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1. Introduction
2. Thumbnails
3. Using AspUpload
4. Image Processing
5. Drawing & Typing
6. Picture-in-Picture
7. Metadata
8. Miscellaneous
9. GIF Output
Object Reference
Live Demos
Support
Chapter 7: Metadata Extraction
7.1 Metadata Overview
7.2 EXIF Item List
7.3 IPTC Item List
7.4 TIFF Support
7.5 Metadata Preservation
7.6 Metadata Editing
7.1 Metadata Overview
The format for camera-embedded metadata is called EXIF, which stands for
Exchangeable Image File Format.
For more information on EXIF, visit www.exif.org.
The format used by Photoshop is described by the International Press Telecommunications Council
(www.iptc.org)
and usually referred to as IPTC.
AspJpeg 1.4+ is capable of extracting EXIF and IPTC metadata from JPEG images via the OpenInfo and
OpenInfoBinary methods. The difference between the two is the same as between Open
and OpenBinary - the former opens a source image from disk, the latter from memory.
The OpenInfo and OpenInfoBinary methods both return an instance of the Info object
which is a collection of InfoItem objects, each representing a separate EXIF or IPTC field.
The InfoItem object supports the following properties: Name (String), Value (Variant, default property), Tag (Integer),
and Description (String).
The following code sample extracts and displays all metadata fields from a JPEG image:
VB Script:
Set Jpeg = Server.CreateObject("Persits.Jpeg")
' Open image for metadata exraction
' Display collection of items
Response.Write "</TD></TR>"
void Page_Load(Object Source, EventArgs E)
// Compute path to source image
// Open source image for metadata exraction
foreach( IInfoItem objItem in objInfo )
TableCell objCell1 = new TableCell();
TableCell objCell2 = new TableCell();
TableCell objCell3 = new TableCell();
objRow.Cells.Add( objCell1 );
}
Click the links below to run this code sample:
http://localhost/aspjpeg/manual_07/07_metadata.asp
To obtain a value for a specific metadata field, such as a camera make, you should use
Info's default Item property which accepts this field's name as an index.
Since Item is the default property, the word "Item" can be omitted. In C#, square brackets
must be used. The following code snippet obtains camera make information and assigns it to a string variable:
VB Script:
All valid EXIF and IPTC field names are listed below.
7.2 EXIF Item List
In addition to the pre-defined fields, some images may contain custom fields not
described in the EXIF specifications. Custom field names have the form Tag#nnn
where nnn is a decimal number, e.g. Tag#37388.
7.3 IPTC Item List
Note: The IptcKeywords field may appear multiple times in the Info collection.
IptcCopyrighted was introduced in version 2.0 of AspJpeg and is a True/False value.
7.4 TIFF Support
Set Info = jpeg.OpenInfo(path)
For i = 1 To nPages
7.5 Metadata Preservation
Jpeg.PreserveMetadata = True
This property must be set before calling Open or OpenBinary, an exception will be thrown
otherwise.
Note that preserving metadata in a thumbnail can considerably increase its file size.
7.6 Metadata Editing
Jpeg.PreserveMetadata = True
All IPTC fields are strings with one exception: the IptcCopyrighted tag introduced in version 2.0
is an on/off flag. Use the string "True" to set this flag or "False" to clear it.
Most digital cameras nowadays embed various pieces of information into the JPEG images they generate,
including the current date/time, shooting conditions (e.g. whether a flash was used),
camera settings (shutter, aperture, focal length), etc. Adobe Photoshop,
the leading image editing package, is also capable of embedding
various pieces of metadata into the JPEGs it produces, such as an author, title, copyright notice, etc.
