Fast Real-Time blur for applet

Java 2D
#1

hi guys!
i’m new here and i guess that i will learn a lot reading deep into this forum ;D

but now a question… i’m trying to build a library to handle the animation and effects of my applets and i’m getting some problems with performance :(… i’m using Java2D api to avoid problem of compatibility and i’m becoming crazy finding a fast way to implement a blur algorithm that i will use in animation… the first try was with a ConvolveOp class but it’s too much slow with a 8x8 kernel…

so any suggestion??
thanks :smiley:

… forgive me for my inglish i’m italian :persecutioncomplex:

#2

this is really fast:

I think Pulpcore uses a similar approach, you can browse the source code.

#3

thaks a lot for helping me :smiley:

i will try to implement this trick, they seam good and fast ::slight_smile:

#4

I’ve implemented the second one before, operating on an int[] raster. I think the fastest I managed to get it after a couple of days of optimisation was 20 blurs per second of 640x480 RGB on a 2006-era mid-range desktop.

#5

can you post some code?
i’m not very good in math :-X

#6

I’d have to write it from scratch. When I did it before it was for a company (and I can’t even violate my contract to post it :wink: because I no longer work there).

Do you want it done in place, or output to a different int[] to the input?

#7

There is C source code in that Gamasutra article, converting it to Java (and extending to ARGB) should not be difficult.

this could help you too (but I think converting the C code is easier):
http://code.google.com/p/pulpcore/source/browse/src/pulpcore/image/filter/Blur.java

#8

EDIT: double post sorry :-\

#9

i work with BufferedImage :stuck_out_tongue:

i will take a look at the source code in C, i will try ::slight_smile:

#10

Depending on how the BufferedImage was constructed, you can get a significant speed up with:

DataBuffer imageData = myBufferedImage.getRaster().getDataBuffer();

and modify the DataBuffer directly with getElem() and setElem().

Edit: I just realised that doesn’t really solve your problem. The WritableRaster you get from getRaster() has a method for setting all the image data from an array: setPixels(x,y,w,h,iArray)

#11

Even faster if you cast the DataBuffer to a DataBufferInt, and use DataBufferInt#getData() to obtain the underlying int[].
You are then manipulating the Image’s data array directly - no copying necessary.

Obviously you need to ensure your BufferedImage is of a suitable type.

#12

thaks for the reply ! :slight_smile:

but i still don’t understand exactly the algorithm…
for example what means “each destination pixel is simply the average of a short horizontal line of pixels in the source image”?
means the average of all color component?

(i’m trying to implement the second trick because is more flexible i think…)

#13

Yes, you do red, green, and blue separately.

#14

really ? arf… as long as it is bunch or little piece of code I really really will never care…

@OP (andre90boss ):

you could use something like that :

int pixels[];
Image image;

BufferedImage BIImage;
BIImage = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB);
pixels=((DataBufferInt)(BIImage.getRaster().getDataBuffer())).getData(); 
image=(Image)BIImage;

then later modify pixels array to access image pixels and use regular graphics.drawImage( … ) when requiered to draw.

About pixels manipulation you can have a look here http://dzzd.net/SimpleParticle/ source code here http://dzzd.net/SimpleParticle/sources.zip there is similar pixels processing than bluring (as I remember it use MemoryImageSource but you can easily (with the above code) convert it to use BufferedImage)

#15

It wasn’t particularly small. 200 or 300 lines of code because of unrolled loops, extracted special cases, etc.

#16

Wouldn’t it be fastest (least cache misses) to only work on scanlines (no columns)

  1. blur on scanline
  2. transpose pixels
  3. blur on scanline
  4. transpose pixels
#17

as working with scanline is always a lot faster I suppose you are right, sure it will.

like a common error when dealing with int buffer Image wich is : (EDIT: or any two dimensional array using “a single dimensional array.”…)

for(x=0;x<w;x++)
 for(y=0;y<h;y++)
  pix[x+y*w]=something

;

instead of

for(y=0;y<h;y++)
   for(x=0;x<w;x++)
    pix[x+y*w]=something;
#18

thanks for the replies!

i will try to follow yours suggestions :wink:
in the worst case i will post again ;D

#19

Why? You’re going to get your cache misses in the transpose operations rather than the blurring, aren’t you?

#20

Lets say the image is 1024 pixels wide, so each scanline is exactly one page (4K).

If you blur ‘radius’ is 4 pixels, you need 4+1+4=9 pixel reads for each pixel write. When reading/writing columns, you have to continuously read from 9 different pages for each pixel write. Something tells me the CPU (or JVM) won’t find the ‘fast path’ for such code.

Anyway, I’ll benchmark it properly.