Reading and Writing Images in Java

1
Lecture08

• Reading and Writing Images in Java

2
Imaging Models of Java

• Push Imaging Model
• Immediate Mode Imaging Model
• Pull Imaging Model. This is fully implemented in
  Java Advanced Imaging API. Some parts of this
  could be seen in java.awt.

3
Push Imaging Model

• In push imaging model the image data isnt
  introduced into the imaging pipeline until it is
  needed at which time an object called
  ImageProducer starts pushing the data into this
  pipeline. On the other end of this pipeline is an
  ImageConsumer that must wait for the data to get
  pushed to it. This model was designed to provide
  a simple way to load images into applets and
  applications.

4
Push Imaging Model

• Advantages
• It can load and display images incrementally as
  they become available.
• Disadvantages
• The image data isnt collected into an accessible
  location, making anything more than simple image
  processing difficult.
• The programming interface can be confusing.

5
The Image Class

• It is better to think of the java.awt.image class
  as a group of resources and methods that provide
  a means for transferring and inquiring about a
  collection of image data and not as the
  collection itself.

6
Image rendering situations in java

• In an applet
• // ...
• URL url
• // ...
• Image img getImage(url) // first step
• // ...
• public void paint(Graphics g)
• // ...
• g.drawImage(img, 0, 0, this) // second step
• // ...
• // ...

7
Image rendering situations in java

• In an application
• // ...
• Image img Toolkit.getDefaultToolkit().getImage(
  filename)
• // ...
• public void paint(Graphics g)
• // ...
• g.drawImage(img, 0, 0, this) // second step
• // ...
• // ...

8
Image rendering situations in java

• In both cases, the initial step doesnt start
  loading the image data, but instead instantiates
  an Image object that creates the resources
  necessary to process the image data.
• The second method begins image loading, although
  the method returns immediately regardless of how
  much of the image is available to display.
• The actual loading continues in a separate
  thread, where an object implementing the
  java.awt.ImageProducer interface sends image data
  to an object implementing the java.awt.ImageConsum
  er interface.
• While ImageProducer sends image data into the
  ImageComsumer, the ImageObserver interface
  asynchronously receives the status information
  about the image transfer.

9
ImageObserver interface

• This status information is passed to the
  ImageObserver interface via the method
• public boolean imageUpdate(Image img, int
  infoFlags, int x, int y,
• int width, int height)
• of the ImageObserver class.
• Remember the Component class and any decendent of
  it such as the Applet class, is an ImageObserver.
  
• The default behaviour of the Applets imageUpdate
  method is to repaint the applet whenever new data
  bits are available.

10
Introduction to Image I/O API

• Java Image I/O package was created to overcome
  the limitations of reading/writing of formatted
  images of then Java APIs. Now Java image I/O API
  is integrated with the core java language. Two
  useful properties of Java image I/O API
• Plug-ins The run time Java Vitual Machine (JVM)
  discovers which image readers/writers are
  available and what types of image formats they
  can decode/encode.
• Metadata The non-pixel information about the
  input images and output images.

11
Supported Formats

• Readers
• GIF
• JPEG
• PNG
• Writers
• JPEG
• PNG

12
Image Readers

• With the Java2D package, the input images are
  converted to Image objects using the getImage
  methods of the Applet class and the Toolkit
  class.
• With Image I/O package, input images are
  converted to BufferedImages using the read
  methods of the javax.imageio.ImageReader class.
• Generally you have more than one ImageReader
  subclasses.

13
javax.imageio.ImageReaderSpis

• The initial step in reading an image is to choose
  an ImageReader that can decode the format of the
  image of interest. This is done by providing
  information about that images format to a set of
  ImageReader service providers javax.imageio.ImageR
  eaderSpis. This information can be
• Image file suffix
• Image MIME type
• Image format
• Image data

14
MIME type

• Multipurpose Internet Mail Extensions.
• Examples
• Extension Type Use
• jpg image/jpeg JPEG image
• jpeg image/jpeg JPEG image
• mpg video/mpeg MPEG video
• au audio/basic ULAW audio data
• avi video/x-msvideo Microsoft video
• For details check http//www.iana.org/assignments/
  media-types/

15
Reading and Writing Basics

• One of the ImageReaders whose service provider
  responds positively will be choosen to convert
  the image into a BufferedImage.
• While some ImageReaders are part of Java SDK, the
  rest can be downloaded from third party vendors,
  freeware, and shareware sites.
• If no appropriate ImageReader available, then one
  can be written.
• The process of writing images is simmilar and has
  the corresponding classes ImageWriters and
  javax.imageio.ImageWriterSpis.

16
ImageIO class

• The ImageIO class contains static methods that
  are mainly used for locating ImageReaders and
  ImageWriters. To find out plugins by format
  names, you can use
• static String getReaderFormatNames()
• static String getWriterFormatNames()
• To find out plugins by MIME types
• static String getReaderMIMETypes()
• static String getWriterMIMETypes()

17
ImageIO class

• In order to find out ImageReaders for a
  particular image the following static methods of
  ImageIO class can be used
• static Iterator getImageReadersByFormatName(Strin
  g formatName)
• static Iterator getImageReadersByMIMEType(String
  MIMEType)
• static Iterator getImageReadersBySuffix(String
  fileSuffix)
• The following method find ImageReaders by
  examining the object representing the image input
  stream ( of the class javax.imageio.stream.ImageIn
  putStream)
• static Iterator getImageReaders(Object input)

18
ImageInputStream

• The ImageInputStreams can be created as follows
• URL url new URL(imageURL)
• ImageInputStream iis ImageIO.createImageInput
  Stream(url.openStream())
• or
• Socket s new Socket(imageHost, imagePort)
• ImageInputStream iis ImageIO.createImageInputS
  tream(s.getInputStream())
• or
• FileInputStream fis new FileInputStream(imageFi
  leName)
• ImageInputStream iis ImageIO.createImageInpu
  tStream(fis)
• Note that the most image formats begin with
  something called a magic number, which is the
  part of ImageInputStream that most
  ImageReaderSpis use to decide whether they can
  decode an image format.

