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Article: Digital image processing. I. Evaluation of gray level correction methods in vitro.

TitleDigital image processing. I. Evaluation of gray level correction methods in vitro.
Authors
Issue Date1994
PublisherWiley-Blackwell Publishing, Inc.. The Journal's web site is located at http://www.blackwellpublishing.com/journals/CLR
Citation
Clinical Oral Implants Research, 1994, v. 5 n. 1, p. 37-47 How to Cite?
AbstractThe aims of this study were a) to assess in an in vitro model the amount of density changes measured in digitally subtracted images due to electronic noise and image alignment error, and b) to test the accuracy of different gray level correction procedures in the reduction of densitometric image mismatches. A section of a pig mandible in which a hollow cylinder ITI Bonefit implant had been placed was used to obtain pairs of standardized radiographs. Series of radiographs were obtained with different exposure times (0.34, 0.39, 0.44, 0.51, 0.58 s). The radiographs were captured through a video camera, digitized and stored in a personal computer. The same radiographic image was recorded and subtracted from itself 10 times to study the error of the method due to electronic transformations of the images and image alignment. The noise due to the analog-to-digital transformation of the radiographic images was calculated to be +/- 2 gray levels i.e., 2% of the scale of gray levels. This kind of error was reduced up to 40% by capturing the images more than once and averaging the values per pixel. The manual superimposition of the images to be subtracted caused an increase of the error to +/- 3 gray levels (2.7%). Seven methods of gray level correction based either on a linear least squares approximation or on the cumulative density function (CDF) were tested. The group based on the CDF algorithm gave significantly better results than any other method. Pixels yielding differences smaller or equal to +/- 7 gray levels (5.5% of the scale of gray levels) should be excluded from further calculations in order to eliminate (false-positive) errors due to the normalizing algorithms. Furthermore, the CDF method on an arbitrarily chosen area of the image or on the wedge seems to give to subtraction images the ability of revealing real subtle changes in tissue density (fewer false-negative errors). The use of reference structures did not futher improve the ability of the normalization methods to correct gray level mismatches between radiographic pairs.
Persistent Identifierhttp://hdl.handle.net/10722/153874
ISSN
2015 Impact Factor: 3.464
2015 SCImago Journal Rankings: 1.427
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorFourmousis, Ien_US
dc.contributor.authorBrägger, Uen_US
dc.contributor.authorBürgin, Wen_US
dc.contributor.authorTonetti, Men_US
dc.contributor.authorLang, NPen_US
dc.date.accessioned2012-08-08T08:22:02Z-
dc.date.available2012-08-08T08:22:02Z-
dc.date.issued1994en_US
dc.identifier.citationClinical Oral Implants Research, 1994, v. 5 n. 1, p. 37-47en_US
dc.identifier.issn0905-7161en_US
dc.identifier.urihttp://hdl.handle.net/10722/153874-
dc.description.abstractThe aims of this study were a) to assess in an in vitro model the amount of density changes measured in digitally subtracted images due to electronic noise and image alignment error, and b) to test the accuracy of different gray level correction procedures in the reduction of densitometric image mismatches. A section of a pig mandible in which a hollow cylinder ITI Bonefit implant had been placed was used to obtain pairs of standardized radiographs. Series of radiographs were obtained with different exposure times (0.34, 0.39, 0.44, 0.51, 0.58 s). The radiographs were captured through a video camera, digitized and stored in a personal computer. The same radiographic image was recorded and subtracted from itself 10 times to study the error of the method due to electronic transformations of the images and image alignment. The noise due to the analog-to-digital transformation of the radiographic images was calculated to be +/- 2 gray levels i.e., 2% of the scale of gray levels. This kind of error was reduced up to 40% by capturing the images more than once and averaging the values per pixel. The manual superimposition of the images to be subtracted caused an increase of the error to +/- 3 gray levels (2.7%). Seven methods of gray level correction based either on a linear least squares approximation or on the cumulative density function (CDF) were tested. The group based on the CDF algorithm gave significantly better results than any other method. Pixels yielding differences smaller or equal to +/- 7 gray levels (5.5% of the scale of gray levels) should be excluded from further calculations in order to eliminate (false-positive) errors due to the normalizing algorithms. Furthermore, the CDF method on an arbitrarily chosen area of the image or on the wedge seems to give to subtraction images the ability of revealing real subtle changes in tissue density (fewer false-negative errors). The use of reference structures did not futher improve the ability of the normalization methods to correct gray level mismatches between radiographic pairs.en_US
dc.languageengen_US
dc.publisherWiley-Blackwell Publishing, Inc.. The Journal's web site is located at http://www.blackwellpublishing.com/journals/CLRen_US
dc.relation.ispartofClinical oral implants researchen_US
dc.subject.meshAbsorptiometry, Photon - Methodsen_US
dc.subject.meshAnalysis Of Varianceen_US
dc.subject.meshAnimalsen_US
dc.subject.meshArtifactsen_US
dc.subject.meshDental Implantsen_US
dc.subject.meshImage Processing, Computer-Assisteden_US
dc.subject.meshJaw, Edentulous - Radiographyen_US
dc.subject.meshMandible - Radiographyen_US
dc.subject.meshRadiography, Dental - Methodsen_US
dc.subject.meshReproducibility Of Resultsen_US
dc.subject.meshSensitivity And Specificityen_US
dc.subject.meshSubtraction Techniqueen_US
dc.subject.meshSwineen_US
dc.titleDigital image processing. I. Evaluation of gray level correction methods in vitro.en_US
dc.typeArticleen_US
dc.identifier.emailLang, NP:nplang@hkucc.hku.hken_US
dc.identifier.authorityLang, NP=rp00031en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.pmid8038343-
dc.identifier.scopuseid_2-s2.0-0028397861en_US
dc.identifier.volume5en_US
dc.identifier.issue1en_US
dc.identifier.spage37en_US
dc.identifier.epage47en_US
dc.identifier.isiWOS:A1994NE44400005-
dc.publisher.placeUnited Statesen_US
dc.identifier.scopusauthoridFourmousis, I=6602718088en_US
dc.identifier.scopusauthoridBrägger, U=7005538598en_US
dc.identifier.scopusauthoridBürgin, W=7003413848en_US
dc.identifier.scopusauthoridTonetti, M=35602248900en_US
dc.identifier.scopusauthoridLang, NP=7201577367en_US

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