resulting in the typical text compression artifacts.
	ai.fri.uni-lj.si /~aleks/jpeg/artifacts.htm (1102 words)

	Macromedia - Developer Center : Converting Images to Successful Web Graphics (Site not responding. Last check: 2007-11-06)
		Just like flat-pack furniture or a can of condensed soup, images can be "compressed" so that they're small while in transit yet are "reconstituted" to their original state (or very nearly so) when they appear in the browser.
		To compress an image file, it just needs to be saved in the appropriate file format; the browser does the rest.
		After you find the ideal compression size for your photos, be sure to keep a copy of the original, uncompressed file at hand in the editing program's native file format.
	www.macromedia.com /desdev/contribute/articles/convert_images.html (1898 words)

	compression artifact - a Whatis.com definition (Site not responding. Last check: 2007-11-06)
		A compression artifact is the fuzz or distortion in a compressed image or sequence of video images.
		When a photo is compressed into a JPEG format, some data is lost, which is why this type of compression is called lossy compression.
		Artifacts are more evident on a computer image than in a printed photograph.
	searchstorage.techtarget.com /sDefinition/0,,sid5_gci553525,00.html (260 words)

	Codec Comparisons - The Explanation (Site not responding. Last check: 2007-11-06)
		The compression artifacts in heavily compressed MP3 make the audio sound as though it was gargled through water.
		Compression error is what I will use to talk about quantified compress loss, effectively the error or deviation of the compressed image from the original uncompressed image.
		If you use the analogy that the compressed file needs to be held in a container of a certain size, then after the first compression, anything that didn't “fit” inside the compressed container has been discarded.
	home.insightbb.com /~george/codec/Explanation.html (635 words)

	Macromedia - Developer Center : Converting Images to Successful Web Graphics
		The way that the JPEG format compresses files is quite complicated, but all you need to worry about is the fact that you trade off image quality for smaller file sizes.
		As the file size and quality lessen, unsightly blemishes ("compression artifacts") appear in areas of flat color and around edges of objects.
		When there is little or no trace of compression artifacts, you've reached the compression limit without compromising visual quality.
	www.macromedia.com /devnet/contribute/articles/convert_images.html (1898 words)

	IGN: DVD Video Problems Explained
		Compression Artifacts: There are many different types of artifacts that can rear their ugly head on a bad DVD transfer.
		Artifacts are rare in newer DVD transfers, but we'll show you some bad examples of what to look for.
		If you want to see examples of compression artifacts, continue on to the next page, while Edge Enhancement can be seen on page three.
	dvd.ign.com /articles/355/355062p1.html (277 words)

	Effects of DWT Resolutions in Reduction of Ringing Artifacts in JPEG-2000
		Image compression is aimed to minimize the number of bits needed to represent an image without sacrificing quality.
		In lossy compression, data redundancies as well as data which are not noticeable to human visual systems are discarded.
		Compression rate is the reciprocal of compression ratio.
	www.gisdevelopment.net /technology/ic/techic001pf.htm (1379 words)

	iStockphoto.com : royalty free stock photography community
		Compression: The JPEG file format uses a "lossy" compression method, in order to make the file smaller information is thrown away, or lost.
		At a certain point, with lower quality settings, the removal of information during the compression process can become visible in the form of compression artifacts (places in the image where too much detail has been lost).
		Artifacting: Compression artifacting can be introduced by the camera and/or by your image editing software at lower quality settings.
	www.istockphoto.com /tutorial_2.3_noise.php (602 words)

	Comments on 14259 \| Ask MetaFilter
		It is just possible that you are referring to dynamic range compression (the process of making loud passages and quite passages in the original come out at the same volume after the compression).
		I know the information is gone, since that's the basic problem with most audio compression, but it occurred to me that if the artifacts were added by compression--which uses a known formula which means that given a specific input, it should always yield a specific result--that the compression artifacts would be predictable.
		On the other hand, dither doesn't compress well at all, so once you recompress at 64k you might actually be doing more harm than good (you probably are doing more harm, actually).
	ask.metafilter.com /mefi/14259 (619 words)

	COMPRESSION ARTIFACTS (Site not responding. Last check: 2007-11-06)
		Minor compression artifacts can be seen along the outside edge of her right arm, and some discoloration on the fingers of her left hand.
		The artifacts along her right arm are more pronounced, her left fingers are quite blotchy, and the skin tones (look between her eyebrows and around the nostrils) are not so smooth:
		The edges of both arms and both hands suffer from compression artifacts, as do the background and the white sweater, and there is annoying discoloration around her nose and eye.
	www.landiss.com /compression.htm (390 words)

	DV vs M-JPEG: codec issues
		To really see the effect of this chroma filter or decimation I suggest that the same picture be compressed in multi-pass with and without the chroma information (i.e., compress both a color and a fl-and-white version of the same picture).
		However, the algorithms that choose the DCT modes during compression are not defined by the Blue Book specification, and are proprietary to the companies developing them.
		From this point on the data must be further compressed using the same process as MJPEG: quantization of the AC coefficients and entropy coding.
	www.adamwilt.com /DVvsMJPEG.html (1536 words)

	Compression and artifacts - AVS Forum (Site not responding. Last check: 2007-11-06)
		Compression levels have an effect on both the video and audio.
		The only way around the additional compression is to acquire the signal directly from the master C-Band feeds ("BUD").
		He thinks that they apply less compression during prime hours, more during the hours less people are at home.
	www.avsforum.com /avs-vb/showthread.php?goto=newpost&t=546593 (624 words)

	JPEG
		This enables the next step which is to reduce the U and V components to half size in both vertical and horizontal directions (called "downsampling" or "chroma subsampling"), thereby reducing the size in bytes of the whole image by a factor of two.
		The resulting compression ratio can be varied according to need, by being more or less aggressive in the divisors used in the quantization phase.
		Ten to one compression usually results in an image that can't be distinguished by eye from the original.
	www.php-include.com /JPEG.php (1106 words)

	GRAPHICS: JPEG graphics
		The checkered pattern and the dark "noise" pixels in the compressed image are classic JPEG compression artifacts.
		Note the extensive compression noise and distortion present in the bottom dolphin — the download time saved is not worth the degrading of the images.
		Once an image is compressed using JPEG compression, data is lost and you cannot recover it from that image file.
	www.webstyleguide.com /graphics/jpegs.html (483 words)

	DV video compression artifacts - Reduce with post-processing? (Site not responding. Last check: 2007-11-06)
		I'm quite familiar with the phenomenon that encoding video that already has Mpeg-like artifacts will tend to MORE than double the prevalence of compression artifacts.
		So it makes a lot of sense to take some steps to reduce those artifacts, since the result will be, in theory, better than twice as much improvement over what you get without taking such steps.
		It specifically addresses compression artifacts like blockiness or "ringing", taking advantage of the known interdependency between frames of video in any such encoding, and works to reduce them.
	www.thehelparchive.com /new-2934790-86.html (501 words)

	Compression (Site not responding. Last check: 2007-11-06)
		Without data compression, DVD's would not be possible, but the movie data must be compressed to 1/18th its original size to fit on a dual-layer DVD disk.
		There are unsightly compression artifacts everywhere in the R1 that barely exist in the R2, and they're so bad they've altered the picture with macro blocking.
		The compression has caused the picture to become softer, lose detail, and has caused noticeable alteration of the image in areas.
	www.wjsavage.com /web/R1DVD/Spirited/compression.htm (404 words)

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