Once you decide you want or need a digital camera, the first issue
you should address is megapixels (MP). A pixel is a single point on
your screen or in your image. The number of pixels in an image
determines how big you can make it without losing quality.
But instead of starting with megapixels, we need to go back a step
and ask, "What's the largest print you ever expect to make from your
digital camera?" If you want a crisp 8x10, you'll need more pixels than
you would to create a sharp 4x6. And with photo quality inkjet
printers, it's increasingly likely that you'll be printing an 8x10 now
and then.
Once you've determined the maximum image size, you need to determine
how many dots per inch (dpi) will provide the sharpness you need. For
general work on an inkjet printer, I've found that 180-200 dpi is
excellent, although if you're working for high quality magazine or art
book output, you should probably be working in the 250-300 dpi range.
(Don't confuse print resolution with printer resolution.
Most color printers today work anywhere from 300 dpi to 720 dpi. As
long as this number is at least 40% higher than your print
resolution, you don't need to worry about it.)
Let's look at how many pixels some common print sizes need:
size 180 dpi 200 dpi 250 dpi
4x6 720x1080 0.78 800x1200 0.96 1000x1500 1.5
5x7 900x1260 1.21 1000x1400 1.4 1250x1750 2.2
6x9 1080x1620 1.75 1200x1800 2.2 1500x2250 3.4
8x10 1440x1800 2.6 1600x2000 3.2 2000x2500 5.0
8x12 1440x2160 3.1 1600x2400 3.8 2000x3000 6.0
11x14 1980x2520 5.0 2200x2800 6.2 2750x3500 9.6
11x17 1980x3060 6.1 2200x3400 7.5 2750x4250 11.7
12x18 2160x3240 7.0 2400x3600 8.6 3000x4500 13.5
16x20 2880x3600 10.3 3200x4000 12.8 4000x5000 20.0
There's a little leeway here, but even a 2 MP camera should be
adequate for top quality prints up to 4x6 - even in high quality print
publications! For the average home user with a color inkjet printer,
entry-level 1.3 MP cameras did fine at 5x7 and 2 MP cameras can
produce a sharp 6x9 - but you really want a 3 MP camera to get
that nice sharp 8x10.
If you plan on going larger than that, keep in mind that larger
prints are generally viewed from a bit farther away, so you can use the
180 dpi column as your guide for 11x14 and 11x17. That 5 MP
digicam can produce a very nice 11x14, and 6 MP cameras can
produce very nice 12x18 prints. But if you want to go to 16x20s,
they're a bit out of your reach at 5-6 MB unless you resort to
sharpening your image in Photoshop. This is where 8 MP and better
cameras come into play.
Online Images
What about images for the Web? Compared with even a 4x6 print, Web
images are tiny. Even a high resolution 1280x1024 screen is just 1.2
MP, and since your pictures will tend to be a lot less than full
screen, a sub-megapixel cameras could be adequate if all you need is
Web output (then again, most sub-megapixel cameras, such as those built
into mobile phones, have so many other compromises that you'll want a
better camera).
Don't be afraid to get a camera with more pixels than you need,
either. That will give you room to crop and manipulate the print with
minimal loss of detail. Remember, you can always make a picture
smaller, but you can't put in detail that wasn't there to begin
with.
That said, there are a couple of drawbacks to excessive megapixels.
The first is that the images take up more storage space on your memory
card and hard drive - and take longer to write to your memory card. The
second is that especially with smaller point-and-shoot digicams
dividing a small image sensor into more and more pixels means more
unwanted noise in your images.
Based on all this, I usually recommended that most of my customers
start by looking at 3 MP cameras, and five years after writing this, I
almost always shoot my 5 MP and 8 MP digicams at the
3 MP setting.
Go to Picking a Type of Digicam.
