Time for jpeg decoding

Question

Hi to all!
i'm working with a thread that read a stream from a camera (stream of Jpeg ) end show the video on the screen.
I'm testing with max resolutions (704x576) e low compression at 25 fps.
The result is very far from 25 fps! and depending from the library for decoding. I have tested with:
1) immagine = ImageIO.read(test);
2) immagine=Toolkit.getDefaultToolkit().createImage(imageData);
3) with Reader: immagine = reader.read(0);
4) with JPEGDecoder: immagine = decoderA.decodeAsBufferedImage();
The target is 40 ms for one of that line.
Analysing the problem i have found that the time for decoding Increases enormously every 3-4 frame (at 704x576 while at low resolutions the number increases) like:
67 ms,70 ms,68 ms, 240 ms,68 ms,72 ms,77 ms,220 ms,69 ms,68 ms,77 ms,79 ms,199 ms,62 ms,59 ms, ecc..ecc...
The size is consistently about 34000 byte (also when employs 200 ms....).
and obviously average values of FPS collapse up to 3-6 fps (at 704x576) precisely those values up 200 ms !
I can not understand why!
that is for linux on pentium or for windows (java VM is version 6up5).
No sleep or other operation is done at regular intervals that could cause this.
Someone has had a similar problem or have a suggestion?
thanks in advance,
Nicola
Edited by: nicopalm on Apr 10, 2008 2:07 AM
Edited by: nicopalm on Apr 10, 2008 2:16 AM

Answer 1

Thanks Andrew,
I have tetsted your suggestion but i have some problem with my Reader ...
i create imageinputstream for Reader from bytearrayinputstream and i must allocate a new test every time because the imagedata is different every time...
test = new ByteArrayInputStream(bufferArray, 0,lungbyte);
iis = ImageIO.createImageInputStream (test);
I try to say as I did to find out if I have done well.....(sorry for my english...)
1) I have a stream come from network camera.
2) I open DataInputStream (iStrm).
I know the lenght (L) of each image end i read from iStrm imageLength bytes (after i have fount the boundary e read the info between two images) .
3) With these values fill a byte array (imageData). Because each images have different lenght, i must allocate imageData=new byte[imageLength]. (After draw i make imageData=null).
4) With imageData i create a ByteArrayInputStream. test= new ByteArrayInputStream(imageData).
5) Finally i have the multiple way to decode like image=ImageIO.read(test) or other....
Is the proper procedure?
My doubt is this:
The new ByteArrayInputStream have the imageData like is buffer.
Can i create a buffer of fixed size (example higher than the average value of images length)      so that i can make a new ByteArrayInputStream one time only ?
In this way could fill the array (which is certainly less buffer).
thanks
Nicola