C#:
<%
' Directory with images
Path = Server.MapPath("../images/photo.jpg")
Set Info = Jpeg.OpenInfo( Path )
For Each Item in Info
Response.Write "<TR><TD>"
Response.Write Item.Name & "</TD><TD>"
Response.Write Item.Description & "</TD><TD>"
Response.Write Item.Value & "</TD>"
Next
%>
<script runat="server" LANGUAGE="C#">
{
IASPJpeg objJpeg;
objJpeg = new ASPJpeg();
String strPath = Server.MapPath("../images/photo.jpg");
IInfo objInfo = objJpeg.OpenInfo( strPath );
{
TableRow objRow = new TableRow();
objCell1.Controls.Add( new LiteralControl( objItem.Name ) );
objCell2.Controls.Add(new LiteralControl(objItem.Description));
objCell3.Controls.Add(
new LiteralControl( objItem.Value.ToString() ) );
objRow.Cells.Add( objCell2 );
objRow.Cells.Add( objCell3 );
objTable.Rows.Add( objRow );
}
</script>
http://localhost/aspjpeg/manual_07/07_metadata.aspx
C#:
Dim s
s = Info("Make")
String s = Info["Make"].Value;
The following table lists all valid EXIF field names and descriptions. Most real-world
images only contain a small subset of these items, if any. Note that in addition to
general image and camera setting information, EXIF also provides for GPS-related data.
Name Description NewSubfileType Subfile type ImageWidth Image width ImageLength Image height BitsPerSample Number of bits per component Compression Compression scheme PhotometricInterpretation Pixel composition ImageDescription Image title Make Manufacturer of image input equipment Model Model of image input equipment StripOffsets Image data location Orientation Orientation of image SamplesPerPixel Number of components RowsPerStrip Number of rows per strip StripByteCounts Bytes per compressed strip XResolution Image resolution in width direction YResolution Image resolution in height direction PlanarConfiguration Image data arrangement ResolutionUnit Unit of X and Y resolution TransferFunction Transfer function Software Software used DateTime File change date and time Artist Person who created the image HostComputer The computer and/or operating system in use WhitePoint White point chromaticity PrimaryChromaticities Chromaticities of primaries JPEGInterchangeFormat Offset to JPEG SOI JPEGInterchangeFormatLength Bytes of JPEG data YCbCrCoefficients Color space transformation matrix coefficients YCbCrSubSampling Subsampling ratio of Y to C YCbCrPositioning Y and C positioning ReferenceBlackWhite Pair of black and white reference values Copyright Copyright holder ExifTag Exif IFD Pointer GPSTag GPSInfo IFD Pointer ExposureTime Exposure time FNumber F number ExposureProgram Exposure program SpectralSensitivity Spectral sensitivity ISOSpeedRatings ISO speed ratings OECF Optoelectric coefficient ExifVersion Exif Version DateTimeOriginal Date and time original image was generated DateTimeDigitized Date and time image was made digital data ComponentsConfiguration Meaning of each component CompressedBitsPerPixel Image compression mode ShutterSpeedValue Shutter speed ApertureValue Aperture BrightnessValue Brightness ExposureBiasValue Exposure bias MaxApertureValue Maximum lens aperture SubjectDistance Subject distance MeteringMode Metering mode LightSource Light source Flash Flash FocalLength Lens focal length SubjectArea Subject area MakerNote Manufacturer notes UserComment User comments SubSecTime DateTime subseconds SubSecTimeOriginal DateTimeOriginal subseconds SubSecTimeDigitized DateTimeDigitized subseconds FlashpixVersion Supported Flashpix version ColorSpace Color space information PixelXDimension Valid image width PixelYDimension Valid image height RelatedSoundFile Related audio file InteroperabilityTag Interoperability IFD Pointer FlashEnergy Flash energy SpatialFrequencyResponse Spatial frequency response FocalPlaneXResolution Focal plane X resolution FocalPlaneYResolution Focal plane Y resolution FocalPlaneResolutionUnit Focal plane resolution unit SubjectLocation Subject location ExposureIndex Exposure index SensingMethod Sensing method FileSource File source SceneType Scene type CFAPattern CFA pattern CustomRendered Custom image processing ExposureMode Exposure mode WhiteBalance White balance DigitalZoomRatio Digital zoom ratio FocalLengthIn35mmFilm