org.w3c.tools.jpeg
Class Exif

java.lang.Object
  org.w3c.tools.jpeg.Exif

public class Exif
extends java.lang.Object

An API for accessing EXIF encoded information in a JPEG file.

JPEG images are stored in a tagged format reminiscent of TIFF files. Each component of the image is identified with a tag number and a size. This allows applications that read JPEG files to skip over information that they don't understand.

Additional resources:

• Official standards, http://www.exif.org/specifications.html
• TsuruZoh Tachibanaya's excellent description, http://www.ba.wakwak.com/~tsuruzoh/Computer/Digicams/exif-e.html
• Matthias Wandel's JHead, http://www.sentex.net/~mwandel/jhead

This class treats a byte array as a JPEG image and parses the tags searching for EXIF data. EXIF data is also tagged. Based on information provided by the caller, this class builds a hash of EXIF data and makes it available to the caller.

Most simple EXIF values are tagged with both their identity and their format. For example, ExposureTime (0x829A) is a rational number and this class can extract that value. However, some fields are of "unknown" format. If you decode one of these, you can add a special purpose decode for that field by associating the name of the decoder class with the field name. For example, my Nikon CoolPix 950 includes a MakerNote (0x927C) field that's tagged "unknown" format. Using information from TsuruZoh's page, I've built a decoder for that field and added it as an example.

In addition to the tagged data, JPEG images have five intrinisic properties: height, width, the compression algorithm used, the number of bits used to store each pixel value, and the number of color components. This class allows the caller to unify those intrinsic components with the tagged data.

In an effort to be flexible without requiring users to change the source, a fair bit of setup is needed to use this class.

The caller must:

1. Construct an Exif object, exif = new Exif().
2. Associate names with each of the tags of interest, exif.addTag(nnn, "name").
3. Associate names with the intrinsic values:
   • exif.addHeight("name")
   • exif.addWidth("name")
   • exif.addCompression("name")
   • exif.addNumberOfColorComponents("name")
   • exif.addBitsPerPixel("name")
4. Finally, the caller may associate a decoder with specific fields: exif.addDecoder("name", "java.class.name").

Having setup the exif object, it can be passed to JpegHeaders to be filled in when the JPEG file is parsed.

The caller must also explicitly set the intrinsic values since they do not come from the EXIF data.

After parsing the JPEG, call exif.getTags() to get back the has of name/value pairs.

See Also:

ExifData, TagDecoder, JpegHeaders

Constructor Summary

Exif()

Method Summary

void	addBitsPerPixel(java.lang.String name)
void	addCompression(java.lang.String name)
void	addDecoder(java.lang.String name, java.lang.String className)
void	addHeight(java.lang.String name)
void	addNumberOfColorComponents(java.lang.String name)
void	addTag(int tag, java.lang.String tagName)
void	addWidth(java.lang.String name)
protected void	assignByte(java.lang.String tagName, int offset)
protected void	assignRational(java.lang.String tagName, int offset)
protected void	assignSByte(java.lang.String tagName, int offset)
protected void	assignSLong(java.lang.String tagName, int offset)
protected void	assignSShort(java.lang.String tagName, int offset)
protected void	assignString(java.lang.String tagName, int offset, int length)
protected void	assignULong(java.lang.String tagName, int offset)
protected void	assignUndefined(java.lang.String tagName, int offset, int length)
protected void	assignUShort(java.lang.String tagName, int offset)
java.util.Hashtable	getTags()
void	parseExif(byte[] exifData)
protected void	processExifDir(int dirStart, int offsetBase)
void	setBPP(int bitsPP)
void	setCompression(java.lang.String comp)
void	setHeight(int height)
void	setNumCC(int numCC)
void	setWidth(int width)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Exif

public Exif()

Method Detail

parseExif

public void parseExif(byte[] exifData)

setHeight

public void setHeight(int height)

setWidth

public void setWidth(int width)

setCompression

public void setCompression(java.lang.String comp)

setBPP

public void setBPP(int bitsPP)

setNumCC

public void setNumCC(int numCC)

addHeight

public void addHeight(java.lang.String name)

addWidth

public void addWidth(java.lang.String name)

addCompression

public void addCompression(java.lang.String name)

addBitsPerPixel

public void addBitsPerPixel(java.lang.String name)

addNumberOfColorComponents

public void addNumberOfColorComponents(java.lang.String name)

addTag

public void addTag(int tag,
                   java.lang.String tagName)

addDecoder

public void addDecoder(java.lang.String name,
                       java.lang.String className)

getTags

public java.util.Hashtable getTags()

processExifDir

protected void processExifDir(int dirStart,
                              int offsetBase)

assignUndefined

protected void assignUndefined(java.lang.String tagName,
                               int offset,
                               int length)

assignString

protected void assignString(java.lang.String tagName,
                            int offset,
                            int length)

assignSByte

protected void assignSByte(java.lang.String tagName,
                           int offset)

assignByte

protected void assignByte(java.lang.String tagName,
                          int offset)

assignUShort

protected void assignUShort(java.lang.String tagName,
                            int offset)

assignSShort

protected void assignSShort(java.lang.String tagName,
                            int offset)

assignULong

protected void assignULong(java.lang.String tagName,
                           int offset)

assignSLong

protected void assignSLong(java.lang.String tagName,
                           int offset)

assignRational

protected void assignRational(java.lang.String tagName,
                              int offset)