.FLYINGHEAD YOUR FIRST DIGITAL CAMERA
.TITLE Megapixels and digital storage media
.AUTHOR David Gewirtz
.FEATURE
.SUMMARY This week, we’re going to finish up our discussion of megapixels and your first digital camera with a short discussion of those little memory cards upon which you store your images.
This week, we’re going to finish up our discussion of megapixels and your first digital camera with a short discussion of those little memory cards upon which you store your images. But before I do, I want to share a comment I got from Tracey Capen, Executive Editor Reviews at PC World:
I was suprised by the information you gave your readers about image compression. All consumer cameras use JPEG by default. TIFF is typically only found on the more advanced models. TIFF files are so big that you’ll only get a few shots on the camera’s media (unless you buy are really large capacity card), and most consumers will not be able to tell the difference between a TIFF file and JPEG. I recommend photographers use TIFF only when saving an edited file on their PC — that way you do not get compression on top of compression.
Obviously, Tracey knows a lot about this stuff. I have seen quite a few digital cameras that support TIFF images, but they are huge by comparison to JPEG. Again, test the results before you buy.
OK, now on to storage media, shown in Figure A.
.FIGPAIR A Here are three different types of memory cards. From left to right: Secure Digital, Compact Flash, and Smart Media.
In my discussions with folks new to digital cameras, I’ve found some elements of confusion about storage media and digital cameras. In part, that’s because the digital cameras work differently than film cameras.
.BREAK_EMAIL To learn how they’re different and to learn about the different types of media, click here.
In a standard film camera, the film itself serves two purposes. Film, of course, is the imaging element itself (i.e., light hitting the film exposes it, creating the picture). Film is also a storage medium, holding typically 12, 24, or 36 pictures per roll.
On a digital camera, the storage medium is typically a memory card. The imaging element is a completely different part of the hardware, something called a CCD (Charged Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor). In this article, we’re only going to be talking about the storage medium.
.H1 Reusable picture storage
If you’ve used film before, you know it’s pretty well a write-once, read-many medium. Let’s assume, for example, you have a 24-exposure roll. After you take your 24 pictures, that roll is used up. You can get it developed, and then you can make a whole bunch of prints from the negatives (assuming it’s negative film), but you can’t take any more pictures using the same roll.
With a digital camera, that’s not the case. To some of you, this might be obvious, but many people I’ve talked to don’t get it on the first try. Memory cards for a digital camera are reusable. After you take your pictures, you can upload your pictures to a computer, erase the memory cards and reuse them.
This is the exact point where a digital camera begins to pay for itself, especially if you’re an avid photographer. If you’re shooting on film, every time you shoot, you need to buy the film and pay for the developing. After a while, it adds up. For me, a typical shoot often costs well in excess of $200-$300. Of course, I shoot a lot of film.
By contrast, as long as you’ve got a big enough memory card, or a few, there’s no incremental cost each time you shoot your pictures on a digital camera. You shoot, using up the card. You upload the pictures to your computer. You then erase and reuse the card. There’s no cash outlay.
Frankly, I’ve long been amazed that this hasn’t been a heavily promoted selling point by the manufacturers. It’s a real, honest-to-goodness, bona-fide benefit.
.H1 The memory card formats
There are a bunch of image storage formats in digital cameras. Three of the most popular are Secure Digital (SD), CompactFlash, and SmartMedia. Sony also offers the Memory Stick format, but that pretty-much runs only on Sony devices, so it’s less of a standard and more of their proprietary game.
This is important, because memory cards don’t just work in cameras. In fact, all three of the formats I’m discussing in this article work in PDAs and MP3 players as well as in cameras. And, some of them work in other devices; in fact the SD Card Association (the trade group for the SD format) claim that SD cards will even store recipes for microwave ovens!
In some cases, the data on the cards is interchangeable from device type to device type, but that’s rare. What’s more common though, is if you buy a bunch of cards of one type, you can use them across a range of your consumer electronics.
For example, I’ve got both an HP Jornada (a Pocket PC) and a digital camera, both of which use the CompactFlash format. Sometimes, I’ll use my 128MB CompactFlash card to hold music and software for my Pocket PC. Other times, like if I’m going out to take some snapshots, I’ll clear off the card and stick it into my camera.
