Class PngImage

java.lang.Object
com.sixlegs.png.PngImage
All Implemented Interfaces:
Transparency

public class PngImage extends Object implements Transparency
A class to decode PNG images. The simplest use is if only a decoded BufferedImage is required:
BufferedImage image = new PngImage().read(new java.io.File("test.png"));
The PngImage instance used to read the image also stores all of the image metadata. For customized PNG decoding, a PngConfig object may be passed to the constructor.

This class is not thread-safe. Do not share a PngImage instance among multiple threads without proper synchronization.

For more information visit http://www.sixlegs.com/

Author:
Chris Nokleberg <chris@sixlegs.com>
See Also:
  • Constructor Details

    • PngImage

      public PngImage()
      Constructor which uses a default instance of PngConfig.
    • PngImage

      public PngImage(PngConfig config)
      Constructor which uses the specified configuration.
  • Method Details

    • getConfig

      public PngConfig getConfig()
      Returns the configuration used by this object.
      Returns:
      the PngConfig instance used by this object
    • read

      public BufferedImage read(File file) throws IOException
      Reads a PNG image from the specified file. Image metadata will be stored in the property map of this PngImage instance, for retrieval via the various helper methods (getWidth(), getHeight(), etc.) and getProperty(java.lang.String). The decoded image itself is returned by this method but not cached.

      If PngConfig.getReadLimit() is anything but PngConfig.READ_ALL, then this method will return null instead of the decoded image.

      Multiple images can be read using the same PngImage instance. The property map is cleared each time this method is called.

      Parameters:
      file - the file to read
      Returns:
      the decoded image, or null if no image was decoded
      Throws:
      IOException - if any error occurred while reading the image
      See Also:
    • read

      public BufferedImage read(InputStream in, boolean close) throws IOException
      Reads a PNG image from the specified input stream. Image metadata will be stored in the property map of this PngImage instance, for retrieval via the various helper methods (getWidth(), getHeight(), etc.) and getProperty(java.lang.String). The decoded image itself is returned by this method but not cached.

      If PngConfig.getReadLimit() is anything but PngConfig.READ_ALL, then this method will return null instead of the decoded image.

      Multiple images can be read using the same PngImage instance. A new property map is created each time this method is called.

      Parameters:
      in - the input stream to read
      close - whether to close the input stream after reading
      Returns:
      the decoded image, or null if no image was decoded
      Throws:
      IOException - if any error occurred while reading the image
      See Also:
    • createImage

      protected BufferedImage createImage(InputStream in, Dimension size) throws IOException
      A hook by which subclasses can access or manipulate the raw image data. All of the raw, compressed image data contained in the IDAT chunks of the PNG image being read is concatenated and passed to this method as a single input stream. The returned image will become the return value of the calling read(java.io.File) or read(java.io.InputStream, boolean) method.

      Unlike readChunk(int, java.io.DataInput, long, int) implementations, subclasses may read less than the correct amount from this stream; the remainder will be skipped.

      Parameters:
      in - the input stream of raw, compressed image data
      size - the size of the image data
      Returns:
      the decoded image, or null
      Throws:
      IOException - if any error occurred while processing the image data
    • handlePass

      protected boolean handlePass(BufferedImage image, int pass)
      A method which subclasses may override to take some action after each pass has been decoded. An interlaced image has seven passes, and non-interlaced image only one. The pass arguments indicates the index of the completed pass, starting with zero.

      For interlaced images, the state of the image data before the last pass is affected by the value of PngConfig.getProgressive().

      Image decoding can be aborted by returning false. The default implementation always returns true.

      Parameters:
      image - the partially or fully decoded image
      pass - the index of the completed pass
      Returns:
      false to abort image decoding
    • handleProgress

      protected boolean handleProgress(BufferedImage image, float pct)
      Reports the approximate degree of completion of the current read call. This method is called periodically during image decoding. The degree of completion is expressed as a percentage varying from 0.0F to 100.0F, and is calculated using the number of pixels decoded.

      Image decoding can be aborted by returning false. The default implementation returns true.

      Parameters:
      image - the partially or fully decoded image
      pct - the approximate percentage of decoding that has been completed
      Returns:
      false to abort image decoding
    • handleWarning

      protected void handleWarning(PngException e) throws PngException
      Callback for customized handling of warnings. Whenever a non-fatal error is found, an instance of PngException is created and passed to this method. To signal that the exception should be treated as a fatal exception (and abort image processing), an implementation should re-throw the exception.

      By default, this method will re-throw the warning if the warningsFatal property is true.

      Throws:
      PngException - if the warning should be treated as fatal
    • getWidth

      public int getWidth()
      Returns the image widt hin pixels.
      Throws:
      IllegalStateException - if an image has not been read
    • getHeight

      public int getHeight()
      Returns the image height in pixels.
      Throws:
      IllegalStateException - if an image has not been read
    • getBitDepth

      public int getBitDepth()
      Returns the image bit depth.
      Returns:
      1, 2, 4, 8, or 16
      Throws:
      IllegalStateException - if an image has not been read
    • isInterlaced

      public boolean isInterlaced()
      Returns true if the image interlace type (PngConstants.INTERLACE) is something other than INTERLACE_NONE.
      Returns:
      true if the image is interlaced
      Throws:
      IllegalStateException - if an image has not been read
    • getColorType

