Package edu.princeton.cs.algs4

Class GrayscalePicture

  • All Implemented Interfaces:
    ActionListener, EventListener
    public final class GrayscalePicture
extends Object
implements ActionListener
    The GrayscalePicture data type provides a basic capability for manipulating the individual pixels of a grayscale image. The original image can be read from a PNG, GIF, or JPEG file or the user can create a blank image of a given dimension. This class includes methods for displaying the image in a window on the screen or saving it to a file.

    Pixel (col, row) is column col and row row. By default, the origin (0, 0) is the pixel in the top-left corner. These are common conventions in image processing and consistent with Java's BufferedImage data type. The method setOriginLowerLeft() change the origin to the lower left.

    The get() and set() methods use Color objects to get or set the color of the specified pixel. The Color objects are converted to grayscale if they have different values for the R, G, and B channels. The getGrayscale() and setGrayscale() methods use an 8-bit int to encode the grayscale value, thereby avoiding the need to create temporary Color objects.

    A W-by-H picture uses ~ 4 W H bytes of memory, since the color of each pixel is encoded as a 32-bit int (even though, in principle, only ~ W H bytes are needed).

    For additional documentation, see Section 3.1 of Computer Science: An Interdisciplinary Approach by Robert Sedgewick and Kevin Wayne. See Picture for a version that supports 32-bit RGB color images.

    Author:
    Robert Sedgewick, Kevin Wayne

    • Constructor Summary

      Constructors 
      Constructor Description
      GrayscalePicture​(int width, int height)
      Creates a width-by-height picture, with width columns and height rows, where each pixel is black.
      GrayscalePicture​(GrayscalePicture picture)
      Creates a new grayscale picture that is a deep copy of the argument picture.
      GrayscalePicture​(String name)
      Creates a grayscale picture by reading an image from a file or URL.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void actionPerformed​(ActionEvent e)
      Opens a save dialog box when the user selects "Save As" from the menu.
      boolean equals​(Object other)
      Returns true if this picture is equal to the argument picture.
      Color get​(int col, int row)
      Returns the grayscale value of pixel (col, row) as a Color.
      int getGrayscale​(int col, int row)
      Returns the grayscale value of pixel (col, row) as an int between 0 and 255.
      JLabel getJLabel()
      Returns a JLabel containing this picture, for embedding in a JPanel, JFrame or other GUI widget.
      int hashCode()
      This operation is not supported because pictures are mutable.
      int height()
      Returns the height of the picture.
      void hide()
      Hides the window on the screen.
      boolean isVisible()
      Is the window containing the picture visible?
      static void main​(String[] args)
      Unit tests this Picture data type.
      void save​(File file)
      Saves the picture to a file in a PNG or JPEG image format.
      void save​(String name)
      Saves the picture to a file in either PNG or JPEG format.
      void set​(int col, int row, Color color)
      Sets the color of pixel (col, row) to the given grayscale value.
      void setGrayscale​(int col, int row, int gray)
      Sets the color of pixel (col, row) to the given grayscale value between 0 and 255.
      void setOriginLowerLeft()
      Sets the origin to be the lower left pixel.
      void setOriginUpperLeft()
      Sets the origin to be the upper left pixel.
      void show()
      Displays the picture in a window on the screen.
      String toString()
      Returns a string representation of this picture.
      int width()
      Returns the width of the picture.

    • Constructor Detail

      • GrayscalePicture

        public GrayscalePicture​(int width,
                        int height)
        Creates a width-by-height picture, with width columns and height rows, where each pixel is black.
        Parameters:
        width - the width of the picture
        height - the height of the picture
        Throws:
        IllegalArgumentException - if width is negative
        IllegalArgumentException - if height is negative

      • GrayscalePicture

        public GrayscalePicture​(GrayscalePicture picture)
        Creates a new grayscale picture that is a deep copy of the argument picture.
        Parameters:
        picture - the picture to copy
        Throws:
        IllegalArgumentException - if picture is null

      • GrayscalePicture

        public GrayscalePicture​(String name)
        Creates a grayscale picture by reading an image from a file or URL.
        Parameters:
        name - the name of the file (.png, .gif, or .jpg) or URL.
        Throws:
        IllegalArgumentException - if cannot read image
        IllegalArgumentException - if name is null

    • Method Detail

      • getJLabel

        public JLabel getJLabel()
        Returns a JLabel containing this picture, for embedding in a JPanel, JFrame or other GUI widget.
        Returns:
        the JLabel

      • setOriginUpperLeft

        public void setOriginUpperLeft()
        Sets the origin to be the upper left pixel. This is the default.

