在Android上获取TIFF图像的单个像素

Question

I ideally need to have offline access to information of the altitude of the terrain of Mexico on an Android app I'm developing. I downloaded a .bil file and converted it to a .tif file with QGIS, and the resulting file is almost 900 MB.

I don'I know if it would work, I'm still learning to develop Android apps, but I was planning to store it in the SD card and I was wondering if it could be possible to access to a single pixel without reading the whole image, because I know that's impossible.

Can anyone tell me if it is possible? And if it is, how to do it? Or any other way to get the information I need maybe converting the .bil file to other format or something like that.

Thanks for answering.

Answer 1

Tiff has images stored as rows of bytes starting at defined offsets. So you can easily retrieve single pixel and certainly no need to load the full image. If you open any tif file in hex editor you will see that first 4 bytes mark tiff by code. And next 4 bytes give offset for metadata about tif image. Use random access file to open image tif file, then seek the offset and you land into metadata space.From here you can pick offset of required pixel. Then go and get it..

We have tiff for this purpose only. That is to access individual pixels. If we needed full load of image then jpeg or BMP was enough.

Answer 2

check this link for full code:- 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);
}