By David Gewirtz
Last week, I wrote a quick piece about getting started with digital photography. The response from readers was absolutely astounding. In fact, I believe we've gotten more letters about that short article than any other we've ever published (except, perhaps, my political commentaries, which managed to piss off 49.9% of the U.S. population).
There were so many questions, comments, and great ideas that we've probably got material for a year's worth of tips. In fact, we've started talking about spinning out a digital camera publication just because of that response. If that's something you're interested in, send me a note at david@ZATZ.com and let me know.
Needless to say, I can't answer every question this week. Next week, we're going to flip back to PDA coverage for a review of some new, hush-hush devices that are pretty exciting. We're also going to continue our discussion of megapixels and camera choice. That said, I suspect we'll be adding more and more digital camera coverage, because it's clearly a topic that's got you interested.
Sifting through the letters, the biggest theme was one of confusion. Many of you asked what camera should you buy and many others told me you were confused by all the specs. Rather than going through individual cameras and recommending them (they change each week), I'm going to help you understand what makes these cameras tick.
The place to start is megapixels.
Since the megapixel count is a simple number, and that number seems to correlate to price, it seems easiest to choose based on this measure. In reality, you'll also want to choose a camera based on its optics, menu system, available storage, responsiveness, and picture quality.
Today, however, we're going to talk megapixels.
Understanding pixels
Let's start off by defining a pixel. The word "pixel" is actually a shortened form of the phrase "picture element." A picture element is, in the computer world, basically a dot. As you know, computer screens (and digital camera images) are made up of grids of dots. Today, a typical computer screen has 1024 dots across by 768 dots down, although older screens have less and gamers often punch their screens up to higher resolution.
Each dot, or each pixel, contains color information. Let's take a look at a simple picture, shown in Figure A.
FIGURE A
Here's an example of how pixels contain color information. (click for larger image)
You can see the original image in the upper left side of the figure. When the image is enlarged, you can see each individual pixel, and you can see that each pixel is basically a square (some devices use slightly different shapes) containing color information.
Here's a simple rule of thumb: the more pixels in a given space the more detailed the image.
You can see this clearly by comparing the little picture to the big one. They're the same image (well, Ok, I cropped out much of the flower pot in the expanded image) but because the little picture has all those dots in a tiny space, the picture looks much more like flowers and a lot less like a quilt of colored squares.
This is the essence of digital photography: your eye blurs dots that are really close together. And understanding the relationship between the number of dots and the quality of the image will make everything a lot more clear (pun intended).
What the heck is a megapixel?
Now that you understand what a pixel is, let's move on to megapixels. Technical, megapixel refers to a million pixels. Before you jump up and down and think that's a lot of pixels, let's see what that really means.
It's all about math. Time for a simple math quiz. Honestly, it's simple, so no freaking out. OK? OK.
If you have 1024 pixels across your screen and 768 pixels down, how many pixels do you have all together? Well, you multiply 1,024 times 768 and you get 786,432 pixels. That's not quite a million pixels, but it is close.
Here's observation number one: if you just want a picture that'll look good on your screen, and your screen is 1024x768, a 1-megapixel camera is just fine.
When the camera manufacturers describe their cameras by the number of megapixels, then, they're really describing the number of picture elements that make up the pictures the camera takes. And they're talking, generally, about pictures in a 1.3 to 1 ratio. In other words, for every one pixel down, there's 1.3 pixels across. This makes sense. There'd be no use for a camera that takes a picture a million pixels long, but only one high.
The relationship of pixels to printing
If all you want to do is make wallpaper for your desktop, you really don't need to know any more. But if you want to print your pictures, maybe put them on your wall, you'll need to know about how printing resolution is measured.
By the way, lots of you asked about printing pictures yourself vs. using a service bureau. I'll talk more about that in another piece, but the short form is I tend to like printing them myself. Details on how to do it right will be another week.
In order to understand the relationship of pixels to printing, we need to know another term: dots per inch (or DPI). If you think about it, DPI makes a lot of sense. It's the number of dots in a given inch of the image. Most computer screens display 72 to 100 dots per inch.
The monitor I'm using right now is a 17 inch display, measured diagonally. That means it's about 13.25 inches across the top and 10.5 inches down. You may remember something called the Pythagorean Theorem that helps you determine the length of the diagonal if you know the length of the two sides. I'm trying to avoid math class here as much as possible, so I won't bore you with all the details.
In any case, my screen is 13.25 inches long as displays 1,024 dots in that space. Dividing 1,024 by 13.25 tells us that my screen displays 77.28 dots for every inch of screen space. In effect, my screen is 77.28 dots per inch.
With me so far?
Printers, these days, print at resolutions above 300 dots per inch, although I've found that often, anything about 220 or so seems fine. For the purpose of our discussion, though, let's use 220 dots per inch as a minimum and relate that to print size.
Here's another math quiz. If you want to print out a 5x7 picture, how many megapixels do you need?
Start with the dots per inch. At 220DPI, there are 1,100 dots in five inches (220x5). Likewise, there are 1,540 dots in seven inches because 7 times 220 equals 1,540. Multiply 1,100 times 1,540 and you get 1,694,000 pixels in the image.
The next step is easy. 1,694,000 pixels is 1.6 megapixels. To print out a nice 5x7 image, you'd need a camera capable of 1.6 megapixels, which, in practice, means you'll get a 2 megapixel camera.
If this stuff still doesn't make sense, re-read the above paragraphs a few times. It's really the dots that fit in the space, multiplied out.
Thinking about megapixels
Now that you know about megapixels and a little about printing, let's learn how to think about what this means for your camera and your usage.
Here are some simple rules of thumb:
- If all you're ever, ever going to do is put the pictures on your Web site, on eBay, or email them to friends, you really don't need much more than a 1 megapixel camera.
- If you're going to print your images, you need to determine the largest size you want to print, then do the math.
- If you're going to want to crop your image, or extract a portion of the picture to print, you'll need to do the math for the area you want to crop.
And it all was so clear until now, huh? Let's examine those last two points in further detail.
I'm a photographic artist and I like to print out my images, frame them, and put them on my wall. My pictures are usually 8x10, but they often go as high as 13x17 and as small as 5x7. If you're like me, you'll want to have a camera that's up there in the megapixels -- or wait and keep using film.
If you're likely to only want to print 5x7 images, then, as we showed above, a 2 megapixel camera is fine. If you're likely to want to print 8x10 images, then a 3 megapixel camera is fine.
If you're an artist or a professional, and you're going to twiddling with the dots per inch on your printer for maximum quality, you will also probably want a higher-end camera.
I'm already way above my word-count limit for this article, so you'll have to wait until next week to learn about cropping and how to plan for it with your first digital camera.
Stay tuned.