• Digital Camera Sensors
  
• Media Card Readers
• Memory Card Types
• Camera Batteries

According to rumors I’ve heard, most digital color cameras have twice as many green pixels as either red or blue pixels. I’m told that this is done because our eyes have more “green” cones than either “red” or “blue” cones and, therefore, most of our visual resolution is in the green part of the visible spectrum. Given a camera with a certain amount of “true pixels,” what would be its true color resolution in pixels? Or would the manufacturer count all the pixels and give it some other resolution?

Rumors? Am I the digital photography gossip columnist now? Well, the rumors are true.

The real data is as follows: Of the approximately five million cones in the human eye, 64% are sensitive to red light, 32% are green-sensitive and only a mere 2% are sensitive to blue light. The story doesn’t end there, however. All of the cones aren’t alike. In fact, the blue-sensitive cones actually are the most light-sensitive, but there are fewer of them.

We need to go beyond the counts and sensitivities of cones. We must look at the efficiency of human vision as it relates to luminance, or the brightness, of a scene. This has been examined through exhaustive testing of human vision.

If you look at three colored objects of equal radiance, the human eye will perceive the green object to be the brightest, the red to be the next brightest and the blue object to be the least bright.

Camera manufacturers then build digital camera sensors that mimic human vision. So they take a CCD with a whole bunch (technical term) of photo receptors, which are essentially color-blind, and they put color filters on them. They use a checkerboard pattern of red, green and blue filters that are arranged in something called the Bayer pattern—and not because staring at the pattern will give you a headache. It’s named after a scientist at Kodak by the name of Bryce Bayer.

One row of filters uses red and green and the other uses green and blue. Obviously, these alternating rows of color filters use twice as many green filters as red or blue. Why? Because the CCD is trying to mimic the human eye’s green luminance sensitivity.

But the picture isn’t there yet. In order to create an image with pixels that each contain red, green and blue values that you can view, the camera must do some interpolation of the raw pixel data. Through pretty sophisticated processing, the electronics derive the color values of each pixel by examining the surrounding pixels. Then every pixel gains a value for all three colors. In response to your comment, it’s not just an average.

Once you get through all of this processing, the camera will output its true resolution based on the total number of pixels.

You’re correct in pointing out that we highly recommend a media card reader as a “must-have” accessory if you’re going to be using your digital camera’s images on your computer.

The most common connection for a media reader is USB, also a very common port available on nearly all computers sold today. It offers a quick connection, provided your computer has a USB port available.

One thing to keep in mind with USB is that it can be operating at three different speeds: 1.5, 12 and 480 Mbps. And be careful about trying to determine at what speed your accessories can operate. A common mistake is to refer to the highest-speed USB as USB 2.0 and the slow speed as the original USB 1.0.

The original 1.0 (or 1.1) USB specification could run at 1.5 or 12 Mbps while the 2.0 version can handle all three speeds. But to make sure your peripheral is capable of running at the highest speed, look for the certified “Hi-Speed USB” logo on the device. Only then can you be assured of running at the highest speed.

FireWire (also known as IEEE 1394 and i.Link) is a faster connection than USB, but it’s not as common on computers. All new Macintosh computers and a few Windows machines will have this port. If you’re using a Windows machine, you may first need to install a FireWire card in your computer.

There’s no difference in quality of transfer between either type of card reader. It’s only a matter of speed. How much faster is FireWire? I did some real-world tests that, while unscientific, will demonstrate a bit of the speed difference.

I put 21.7 MB worth of photos onto a standard CompactFlash card (no speed improvement technology). I copied that data from the card to a standard Pentium Windows machine using a card reader. Using a common USB 1.1 reader, that process took 4 minutes, 9 seconds. With FireWire, that figure dropped by almost half to 2 minutes, 23 seconds.

An even more noticeable test was to browse through the images on the card using Microsoft’s Windows XP built-in picture previewer. Using USB, there was a lag of two to three seconds between each image. With FireWire, that dropped to less than a second between images.

Of course, the actual performance on your system might be different, but this gives you some idea of the speeds involved using both methods.

I’ve been steadily asked this question directly or indirectly as new technology has evolved for storing digital images on cameras. When digital cameras first came out, the only option for storing images was memory built into the camera. Once the camera was full, you had to connect the camera to your computer and download all the images so you could use the camera again.

Now, with CompactFlash Type I & II, xD, SD, SmartMedia, Memory Stick, Memory Stick PRO, MultiMediaCard, and, I’m sure, other technologies on the horizon, it’s all a little bewildering.

So you want a product recommendation? In the past, I’ve avoided giving this kind of explicit advice because I believe people need to make decisions on what’s right for themselves rather than following the advice of what some “sage” thinks is right for them (not to mention all the letters you get from people who disagree with your recommendation). Now, for the first time since I started writing this column, I’m going to give you a product recommendation. Here goes: Buy the camera that has the features you need. Don’t make the type of memory the camera uses the deciding factor. (Okay, so it wasn’t a real product recommendation.)

My digital camera batteries no longer hold a charge. I’m looking for NiCad AAs. All of the places I go to only seem to sell something like NiMH. Can I use them in my camera?

H. Brown Via e-mail

You should be able to use NiMH (Nickel Metal Hydride) batteries. NiMH batteries have replaced the NiCad (Nickel Cadmium) batteries that were used in the past. NiMH batteries offer a greater capacity than NiCad batteries; they also last longer in terms of charge cycles. Lastly, there are less environmental problems associated with NiMH versus the cadmium found in NiCads. (This is why you should never just throw away a NiCad; it should be taken to a battery recycling center for disposal.)

While you can use the NiMH with your camera, you won’t be able to use your old charger; you’ll have to use a NiMH battery charger. The circuitry in your old charger will, at a minimum, shorten the life span of your batteries and, at the maximum, damage the batteries, the charger and anything the charger was sitting on. So get a new NiMH charger with the batteries. And while you’re at it, get three battery sets, so you can have one on the charger, one in your camera and one in your camera bag.

You should mark your batteries, and always use them in sets. Don’t mix batteries that are empty with ones that are half-full in your camera or charger.