用Java读取pgm文件

Question

我需要读取一个pgm文件并将其中包含的值数组存储在二维数组中。 在PGM格式中，每个像素由0和MaxVal之间的灰度值指定。前三行提供与图像有关的信息：幻数，高度，宽度和最大值。该文件还包括空格。以＃开始的行是注释。 这是我迄今为止写的。

public class PGM{ 

public static void main(String args[]) throws Exception { 
    FileInputStream f = new FileInputStream("C:\\......\\brain_001.pgm"); 
    DataInputStream d = new DataInputStream(f); 
    d.readLine();//first line contains P5 
    String line = d.readLine();//second line contains height and width 
    Scanner s = new Scanner(line); 
    int width = s.nextInt(); 
    int height = s.nextInt(); 
    line = d.readLine();//third line contains maxVal 
    s = new Scanner(line); 
    int maxVal = s.nextInt(); 
    byte[][] im = new byte[height][width]; 
    for (int i = 0; i < 258; i++) { 
     for (int j = 0; j < 258; j++) { 
      im[i][j] = -1; 
     } 
    } 
    int count = 0; 
    byte b; 
    try { 
     while (true) { 
      b = (byte) (d.readUnsignedByte()); 
      if (b == '\n') { //do nothing if new line encountered 
      } else if (b == '#') { 
       d.readLine(); 
      } else if (Character.isWhitespace(b)) { // do nothing if whitespace encountered 
      } else { 
       im[count/width][count % width] = b; 
       count++; 
      } 
     } 
    } catch (EOFException e) { 
    } 
    System.out.println("Height=" + height); 
    System.out.println("Width=" + height); 
    System.out.println("Required elemnts=" + (height * width)); 
    System.out.println("Obtained elemnets=" + count); 

} 
} 

当运行该程序时，得到以下输出：

Height=258 
Width=258 
Required elemnts=66564 
Obtained elemnets=43513 

元件（每一个对应于灰度值）的数量是小于所需的。当我用PGM查看器打开文件时，所有内容都正确显示。 另外，当我打印数组的内容时，我看到很多负值。但是他们都必须大于或等于零。 我哪里错了？

Answer 1

最有可能是因为不合法的方法readLine()从DataInputStream。正如注释中提到的那样

*此方法没有正确地将字节转换为字符。从JDK 1.1开始，读取文本行的首选方法是通过BufferedReader.readLine（）方法。使用DataInputStream类读取行的程序可以通过替换下面的代码来转换为使用BufferedReader类： DataInputStream d = new DataInputStream（in）;

有： 的BufferedReader d =新的BufferedReader（新的InputStreamReader（中））; *

当我按照这个建议改变你的程序，它为我工作（我做了一些其他的变化，以及：

（更新处理PGM的P2和P5口味）

public static void main(String args[]) throws Exception { 
     try { 
      InputStream f = ClassLoader.getSystemClassLoader().getResourceAsStream("lena.pgm"); 
      BufferedReader d = new BufferedReader(new InputStreamReader(f)); 
      String magic = d.readLine(); // first line contains P2 or P5 
      String line = d.readLine();  // second line contains height and width 
      while (line.startsWith("#")) { 
       line = d.readLine(); 
      } 
      Scanner s = new Scanner(line); 
      int width = s.nextInt(); 
      int height = s.nextInt(); 
      line = d.readLine();// third line contains maxVal 
      s = new Scanner(line); 
      int maxVal = s.nextInt(); 
      byte[][] im = new byte[height][width]; 

      int count = 0; 
      int b = 0; 
      try { 
       while (count < height*width) { 
        b = d.read() ; 
        if (b < 0) 
         break ; 

        if (b == '\n') { // do nothing if new line encountered 
        } 
//     else if (b == '#') { 
//      d.readLine(); 
//     } 
//     else if (Character.isWhitespace(b)) { // do nothing if whitespace encountered 
//     } 
        else { 
         if ("P5".equals(magic)) { // Binary format 
          im[count/width][count % width] = (byte)((b >> 8) & 0xFF); 
          count++; 
          im[count/width][count % width] = (byte)(b & 0xFF); 
          count++; 
         } 
         else { // ASCII format 
          im[count/width][count % width] = (byte)b ; 
          count++; 
         } 
        } 
       } 
      } catch (EOFException eof) { 
       eof.printStackTrace(System.out) ; 
      } 
      System.out.println("Height=" + height); 
      System.out.println("Width=" + height); 
      System.out.println("Required elements=" + (height * width)); 
      System.out.println("Obtained elements=" + count); 
     } 
     catch(Throwable t) { 
      t.printStackTrace(System.err) ; 
      return ; 
     } 

    } 

Answer 2

下面的代码对我的作品：

FileInputStream f; 
    try { 
     f = new FileInputStream(fileLocation); 
     BufferedReader br = new BufferedReader(new InputStreamReader(f)); 
     String magic = br.readLine(); // first line contains P2 or P5 
     String line = br.readLine();  // second line contains height and width 

     //-scan width and height 
     Scanner s = new Scanner(line); 
     int width = s.nextInt(); 
     int height = s.nextInt(); 
     s.close(); 

     //-scan max value 
     line = br.readLine();// third line contains maxVal 
     s = new Scanner(line); 
     //   int maxVal = s.nextInt(); 
     //-close scanner 
     s.close(); 
     //-close buffer 
     br.close(); 
     f.close(); 

     xvec=new DenseMatrix64F(height*width, 1); 

     int b=0; 
     int counter=0; 
     f = new FileInputStream(fileLocation); 
     DataInputStream dis = new DataInputStream(f); 
     //-move across unused lines 
     dis.readLine(); 
     dis.readLine(); 
     dis.readLine(); 
     while ((b=dis.read()) >= 0) { 
      xvec.set(counter, 0, b); 
      counter++; 
     } 
     dis.close(); 
    } catch (FileNotFoundException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } catch (IOException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    }