Live! Exposed! And on the Web!

The freebie of the week? Yet another case of Internet porn? Nope. The performers were a light bulb, a spinning disk, and a voltmeter. They sat inside a box in front of a Webcam set up by controls vendor Opto 22 to dramatize potential applications of Ethernet I/O. Things were getting steamy because a viewer somewhere had clicked a browser button that turned on the light bulb. Observers could monitor temperature in the display box from thermometer readings fed to an I/O rack and out to the Internet. Though the Opto 22 demonstration in Temecula, Calif., is modest, it looks like a harbinger of industrial tools. Webcams are migrating out of the novelty category and into mainstream industrial practice. Growing Internet bandwidth makes them practical alternatives to closed-circuit TV, and opens up wholly new application areas as well.

For example, Opto 22 says it is working with companies devising Webcam systems for school building security. Sensors that notice a door opening, or other potentially interesting events, will trigger a camera that photographs whoever is going in or out. The image feeds over a net and is available to security personnel through an ordinary browser.

Machinery is another candidate for remote monitoring via Webcam. Among the first applications foreseen in this area are unmanned generator sets. Backup power systems for isolated areas often have no human operator nearby. Webcams are envisioned as a way of ensuring there are no animals, debris, or bystanders in the way before powering up the generator. There are similar ideas afloat for production equipment and tools.

THE BASICS
The simplest Webcams employ USB connections back to either computers or network appliances such as a router, hub, or concentrator. Also called plug-and-play cameras, they are inexpensive, often retailing for about $200 or less, and available from a variety of suppliers. These devices boast an image quality good enough for general-purpose work. (The Opto 22 site uses one of these.) Typical resolution is 640 480 pixels at most, though they can be set up to image at lower resolutions to reduce bandwidth demands. Typical frame rates are in the one to three frames/sec range.

Cameras targeting more demanding uses provide much higher resolution. Those aimed at machine vision or scientific microscopy, for example, can record images at 1,300 1,030 densities or more with 10-bit color representation. They can also put out 12 frames/sec at this resolution.

An alternative to Webcams is to hook an ordinary camcorder into a video capture device. Capture devices digitize NTSC video into MPEG images with resolutions of about 700 575 pixels. Images go to a host or server via ISA or PCI slots.

Network cameras are a refinement. They connect directly to networks via Ethernet connections. Though more expensive, they eliminate the need for a separate computer to host the camera. Similarly, network-video-capture devices are stand-alone electronic boxes that accept camcorder signals and perform similar functions.

Raw images from cameras typically get compressed before being passed to a server. Simple USB cameras depend on software running on the PC or host for compression. Network capture devices generally have their own processor, and one of its tasks is shrinking images.

Image size and frame rate (or image update rate) are trade-offs. To accommodate users with modem/dial-up connections, Webcam operators may deliver relatively low-resolution (and relatively small) images of about 160 120. This lets slow connections update at a rate of about once per second. It's possible to deliver images over the Web at resolutions as high as that of the camera imager itself, but at slower update rates.

There are two methods of getting images to show up in a Web page, one slow, the other fast. Hobbyists Webcasting their aquarium and similar scenes generally use client-pull broadcasting. This sends the last image shot by the camera to the ISP hosting the site. Viewers down-loading the page see a still image, the one that happened to be cached when the download began. To update the image, they hit the browser's reload button. Alternatively, an HTML tag or Java applet on the page could reload the image automatically at periodic intervals.

The main benefit of client-pull is that it works well with browsers on slow connections. The other method, server push, may not. But it is required when real-time video is the goal. In server push, HTML code in the page tells the browser to expect a series of images. The server hosting the camera sends data any time it wants to.

For example, suppose the server software is set to transmit two frames per second onto the Web. Provided their Net connection is fast enough, viewers should see two frames per second appear in their browser. However, sufficiently powerful server software can send video at changing frame rates. The classic example is that of a program which determines if the current video image resembles the previous one. It only sends a frame when the signal changes appreciably. There is an obvious conservation of bandwidth. Clever techniques such as this can make near real-time video practical for viewers on relatively slow hook ups.

TIES TO INDUSTRIAL I/O
Controls vendors such as Opto 22 plan to tie a variety of peripheral devices more closely into industrial I/O modules. Webcams are one of the devices on the list. Eventually, USB cameras will plug directly into an industrial Ethernet I/O module to connect with the Internet.

Another development, XML data standards, is expected to indirectly make Webcams easier to deploy for industrial use. Specifically, XML may slash the effort needed to define Web pages associated with industrial monitoring.

XML defines data elements on a Web page and in business documents. It uses tags analogous to those in HTML. The difference is that HTML tags define how elements are displayed, while XML tags define what the elements contain.

Moreover, the person developing the Web page defines the meaning of specific XML tags. Specifying XML tags for entities such as pressure, temperature, force, and so forth is critical for industrial use. For example, pages containing Webcam images may well contain XML-tagged fields for time, view, magnification, and other entities associated with monitoring scenes in real time.

This sort of identification could let Web pages function like database records. In so doing, it may eliminate some complexity now associated with data logging and monitoring.