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Calibration images

Mon, 05/31/2004 - 8:00pm
Walter S. Ciciora, Ph.D., Recognized Industry Expert on Cable and Consumer Electronics Issues

Walter S. Ciciora
Walter S. Ciciora,
Ph.D., Recognized
Industry Expert on
Cable and Consumer
Electronics Issues
I received a number of comments about my last column (entitled, "Images, 8 mm to HDTV," CED April 2004, p. 46), so I thought I'd expand a bit on this theme.

A cable technologist needs a "calibrated eye." For that reason, I believe that cable technologists should immerse themselves in all manner of visual and aural experiences to build their understanding of the nature of the services we provide. These experiences serve to calibrate the eyes and ears. This is more important than ever because of the current emphasis on "digital quality" and high definition television and the ever-increasing size of television displays.

Certainly, constructing a home theater, getting hands-on experience with really big-screen HDTV, surround sound, and the TiVo and TiVo-like digital video recorders are worthwhile experiences for cable technologists.

An even more fundamental level of experience comes from work with still photographic images and home movies and videos. Digital photography makes this experimentation a lot less messy than it used to be. Gone are the days when experimenting with photography required developer, stop bath and fixer chemicals in a dark room.

Now, all of that has changed. The "free" software that comes with an inexpensive digital camera is all you need to get started. And color is no problem. This is a great way to get a feel for the fundamentals of image science.

The family history project I discussed in the last column has moved on to still pictures. There are boxes and boxes of them and loads of black-and-white and color negatives and 35 mm slides. I've spent a lot of money on scanners and have had disappointments and one pleasant success. I'd be happy to relate the brands of the winners and losers privately (just send me an email).

These old photographs and negatives are just too curled and bent for an automatic feeder. The jams are too frustrating to be worth it. So a fast manual scanner is a joy. Some of the older scanners take up to two minutes for a picture. That makes it a life-time project! The newest scanner does the job in less than 30 seconds. It even has an automatic mode wherein it decides whether the image is color or black-and-white and limits the scan to its correct size.

The importance of electronic exposure and focus is dramatized by the high proportion of out-of-focus and badly exposed pictures and negatives. We take these capabilities for granted in our digital cameras. Auto focus is more amazing than auto exposure, but both make capturing images of good quality almost mindless. This, of course, is the experience of cable subscribers as well. It builds the expectation that cable images should be perfect.

After the photo or negative is scanned into the computer, the fun really begins. Then you get to adjust the parameters. Brightness and contrast are adjustable while you watch the results on the computer monitor. This is a big improvement over the need to develop the print in order to see if your adjustment of brightness or contrast went in the right direction.

Of course, focus is beyond correction. Once incorrect focus enters the chain of steps, its damage seems to be permanent. A significant advantage of digital photography is the elimination of one focusing step. There is no enlarger to focus. The digital photograph enters the computer without the hazard of this step. Even if a negative or print is being scanned into the computer, focus is not part of the scanning process. There are, however, software tricks for increasing "sharpness."

Photographic resolution is dramatically higher than video resolution. Even HDTV resolution pales in comparison. Typical scanning rates for photos are 300 dots per inch for a large negative. But even inexpensive scanners can exceed a thousand dots per inch. This is especially useful if the picture is "cropped" so that only part of the image is scanned.

Photographs need more resolution because they are viewed from much closer distances. Ordinary NTSC video has a "five-times picture height" image. That is, the picture is intended to be viewed from a distance of five times the vertical height of the picture. From that distance and greater distances, the compromises made in the encoding of the picture become invisible. Closer distances will reveal those compromises. HDTV is a two-times picture height image. Viewing HDTV from more than two times its picture height is a waste of its increased resolution.

The next choice to make concerns the encoding. For the cable technologist, the choice to make is JPEG because of its relationship to MPEG. Converting the scanned photographs into various levels of quality is a good way to calibrate eyes to the nature of digital artifacts. This exercise teaches the kinds of detail that give rise to different levels of artifacts.

These experiences build a deeper understanding of the fundamentals of cable.

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