Image resizing using saliency strength map and seam carving for white blood cell analysis

Ko Byoungchul, Kim Seonghoon, Nam, Nam Jaeyeal

Description

A new image-resizing method using seam carving and a Saliency Strength Map (SSM) is proposed to preserve important contents, such as white blood cells included in blood cell images. Methods To apply seam carving to cell images, a SSM is initially generated using a visual attention model and the structural properties of white blood cells are then used to create an energy map for seam carving. As a result, the energy map maximizes the energies of the white blood cells, while minimizing the energies of the red blood cells and background. Thus, the use of a SSM allows the proposed method to reduce the image size efficiently, while preserving the important white blood cells. Results Experimental results using the PSNR (Peak Signal-to-Noise Ratio) and ROD (Ratio of Distortion) of blood cell images confirm that the proposed method is able to produce better resizing results than conventional methods, as the seam carving is performed based on an SSM and energy map. Conclusions For further improvement, a faster medical image resizing method is currently being investigated to reduce the computation time, while maintaining the same image quality.

Informations

• Publié par: biomed
• Publié le: 01 janvier 2010
• Nombre de lectures: 138
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Ko
etal
.
BioMedicalEngineeringOnLine
2010,
9
:54
http://www.biomedical-engineering-online.com/content/9/1/54

RESEARCH

OpenAccess

Imageresizingusingsaliencystrengthmapand
seamcarvingforwhitebloodcellanalysis
ByoungChulKo,SeongHoonKim,JaeYealNam
*

*Correspondence:[e-mail].
rkDepartmentofComputer
Engineering,KeimyungUniversity,
Shindang-Dong,Dalseo-Gu,Daegu,
areKo

Abstract
Background:
Anewimage-resizingmethodusingseamcarvingandaSaliency
StrengthMap(SSM)isproposedtopreserveimportantcontents,suchaswhiteblood
cellsincludedinbloodcellimages.
Methods:
Toapplyseamcarvingtocellimages,aSSMisinitiallygeneratedusinga
visualattentionmodelandthestructuralpropertiesofwhitebloodcellsarethen
usedtocreateanenergymapforseamcarving.Asaresult,theenergymap
maximizestheenergiesofthewhitebloodcells,whileminimizingtheenergiesof
theredbloodcellsandbackground.Thus,theuseofaSSMallowstheproposed
methodtoreducetheimagesizeefficiently,whilepreservingtheimportantwhite
bloodcells.
Results:
ExperimentalresultsusingthePSNR(PeakSignal-to-NoiseRatio)andROD
(RatioofDistortion)ofbloodcellimagesconfirmthattheproposedmethodisable
toproducebetterresizingresultsthanconventionalmethods,astheseamcarvingis
performedbasedonanSSMandenergymap.
Conclusions:
Forfurtherimprovement,afastermedicalimageresizingmethodis
currentlybeinginvestigatedtoreducethecomputationtime,whilemaintainingthe
sameimagequality.

Background
Peripheralbloodcelldifferentialcountingprovidesvaluableinformationforaccurate
patientdiagnoses,yetthemicroscopicreviewislaborintensiveandrequiresahighly
trainedexpert.Currentautomatedcellcountersarebasedonlaser-lightscatterand
flow-cytochemicalprinciples,nonetheless,21%ofallprocessedbloodsamplesstill
requiremicroscopicreviewbyexperts[1].Therefore,variousefforts[1-5]havealready
beenmadetodevelopautomaticcellanalysissystemsusingimageprocessing.Blood
cellimagesconsistofbothwhiteandredbloodcellsscatteredacrosstheentireimage,
however,itisthewhitebloodcells(WBCs)thatprovidetheimportantinformationfor
patientdiagnoses,suchasleukemiaorcancer[2].Thus,inmostresearch,WBC
segmentationistheimportantprocedure,wheretheultimategoalistoextractallthe
WBCsfromacomplicatedbackgroundandthensegmenttheWBCsintotheir
morphologicalcomponents,suchasthenucleusandcytoplasm.
RepresentativeWBCanalysissystems,suchasCellarvisionDiffmasterOctavia[4]and
CellarvisionDM96[5],scanthewholeslideatalowmagnificationfirsttoidentify
potentialWBCsusingthespecificcharacteristicsofWBCs,suchastheircolor,size,and

©2010Koetal;licenseeBioMedCentralLtd.ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommons
AttributionLicense(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse,distribution,andreproductionin
anymedium,providedtheoriginalworkisproperlycited.

