using bitmap overlays

Question

i have an app that places a fisheye distortion effect on a bitmap. to create the distortion i must loop through the entire bitmap checking whether a given pixel falls with a circle bounds. if it does then i manipulate that pixel. This process is labour intensive and takes upto 50 secs. i was thinking of different ways to do this so i don't have to loop through the whole bitmap to apply the effect. one idea i have is to draw the bitmap first and display it. then create a second bitmap overlay which only has the effect on. i could then overlay the second bitmap on the first. i'm just trying to think of ways in which i can apply this effect without looping through as many pixels to speed things up. i'll post the distortion class. thanks.

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class Filters{
    private float xscale;
    private float yscale;
    private float xshift;
    private float yshift;
    private int [] s;
    private int [] scalar;
    private int [] s1;
    private int [] s2;
    private int [] s3;
    private int [] s4;
    private String TAG = "Filters";
    long getRadXStart = 0;
    long getRadXEnd = 0;
    long startSample = 0;
    long endSample = 0;
    public Filters(){

        Log.e(TAG, "***********inside filter constructor");
        s = new int[4];
        scalar = new int[4];
        s1 = new int[4];
        s2 = new int[4];
        s3 = new int[4];
        s4 = new int[4];
    }

    public Bitmap barrel (Bitmap input, float k,float cenx, float ceny){
        //Log.e(TAG, "***********INSIDE BARREL METHOD ");
        Debug.startMethodTracing("barrel");

        //float centerX=input.getWidth()/2; //center of distortion
        //float centerY=input.getHeight()/2;
        float centerX=cenx;
        float centerY=ceny;

        int width = input.getWidth(); //image bounds
        int height = input.getHeight();

        Bitmap dst = Bitmap.createBitmap(width, height,input.getConfig() ); //output pic
       // Log.e(TAG, "***********dst bitmap created ");
          xshift = calc_shift(0,centerX-1,centerX,k);

          float newcenterX = width-centerX;
          float xshift_2 = calc_shift(0,newcenterX-1,newcenterX,k);

          yshift = calc_shift(0,centerY-1,centerY,k);

          float newcenterY = height-centerY;
          float yshift_2 = calc_shift(0,newcenterY-1,newcenterY,k);

          xscale = (width-xshift-xshift_2)/width;
        //  Log.e(TAG, "***********xscale ="+xscale);
          yscale = (height-yshift-yshift_2)/height;
        //  Log.e(TAG, "***********yscale ="+yscale);
        //  Log.e(TAG, "***********filter.barrel() about to loop through bm");
          /*for(int j=0;j<dst.getHeight();j++){
              for(int i=0;i<dst.getWidth();i++){
                float x = getRadialX((float)i,(float)j,centerX,centerY,k);
                float y = getRadialY((float)i,(float)j,centerX,centerY,k);
                sampleImage(input,x,y);
                int color = ((s[1]&0x0ff)<<16)|((s[2]&0x0ff)<<8)|(s[3]&0x0ff);
    //            System.out.print(i+" "+j+" \\");

                dst.setPixel(i, j, color);

              }
            }*/

          int origPixel;
          long startLoop = System.currentTimeMillis();
          for(int j=0;j<dst.getHeight();j++){
              for(int i=0;i<dst.getWidth();i++){
                 origPixel= input.getPixel(i,j);
                 getRadXStart = System.currentTimeMillis();
                float x = getRadialX((float)j,(float)i,centerX,centerY,k);
                getRadXEnd= System.currentTimeMillis();

                float y = getRadialY((float)j,(float)i,centerX,centerY,k);

                sampleImage(input,x,y);

                int color = ((s[1]&0x0ff)<<16)|((s[2]&0x0ff)<<8)|(s[3]&0x0ff);
    //            System.out.print(i+" "+j+" \\");

                //if( Math.sqrt( Math.pow(i - centerX, 2) + ( Math.pow(j - centerY, 2) ) ) <= 150 ){
                if(  Math.pow(i - centerX, 2) + ( Math.pow(j - centerY, 2) )  <= 22500 ){
                dst.setPixel(i, j, color);
                }else{
                    dst.setPixel(i,j,origPixel);
                }
              }
            }
          long endLoop = System.currentTimeMillis();
          long loopDuration = endLoop - startLoop;
          long radXDuration = getRadXEnd - getRadXStart;
          long sampleDur = endSample - startSample;

          Log.e(TAG, "sample method took "+sampleDur+"ms");
          Log.e(TAG, "getRadialX took "+radXDuration+"ms");
          Log.e(TAG, "loop took "+loopDuration+"ms");

        //  Log.e(TAG, "***********filter.barrel()  looped through bm about to return dst bm");
          Debug.stopMethodTracing();
        return dst;

    }

    void sampleImage(Bitmap arr, float idx0, float idx1)
    {
         startSample = System.currentTimeMillis();
       // s = new int [4];
      if(idx0<0 || idx1<0 || idx0>(arr.getHeight()-1) || idx1>(arr.getWidth()-1)){
        s[0]=0;
        s[1]=0;
        s[2]=0;
        s[3]=0;
        return;
      }

      float idx0_fl=(float) Math.floor(idx0);
      float idx0_cl=(float) Math.ceil(idx0);
      float idx1_fl=(float) Math.floor(idx1);
      float idx1_cl=(float) Math.ceil(idx1);

     /* float idx0_fl=idx0;
      float idx0_cl=idx0;
      float idx1_fl=idx1;
      float idx1_cl=idx1;*/