Focal length in 35 mm film SceneCaptureType Scene capture type GainControl Gain control Contrast Contrast Saturation Saturation Sharpness Sharpness DeviceSettingDescription Device settings description SubjectDistanceRange Subject distance range ImageUniqueID Unique image ID RelatedImageFileFormat File format of image file RelatedImageWidth Image width RelatedImageLength Image height GPSVersionID GPS tag version GPSLatitudeRef North or South Latitude GPSLatitude Latitude GPSLongitudeRef East or West Longitude GPSLongitude Longitude GPSAltitudeRef Altitude reference GPSAltitude Altitude GPSTimeStamp GPS time (atomic clock) GPSSatellites GPS satellites used for measurement GPSStatus GPS receiver status GPSMeasureMode GPS measurement mode GPSDOP Measurement precision GPSSpeedRef Speed unit GPSSpeed Speed of GPS receiver GPSTrackRef Reference for direction of movement GPSTrack Direction of movement GPSImgDirectionRef Reference for direction of image GPSImgDirection Direction of image GPSMapDatum Geodetic survey data used GPSDestLatitudeRef Reference for latitude of destination GPSDestLatitude Latitude of destination GPSDestLongitudeRef Reference for longitude of destination GPSDestLongitude Longitude of destination GPSDestBearingRef Reference for bearing of destination GPSDestBearing Bearing of destination GPSDestDistanceRef Reference for distance to destination GPSDestDistance Distance to destination GPSProcessingMethod Name of GPS processing method GPSAreaInformation Name of GPS area GPSDateStamp GPS date GPSDifferential GPS differential correction WinTitle Windows Explorer Title WinAuthor Windows Explorer Author WinSubject Windows Explorer Subject WinComments Windows Explorer Comments WinKeywords Windows Explorer Keywords
The following IPTC fields are supported by AspJpeg:
IptcByline
IptcBylineTitle
IptcCredits
IptcSource
IptcObjectName
IptcDateCreated
IptcCity
IptcState
IptcCountry
IptcOriginalTransmissionReference
IptcCopyrightNotice
IptcCaption
IptcCaptionWriter
IptcHeadline
IptcSpecialInstructions
IptcCategory
IptcSupplementalCategories
IptcUrgency
IptcKeywords
IptcTimeCreated
IptcDigitalCreationDate
IptcDigitalCreationTime
IptcOriginatingProgram
IptcProgramVersion
IptcUno
IptcEditStatus
IptcFixtureIdentifier
IptcReleaseDate
IptcReleaseTime
IptcObjectCycle
IptcImageNotes
IptcTextSaved
IptcCustom1
IptcCustom2
IptcCustom3
IptcCustom4
IptcCustom5
IptcCustom6
IptcCustom7
IptcCustom8
IptcCustom9
IptcCustom10
IptcCustom11
IptcCustom12
IptcCustom13
IptcCustom14
IptcCustom15
IptcCustom16
IptcCustom17
IptcCustom18
IptcCustom19
IptcCustom20
IptcImageURL
IptcCopyrighted
If the image being opened is a TIFF, the Info collection will contain a
special field by the name of "TiffPages" which contains the number of pages (images) in that TIFF file.
This value can be used to iterate through all images in a multi-page TIFF.
To open an image with an index other than 1, the property TiffIndex should be used,
as follows:
<%
path = "c:\path\multipage.tif"
nPages = Info("TiffPages")
jpeg.TiffIndex = i
jpeg.Open path
jpeg.Save "c:\path\" & i & ".jpg"
Next
%>
Starting with Version 1.9, AspJpeg is capable of preserving the Exif and IPTC metadata of the original
image when a thumbnail is created.
To enable this functionality, you need to set the property PreserveMetadata to True
before opening the image, as follows:
<%
Set Jpeg = Server.CreateObject("Persits.Jpeg")
Jpeg.Open Path
...
%>
As of Version 2.0, AspJpeg can be used to add or replace IPTC values in an image
via the method AddMetadataItem. This method accepts two arguments: an IPTC
tag from the table shown in Section 7.3 above, and a string value
to be inserted under that tag. This method can be called multiple times, if necessary.
To use AddMetadataItem, the property
PreserveMetadata described in the previous section must be set to True before the image
is opened:
<%
Set Jpeg = Server.CreateObject("Persits.Jpeg")
Jpeg.Open Path
Jpeg.AddMetadataItem "IptcCaption", "New York City Skyline"
Jpeg.AddMetadataItem "IptcCaptionWriter", "John Smith"
...
Jpeg.Save ...
%>
Copyright © 1998 - 2007 Persits Software, Inc.
All Rights Reserved.
AspJpeg is a trademark of Persits Software, Inc.