All about pixels, megapixels, and image resolution
Feb 15 '01 (Updated Apr 10 '01)
The Bottom Line Digital photography is about balancing three things; file size, information about the picture, and the desired end product. More pixels isn't necessarily better.
A megapixel is a million pixels.
That's about as helpful as knowing that bat guano is a critical ingredient in gun powder. What you need to know is that the "size" of a digital picture is more than the printed dimensions.
HOME, HOME ON THE SCREEN - A MEGAPIXEL IN CONTEXT:
Let's start with the place most digital images are displayed, on a computer screen. You can tell your computer to display the screens and results from your software in a variety of "resolutions." The resolution of your screen is described by the number of pixels displayed across your screen and the number of pixels displayed up and down on your screen. The standard resolutions are: (horizontal x vertical)
640 x 480
800 x 600
1024 x 768
1280 x 1024
1600 x 1200
If you multiply the number of horizontal pixels by the number of vertical pixels, you get the resolution in the kind of number you see attached to a digital camera. So a 640 x 400 resolution image is 256,000 pixels. A 1280 x 1024 resolution image is 1,310,721 pixels... or about 1.3 megapixels. Sooooo... your best monitor resolution is less detailed than an electronic photograph taken with today's average digital camera.
Wow. No wonder you've been getting those HUGE pictures of the new baby's nose. That's the only part of a 3.3 megapixal image that FITS on your 800 x 600 resolution monitor display.
Betcha think we're done now. Hah. It should be so easy. That just explains how they come up with the number the digital camera manufacturer brags about, and why the pictures from your friend's fab new camera look so bad on your computer.
THE FUNCTION OF A PIXEL:
Despite what every ad man employed by Sony, Fuji Film, Olympus, et al would like us to believe... the number of megapixels a digital camera captures isn't the only thing you care about. There are times when more pixels aren't necessarily of value to the average consumer surrounded by twinkling bleeping salesme... er, electronics.
A "pixel" is a tiny container of information about the image in which it lives. Some pixels are "16 bits". That means there are 16 bits of information per (16 bit) pixel, and 32 bits of information per ... well, you get the idea.
Per pixel information includes things like color, location within the image, luminosity, and a whole bunch of stuff that has one of three functions in life:
1) to tell the software how to display it on your screen
2) to tell image editing software what to do with it to achieve those fabulous special effects you've come to love in Cousin Edna's Christmas emails.
3) to tell the software managing a digital printer... how to print the image.
What is important when considering '16 vs 32' bit digital cameras is the impact on file size, and the impact on the end result. A 16 bit megapixel picture contains only half the information a 32 bit megapixel picture. This means it is half as large as the 32 bit picture of an equivalent resolution in megapixels. It also means the 16 bit image has half as much information for an image editing or print program to work with.
Many digital cameras will allow you to adjust the "quality" of the image. What this means is that you can take a 16 bit image and a 32 bit image with the same camera. It also means you can wind up with a grainy looking print because you took a "medium" quality image... and captured fewer bits of information per pixel for that particular digital photograph.
BUYING CAMERAS:
There are three things to consider when buying a digital camera, file size/storage, image information, and the desired end product.
The more megapixels in a digital image, the larger the file. The average 1.3 megapixel image (high quality) is about 480,000 bytes. A high quality 2.1 megapixal image is about 980,000 bytes. A high quality 3.3 megapixel image is about 1.4 MEG PER IMAGE...
The Nikon Coolpix 880 (3.32 megapixel) comes with 8 MEG of flash media storage.
You do the math.
It is rumored that HP sells their inkjet printers at a loss because they make so much money on the print cartridges. This seems to be the digital camera equivalent. File size may seem irrelevant right up to the moment you get to shell out $50 - $80 quid for an extra 32 MEG smart card / memory stick / flash media.
This becomes even more important when you consider your picture taking habits. The more pictures you want to take before downloading them to your computer, the more storage you'll need. If you're on vacation or out for a day at the beach, you'll learn to be very picky about what you keep, or you'll spend a lot of money on storage media.
Naturally there is an alternative, which relates to the second part of your digital camera selection process: the amount of picture information you REALLY need per image... which is directly related to what you want to do with the picture. (the end product)
THE GREAT PICTURE EXCHANGE:
The size of a .jpg version of a digital photo at a print dimension of 8" x 6" at 72 dpi... (or 576 x 432 pixels at 16 bits) is 225,000 bytes. You could fit 4 of these on a diskette. Or, you could attach a copy of the picture to an email without automatically invoking a curse on your house from your ISP or the recipient (barely, this is kind of big for an attachment... you might want to check with the recipient first)
So what do you need with the rest of that image information that is taking up so much space on that pricey little smart card?
WHAT TO BUY IF...
If your primary reason for getting a digital camera is to print out the picture... buy a 35mm SLR with a decent zoom and forget the digital camera. It's just a gadget for you and you're more likely than not to be disappointed in the results.
The majority of people interested in a digital camera, just want to share digital images from computer to computer without much primping and fine-tuning. If this is you, you can safely get by with a 1.3 megapixel camera.
For those of you with a little more cash to throw around, and an interest in image enhancement, start with nothing less than 2.1 megapixels.
And at last... if your primary reason is to gather raw image material to work into large printed works of art... then you NEED that 4+ megapixel Olympus E10 SLR at a mere $2,000. Go for it and bon appetit!
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