Java LZW编码器-解码器-符号表
当我使用长度为256的符号表(字典)时,我的LZW压缩可以工作,编码器和解码器都可以使用256,一切都可以正常工作,但是当我将这个数字增加到例如512、1024、4096时,解码文件输出与第一个输入文件不一样…有什么提示吗 源代码: LZWEncoder.java:Java LZW编码器-解码器-符号表,java,algorithm,encoding,compression,lzw,Java,Algorithm,Encoding,Compression,Lzw,当我使用长度为256的符号表(字典)时,我的LZW压缩可以工作,编码器和解码器都可以使用256,一切都可以正常工作,但是当我将这个数字增加到例如512、1024、4096时,解码文件输出与第一个输入文件不一样…有什么提示吗 源代码: LZWEncoder.java: import java .io .*; public class LZWEncoder { public static void main ( String [] args ) throws File
import java .io .*;
public class LZWEncoder
{
public static void main ( String [] args )
throws FileNotFoundException , IOException
{
File file = new File ("calgary/book1");
File fileOut = new File ( "calgary/book1_enc");
FileInputStream reader = new FileInputStream ( file );
FileOutputStream writer = new FileOutputStream ( fileOut );
int size_st;
long file_size;
file_size = file.length();
size_st = (int) file_size/1024;
System.out.println("File size " + file_size + " Sysmbol tree" + size_st);
if (size_st < 256)
size_st = 256;
else if (size_st < 512)
size_st = 512;
else if (size_st < 1024)
size_st = 1024;
else if (size_st < 2048)
size_st = 2048;
else
size_st = 4096;
byte[] size_stInBytes = (Integer.toString(size_st)+"\n").getBytes();
// writer.write(size_stInBytes);
System.out.println("File size " + file_size + " Sysmbol tree " + size_st);
// input stream with lookahead
LookAheadIn in = new LookAheadIn ( file );
LZWst st = new LZWst (4096); // specialised ST
while (! in.isEmpty ())
{
int codeword = st.getput (in );
writer.write ( codeword );
}
writer.close ();
reader.close ();
}
}
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Scanner;
public class LZWDecoder
{
public static void main ( String [] args )
throws FileNotFoundException , IOException
{
File file = new File ("calgary/book1_enc");
Scanner first_line = new Scanner("calgary/book1_enc");
File fileOut = new File ( "calgary/book1_dec2");
FileInputStream reader = new FileInputStream ( file );
FileOutputStream writer = new FileOutputStream ( fileOut );
String size_st;
size_st =first_line.nextLine();
System.out.println(" Sysmbol tree " + size_st);
String [] st = new String [4096];
int i;
for (i=0; i <128; i++)
st[i] = Character.toString (( char ) i);
String prev = "";
int codeword ;
while (( codeword = reader.read())!= -1)
{
String s;
if ( codeword == i) // Tricky situation !
s = prev + prev.charAt(0);
else
s = st[codeword ];
for (int j = 0; j<s.length(); j++)
writer.write(s.charAt (j));
if ( prev.length() > 0 && i < 4096 )
st[i++] = prev + s.charAt(0);
prev = s;
}
writer.close();
reader.close();
}
}
您正在读取字节,它们无法存储更大的值。如果要使用大于255的代码执行LZW,则需要对位流进行编码,或者为了进行测试(作为临时黑客),需要写入两个字节的字(大小为16的无符号整数) 替换
writer.write ( codeword );
与
然后检查它是否有效。如果是这样,您可以花一些时间实现基于位的流。您还需要更新读卡器和解码器
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
public class LookAheadIn
{
private FileInputStream in = null ;
private int last ;
private boolean backup = true ;
public LookAheadIn ( File file )
throws FileNotFoundException , IOException
{
in = new FileInputStream ( file );
last = in. read ();
backup = true ;
}
public void backup () { backup = true ; }
public int readChar () throws FileNotFoundException , IOException
{
if (! backup ) last = in. read();
backup = false ;
return last ;}
public boolean isEmpty(){ return last == -1; }
}
writer.write ( codeword );
writer.write ( codeword>>8 );
writer.write ( codeword&0xff );