June 2000 Bulletin

Digital imaging: from shoot to show

By Jay D. Mabrey, MD

Initially a novelty among academics, the growth of digital imaging technology within the orthopaedic community is more apparent each year with the increasing number of computer presentations being given at the annual meeting of the Academy. Mere words are never enough to convey the intricacies of orthopaedic techniques and research, so the ability to place radiographs or videos within these presentations is paramount.

Academic presentations are only the tip of the digital iceberg: there are several other areas of orthopaedics where digital imaging technology is proving useful. Many surgeons also find that cataloging and filing the hundreds or thousands of teaching slides they acquire each year to be both cumbersome and expensive. Storing those pictures as digital files, on the other hand, can save both time and money.

The tremendous increase in the use of the World Wide Web for medical research, diagnosis, and consultation now demands that these images go straight to disk in order to share them over the Web.

Definition of terms

As Napoleon once said: "Un croquis vaut mieux qu’un long discours." (A picture is worth a thousand words,) but it’s helpful to understand a few key words in defining digital pictures:

A pixel, short for Picture Element, is a single point in a graphic image. A high resolution computer screen or digital projector typically displays 1,024 by 768 pixels, or nearly 800,000 elements. The depth of the color is determined by the number of bits: 8 bits displays 2 to the 8th power (256) different colors or shades of gray; 24 bits per pixel generated the most lifelike images with more than 16 million different colors.

Dots per inch (dpi) refers to the number of pixels that fit along a one inch line on printer output, the higher the dpi, the clearer the image.

USB (Universal Serial Bus) is a "plug-and-play" interface between a computer and add-on devices such as digital cameras, printers, and scanners and it supports a data speed of 12 megabits per second (Mbps).

FireWire, also known as IEEE 1394 or i.LINK is the latest technology for connecting video cameras to personal computers. It supports data transfer speeds up to 400Mbps. This level of speed becomes important when one begins to download huge video files.

PCMCIA (Personal Computer Memory Card International Association) refers to the credit card sized devices that slip into one or two slots in the side of your laptop computer. Also known as PC cards, they provide a number of useful functions including: modem, network interface, peripheral interface, small hard drives, and FireWire connections.

Digital still cameras

Digital still cameras are available with a wide array of features and resolution. Cameras offering an image resolution of 2 megapixels (a megapixel [MP] is a million pixels, so 2 megapixels is the product of a 1600 x 1200 pixel image) are now the standard. Two new 2MP designs, the Olympus C-2000 Zoom and Nikon CoolPix 950 (both at around $800), offer significantly greater control over the picture-taking process than their predecessors, including features such as shutter- and aperture-priority metering, and extended ISO (light sensitivity) capabilities; 3MP cameras are available at a higher cost.

These cameras are particularly useful for intraoperative shots, especially with the zoom capable models, as well as transferring radiographs from the viewbox to the computer screen. A 1MP image takes up 3MB of disk space and provides a 3"x5" print comparable to that generated from a 35mm negative. A 2MP image takes up 6MB of disk space and provides a comparable 4"x6" print; 3MP image, 9MB disk space, 5"x7" print; 6MP image, 20 MB disk space 8"x10" print.

High resolution images, however, take up huge amounts of memory. These images are usually stored on removable cards that hold anywhere from 8 megabytes (MB) to 98MB of memory. You place the card in a device that allows your computer to read the data onto your hard drive.

A good start on your research for a new camera is to go to : http://www.pcphotomag.com/ which provides an online review of most products. Another helpful site is: http://www.imaging-resource.com/.

Digital video cameras

The latest innovation in digital imaging is digital video (DV). DV’s greatest advantage is the sharpness of the picture. On a standard scale used to measure video clarity, a VHS recording has 240 lines of horizontal resolution, while broadcast or cable television have a maximum of 330 lines. High-resolution home camcorders (Super VHS and Hi-8 formats) boast between 400 and 425 lines of resolution, provided they are connected to a television using separate audio and video inputs, rather than a single-line radio frequency (RF) connection that combines the audio and video. The new DV camcorders record a picture with 500 lines of resolution.

Digital video images aren’t diminished when copied–even copies of a copy of a copy. In contrast with analog home video recordings, which get smeary, bleached-out and noisy when transferred from one tape to another, digitally produced video copies are next to perfect no matter how many generations removed from the original. DV virtually eliminates color blur and noise by separating the color into separate signals and record three times more data than analog NTSC video. The DV tape cassette is about 2 5/8" x 1 7/8" x 1/2" and a one-hour tape – the longest recording time now available – holds 11GB of data.

DV cameras utilize FireWire technology to connect to your computer for download and editing. FireWire is built in to all of the new Macs while separate cards are available for PCs. Orange Micro (http://www.orangemicro.com/) even offers a FireWire PC card that will work with both Mac and PC laptops, providing mobile DV editing capabilities.

