Maintain your old Siemens Hipath system

Digital Image Files ? Megapixels, Megabytes, or DPI?

When I promised readers that I was going to do an article on this topic I was scared. For two reasons - firstly, it's a HUGE subject. I get lots of questions about it, and I see a fair bit of misunderstanding about it. Secondly, there are already a lot of good articles about it on the web, like this one on luminous-landscape.com.

But I know that trawling the internet for technical information is not your idea of fun. That's my job! So here's my attempt at summing this up quickly for you:

DPI - Dots Per Inch

The most common question I get on this topic is, "My client / boss / nephew has asked me to send an image at a size of 300 dpi. What does that mean"?

The answer: Not much.

You see, DPI stands for Dots Per Inch. It's a useful measure of image resolution (in other words, how much information is resolved in the picture). But if you don't know the image size in inches (or feet, miles, centimetres, millimitres, or some other measure of size), then the amount of dots per inch doesn't mean much.

Using DPI to measure size is like using km/h to measure distance: "How far is it from here to the beach?" "Oh, about 60 miles per hour". For this to make sense the answer would need to be "about 10 minutes at 60 miles per hour".

Likewise, the size of an image needs to be expressed as, say, "six by six inches at 300dpi".

Different resolutions are used for different purposes. The most common are 72 or 75 dpi for screen viewing (Web use or PowerPoint presentations) and 300 dpi for printing.

OK, so to give an example - 1 inch by 1 inch, 300 dpi image would be 300 pixels by 300 pixels in size. A 2 by 2 inch image at 300 dpi would be 600 by 600 pixels in size. Here's where megapixels and megabytes come into it. Mega!

Megapixels

The term megapixels is usually used to describe the output size of digital camera images. For example, the Canon Ixus 50 produces images which are 2592 x 1944 pixels in size. Multiply these numbers together and you get 5,038,848 - just over 5 million. Hence this is described as a "5 megapixel" camera.

The last byte

On a couple of occasions, I've sent an image of a certain size to someone and they've said, "that's no good, we need a 10 megabyte file". Now, this I'm sure they were well-intentioned but they were also a little misguided.

The size in bytes (or megabytes - millions of bytes) represents how much storage the image takes up on your computer. This depends on all sorts of things, mainly the bit depth of the image and the file format - for example TIFF or JPEG.

So what should I do?

To avoid confusion, when specifying the file size you need, use pixels.

How do you work out how many pixels you need? Well, that's why I started this discussion with DPI. Work out the largest size you're going to want to reproduce the image, in inches; and the resolution - for example 72 dpi for or 300dpi for most print applications. Then just multiply the size in inches by the DPI figure you came up with.

Example: I want to reproduce the image A4 size in a printed magazine. A4 is 210mm x 297mm, or about 8.3 x 11.7 inches. The magazine needs artwork at 300dpi, so:

8.3 x 300 = 2490 and 11.7 x 300 = 3510 so I need an image sized about 2490 x 3510 pixels (about 8.7 megapixels)

By the way: 1 inch = 2.54 centimetres. Did you know you can also do conversions on google? Try it yourself.

Happy pixelling!

Steven Pam is a digital commercial photographer based in Melbourne, Australia, specializing in people, aviation and music photography. http://www.stevenpam.com.au

In The News:


Warning: simplexml_load_file() [function.simplexml-load-file]: http://feeds.skynews.com/feeds/rss/world.xml:1: parser error : Document is empty in /home/infob/public_html/includes/rss.php on line 2

Warning: Invalid argument supplied for foreach() in /home/infob/public_html/includes/rss.php on line 9


tikatoshop.it

Erfahrungen mit Pallhuber Wein
Agen Bola SBOBET Terpercaya

Travel in comfort and at your leisure with CT Airlink Limousine & Car Service for top quality private transportation and exceptional customer service. We operate Sedans, SUVs & Vans for CT Car Services to covering all Connecticut airports including Car Service from CT to Newark Airport , Mohegan Casino Uncasville CT, Foxwoods Casino Mashantucket CT, Manhattan Cruise Terminal NYC, Brooklyn Cruise Terminal NYC and Bayonne Cruise Terminal NJ. CT Airlink hire licensed and friendly chauffeurs who have in-depth knowledge of the Areas.

Top of the Line Digital Cameras

If you think that digital cameras are for snapshots only,... Read More

Applications of Underwater Video Cameras

There's so much you can do with an underwater video... Read More

Online Photo Sharing: Not Just for Family and Vacation Photos

You may have joined the photo-sharing craze to share your... Read More

Tiny Cameras, Big Pictures and Make Your Photos Great!

The path to picking a digital camera usually leads to... Read More

Review of the Photek Product Shooting Tent

Here's the challenge. You have to photograph small items for... Read More

HP Digital Cameras - History and Beyond

HP has started making digital cameras only recently. However, the... Read More

Christmas Rush this Holiday Season to go to Digital Photography

So you have rushed out into the malls in a... Read More

Infrared Photography and the Car Thief ? Successful Digital Imaging

Infrared photography is sometimes placed on the outside edge of... Read More

Digital Camera Reviews and Ratings De-Mystify the Choices

Shopping for a new digital camera can be quite frustrating... Read More

Passionate Organizing: How To Create A System To Organise Your Digital And Traditional Photos

Digital photography promises much. Store your photographs on your computer,... Read More

The Venice Rookery

Love is in the air at the Venice Rookery. The... Read More

Choosing The Right Digital Camera

Let's get something straight right out of the box. If... Read More

Nude Art Photography

Nude photography is the genre of art photography, whose subject... Read More

Digital Camera Batteries

Every device needs a driving force to operate, just as... Read More

The Well-Dressed Photographer - Summer

Outdoor photographers shoot year round. That includes the hot summer.... Read More

The Best Wildlife Camera To Take On Safari

Good wildlife camera equipment on safari can make the difference... Read More

Easy Tips for Digital Photo Touchups

Using a digital camera to take pictures is great. It's... Read More

Photography 101 Part 2

Basic CompositionNow that you are beginning to understand how your... Read More

Portrait Photography: Tips and Methods

Portrait is defined as, "A likeness of a person, especially... Read More

African Safari Photography Best Five Destinations

Good wildlife safari photography is not only about composition and... Read More

Start Up a Nude Photography Business

There are major obstacles to overcome to get into nude... Read More

9 Tips For Taking Great Digital Photos

IntroductionModern cameras are highly automatic in operation. They have auto... Read More

Getting Rid of Red Eye

The photos you took of the party are really great... Read More

The Paradigm: Going Digital

As you might imagine the paradigm shift from traditional film-based... Read More

Taking Professional Quality Pictures

By now I'm sure you've used Either a digital or... Read More