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
7.7 Adobe XMP Support
7.8 EXIF Editing

7.1 Metadata Overview

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.

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.

UPDATE: As of AspJpeg 2.9.0.2, metadata can be retrieved from PNG images as well, and the code is exactly the same. Metadata preservation and editing (described below) is still limited to JPEG files, however.

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:

<% ' Directory with images Path = Server.MapPath("../images/photo.jpg") Set Jpeg = Server.CreateObject("Persits.Jpeg") ' Open image for metadata exraction Set Info = Jpeg.OpenInfo( Path ) ' Display collection of items 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>"   Response.Write "</TD></TR>" Next %>

C#:

<script runat="server" LANGUAGE="C#"> void Page_Load(Object Source, EventArgs E) { IASPJpeg objJpeg; objJpeg = new ASPJpeg(); // Compute path to source image String strPath = Server.MapPath("../images/photo.jpg"); // Open source image for metadata exraction IInfo objInfo = objJpeg.OpenInfo( strPath ); foreach( IInfoItem objItem in objInfo ) {   TableRow objRow = new TableRow();   TableCell objCell1 = new TableCell();   objCell1.Controls.Add( new LiteralControl( objItem.Name ) );   TableCell objCell2 = new TableCell();   objCell2.Controls.Add(new LiteralControl(objItem.Description));   TableCell objCell3 = new TableCell();   objCell3.Controls.Add(     new LiteralControl( objItem.Value.ToString() ) );   objRow.Cells.Add( objCell1 );   objRow.Cells.Add( objCell2 );   objRow.Cells.Add( objCell3 );   objTable.Rows.Add( objRow ); } } </script>

Click the links below to run this code sample:

http://localhost/aspjpeg/manual_07/07_metadata.asp
http://localhost/aspjpeg/manual_07/07_metadata.aspx  

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:

Dim s s = Info("Make")

C#:

String s = Info["Make"].Value;

All valid EXIF and IPTC field names are listed below.

7.2 EXIF Item List

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
LensSpecification	Focal and aperture ranges
PanasonicTitle	Panasonic Title
PanasonicTitle2	Panasonic Title 2
PrintIM	Print Image Matching
CameraOwnerName	Owner of the camera
BodySerialNumber	Camera body serial number
LensMake	Lens manufacturer
LensModel	Lens model
Gamma	Gamma coefficient value
Rating	Rating tag used by Windows
TimeZoneOffset	Time zone of the camera clock relative to GMT
ExposureIndex	Camera exposure index setting

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

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 IptcXMP

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. IptcXMP was introduced in version 2.7.0.5 and is described below.

7.4 TIFF Support

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" Set Info = jpeg.OpenInfo(path) nPages = Info("TiffPages") For i = 1 To nPages   jpeg.TiffIndex = i   jpeg.Open path   jpeg.Save "c:\path\" & i & ".jpg" Next %>

7.5 Metadata Preservation

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.PreserveMetadata = True Jpeg.Open Path ... %>

As of version 2.4, AspJpeg is also capable of preserving the ICC profile of the original image. For more information on the International Color Consortium and ICC profiles, visit www.color.org.

<% ... Jpeg.PreserveICCProfile = True ... %>

The PreserveMetadata and PreserveICCProfile properties must be set before calling Open or OpenBinary, an exception will be thrown otherwise.

Note that preserving metadata and ICC profiles in a thumbnail can considerably increase its file size.

7.6 Metadata Editing

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.PreserveMetadata = True Jpeg.Open Path Jpeg.AddMetadataItem "IptcCaption", "New York City Skyline" Jpeg.AddMetadataItem "IptcCaptionWriter", "John Smith" ... Jpeg.Save ... %>

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.

As of Version 2.0.0.1, you can add multiple IptcKeywords entries to an image by using the special tag "IptcKeywordsAdd". Unlike "IptcKeywords", it adds a new keyword entry instead of replacing an existing one. For example, the code snippet

Jpeg.AddMetadataItem "IptcKeywordsAdd", "Art"
Jpeg.AddMetadataItem "IptcKeywordsAdd", "Portrait"

adds two keyword entries to an image, "Art" and "Portrait", whereas the snippet

Jpeg.AddMetadataItem "IptcKeywords", "Art"
Jpeg.AddMetadataItem "IptcKeywords", "Portrait"

only adds a single entry, "Portrait" ("Art" is overwritten.)

