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MARCH 2008 • VOL 2 • ISSUE 3

Digital Cameras Close Up

I was all set to give you the skinny on digital cameras and megapixels and all that stuff. So, I did a search on 'What are megapixels?' to be sure I knew what I was talking about and what do you think I found? An article by a photographer debunking the importance of megapixels and explaining how they are basically a ploy of camera manufacturers to get you to spend thousands of dollars on a camera you don't really need. You can read the article for yourself at: http://www.kenrockwell.com/tech/mpmyth.htm.

Aside from that, it may still be valuable to share some the technicalities of digital cameras that are good to know, regardless of your camera's pixel output. Mr. Rockwell had a good recap of these facts so I'll summarize his comments here:

PIXELS, RESOLUTION and PIXEL COUNT (MEGAPIXELS)

Pixels

Digital images are made up of little dots called pixels. Pixel stands for PICture ELement. Put enough of them together and you have a picture. They are arranged horizontally and vertically. You'll see them if you get close enough to your computer screen (and your eyes are good enough).

Resolution (Linear Resolution)

Image Resolution

Resolution is how many pixels are counted horizontally or vertically when used to describe a stored image. Digital cameras today have between 2,048 and 4,500 pixels horizontally. 3 MP cameras have 2,048 pixels horizontally and 14 MP cameras have 4,500 pixels. They have fewer pixels vertically since the images aren't as tall as they are wide.

Print Resolution

Resolution is also how many pixels you have per inch or other linear unit when you print on paper. Most prints are made at 300 pixels per inch (PPI or DPI, dots per inch) and up. This is the image resolution and has nothing to do with the technology by which the print is made. (For instance, some inkjet printers' nozzle sizes are 2880 DPI. This only refers to how the ink is applied to the paper.

Screen Resolution

The resolution of most computer screens today is between 72–100 DPI. It's easy to figure out: most computer screens are about 1,024 x 768 pixels. If your screen is 10" wide then divides 1,024 by 10 and you have a 102.4 DPI screen. Bigger screens tend to have more pixels, for instance, a 22" CRT has 1,600 x 1,200 pixels and has a viewing area of 16 x 12."

Pixel Count, expressed as Megapixels

Pixel Count, expressed as Megapixels, is simply multiplying the number of horizontal pixels by the number of vertical pixels. It's exactly like calculating area. A 3 MP camera has 2,048 (horizontal) x 1,536 (vertical) pixels, or 3,145,728 pixels. We call this simply 3 MP.

Small differences in pixel count, between say 5 MP and 8MP, are unimportant because pixel counts are a square function. It's exactly like calculating area or square footage. It only takes a 40% increase in linear dimensions to double the pixel count! Doubling pixel count only increases the real, linear resolution by 40%, which is pretty much invisible.

Here's an easy reference chart, courtesy of Andrea Steed.

Megapixels

Image in
Pixel Size

Pro Quality
Print Size
2.0 1200 x 1600 4" x 6"
3.0 1500 x 2100 5" x 7"
4.0 1800 x 2400 8' x 10'
5.0 1900 x 2500 9" x 12"
6.0 2000 x 3000 11" x 14"
8.0 2000 x 4000 12" x 16"