      public int getColorType()
      Returns the image color type.
      Returns:
      COLOR_TYPE_GRAY,
      COLOR_TYPE_GRAY_ALPHA,
      COLOR_TYPE_PALETTE,
      COLOR_TYPE_RGB,
      or COLOR_TYPE_RGB_ALPHA
      Throws:
      IllegalStateException - if an image has not been read
    • getTransparency

      public int getTransparency()
      Returns the type of this Transparency.
      Specified by:
      getTransparency in interface Transparency
      Returns:
      the field type of this Transparency, which is either OPAQUE, BITMASK or TRANSLUCENT.
      Throws:
      IllegalStateException - if an image has not been read
    • getSamples

      public int getSamples()
      Returns the number of samples per pixel. Gray and paletted images use one sample, gray+alpha uses two, RGB uses three, and RGB+alpha uses four.
      Returns:
      1, 2, 3 or 4
      Throws:
      IllegalStateException - if an image has not been read
    • getGamma

      public float getGamma()
      Returns the gamma exponent that was explicitly encoded in the image, if there was one, or the value of PngConfig.getDefaultGamma() otherwise.
      Returns:
      the gamma exponent
      Throws:
      IllegalStateException - if an image has not been read
    • getGammaTable

      public short[] getGammaTable()
      Returns a gamma table which can be used for custom gamma correction. The table is 256 entries unless the bit depth is 16 and PngConfig.getReduce16() is false, in which case the table is 65535 entries.

      The values in the table take into account getGamma() and PngConfig.getDisplayExponent().

      Returns:
      a table of component values to be used in gamma correction
      Throws:
      IllegalStateException - if an image has not been read
    • getBackground

      public Color getBackground()
      Returns the background color explicitly encoded in the image. For 16-bit images the components are reduced to 8-bit by shifting.
      Returns:
      the background color, or null
      Throws:
      IllegalStateException - if an image has not been read
    • getProperty

      public Object getProperty(String name)
      Returns a per-image property by name. All common property names are defined in PngConstants; their types are listed in the following table. The use of the various helper methods defined in this class, such as getBackground(), is normally preferrable to working with the raw property values.

      PropertyType Description
      BIT_DEPTH Integer Bit depth
      COLOR_TYPE Integer Color type
      COMPRESSION Integer Compression method
      FILTER Integer Filter method
      GAMMA Float Gamma
      WIDTH Integer Width
      HEIGHT Integer Height
      INTERLACE Integer Interlace method
      PALETTE byte[] Palette entries
      PALETTE_ALPHA byte[] Palette alpha
      TRANSPARENCY int[] Transparency samples
      BACKGROUND int[] Background samples
      PIXELS_PER_UNIT_X Integer Pixels per unit, X axis
      PIXELS_PER_UNIT_Y Integer Pixels per unit, Y axis
      UNIT Integer Unit specifier
      RENDERING_INTENT Integer Rendering intent
      SIGNIFICANT_BITS byte[] Significant bits
      TEXT_CHUNKS List List of text chunks
      TIME Date Image last-modification time
      CHROMATICITY float[] Chromaticity
      ICC_PROFILE byte[] ICC profile
      ICC_PROFILE_NAME String ICC profile name
      HISTOGRAM int[] Palette histogram
      SUGGESTED_PALETTES List List of suggested palettes
      GIF_DISPOSAL_METHOD Integer GIF disposal method
      GIF_USER_INPUT_FLAG Integer GIF user input flag
      GIF_DELAY_TIME Integer GIF delay time (hundredths of a second)
      SCALE_UNIT Integer Unit for physical scale of image subject
      PIXEL_WIDTH Double Physical width of pixel
      PIXEL_HEIGHT Double Physical height of pixel
      POSITION_UNIT Integer Unit for image offset
      STEREO_MODE Integer Indicator of stereo image
      Parameters:
      name - a property name
      Returns:
      the property value, or null if no such property exists
      Throws:
      IllegalStateException - if an image has not been read
    • getProperties

      public Map getProperties()
      Returns the map which stores all of this image's property values. The map is mutable, and storing a value with the wrong type may result in other methods in this class throwing IllegalStateException or ClassCastException.
      Returns:
      the mutable map of image properties
    • getTextChunk

      public TextChunk getTextChunk(String key)
      Returns a text chunk that uses the given keyword, if one exists. If multiple text chunks share the same keyword, this method will return the first one that was read. The full list of text chunks may be accessed by calling
      getProperty(PngConstants.TEXT_CHUNKS)
      Parameters:
      key - the text chunk keyword
      Returns:
      a TextChunk implementation, or null
      Throws:
      IllegalStateException - if an image has not been read
    • readChunk

      protected void readChunk(int type, DataInput in, long offset, int length) throws IOException
      Read the chunk data from the image input stream, storing properties into this PngImage instance.

      By default this method will handle all of the chunk types defined in Version 1.2 of the PNG Specification, and most of the registered extension chunks. IDAT chunks will be processed through this method only if PngConfig.getReadLimit() is set to PngConfig.READ_EXCEPT_DATA.

      Attempting to read past the end of the chunk data will result in an EOFException. Unread data will be skipped.

      Parameters:
      type - the chunk type
      in - the chunk data
      offset - the location of the chunk data within the entire PNG datastream
      length - the length of the chunk data
      Throws:
      IOException
    • isMultipleOK

      protected boolean isMultipleOK(int type)
      Returns whether a chunk is allowed to occur multiple times.

      By default this method returns true only for sPLT, iTXt, tEXt, zTXt, and IDAT.

      Parameters:
      type - the chunk type
      Returns:
      whether multiple chunks of the given type are allowed