As of Version 2.1, there is another special tag, "IptcKeywordsRemove", which removes all keyword entries. In previous versions, it was not possible to completely remove all existing keywords from an image, only overwrite (or clear) the last keyword entry while leaving all others intact. The IptcKeywordsRemove tag is to be used as follows:

Jpeg.AddMetadataItem "IptcKeywordsRemove", ""

As of Version 2.9, most EXIF tags can be modified as well. See Section 7.8 below for more information.

In addition to EXIF and IPTC information described above, JPEG images often contain metadata based on Adobe's Extensible Metadata Platform (XMP) specifications. XMP metadata uses the XML format.

Typical XMP data embedded in a JPEG image may look as follows (the right side of the XML code is truncated for brevity):

As of version 2.7.0.5, AspJpeg is capable of retrieving and setting the XMP metadata in its entirety as if it were a regular IPTC tag, via the Info collection and AddMetadataItem method. The name of the tag is "IptcXMP". It is the application developer's responsibility to perform XML parsing to retrieve and set various components of the XMP metadata. XML processing can be performed quite easily using the Microsoft.XMLDOM object in classic ASP and XmlDocument object in .NET.

For the IptcXMP item to be accessible via the Info collection, you must set the property Jpeg.PreserveMetadata to True before calling Jpeg.Open/OpenBinary.

The following code sample retrieves XMP data from an image, changes the value of the dc:creator item and plugs the modified XML string back into the image. The .NET code snippet requires that the System.Xml namespace be imported.

VB Script:

Set Jpeg = Server.CreateObject("Persits.Jpeg") Jpeg.PreserveMetadata = true Path = "c:\path\birds.jpg" Jpeg.Open Path Set Info = Jpeg.OpenInfo( Path ) Set XmlDom = Server.CreateObject("Microsoft.XMLDOM") XmlDom.Async = False ' need synchronous operation XmlDom.LoadXml( Info("IptcXMP") ) Set XmlNode = XmlDom.DocumentElement.SelectSingleNode ("rdf:RDF/rdf:Description/dc:creator/rdf:Seq/rdf:li") XmlNode.text = "John Smith" Jpeg.AddMetadataItem "IptcXMP", XmlDom.xml Jpeg.SaveUnique "c:\path\out.jpg"

C#:

IASPJpeg objJpeg = new ASPJpeg(); objJpeg.PreserveMetadata = 1; string strPath = @"c:\path\birds.jpg"; objJpeg.Open( strPath ); IInfo objInfo = objJpeg.OpenInfo( strPath ); XmlDocument XmlDom = new XmlDocument(); XmlDom.LoadXml( objInfo["IptcXMP"].Value.ToString() ); XmlNamespaceManager objMgr = new XmlNamespaceManager(XmlDom.NameTable); objMgr.AddNamespace("rdf", "http://www.w3.org/1999/02/22-rdf-syntax-ns#"); objMgr.AddNamespace("dc", "http://purl.org/dc/elements/1.1/"); objMgr.AddNamespace("x", "http://www.w3.org/1999/02/22-rdf-syntax-ns#"); XmlNode node = XmlDom.DocumentElement.SelectSingleNode ("rdf:RDF/rdf:Description/dc:creator/rdf:Seq/rdf:li", objMgr); node.InnerText = "John Smith"; objJpeg.AddMetadataItem( "IptcXMP", XmlDom.InnerXml ); objJpeg.SaveUnique( @"c:\mpath\out.jpg" );

The following code snippet adds a new keyword to the dc:subject list:

VB Script:

... Set XmlNode = XmlDom.DocumentElement.SelectSingleNode ("rdf:RDF/rdf:Description/dc:subject/rdf:Bag") Set NewNode = XmlDom.createNode( 1, "rdf:li", "http://www.w3.org/1999/02/22-rdf-syntax-ns#") NewNode.text = "John Smith" & chrw( &H0416 ) XmlNode.AppendChild( NewNode ) ...

C#:

... XmlNode XmlNode = XmlDom.DocumentElement.SelectSingleNode( "rdf:RDF/rdf:Description/dc:subject/rdf:Bag", objMgr); XmlNode NewNode = XmlDom.CreateNode( XmlNodeType.Element, "rdf:li", "http://www.w3.org/1999/02/22-rdf-syntax-ns#"); NewNode.InnerText = "John Smith"; XmlNode.AppendChild( NewNode ); ...

7.8.1 ChangeExifItem Method

As of Version 2.9, AspJpeg is capable of setting or modifying most EXIF fields in an image via the method ChangeExifItem. This method expects three arguments: the EXIF field name to modify (see Section 7.3 for the list of valid names), the double-precision value to set a numeric field to, and an optional string value to set a text field to. The 3rd argument must be specified if the EXIF field specified by the first argument is of the EXIF type ASCII or UNDEFINED, in which case the 2nd argument is ignored. To be able to use the ChangeExifItem method, the property PreserveMetadata must be set to True before opening the image.

