java在Android上获得单像素TIFF图像

Question

理想情况下，我需要在我正在开发的Android应用程序上离线访问墨西哥地形的高度信息。我下载了一个。bil文件并将其转换为。tif文件与QGIS一起使用，生成的文件几乎为900 MB

我不知道它是否有效，我仍在学习开发Android应用程序，但我计划将其存储在SD卡中，我想知道是否可以在不读取整个图像的情况下访问单个像素，因为我知道这是不可能的

有人能告诉我这是否可能吗？如果是，怎么做？或者通过其他方式获取我需要的信息，比如转换。将bil文件转换为其他格式或类似的格式

谢谢你的回答

Answer 1

Tiff将图像存储为以定义的偏移量开始的字节行。因此，您可以轻松检索单个像素，当然无需加载完整图像。 如果在hex editor中打开任何tif文件，您将看到前4个字节以代码标记tiff。接下来的4个字节给出了tif图像元数据的偏移量。 使用随机访问文件打开图像tif文件，然后查找偏移量，然后进入元数据空间。从这里可以选择所需像素的偏移量。那就去拿吧

我们的tiff仅用于此目的。即访问单个像素。如果我们需要完整的图像，那么jpeg或BMP就足够了

Answer 2

检查此链接以获取完整代码：-full example to decode tiff image

package com.tif;

   import android.os.*;import android.content.*;import android.app.*;import                  android.widget.*;import android.view.*;
   import android.view.View.*;import android.graphics.*;import  java.io.*;import java.util.*;import android.util.*;
   import java.lang.*;import java.nio.*;import java.nio.channels.*;

   public class Main extends Activity
  {
private static final int CLEAR_CODE = 256;
private static final int EOI_CODE = 257;
long bytesCount=0L;

    ScrollView sv;TextView tv;ImageView iv;
    List intList;
    long[] stripOffs,stripBytes;
    byte[] bytes,ubytes,bmpBytes;
    ByteBuffer bBuff;
    BitBuffer bitBuff;

    int entries,type,tag;
    long count,value,ifd,stripAt,stripCount,stripBytesAt,rows,cols;
    String txt="Null",path="",decompressed="";
    String[] info=  {"width","length","bitsPerSample","Compression","PhotometricInterpretation","FillOrder","StripOffsets","SamplesPerPixel","RowsPerStrip"
            ,"StripBytes","XResolution","YResolution","PlanarConfig","ResolutionUnit","extra","NextIFD"};
    Bitmap bmp=null;


   class DotsView extends View
   {
       int i = 0;Bitmap bmp;Canvas cnv;Rect bounds;Paint p;int width,height;
         int alfa,red,green,blue;
         public DotsView(Context context ,int width ,int height)
        {
          super(context);
           this.width = width;
           this.height = height;
            bmp = Bitmap.createBitmap(width,height,Bitmap.Config.ARGB_8888);
                 cnv = new Canvas(bmp);
                 bounds = new Rect(0 , 0, width,height);
                p = new Paint();
            }

       @Override
          protected void onDraw(Canvas c)
       {

        for(int i=0;i<width;i++) 
          for(int j=0;j<height;j++)
            {
        for(int pix=0;pix<3;pix++)
        {
        if(pix==0)blue=bmpBytes[i+j+pix];
        if(pix==1)green=bmpBytes[i+j+pix];
        if(pix==2)red=bmpBytes[i+j+pix];
    }

p.setColor( Color.argb(255, red,green,blue) );
cnv.drawPoint(i,j, p);
}
      c.drawBitmap(bmp, null, bounds , null);
        invalidate();
 }
 }