So, one criteria for choosing the format of the card is whether or not you’ve got other devices using the same format. Most PDAs (including Palm) seem to be moving to SD format, so if you’re going to be using a Palm PDA, you may want to consider finding a camera that also uses SD.
There are electrical and performance differences in the formats, but from a consumer perspective, those differences don’t matter. They all function quite nicely. Personally, I’m a tad bit less comfortable with SD because the format is supposed to incorporate some form of digital rights management, but I’ve yet to see that "feature" (a feature designed to hamper our use of the technology, not add to consumer enjoyment) incorporated in cameras or PDAs, so at this time there’s no good reason for me to advise against it.
Another criteria for choosing one format over the other might be price. In reality, though, there’s a great deal of price parity across all the formats (although, given that Memory Stick is a Sony proprietary format, it tends to be a bit more costly).
There is one factor I feel strongly about, but you’re probably not going to read about it in many other magazines: solidity. Figure B shows side shots of the three formats.
.FIGPAIR B You can see the relative flimsiness of each format.
I (and this is strictly a personal opinion) really dislike Smart Media because the cards seem so incredibly flimsy. They’re very thin and very large compared to the other formats. And they have a huge open area where the electrical contacts are made. Whenever I handle one of these cards, I’m always convinced I’m going to break it.
My personal favorite is CompactFlash. While it’s considerably bigger than the postage stamp-sized SD cards, that’s precisely why I like it. I have big hands and I feel more confident I’m not going to lose my CompactFlash cards. I’m always paranoid I’m going to lose the SD cards.
SD is a very nice format, however. If you’re more secure in your ability to handle small things, SD is amazing. And, if you’re going to be a Palm user as well, you might want to make SD your first thought.
.H1 Memory cards and the number of pictures you can take
Now it’s time to harken back to math class, otherwise known as my article, "What the heck is a megapixel?" at http://www.computingunplugged.com/issues/issue200309/00001105001.html. In that article, we discussed the number of megapixels needed to take pictures that could be printed at various sizes. If you don’t remember all the gory details, now would be a good time to go back for a refresher and re-read the article.
It turns out there’s not a direct mathematical relationship between the number of megapixels in an image and the amount of storage space taken up by the resulting image file. That’s because of compression. If you remember all the discussion about lossy and lossless compression from "Understanding how image compression works," at http://www.computingunplugged.com/issues/issue200310/00001115001.html, you’ll recall that the compression algorithms work based on the image itself. This means that an image of a face and an image of a forest might wind up taking up different amounts of space on your memory card.
Further, because many cameras let you set the quality level of the compression, from the "compress-the-crap-out-of-it" low quality compression to "do-your-best-but-try-not-to-compromise-image-quality" of higher quality compression, you can make images take up more or less space as you save them.
Here’s a rule of thumb: try to keep your compression set to high quality and just get a bigger memory card. It’ll result in better images.
And now, another rule of thumb, this time about image sizes. In general, an image taken with a one megapixel camera and saved at high quality will take about a bit under half a megabyte. A similarly high quality image taken with a two megapixel camera will take about a megabyte. And a three megapixel camera image will take a bit under 1.5 megabytes.
So, for argument’s sake, let’s assume you have a 3 megapixel camera with a 64 megabyte CompactFlash card. If each high quality, three megapixel image takes about 1.5 megabytes, then you can divide 64 by 1.5 to get 42.666. This means you can hold approximately 42 (plus or minus a few) images on your card.
But, and now we introduce another nice feature of digital cameras, you don’t always have to save your images at the highest megapixel size. Most cameras save images as small, medium, and large, usually corresponding to one, two, and three megapixel images. And most cameras allow you to save any given image at any given one of those sizes.
This means that our example camera could also save 128 or so one megapixel images on the same 64MB card. Likewise, it could probably store about 20 large images (1.5MB per image x 20 = 30MB). This leaves 34 megabytes for smaller images, or around 68 smaller images, for a combined total of 88 images.
See where I’m going here? You can choose the maximum megapixel size of your camera, but with judicious adjustment of both the size of the image and the compression quality, along with the size of your storage card, you have a wide range of picture storage options available to you.
Take care. Here’s lookin’ at you!
.BIO