     /* int [] s1 = getARGB(arr,(int)idx0_fl,(int)idx1_fl);
      int [] s2 = getARGB(arr,(int)idx0_fl,(int)idx1_cl);
      int [] s3 = getARGB(arr,(int)idx0_cl,(int)idx1_cl);
      int [] s4 = getARGB(arr,(int)idx0_cl,(int)idx1_fl);*/

       s1 = getARGB(arr,(int)idx0_fl,(int)idx1_fl);
       s2 = getARGB(arr,(int)idx0_fl,(int)idx1_cl);
       s3 = getARGB(arr,(int)idx0_cl,(int)idx1_cl);
       s4 = getARGB(arr,(int)idx0_cl,(int)idx1_fl);

      float x = idx0 - idx0_fl;
      float y = idx1 - idx1_fl;

      s[0]= (int) (s1[0]*(1-x)*(1-y) + s2[0]*(1-x)*y + s3[0]*x*y + s4[0]*x*(1-y));
      s[1]= (int) (s1[1]*(1-x)*(1-y) + s2[1]*(1-x)*y + s3[1]*x*y + s4[1]*x*(1-y));
      s[2]= (int) (s1[2]*(1-x)*(1-y) + s2[2]*(1-x)*y + s3[2]*x*y + s4[2]*x*(1-y));
      s[3]= (int) (s1[3]*(1-x)*(1-y) + s2[3]*(1-x)*y + s3[3]*x*y + s4[3]*x*(1-y));

      endSample = System.currentTimeMillis();
    }

    int [] getARGB(Bitmap buf,int x, int y){

        int rgb = buf.getPixel(y, x); // Returns by default ARGB.
       // int [] scalar = new int[4];
        scalar[0] = (rgb >>> 24) & 0xFF;
        scalar[1] = (rgb >>> 16) & 0xFF;
        scalar[2] = (rgb >>> 8) & 0xFF;
        scalar[3] = (rgb >>> 0) & 0xFF;
        return scalar;
    }

    float getRadialX(float x,float y,float cx,float cy,float k){

      x = (x*xscale+xshift);
      y = (y*yscale+yshift);
      float res = x+((x-cx)*k*((x-cx)*(x-cx)+(y-cy)*(y-cy)));
      return res;
    }

    float getRadialY(float x,float y,float cx,float cy,float k){

      x = (x*xscale+xshift);
      y = (y*yscale+yshift);
      float res = y+((y-cy)*k*((x-cx)*(x-cx)+(y-cy)*(y-cy)));
      return res;
    }

    float thresh = 1;

    float calc_shift(float x1,float x2,float cx,float k){

      float x3 = (float)(x1+(x2-x1)*0.5);
      float res1 = x1+((x1-cx)*k*((x1-cx)*(x1-cx)));
      float res3 = x3+((x3-cx)*k*((x3-cx)*(x3-cx)));

      if(res1>-thresh && res1 < thresh)
        return x1;
      if(res3<0){
        return calc_shift(x3,x2,cx,k);
      }
      else{
        return calc_shift(x1,x3,cx,k);
      }
    }



}// end of filters class

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[update] Hi, i've not watched all the vid cos i've only so much data allowance on dongle so going to wait till at work to watch it. I've modified the code to the one below. This stores the pixel data in an int array, so there's no call to dst.setPixel. it's still very slow(14 secs on 3.2MP camera) not at all like a few seconds as your code does. can you share that code or tell me if this is not what you meant. thanks Matt.

int origPixel = 0;
          int []arr = new int[input.getWidth()*input.getHeight()];
          int color = 0;

          int p = 0;
          int i = 0;
          for(int j=0;j<dst.getHeight();j++){
              for( i=0;i<dst.getWidth();i++,p++){
                 origPixel= input.getPixel(i,j);

                float x = getRadialX((float)j,(float)i,centerX,centerY,k);


                float y = getRadialY((float)j,(float)i,centerX,centerY,k);

                sampleImage(input,x,y);

                 color = ((s[1]&0x0ff)<<16)|((s[2]&0x0ff)<<8)|(s[3]&0x0ff);
    //            System.out.print(i+" "+j+" \\");

                //if( Math.sqrt( Math.pow(i - centerX, 2) + ( Math.pow(j - centerY, 2) ) ) <= 150 ){
                if(  Math.pow(i - centerX, 2) + ( Math.pow(j - centerY, 2) )  <= 22500 ){
                //dst.setPixel(i, j, color);
                    arr[p]=color;
                    Log.e(TAG, "***********arr = " +arr[i]+" i = "+i);
                }else{
                    //dst.setPixel(i,j,origPixel);
                    arr[p]=origPixel;

                }
              }
            }



        //  Log.e(TAG, "***********filter.barrel()  looped through bm about to return dst bm");
          Debug.stopMethodTracing();
         Bitmap dst2 = Bitmap.createBitmap(arr,width,height,input.getConfig());
        return dst2;

    }

Answer 1

I bet you'd cut down considerably on your execution time if you eliminated the call to dst.setPixel inside your inner loop. Instead of operating on the Bitmaps inside your loop, stuff the values into integer arrays during your loop and call setPixels at the end passing in the array.

I have image manipulation code that can loop through an entire 2MP image in a few seconds.

On older Android api's (I believe earlier than 2.3, but it might even include 2.3), the actual image data does not reside in the managed heap so there's probably some expensive operation going on to find the actual location of the bits you're overwriting in the call to setPixel. The source of my information is the Google I/O 2011 video on memory management in Android. If you're doing this kind of work in Android, it's a must watch:

http://www.youtube.com/watch?v=_CruQY55HOk