public int myShort(short sh)
{   int i;
    ByteBuffer shortBuff=ByteBuffer.allocate(4);
    shortBuff.order(ByteOrder.BIG_ENDIAN);shortBuff.putShort(sh);shortBuff.rewind();
    shortBuff.order(ByteOrder.LITTLE_ENDIAN);sh=shortBuff.getShort();
    if(sh<0)i=(int)(sh+32768); else i=(int)sh;
    return i;
}
public long myInt(int i)
{    long l=0L;
     ByteBuffer intBuff=ByteBuffer.allocate(4);
     intBuff.order(ByteOrder.BIG_ENDIAN);intBuff.putInt(i);intBuff.rewind();
     intBuff.order(ByteOrder.LITTLE_ENDIAN); i=intBuff.getInt();
     if(i<0)l=(long)(i+2147483648L);     else l=(long)i; 
     return l;
}
public String tagInfo(int tag)
{   int i=0;
    switch(tag)
    {case 256: i=0;break;case 257: i=1;break;case 258: i=2;break;case 259: i=3;break;case 262: i=4;break;case 266: i=5;break;
        case 273: i=6;break;case 277: i=7;break;case 278: i=8;break;case 279: i=9;break;case 282: i=10;break;case 283: i=11;break;
        case 284: i=12;break;case 296: i=13;break;case 1496: i=14;break;case 0: i=15;break;
    }
    return info[i];
}
public void extractTif()
{
    String taginfo="";String strVal="";
    FileInputStream fis;BufferedInputStream bis;DataInputStream dis;
    path=Environment.getExternalStorageDirectory().getPath();   
    path=path+"/DCIM"+"/kpd.tif";
    try     {
         fis=new FileInputStream(path);bis=new BufferedInputStream(fis);dis=new DataInputStream(bis);
         dis.skip(4);ifd=myInt(dis.readInt()); 
         txt="TIFF-IFD: "; txt=txt+ifd;
         dis.skip(ifd-8); entries=myShort(dis.readShort());  
         txt=txt+"\nNo.OfEntries="+entries;
         for(int i=0;i<=entries;i++)
           {    tag=myShort( dis.readShort() );taginfo=tagInfo(tag);
            type=myShort( dis.readShort() );count=myInt( dis.readInt() );value=myInt( dis.readInt() ); 
            if(type==3)strVal="Value="; else strVal="Offset=";
            if( strVal.equals("Offset=") )
            {
                if( taginfo.equals("StripOffsets") ){stripAt=value;stripCount=count;}
                if( taginfo.equals("StripBytes")   ){stripBytesAt=value;}
            }
            if( taginfo.equals("width") ){cols=value;}
            if( taginfo.equals("length") ){rows=value;}
                txt=txt+"\ntag="+tag+" "+tagInfo(tag)+",type="+type+",count="+count+strVal+value;
           }
         dis.close();bis.close();fis.close();  
        }catch(Exception e)     {txt=txt+"\nerror="+e.toString();}

    txt=txt+"\nNo.OfStrips="+stripCount+",array of strip locations at: "+stripAt+" and array of bytesPerStrip at "+stripBytesAt ;
    extractBMP();
}

public void extractBMP()
{try{   File f=new File(path);RandomAccessFile raf=new RandomAccessFile(f,"r");

    raf.seek(stripAt);stripOffs=new long[(int)stripCount];
    txt=txt+"\nArray Of Image Offsets=";
    for(int i=0;i<stripCount;i++){stripOffs[i]=myInt( raf.readInt() ); txt=txt+","+stripOffs[i]; }
    raf.seek(stripBytesAt); stripBytes=new long[(int)stripCount];
    txt=txt+"\nArray Of Strip Bytes =";
    for(int i=0;i<stripCount;i++){stripBytes[i]=myInt(raf.readInt()); txt=txt+","+stripBytes[i];bytesCount+=stripBytes[i];}
    txt=txt+stripBytes;

    bBuff =ByteBuffer.allocate((int)(rows*cols*3));
    for(int i=0;i<stripCount;i++)
    {
        bytes =new byte[(int)stripBytes[i]];
        raf.seek(stripOffs[i]);
        raf.read(bytes);
        bBuff.put(lzwUncompress(bytes));
        bytes=null;
    }

    txt=txt+"\nBuffered Image Bytes Size="+bBuff.position();    
    bBuff.rewind();
    bmpBytes=new byte[bBuff.remaining()];
    bmpBytes=bBuff.array();
    txt=txt+"\nCount of bmpBytes="+bmpBytes.length;

    bmp=BitmapFactory.decodeByteArray(bmpBytes,0,bmpBytes.length);

    SystemClock.sleep(5000);

    txt=txt+"Bitmap Object, bmp="+bmp;
    if(bmp!=null){iv.setImageBitmap(bmp);sv.addView(iv);}
    raf.close();

        }catch(Exception e){txt=txt+"\nerror="+e.toString();}
}
public void lzw()
{
    //String[] table=new String[4096];
    byte b;char ch;String s;String pre="";short sh;
    //List strTable=Arrays.asList(table);
    //for(int i=0;i<255;i++)table[i]=Character.toString((char)i);

    for(int i=0;i<100;i++)
    {
        b=bytes[i];
        if(b<0)sh=(short)(128+b);
        else sh=(short)b;
        //ch=(char)b;
        s=String.valueOf(sh);
        //s=s+pre;
        //if(strTable.contains(s)){pre=s;}
        //else{  }
        txt=txt+"Byte No."+i+"="+s+" ";
    }
}
public void onCreate(Bundle bnd)
{
    super.onCreate(bnd);

    extractTif();

    //sv=new ScrollView(this);
    //tv=new TextView(this);
    //iv=new ImageView(this);

    //tv.setTextSize(7);
    //sv.addView(tv);
    //sv.addView(iv);

    //tv.setText(txt);

    //setContentView(sv);

    Point res=new Point(); getWindowManager().getDefaultDisplay().getSize(res);

    DotsView myView = new DotsView(this,res.x,res.y);
    setContentView(myView);
}