I have used my Canon Elura (http://www.canondv.com/) to record images directly from the video output ports of both arthroscope and fluoroscope monitors.

Scanners

Digital images may be generated from previously published materials using a flatbed scanner. If you’ll be scanning detailed images and line art from photos or other printed originals, then go with an optical resolution of 600 dpi. The latest scanners use USB technology and are cheap (less than $200) and easy to set up.

For converting an existing slide collection into digital format, an $800 slide and film scanner works best, although you can also project the image on a screen and capture it with a digital camera. Optical resolutions of 2400 dpi and higher are necessary to achieve sharp resolution of these 35mm slides. Remember, your 600 dpi flatbed scanner is looking at an 8.5"x11" sheet, not a 35 x 24mm piece of film.

Photo editing

Virtually any scanner or digital camera will come with some type of photo-editing software that allows you to tune up your pictures by cropping, rotating and enhancing the contrast. The most popular program available is Adobe Photoshop 5.5 (www.adobe.com) followed by a slimmer version known as Adobe PhotoDelux. One rule of thumb for editing images for digital presentation: edit them at full size on the monitor to see how well they will project on the screen.

Video editing

Not surprisingly, one of the most popular video editing packages is also from Adobe: Premier 5.1. This program, and others like it, provides tools for cutting and editing videos as well as adding transitions, titles, and other special effects. Video, in its raw form, takes up huge amounts of space. For example, uncompressed NTSC video is about 27 megabytes per second. At this size, you could fit only about 24 seconds of video on a CD-ROM and no CD-ROM drive could transfer such a file fast enough to play it smoothly.

In order to make desktop movies feasible, compression algorithms (Codecs) were created. Compression is the process by which large movie files are reduced in size by the removal of redundant audio and video data. For more dramatic size reduction, less important data may also be removed, resulting in image and/or sound degradation.

The codec is the algorithm that handles the compression of your video or audio, as well as the decompression when it is played. QuickTime has several codecs available within it for free, and there are professional versions of certain codecs which may be purchased for superior quality and additional options. One helpful source for information on video editing techniques and hardware is: http://www.digitalorigin.com/default.html.

Presentation programs

The most commonly used presentation software is Microsoft’s PowerPoint which usually comes bundled within the Microsoft Office package. The program is available for both the Macintosh and Windows platforms. It is reasonable to assume that all presentations at annual meetings within the next few years will be digital in nature and that photographic slides will be relegated to the archives. PowerPoint also has the capability to make Web-based presentations.

The digital images from both still and video cameras are easily imported into PowerPoint, although the size of the presentation can grow rapidly, especially with video files. The use of codecs reduces the size of these files significantly.

Projectors

There would be no digital presentations without projectors which provide anywhere from 800 by 600 pixel resolution up to 1072 by 768 pixels for higher end computers. Keep in mind that the resolution of any projector is still 72 dpi, so higher resolution images only increase the size of the presentation. At most, I will use images at 144 dpi to avoid a pixilated appearance. Digital video can be directly input through the projector using a separate video player, giving a much crisper image than the compressed version.

Color printers

You can’t buy a computer system from one of the big mail order firms without them forcing a color printer on you for free. Even the cheaper printers have a basic resolution of 720 by 360 dpi with better printers having 1440 by 720 dpi. The best results are obtained with the photo quality paper that looks and feels just like photo print paper. If you are printing out photos for publication, check with the publisher and see if they will accept high resolution formats on disk, otherwise they will have to re-scan the image and lose some detail.

Slide printers

For those cases where digital presentations are not available, slide printing services are available on the Web or through most university graphics services. Output is typically 4,000 to 8,000 lines per slide, in contrast to the 768 lines on a high resolution display. Slides may be output directly from PowerPoint to image files for the printer, but standards vary, so check with your individual service. Because of the higher resolution on photographic slides, it is advisable to use higher resolution images of 300 dots per inch, otherwise the image appears pixilated on the final projection.

Hardware requirements

Digital imaging requires enormous amounts of RAM and hard disk space as well as a brisk processor. Both Macs and PCs require a minimum of 64MB of RAM although 128MB allows other applications to remain open during the editing process, even more for video editing is advisable. Be aware that 4GB hard disk space is the bare minimum for accommodating the operating system and photo- or video-editing software; 10GB disks are common on entry level PC’s, but 20GB or higher allows editing and storage of video files. Available even on entry level systems at a modest price, CD-R (recordable) disks store up to 650MB of data and are very useful in archiving up to hundreds of high resolution images.

Digital imaging technology is no longer the expensive hobby it once was only a couple of years ago. For the novice, the easiest way to get started is with one of the less expensive 2MP cameras, PowerPoint, and a decent hard drive.

Jay D. Mabrey, MD, is Associate Professor of Orthopaedics, University of Texas Health Science Center; Chief, Division of Orthopaedics, Audie Murphy VA, San Antonio, Texas. Dr. Mabrey is Chair, AAOS Committee on Electronic Media and Education.


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