图像文件格式BMP.docx

图像文件格式BMP.docx

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图像文件格式BMP

课程名称专业英语

题目名称图像格式——BMP

学生学院机电工程学院

专业班级09数媒一班

学号3109000746

学生姓名李林钢

指导教师黄宪明

2013年1月12日

TheGraphicsFileFormat--BMP

TheBMPfileformat,alsoknownasbitmapimagefileordeviceindependentbitmap（DIB）fileformatorsimplyabitmap,isarastergraphicsimagefileformatusedtostorebitmapdigitalimages,independentlyofthedisplaydevice（suchasagraphicsadapter）,especiallyonMicrosoftWindowsandOS/2operatingsystems.

TheBMPfileformatiscapableofstoring2Ddigitalimagesofarbitrarywidth,height,andresolution,bothmonochromeandcolor,invariouscolordepths,andoptionallywithdatacompression,alphachannels,andcolorprofiles.

Device-independentbitmapsandtheBMPfileformat

Microsofthasdefinedaparticularrepresentationofcolorbitmapsofdifferentcolordepths,asanaidtoexchangingbitmapsbetweendevicesandapplicationswithavarietyofinternalrepresentations.Theycalledthesedevice-independentbitmapsorDIBs,andthefileformatforthemiscalledDIBfileformatorBMPimagefileformat.AccordingtoMicrosoftsupport:

[1]

Adevice-independentbitmap（DIB）isaformatusedtodefinedevice-independentbitmapsinvariouscolorresolutions.ThemainpurposeofDIBsistoallowbitmapstobemovedfromonedevicetoanother（hence,thedevice-independentpartofthename）.ADIBisanexternalformat,incontrasttoadevice-dependentbitmap,whichappearsinthesystemasabitmapobject（createdbyanapplication...）.ADIBisnormallytransportedinmetafiles（usuallyusingtheStretchDIBits（）function）,BMPfiles,andtheClipboard（CF_DIBdataformat）.

ThefollowingsectionsdiscussthedatastoredintheBMPfileorDIBindetail.ThisisthestandardBMPfileformat.[1]SomeapplicationscreatebitmapimagefileswhicharenotcompliantwiththecurrentMicrosoftdocumentation.Also,notallfieldsareused;avalueof0willbefoundintheseunusedfields.

Filestructure

Thebitmapimagefileconsistsoffixed-sizestructures（headers）aswellasvariable-sizestructuresappearinginapredeterminedsequence.Manydifferentversionsofsomeofthesestructurescanappearinthefile,duetothelongevolutionofthisfileformat.

Diag.1–Thestructureofthebitmapimagefile

Referringtothediagram1,thebitmapfileiscomposedofstructuresinthefollowingorder:

StructureName

Optional

Size

Purpose

Comments

BitmapFileHeader

No

14Bytes

TostoregeneralinformationabouttheBitmapImageFile

Notneededafterthefileisloadedinmemory

DIBHeader

No

Fixed-size

（however7differentversionsexist）

Tostoredetailedinformationaboutthebitmapimageanddefinethepixelformat

ImmediatelyfollowstheBitmapFileHeader

Extrabitmasks

Yes

3or4DWORDs[2]

（12or16Bytes）

Todefinethepixelformat

PresentonlyincasetheDIBHeaderistheBITMAPINFOHEADER

ColorTable

Semi-optional

Variable-size

Todefinecolorsusedbythebitmapimagedata（PixelArray）

Mandatoryforcolordepths<=8

Gap1

Yes

Variable-size

Structurealignment

AnartifactoftheFileOffsettoPixelArrayintheBitmapFileHeader

PixelArray

No

Variable-size

Todefinetheactualvaluesofthepixels

ThepixelformatisdefinedbytheDIBHeaderorExtrabitmasks.EachrowinthePixelArrayispaddedtoamultipleof4bytesinsize

Gap2

Yes

Variable-size

Structurealignment

AnartifactoftheICCProfileDataoffsetfieldintheDIBHeader

ICCColorProfile

Yes

Variable-size

Todefinethecolorprofileforcolormanagement

Canalsocontainapathtoanexternalfilecontainingthecolorprofile.Whenloadedinmemoryas"non-packedDIB",itislocatedbetweenthecolortableandgap1.[3]

DIBsinmemory

AbitmapimagefileloadedintomemorybecomesaDIBdatastructure–animportantcomponentoftheWindowsGDIAPI.Thein-memoryDIBdatastructureisalmostthesameastheBMPfileformat,butitdoesnotcontainthe14-bytebitmapfileheaderandbeginswiththeDIBheader.ForDIBsloadedinmemory,thecolortablecanalsoconsistof16bitentries,thatconstituteindexestothecurrentlyrealizedpalette[4]（anadditionallevelofindirection）,insteadofexplicitRGBcolordefinitions.Inallcases,thepixelarraymustbeginatamemoryaddressthatisamultipleof4bytes.Innon-packedDIBsloadedinmemory,theoptionalcolorprofiledatashouldbelocatedimmediatelyafterthecolortableandbeforethegap1andpixelarray[3]（unlikeindiag.1）.