      • setOriginLowerLeft

        public void setOriginLowerLeft()
        Sets the origin to be the lower left pixel.

      • show

        public void show()
        Displays the picture in a window on the screen.

      • hide

        public void hide()
        Hides the window on the screen.

      • isVisible

        public boolean isVisible()
        Is the window containing the picture visible?
        Returns:
        true if the picture is visible, and false otherwise

      • height

        public int height()
        Returns the height of the picture.
        Returns:
        the height of the picture (in pixels)

      • width

        public int width()
        Returns the width of the picture.
        Returns:
        the width of the picture (in pixels)

      • get

        public Color get​(int col,
                 int row)
        Returns the grayscale value of pixel (col, row) as a Color.
        Parameters:
        col - the column index
        row - the row index
        Returns:
        the grayscale value of pixel (col, row)
        Throws:
        IllegalArgumentException - unless both 0 <= col < width and 0 <= row < height

      • getGrayscale

        public int getGrayscale​(int col,
                        int row)
        Returns the grayscale value of pixel (col, row) as an int between 0 and 255. Using this method can be more efficient than get(int, int) because it does not create a Color object.
        Parameters:
        col - the column index
        row - the row index
        Returns:
        the 8-bit integer representation of the grayscale value of pixel (col, row)
        Throws:
        IllegalArgumentException - unless both 0 <= col < width and 0 <= row < height

      • set

        public void set​(int col,
                int row,
                Color color)
        Sets the color of pixel (col, row) to the given grayscale value.
        Parameters:
        col - the column index
        row - the row index
        color - the color (converts to grayscale if color is not a shade of gray)
        Throws:
        IllegalArgumentException - unless both 0 <= col < width and 0 <= row < height
        IllegalArgumentException - if color is null

      • setGrayscale

        public void setGrayscale​(int col,
                         int row,
                         int gray)
        Sets the color of pixel (col, row) to the given grayscale value between 0 and 255.
        Parameters:
        col - the column index
        row - the row index
        gray - the 8-bit integer representation of the grayscale value
        Throws:
        IllegalArgumentException - unless both 0 <= col < width and 0 <= row < height

      • equals

        public boolean equals​(Object other)
        Returns true if this picture is equal to the argument picture.
        Overrides:
        equals in class Object
        Parameters:
        other - the other picture
        Returns:
        true if this picture is the same dimension as other and if all pixels have the same color; false otherwise

      • toString

        public String toString()
        Returns a string representation of this picture. The result is a width-by-height matrix of pixels, where the grayscale value of a pixel is an integer between 0 and 255.
        Overrides:
        toString in class Object
        Returns:
        a string representation of this picture

      • hashCode

        public int hashCode()
        This operation is not supported because pictures are mutable.
        Overrides:
        hashCode in class Object
        Returns:
        does not return a value
        Throws:
        UnsupportedOperationException - if called

      • save

        public void save​(String name)
        Saves the picture to a file in either PNG or JPEG format. The filetype extension must be either .png or .jpg.
        Parameters:
        name - the name of the file
        Throws:
        IllegalArgumentException - if name is null

      • save

        public void save​(File file)
        Saves the picture to a file in a PNG or JPEG image format.
        Parameters:
        file - the file
        Throws:
        IllegalArgumentException - if file is null

      • main

        public static void main​(String[] args)
        Unit tests this Picture data type. Reads a picture specified by the command-line argument, and shows it in a window on the screen.
        Parameters:
        args - the command-line arguments