For Position Only: Your Web Graphics Are About to Change

Anita Dennis

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We’re all swimming in a sea of acronyms these days, but get ready for two more: JP2 and JPX. If you haven’t heard of them, you will soon enough. They’re the offspring to another acronym that is near and dear to all of our (Web publishing) hearts: JPEG.

JP2 and JPX are the file extensions that will identify still images saved in the forthcoming JPEG 2000 format, currently being approved by a troika of international standards bodies: ISO, IEC, and ITO. Although it’s already 2001 and the standard’s name is outdated before it’s even released, you can be sure that it brings many new and much-needed improvements to the image file format that has become increasingly prominent with the rise of the World Wide Web. I’ll be the first to admit that file formats and image compression aren’t the sexiest of technologies, at least not on the surface. But JPEG 2000 will change the way you publish. Honest.

(A brief disclaimer: My husband, a color researcher at Ricoh Innovations, Inc., is the editor of the JPEG 2000 standard and has been involved with it since early 1994. However, I’m not sure if that makes me more or less of a fan of the technology <g>.)

JPEG 101
The first question you probably have is: What’s wrong with the current JPEG? Isn’t it used to display millions of images on the Web just fine, thank you very much? Yes, it is, but the file format’s drawbacks are plentiful.

First, JPEG is a one-trick pony. It compresses photographic images using such magical mathematics as the discrete cosine transform, quantization, and statistical coding (like I said, my husband is an image-processing engineer), and then the images are decompressed to the same resolution and bit depth as the original. That might suit many people just fine, but in that process some of the original data is lost, which can cause unsightly errors such as shadows of edges in flat areas of color, blockiness, and color shifts. Although publishers can choose to balance final image size with the degree of quality they want, there are trade-offs. In other words, if you don’t want artifacts, your file size is larger, as you don’t get much compression. And if compact size is your top priority, then you pay with artifacts.

Compromises in image quality aren’t necessarily a problem in producing images for the Web, where they’re partially masked by 72-dpi viewing conditions and a limited color palette, but JPEG has always been unsuitable for print publishing. Not only are artifacts glaringly obvious in high-resolution commercial print publishing, but JPEG is also limited in its handling of color for two reasons: It supports only 8 bits per pixel, and its code “container” (called JFIF) describes only RGB color, not CYMK.

Since JPEG’s genesis more than 10 years ago as a means of allowing photojournalists to transmit images from the field — its acronym stands for Joint Photographic Experts Group — there have been numerous improvements in terms of compression algorithms and CPU speed that allow the format to be improved. JPEG 2000, based on what’s called wavelet transform, not only results in truer decompressed images but also offers several new benefits. Most notably, JPEG 2000 images let designers and publishers determine the bit depth and resolution of the final decompressed image, making it a much more dynamic and flexible format.

JPEG 2000
Wavelets have two distinct advantages over the transform used in the old JPEG. First, they encode image data in a stream rather than in chunks as in the original JPEG, minimizing the artifacts we’re so used to with JPEG. Second, wavelets decompress an image in a series of passes, each one of which improves the quality and the color of the displayed image. This means that whoever produces or views the JPEG 2000 image can control the final resolution and color depth; final images can be completely lossless if desired. Depending on their viewing software, the viewer may even be able to pan and zoom.

But there are even more features of JPEG 2000 that make it powerful for both print and Web publishing. JPEG 2000 images have a defined color space — sRGB — which gives designers and publishers a baseline for managing their color. And because JPEG 2000 images can have ICC color profiles attached, they can be used with confidence in CYMK, Hexachrome, and other color workflows. JPEG 2000 images can also contain spot-color layers, alpha channels, and masks; they can contain metadata such as copyright information or watermarks; and they have built-in error tolerance to prevent image corruption caused by noisy transmission lines. Eventually JPEG 2000 will support multiple coding methods so that you can optimize the compression of images that contain both continuous-tone and graphic elements. A Motion JPEG 2000 standard, using QuickTime, is also in the works.

JPEG uber alles
As publishers increasingly need to use the same images both onscreen and in print, JPEG 2000 may be the only file format they need. (By the way, JPEG 2000 doesn’t replace the original JPEG; it complements it.)

Fast forward four years: Imagine you’re preparing a print product brochure for your company and some corresponding Web pages; site visitors will also be able to download product information to a handheld device if they like. You’ll need several versions of the same digital image — 300-dpi CMYK and 72-dpi RGB, each at multiple sizes, at the very least. Today that means spending a lot of time sizing, editing, and saving in Photoshop. But now imagine preparing all of that content in a single XML document using JPEG 2000 images. Your server will deliver the appropriate text and image data to your prepress shop and to your Web master in one fell swoop.

Some of you might be flashing on FlashPix, the format developed a few years ago by Kodak and others, which accomplished some of the same tasks as JPEG 2000 but actually resulted in larger, not smaller, files. JPEG 2000 does more with fewer bits than FlashPix, which is partly why it has a much more promising future. The other reason is industry support. Although most of the major graphic arts software publishers haven’t made specific promises, many are either on the JPEG committee itself or are part of the Digital Imaging Group, an industry association backing the file format. Industry support is how a theoretical standard becomes a de facto standard.

I know, I know, JPEG 2000 isn’t even out yet, and it will take a while for it to be incorporated into products and for designers and publishers to catch on. But it’s coming, I swear, and I’m excited about it. I have it from a good source.