19
ImageWriter

• For a known ImageWriter the corresponding
  ImageReaders can be found by
• static ImageReader getImageReader(ImageWriter
  writer)
• The corresponding ImageWriter static methods of
  ImageIO are
• static Iterator getImageWritersByFormatName(Strin
  g formatName)
• static Iterator getImageWritersByMIMEType(String
  MIMEType)
• static Iterator getImageWritersBySuffix(String
  fileSuffix)
• static Iterator getImageWriters(ImageTypeSpecifie
  r type, string format)
• static ImageWriter getImageWriter(ImageReader
  reader)
• The javax.imageio.ImageTypeSpecifier is a class
  that specifies ColorModel/SampleModel combination.

20
Using The ImageReader

• An application need to do two things in order to
  interact with an ImageReader
• provide it with an input source
• Use it to read the source image(s)
• The following method of ImageReader is used to
  provide it with an input source
• public void setInput(Object input, boolean
  seekForwardOnly)
• where input is usually an ImageInputStream and
  seekForwardOnly parameter is used to specify
  whether an application can go backwards in the
  input stream.

21
Using The ImageReader

• Once an input source is defined either of the
  following methods can be used to read images
• public void read(int imageIndex)
• public void read(int imageIndex, ImageReadPar
  am param)
• where imageIndex is the index of the image that
  will be read and param parameter provides control
  over how this image is to be read.

22
Using The ImageReader

• The number of images can be obtained using the
  method
• public int getNumImages(boolean
  allowSearch)
• where the allowSearch parameter specifies
  whether you want the entire ImageInputStream
  examined to determine the number of available
  images. If allowSearch parameter is false, the
  number of images is returned only if it is
  immediately available otherwise -1 is returned.

23
Example

• URL url
• try
• url new URL(inputURL)
• catch (MalformedURLException mue)
• // Process the exception
• ImageInputStream iis
• try
• iis ImageIO.createImageInputStream(url.ope
  nStream())
• catch (IIOException iioe)
• // Process the exception
• catch (IOException ioe)
• // Process the exception

24
Example

• Iterator readers ImageIO.getImageReaders(iis)
• ImageReader reader
• if (readers.hasNext())
• reader (ImageReader) readers.next()
• reader.setInput(iis,true)
• if (reader null)
• // Process the error message

25
Example

• BufferedImage bi
• int imageIndex 0
• try
• while (bi reader.read(imageIndex))
• // process bi here
• catch (IOException ioe)
• // Process the exception
• catch (IndexOutOfBoundsException iobe) / all
  the images have been read /
• // ...

26
Using The ImageWriter

• As with ImageReader, an application does two
  things when interacting with an ImageWrier
• provide it with an output source
• Use it to write the image(s) into the output
  source
• The setOutput method of ImageWriter is used to
  define an output source
• public void setOutput(Object output)
• where output is typically an ImageOutputStream

27
ImageOutputStream

• Socket s new Socket(imageHost, imagePort)
• ImageOutputStream ios ImageIO.createImageOutputS
  tream(
• s.getOutputStream())
• or
• FileOutputStream fos new FileOutputStream(imageF
  ileName)
• ImageOutputStream ios ImageIO.createOutputStream
  (fos)

28
Using Writers

• The main write method is
• public void write(IIOMetadata streamMetadata,
• IIOImage iioImage,
• ImageWriteParam param)
• where streamMetadata can be set to null, if
  there is no stream metadata. javax.imageio.IIOImag
  e is a container class used for holding the
  following information
• The image
• The images associated thumbnail images,
  represented as java.util.List of BufferedImages.
• If the image format does not support thumbnail
  images this can be set to null.
• The images metadata. If the image format does
  not support metadata this can be set to null.

29
Simple Image Reading

• The ImageIO class has the following methods
• public static BufferedImage read(File input)
  throws IIOException
• public static BufferedImage read(URL input)
  throws IIOException
• public static BufferedImage
• read(InputStream stream) throws
  IIOException
• public static BufferedImage read(ImageInputSt
  ream stream) throws IIOException

30
Example Reading an Image

• public static BufferedImage readAsBufferedImage(St
  ring filename)
• try
• BufferedImage img ImageIO.read(new
  File(filename))
• return img
• catch (Exception e)
• e.printStackTrace()
• return null

31
Simple Image Writing

• The ImageIO has following methods.
• public static boolean write(RenderedImage im,
  String formatName,
• File output) throws IIOException
• public static boolean write(RenderedImage im,
  String formatName,
• OutputStream output) throws
  IIOException
• public ststic boolean write(RenderedImage im,
  String formatname
• ImageOutputStream output) throws
  IIOException

32
Example Writing an Image

• public void save(BufferedImage image, String
  filename)
• try
• ImageIO.write((RenderedImage)
  image,"jpg", new File(filename))
• catch (exception e)
• // Process the exception