Whenthesizeofgap1andgap2iszero,thein-memoryDIBdatastructureiscustomarilyreferredtoas"packedDIB"andcanbereferredtobyasinglepointerpointingtothebeginningoftheDIBheader.Inallcases,thepixelarraymustbeginatamemoryaddressthatisamultipleof4bytes.Insomecasesitmaybenecessarytoadjustthenumberofentriesinthecolortableinordertoforcethememoryaddressofthepixelarraytoamultipleof4bytes.[4]For"packedDIBs"loadedinmemory,theoptionalcolorprofiledatashouldimmediatelyfollowthepixelarray,asdepictedindiag.1（withgap1=0andgap2=0）.[3]

"PackedDIBs"arerequiredbyWindowsclipboardAPIfunctionsaswellasbysomeWindowspatternedbrushandresourcefunctions.[5]

Bitmapfileheader

Thisblockofbytesisatthestartofthefileandisusedtoidentifythefile.AtypicalapplicationreadsthisblockfirsttoensurethatthefileisactuallyaBMPfileandthatitisnotdamaged.ThefirsttwobytesoftheBMPfileformatarethecharacter'B'thenthecharacter'M'in1-byteASCIIencoding.Alloftheintegervaluesarestoredinlittle-endianformat（i.e.least-significantbytefirst）.

Offset#

Size

Purpose

0000h

2bytes

theheaderfieldusedtoidentifytheBMP&DIBfileis0x420x4Dinhexadecimal,sameasBMinASCII.Thefollowingentriesarepossible:

BM–Windows3.1x,95,NT,...etc.

BA–OS/2structBitmapArray

CI–OS/2structColorIcon

CP–OS/2constColorPointer

IC–OS/2structIcon

PT–OS/2Pointer

0002h

4bytes

thesizeoftheBMPfileinbytes

0006h

2bytes

reserved;actualvaluedependsontheapplicationthatcreatestheimage

0008h

2bytes

reserved;actualvaluedependsontheapplicationthatcreatestheimage

000Ah

4bytes

theoffset,i.e.startingaddress,ofthebytewherethebitmapimagedata（pixelarray）canbefound.

DIBheader（bitmapinformationheader）

Thisblockofbytestellstheapplicationdetailedinformationabouttheimage,whichwillbeusedtodisplaytheimageonthescreen.

TheblockalsomatchestheheaderusedinternallybyWindowsandOS/2andhasseveraldifferentvariants.Allofthemcontainadword（32bit）field,specifyingtheirsize,sothatanapplicationcaneasilydeterminewhichheaderisusedintheimage.

ThereasonthattherearedifferentheadersisthatMicrosoftextendedtheDIBformatseveraltimes.ThenewextendedheaderscanbeusedwithsomeGDIfunctionsinsteadoftheolderones,providingmorefunctionality.SincetheGDIsupportsafunctionforloadingbitmapfiles,typicalWindowsapplicationsusethatfunctionality.Oneconsequenceofthisisthatforsuchapplications,theBMPformatsthattheysupportmatchtheformatssupportedbytheWindowsversionbeingrun.Seethetablebelowformoreinformation.

Size

HeaderName

OSsupport

FeaturesAdded（incremental）

inBitmapFilesWrittenby

12

BITMAPCOREHEADER

OS21XBITMAPHEADER

OS/2andalsoallWindowsversionssinceWindows3.0

64

BITMAPCOREHEADER2

OS22XBITMAPHEADER

OS/2

Addshalftoning.AddsRLEandHuffman1Dcompression.

40

BITMAPINFOHEADER

allWindowsversionssinceWindows3.0

RemovesRLE-24andHuffman1Dcompression.Adds16bppand32bpppixelformats.AddsoptionalRGBbitmasks.

AdobePhotoshop

52

BITMAPV2INFOHEADER

Undocumented.

RemovesoptionalRGBbitmasks.AddsmandatoryRGBbitmasks.

56

BITMAPV3INFOHEADER

Undocumented.

Addsmandatoryalphachannelbitmask.

AdobePhotoshop

108

BITMAPV4HEADER

allWindowsversionssinceWindows95/NT4

Addscolorspacetypeandgammacorrection

124

BITMAPV5HEADER

Windows98/2000andnewer

AddsICCcolorprofiles

VersionsafterBITMAPCOREHEADERonlyaddfieldstotheendoftheheaderofthepreviousversion.Forexample:

BITMAPV2INFOHEADERaddsfieldstoBITMAPINFOHEADERandBITMAPV3INFOHEADERaddsfieldstoBITMAPV2INFOHEADER（or,BITMAPINFOHEADERisastrippedversionofBITMAPV2INFOHEADER）

Forcompatibilityreasons,mostapplicationsusetheolderDIBheadersforsavingfiles.WithOS/2beingobsolete,fornowthecommonformatistheBITMAPINFOHEADERheader.Seenexttableforitsdescription.Allvaluesarestoredasunsignedintegers,unlessexplicitlynoted.

Offset#

Size

Purpose

0Eh

4

thesizeofthisheader（40bytes）

12h

4

thebitmapwidthinpixels（signedinteger）.

16h

4

thebitmapheightinpixels（signedinteger）.

1Ah

2

thenumberofcolorplanesbeingused.Mustbesetto1.

1Ch

2

thenumberofbitsperpixel,whichisthecolordepthoftheimage.Typicalvaluesare1,4,8,16,24and32.

1Eh

4

thecompressionmethodbeingused.Seethenexttableforalistofpossiblevalues.

22h

4

theimagesize.Thisisthesizeoftherawbitmapdata（seebelow）,andshouldnotbeconfusedwiththefilesize.

26h

4

thehorizontalresolutionoftheimage.（pixelpermeter,signedinteger）

2Ah

4

theverticalresolutionoftheimage.（pixelpermeter,signedinteger）

2Eh

4

thenumberofcolorsinthecolorpalette,or0todefaultto2n.

32h

4

thenumberofimportantcolorsused,or0wheneverycolorisimportant;generallyignored.

Note:

Theimagesizefieldcanbe0forBI_RGBbitmaps.

Thecompressionmethodfield（bytes#30-33）canhavethefollowingvalues:

Value

Identifiedby

Compr