Go to my Home page.
Go to my Joy of High Tech page.

The Joy of High Tech


Rodford Edmiston

     This being a collection of random thoughts on bits and pieces of information which should interest the technically oriented reader.

Please note that while I am an engineer (BSCE) and do my research, I am not a professional in this field. Do not take anything here as gospel; check the facts I give. And if you find a mistake, please let me know about it.

Recording Images

     There have been several attempts to market digital still cameras for the average consumer. All have failed. The problem is simple: getting adequate resolution and storage for a reasonable price. Let's take resolution first.

     A good-quality 35mm negative contains the digital equivalent of between 4 and 8 million picture elements (PEL) in 16 million colors. This is roughly 2600 lines per inch (lpi). The CCD imaging element in a typical camcorder has a 320 by 200 array, for 64,000 PEL. A very good quality commercial CCD has a 900 by 500 array, for 450,000 PEL. Some special purpose CCD arrays - such as those used in astronomy and reconnaissance work - can go much higher, around 1.5 million PEL. Recently, one company has produced a state-of-the-art CCD array with 26.2 million PEL, which is a third better than Kodachrome professional format film. However, the chip alone can cost as much as $50,000. You can buy a lot of film for that amount! Not to mention professional quality medium- and large-format cameras which make 35mm look like a child's crayon drawings.

     Magazines and other publications which print high-quality images normally use flatbed scanners to digitize photographs. A typical CCD flatbed scanner has a resolution of 1600 dpi. A good quality scanner produces 5000 dpi. However, a trick is used to get the most out of this equipment. An enlarged print is made for the digitization process. Some small amount of data is lost in printing the photo, but that is minor. The larger format allows practically all the information in the photo to be digitized at the scanner's limit of resolution.

     Now for the storage problem. A good quality 35mm negative contains the equivalent of around 24 million bytes of information. Analog systems are still better than digital at some things, and storing visual information is one of them. A roll of 36-exposure, 35mm color film contains nearly a gigabyte of information. You would need an optical worm drive just to store your vacation photos! (Note that photo CD units have come on the market recently.)

     So why have video cameras replaced film cameras for home use? There are several reasons. First, even Super-8 format movie film is very small, and has a much poorer image than a 35mm still photo. Second, "moving" images are actually a series of rapidly-viewed still images. The mind fills in the gaps, interpolating between the discrete images to create a whole, using a sort of built-in version of interferometry to add detail. Finally, video tape is much more convenient to use than movie film. You don't have the problems of loading and unloading light- sensitive film, and having it processed.

     The strengths of CCD imaging are sensitivity and speed. A CCD camera can take pictures in very low lighting. It can also cycle very quickly, taking 50 images a second or more. The strengths of the traditional film and print process are very good resolution, non-volatile storage and easy access to the image without special equipment. So, even with all the advancements made in electronic imaging over the last couple of decades, chemical-based film photography still has a lot going for it. It will be a long time before there is anything as good for such a low price available in electronic equipment.

     Now for something which will surprise a lot of you. There is an imaging system which has a much larger dynamic luminance range (that is, capable of seeing details in situations where lighting varies greatly) than either film or CCD. It is also smaller, lighter, more compact, and much cheaper. Moreover, it has a higher image density for the same luminance (within its operating range) than either film or video, and the storage/retrieval mechanism is faster, more compact and much handier than a photo album or TV. It produces real-time, three-dimensional, moving, color images, and has automatic image processing hardwired in. Most humans have this system as original equipment.

     This document is Copyright 2002 Rodford Edmiston Smith. Anyone wishing to reproduce it must have permission from the author, who can be reached at: stickmaker@usa.net