Ko
etal
.
BioMedicalEngineeringOnLine
2010,
9
:54
http://www.biomedical-engineering-online.com/content/9/1/54

shape,andthentakedigitalimagesatahighmagnification.Thereafter,pre-classification
isperformedusingonlythecroppeddigitalimages.Whilethismethodismoreefficient
thanscanningWBCsfromahigh-resolutionimageofthewholeslide,additionaltimeis
requiredfortheWBCsearch,especiallywhentheimagecontainsseveralWBCs.
Furthermore,additionalstorageisneededtosavetheindividualpotentialWBCsand
extratimerequiredtoclassifytheWBCs,asthesystemhastocheckallpotentialWBC
imagestoanalyzejustoneslide.
Meanwhile,othermethods[2,3]useonlyanoriginalhigh-resolutionimageforthe
WBCanalysis.However,analyzingWBCsfromthewholeimageistimeconsuming,
sincethesizeofbloodcellimagesisnormallyatleast800×600.Therefore,animage-
resizingmethodisneededthatretainsalltheWBCswithoutmorphologicaldistortion
inordertoreducethepost-segmentationclassificationtime.Furthermore,sinceresized
high-qualityimagesrequirelessstorage,thepost-imagesegmentationandclassification
canbemoreaccuratethanwithconventionalimagecompression,suchasJPEG.
Relatedworkcanbedividedintotwoparts;imagecompressionandimageresizing.
First,variouslosslesscompressiontechniquesalreadyexistthatcanpreservethe
characteristicsofanimage,yetwithalowcompressionrate.Forexample,several
researchers[6-8]haveproposedtransformcodingschemes,suchasaPrincipalCom-
ponentAnalysis(PCA)andDiscreteCosineTransform(DCT),whileKarrasetal.[9]
usedadiscretewavelettransformation(DWT)andfuzzyc-meansclusteringtechnique.
Plus,toachievehighercompressionrateswithoutdetractingfromthequality,region
ofinterest(ROI)methodswithaDCThavealsobeeninvestigated[6,10].Inparticular,
Gokturketal.[10]proposedahybridmodel,usinglosslesscompressioninregionsof
interestandhigh-ratemotion-compensatedlossycompressioninotherregionsinthe
caseofasequenceofCTimages.Nonetheless,eventhoughlosslesscompressionpro-
ducesahighercompressionratewithoutdistortingROIs,theexactpreservationofa
ROIisstilldifficultwhenthecompressionrateisaboveaspecificlimitation.Therefore,
anewalgorithmisneededthatcanefficientlypreserveROIs,regardlessofthecom-
pressionrate.
Inadditiontoimagecompressionmethodsthatmerelypreservetheoriginalimage
size,someresearchershaveattemptedtoresizeorcrop[11,12]imagesaccordingto
theimagecontents.Yet,asshowninFig.1-(b),standardresizinghomogeneously
reducestheimagesize,therebydamagingalltheimagecontentsbasedontheratioof
theresizing.Similarly,whilecroppingcanbeusedtodisplaythemostimportant
regioninanimage,asshowninFig.1-(c),cellimagescontainmanyROIs,making
croppinginappropriateforcellimagecompression.
Meanwhile,seamcarving[13]changesthesizeofanimagebysubtlyremovingor
insertingaconnectedpathofpixelsfromadifferentpartoftheimageaccordingtothe
measuredenergy,asshowninFig.2-(b).However,eventhoughseamcarvingcaneffi-
cientlyremovenon-ROIpixels,iftheoperationisappliedtooharshly(i.e.resizingan
800×600imageto200×120),importantROIscanstillbedamaged,asshowninFig.
2-(d).Furthermore,sinceseamcarvingwasoriginallydevelopedfornatureimages,its
applicationtomedicalimagesissomewhatlimited.Forexample,theenergydistribu-
tionofWBCsisnotdistinctiveinbloodimages,makingithardtoapplyaseamcar-
vingoperatortobloodcellimages,whichresultsinaninevitableremovalorinsertion
ofpixelsinWBCs.

