Package org.loboevolution.pdfview.function

Class PDFFunction

java.lang.Object
org.loboevolution.pdfview.function.PDFFunction
Direct Known Subclasses:
FunctionType0, FunctionType2, FunctionType3, FunctionType4
public abstract class PDFFunction extends Object

PDF Functions are defined in the reference as Section 3.9.

A PDF function maps some set of m inputs into some set of n outputs. There are 4 types of functions:

  • Type 0: Sampled functions. (PDF 1.2)
    A sampled function (type 0) uses a table of sample values to define the function. Various techniques are used to interpolate values between the sample values (see Section 3.9.1, "Type 0 (Sampled) Functions").
  • Type 2: Exponential Interpolation. (PDF 1.3)
    An exponential interpolation function (type 2) defines a set of coefficients for an exponential function (see Section 3.9.2, "Type 2 (Exponential Interpolation) Functions").
  • Type 3: Stitching functions. (PDF 1.3)
    A stitching function (type 3) is a combination of other functions, partitioned across a domain (see Section 3.9.3, "Type 3 (Stitching) Functions").
  • Type 4: Postscript calculations. (PDF 1.3)
    A PostScript calculator function (type 4) uses operators from the PostScript language to describe an arithmetic expression (see Section 3.9.4, "Type 4 (PostScript Calculator) Functions").

The function interface contains a single method, calculate which takes an array of m floats an interprets them into an array of n floats. PDFFunctions do not have accessible constructors. Instead, use the static getFunction() method to read a functions from a PDF Object.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    TYPE_0
    Sampled function
    static final int
    TYPE_2
    Exponential interpolation function
    static final int
    TYPE_3
    Stitching function.
    static final int
    TYPE_4
    PostScript calculator function.

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    protected
    PDFFunction(int type)
    Creates a new instance of PDFFunction

  • Method Summary

    Modifier and Type
    Method
    Description
    float[]
    calculate(float[] inputs)
    Map from m input values to n output values.
    float[]
    calculate(float[] inputs, int inputOffset, float[] outputs, int outputOffset)
    Map from m input values to n output values.
    protected abstract void
    doFunction(float[] inputs, int inputOffset, float[] outputs, int outputOffset)
    Subclasses must implement this method to perform the actual function on the given set of data.
    protected float
    getDomain(int i)
    Get a component of the domain of this function
    static PDFFunction
    getFunction(PDFObject obj)
    Get a PDFFunction from a PDFObject
    int
    getNumInputs()
    Get the number of inputs, m, required by this function
    int
    getNumOutputs()
    Get the number of outputs, n, returned by this function
    protected float
    getRange(int i)
    Get a component of the range of this function
    static float
    interpolate(float x, float xmin, float xmax, float ymin, float ymax)
    Perform a linear interpolation.
    protected abstract void
    parse(PDFObject obj)
    Read the function information from a PDF Object

    Methods inherited from class java.lang.Object

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

  • Field Details

  • Constructor Details

    • PDFFunction

      protected PDFFunction(int type)
      Creates a new instance of PDFFunction
      Parameters:
      type - a Integer object.

  • Method Details

    • getFunction

      public static PDFFunction getFunction(PDFObject obj) throws IOException
      Get a PDFFunction from a PDFObject
      Parameters:
      obj - a PDFObject object.
      Returns:
      a PDFFunction object.
      Throws:
      IOException - if any.

    • interpolate

      public static float interpolate(float x, float xmin, float xmax, float ymin, float ymax)
      Perform a linear interpolation. Given a value x, and two points, (xmin, ymin), (xmax, ymax), where xmin <= x <= xmax, calculate a value y on the line from (xmin, ymin) to (xmax, ymax).
      Parameters:
      x - the x value of the input
      xmin - the minimum x value
      xmax - the maximum x value
      ymin - the minimum y value
      ymax - the maximum y value
      Returns:
      the y value interpolated from the given x

    • getNumInputs

      public int getNumInputs()
      Get the number of inputs, m, required by this function
      Returns:
      the number of input values expected by this function

    • getNumOutputs

      public int getNumOutputs()
      Get the number of outputs, n, returned by this function
      Returns:
      the number of output values this function will return

    • getDomain

      protected float getDomain(int i)
      Get a component of the domain of this function
      Parameters:
      i - the index into the domain array, which has size 2 * m. the ith entry in the array has index 2i, 2i + 1
      Returns:
      the ith entry in the domain array

    • getRange

      protected float getRange(int i)
      Get a component of the range of this function
      Parameters:
      i - the index into the range array, which has size 2 * n. the ith entry in the array has index 2i, 2i + 1
      Returns:
      the ith entry in the range array

    • calculate

      public float[] calculate(float[] inputs)
      Map from m input values to n output values. The number of inputs m must be exactly one half the size of the domain. The number of outputs should match one half the size of the range.
      Parameters:
      inputs - an array of >= m input values
      Returns:
      the array of n output values

    • calculate

      public float[] calculate(float[] inputs, int inputOffset, float[] outputs, int outputOffset)
      Map from m input values to n output values. The number of inputs m must be exactly one half the size of the domain. The number of outputs should match one half the size of the range.
      Parameters:
      inputs - an array of >= m input values
      inputOffset - the offset into the input array to read from
      outputs - an array of size >= n which will be filled with the output values
      outputOffset - the offset into the output array to write to
      Returns:
      the array of n output values

    • doFunction

      protected abstract void doFunction(float[] inputs, int inputOffset, float[] outputs, int outputOffset)
      Subclasses must implement this method to perform the actual function on the given set of data. Note that the inputs are guaranteed to be clipped to the domain, while the outputs will be automatically clipped to the range after being returned from this function.
      Parameters:
      inputs - an array of
      invalid reference 
      float
      objects.
      inputOffset - the offset into the inputs array to read from
      outputs - guaranteed to be at least as big as getNumOutputs(), but not yet clipped to domain
      outputOffset - the offset into the output array to write to

    • parse

      protected abstract void parse(PDFObject obj) throws IOException
      Read the function information from a PDF Object
      Parameters:
      obj - a PDFObject object.
      Throws:
      IOException - if any.