The image does not need to have existing EXIF information for the ChangeExifItem method to work. If the image has no EXIF data block to begin with, the method creates it.

The GPS-related coordinate and timestamp values (GPSLatitude, GPSLongitude, GPSDestLatitude, GPSDestLongitude, and GPSTimeStamp) must be specified in a decimal form. Positive values correspond to the North latitudes and East longitudes, and negative values to the South latitudes and West longitudes. The latitude/longitude reference fields such as GPSLongitudeRef or GPSDestLongitudeRef should not be set directly.

The following code snippet sets the Artist and Software information for the image to arbitrary text values. It also sets the GPS coordinates of the image to the center of Canberra, Australia, GPS timestamp to 14:30 and GPS date stamp, a text field, to "2016:08:22".

VB Script:

Set Jpeg = Server.CreateObject("Persits.Jpeg") Jpeg.PreserveMetadata = True Jpeg.Open Path Jpeg.ChangeExifItem "Artist", 0, "John Smith" Jpeg.ChangeExifItem "Software", 0, "Persits Software, Inc." Jpeg.ChangeExifItem "GPSLatitude", -35.2809 Jpeg.ChangeExifItem "GPSLongitude", 149.13 Jpeg.ChangeExifItem "GPSTimeStamp", 14.5 Jpeg.ChangeExifItem "GPSDateStamp", 0, "2016:08:22" Jpeg.SaveUnique "c:\path\out.jpg"

C#:

IASPJpeg objJpeg = new ASPJpeg(); objJpeg.PreserveMetadata = 1; objJpeg.Open( strPath ); objJpeg.ChangeExifItem( "Artist", 0, "John Smith" ); objJpeg.ChangeExifItem( "Software", 0, "Persits Software, Inc." ); objJpeg.ChangeExifItem( "GPSLatitude", -35.2809d, Missing.Value ); objJpeg.ChangeExifItem( "GPSLongitude", 149.13d, Missing.Value ); objJpeg.ChangeExifItem( "GPSTimeStamp", 14.5d, Missing.Value ); objJpeg.ChangeExifItem( "GPSDateStamp", 0, "2016:08:22" ); objJpeg.SaveUnique( @"c:\path\out.jpg" );

7.8.2 ApplyOrientation Method

Most digital images store their pixel information in "standard" orientation: the 0th row of pixels corresponds to the top of the image, and the 0th column of pixels to the left side of the image. However, when the camera or mobile device taking the picture is turned sideways or upside-down, the resultant image may have its pixels stored differently (for example, its 0th row of pixels corresponds to the right side of the image and the 0th column to the top side.)

When that happens, the camera stores the camera orientation information in the EXIF "Orientation" tag. When the image is in standard orientation, this EXIF value is 1. The values of 2 to 8 correspond to various other possible orientations as summarized by the following table:

Value	0th Row	0th Column
1	top	left side
2	top	right side
3	bottom	right side
4	bottom	left side
5	left side	top
6	right side	top
7	right side	bottom
8	left side	bottom

The problem with images with the "Orientation" tag set to anything other than 1 is that some image viewers and browsers take this tag into account when displaying the image (such as Google Chrome), while others ignore it altogether. As a result, the same image may come up correctly in some viewers while appear rotated and/or flipped in others.

As of Version 2.9, AspJpeg offers the method ApplyOrientation which rotates and/or flips the image according to its Orientation tag, and then sets this tag to 1. As a result, the image is always displayed consistently across all viewers and browsers. To be able to use the ApplyOrientation method, the property PreserveMetadata must be set to True before opening the image. This method expects no arguments, and its return value is the original Orientation value of the image. If the image contains no Orientation tag, the method does nothing.

VB Script:

Set Jpeg = Server.CreateObject("Persits.Jpeg") Jpeg.PreserveMetadata = True Jpeg.Open Path Jpeg.ApplyOrientation Jpeg.SaveUnique "c:\path\out.jpg"

C#:

IASPJpeg objJpeg = new ASPJpeg(); objJpeg.PreserveMetadata = 1; objJpeg.Open( strPath ); objJpeg.ApplyOrientation(); objJpeg.SaveUnique( @"c:\path\out.jpg" );

 

Advanced Image Management for ASP and .NET

Copyright © 1998 - 2022 Persits Software, Inc. All Rights Reserved. AspJpeg is a trademark of Persits Software, Inc.