Forum Moderators: not2easy
JPEG 2000 format
What is the JPEG 2000 format?
Thanks, Richard LOwe
I haven't had a chance to investigate it yet.
JPEG 2000 is not intended to become a proprietary format. The JPEG committee is hoping that it'll become an internationally accepted standard (it might eventually replace the JPG-format).
The implementation of the JPEG 2K encoders/decoders however, can and do differ from company to company.
I use both PNG and JPEG 2000 on my website (in addition to JPG and GIF, of course):
PNG is used for lossless compression of certain images in which 24-bit color depth is essential. GIF is limited to a color depth of 8-bit, which won't do in this particular case. JPG does support lossless compression of 24-bit images, but no browsers (AFAIK) and very few image editors support processing (encoding/decoding) of lossless JPGs. Before I used TIFF, but the advantage of using PNG is that the 24-bit images can be displayed in the browser itself (unless you're using an old browser) without having to rely on external image viewers.
JPEG 2K is used for compression of wallpapers (I'm using the JP2 compliant Kakadu encoder/decoder for processing JP2 images). Users can convert the images to BMP or other formats (for wallpapering) using small browser-plugins. The reduction in filesize compared to JPG is about 30% at lower compression levels (~1:5-1:15).
(I've not posted any links to my site because I don't want this post to look like a shameless ad.)
[jpeg.org...]
You'll find lots of info about the JPG2K format there.
Here's a JPEG2K tutorial:
[jj2000.epfl.ch...]
Some of the most notable features of JPEG 2K are:
* Wavelet Compression Technology. In contrast, JPEG is based on DCT (Discrete Cosine Transform) which causes noticeable blockiness (and other artifacts) at higher compression levels.
* Multiple resolutions. The data is stored in a continuous stream, which reduces storage and transfer overhead. Users may choose the desired resolution from a single file.
* Improved color handling. A new colorspace (sRGB) and the embedding of ICC color profiles will help to ensure correct color reproduction across platforms and devices.
* Improved metadata capacity. Allows for the embedding of additional information about the image, such as name of the author, sources, calibration data, etc.
You should read this technical paper for a comparison between JPG2K and PNG (and other images formats as well):
[jpeg.org...]
Excerpt:
... The results show that the choice of the "best" standard depends strongly on the application at hand, but that JPEG 2000 supports the widest set of features among the evaluated standards, while providing
superior rate-distortion performance in most cases. ...
zeus
Never use PNG to replace JPEG. Although you can have non-indexed PNGs, they are far, far less efficient than JPEGs, and are, in fact, designed as an alternative to TIFF.
Use JPEG2000 as an alternative to JPEG, and indexed (max 8 bit) PNG as an alternative to GIF.
Neither of these formats have really taken off yet, although they are actually more efficient, and JPEG2000 especially produces better-looking images. It appears that they are not yet adequately supported by graphics editors, and PNG not properly supported by browsers yet. (A few servers may be unable to serve up the correct MIME types, but I should think by now that most do, whatever Netscape say.)
PNG seemed set to replace GIF very quickly because Unisys are enforcing their patent on LZW compression used by GIF. Graphics editors can only use LZW compression if they have a license to do so; PNG is free. But, of course, the big software houses can easily afford the license and most webmasters are familiar with GIF and have the same attitude as Zeus -- there is a lot of inertia here.
Already, the GD library used by PHP to create dynamic images has dropped GIF in favour of PNG for reasons of cost. But I don't think this trend is going to affect Macromedia, Corel et al; they recoup the cost of the Unisys license by passing it on to their customers.
