for blurring an image fast, i can recommend mario klingemanns
superfastblur example

http://incubator.quasimondo.com/processing/superfastblur.pde

That's an interesting example! However, I wonder if the old syntax (Processing Alpha I guess) would turn beginners away. Below is the same code with the minimal changes to run it in current Processing.

Andreas

1. // Super Fast Blur v1.1
2. // by Mario Klingemann <http://incubator.quasimondo.com>
3. //
4. // Tip: Multiple invovations of this filter with a small
5. // radius will approximate a gaussian blur quite well.
6. //
7. PImage a;
8. PImage b;
9. void setup()
10. {
11.   a=loadImage("dog.jpg");
12.   size(a.width, a.height);
13.   b=new PImage(a.width, a.height);
14.   fill(255);
15.   noStroke();
16.   frameRate(25);
17. }
18. void draw()
19. {
20.   System.arraycopy(a.pixels,0,b.pixels,0,a.pixels.length);
21.   fastblur(b,mouseY/8);
22.   image(b, 0, 0);
23. }
24. void fastblur(PImage img,int radius) {
25.   if (radius<1) {
26.     return;
27.   }
28.   img.loadPixels();
29.   int w=img.width;
30.   int h=img.height;
31.   int wm=w-1;
32.   int hm=h-1;
33.   int wh=w*h;
34.   int div=radius+radius+1;
35.   int r[]=new int[wh];
36.   int g[]=new int[wh];
37.   int b[]=new int[wh];
38.   int rsum,gsum,bsum,x,y,i,p,p1,p2,yp,yi,yw;
39.   int vmin[] = new int[max(w,h)];
40.   int vmax[] = new int[max(w,h)];
41.   int[] pix=img.pixels;
42.   int dv[]=new int[256*div];
43.   for (i=0;i<256*div;i++) {
44.     dv[i]=(i/div);
45.   }
46.   yw=yi=0;
47.   for (y=0;y<h;y++) {
48.     rsum=gsum=bsum=0;
49.     for(i=-radius;i<=radius;i++) {
50.       p=pix[yi+min(wm,max(i,0))];
51.       rsum+=(p & 0xff0000)>>16;
52.       gsum+=(p & 0x00ff00)>>8;
53.       bsum+= p & 0x0000ff;
54.     }
55.     for (x=0;x<w;x++) {
56.       r[yi]=dv[rsum];
57.       g[yi]=dv[gsum];
58.       b[yi]=dv[bsum];
59.       if(y==0) {
60.         vmin[x]=min(x+radius+1,wm);
61.         vmax[x]=max(x-radius,0);
62.       }
63.       p1=pix[yw+vmin[x]];
64.       p2=pix[yw+vmax[x]];
65.       rsum+=((p1 & 0xff0000)-(p2 & 0xff0000))>>16;
66.       gsum+=((p1 & 0x00ff00)-(p2 & 0x00ff00))>>8;
67.       bsum+= (p1 & 0x0000ff)-(p2 & 0x0000ff);
68.       yi++;
69.     }
70.     yw+=w;
71.   }
72.   for (x=0;x<w;x++) {
73.     rsum=gsum=bsum=0;
74.     yp=-radius*w;
75.     for(i=-radius;i<=radius;i++) {
76.       yi=max(0,yp)+x;
77.       rsum+=r[yi];
78.       gsum+=g[yi];
79.       bsum+=b[yi];
80.       yp+=w;
81.     }
82.     yi=x;
83.     for (y=0;y<h;y++) {
84.       pix[yi]=0xff000000 | (dv[rsum]<<16) | (dv[gsum]<<8) | dv[bsum];
85.       if(x==0) {
86.         vmin[y]=min(y+radius+1,hm)*w;
87.         vmax[y]=max(y-radius,0)*w;
88.       }
89.       p1=x+vmin[y];
90.       p2=x+vmax[y];
91.       rsum+=r[p1]-r[p2];
92.       gsum+=g[p1]-g[p2];
93.       bsum+=b[p1]-b[p2];
94.       yi+=w;
95.     }
96.   }
97.   img.updatePixels();
98. }

I am also trying to implement the blur filter....