Page2of14

Ko
etal
.
BioMedicalEngineeringOnLine
2010,
9
:54
http://www.biomedical-engineering-online.com/content/9/1/54

Figure1
Examplesofdifferentscaling-downmethods
.

Accordingly,thispaperpresentsanewmethodforresizingbloodcellimageswhile
preservingthesizeandshapeofWBCs.Inperipheralblood,WBCsaredividedinto
fiveclassesaccordingtotheirmaturationstage,makingitessentialtopreservethesize
andshapeofthenucleus.Thus,toprovideanefficientimage-resizingmethodthat
treatsWBCsasROIs,aSaliencyStrengthMap(SSM)isproposedusingavisualatten-
tionmodelandthestructuralpropertiesofWBCstogenerateanewenergymap.As
such,thismapmaximizestheenergiesoftheWBCs,whileminimizingtheenergiesof
theredbloodcellsandbackground.Therefore,incontrasttopreviousalgorithms,the
maincontributionofthisstudyistoimprovetheresizingperformancewithalower
filesize,whilepreservingtheWBCsusingtheproposedSSMwithanenergymap.
Fig.3showsthearchitectureofthecellimageresizingusingtheproposedSSMand
seamcarving.
Theremainderofthispaperisorganizedasfollows.
Methods
describesthealgo-
rithmsusedtocreatethesaliencystrengthmap,anEllipseAttentionWindow(EAW)
thatremovesuselessregionsfromtheimage,andtheseamremovalusinganenergy
mapbasedonthesaliencystrength.
ResultsandDiscussion
evaluatestheaccuracy

Page3of14

Ko
etal
.
BioMedicalEngineeringOnLine
2010,
9
:54
http://www.biomedical-engineering-online.com/content/9/1/54

Figure2
Exampleofseamcarving
:(a)originalimage,(b)energymapof(a),(c)reducedimageusing
seamcarvingthatpreservesshapeofimportantcontents(WBCs),(d)distortedimageusingharshseam
carving,whereshapesofWBCnucleiaredistorted.

Figure3
Architectureofproposedmethod
.

Page4of14

Ko
etal
.
BioMedicalEngineeringOnLine
2010,
9
:54
http://www.biomedical-engineering-online.com/content/9/1/54

andapplicabilityoftheproposedresizingmethodbasedonexperiments,andsome
finalconclusionsandareasforfutureworkarepresentedin
Conclusions
.
Methods
Thispaperproposesanewimage-resizingmethodwithalowerfilesizethatcanefficiently
preserveWBCsusingavisualsaliencymapbasedonthefollowingtwoassumptions:

▪
thenucleiofWBCsarenearlyround.
▪
thenucleiofWBCsarehighlightedinpurpleonawhitebackgroundwithmono-
chromaticredbloodcells.

Usingthesecharacteristics,aSaliencyStrengthMap(SSM)isproposedusingavisual
attentionmodel,whilethestructuralpropertiesofWBCsareusedtogeneratean
energymap.
Saliencymapgeneration
Incontrasttonatureimages,microscopicimages,especiallybloodcellimages,have
differentcharacteristicswithdistinctdiagnosticmeanings,suchasavaryingcolorand
saturationaccordingtofluorescencestaining.Forexample,inthecaseofbloodcell
images,thesalientparts,theWBCs,tendtobehighlysaturatedandpurpleincolor,
whiletheremainingparts,theredbloodcells,haveamoremonotonousappearance.
Thus,forsemanticseamcarving,knowledgeoftheexactpositionsoftherelevant
WBCsiscrucial.Therefore,toobtainthepositionofWBCs,amodifiedvisualatten-
tionmodelisused,asproposedinourpreviousresearch[14].
Theoriginalsaliency-basedvisualattentionmodelw