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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 www.luminous-landscape.com/tutorials/understanding-series/res-demyst.shtml">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? www.google.com.au/search?hl=en&q=9+in+in+cm">Try it yourself. Happy pixelling! Steven Pam is a digital commercial photographer based in Melbourne, Australia, specializing in people, aviation and music photography. www.stevenpam.com.au">http://www.stevenpam.com.au
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The Alligator Farm - Home to Beautiful Winged Creatures Your first thought when you read "Alligator Farm" might be "tourist trap," but that could not be more inaccurate. And while the alligators are wonderful and plentiful at the place fondly referred to as the "Gator Farm," it is the birds that attract the world's best photographers. Christmas Rush this Holiday Season to go to Digital Photography So you have rushed out into the malls in a mad panic for this christmas holiday and are going to purchase a electronic item on Credit think again. Consumers are paying again through the nose agin this year 1. Seven Ways for Saving Your Digital Images Forever! So, you have taken lots of pictures with your new digital camera, the memory card is full, and you are wondering how to store and archive your images.1 Buy another memory cardThe method of storing your images with least effort is to buy a new memory card and keep your images on the first card. Infrared Photography and Big City Crime One of the major problems of the larger cities of the word these days is crime. It appears that the larger the city the more-acceptable serious crime seems to be. Selecting Good Stock Photography in the Age of Digital The business of stock photography has drastically changed over the last few years. Ten years ago, selecting photographs for your brochure or newsletter meant spending hours pouring over stock photography catalogs and ordering photo research to find the exact image. Types of Digital Cameras If you are in the market to purchase a digital camera, you have surely seen several different types of cameras. It isnt exactly clear what the differences between the types are, and it can be confusing trying to choose the digital camera thats right for you. Color Management, the Digital Darkroom, and Adobe Photoshop PrefaceIn order to understand color management, it is important to get your hands around some of the workflow. It is also important to understand a little bit about the ICC itself. The Benefits of Disposable Cameras Disposable cameras are cheap and easy to use. If you just want to take some snapshots and have fun then this is the camera for you. The Photography Portfolio: Building Your Reputation If you have hopes of becoming a professional photographer, or even just of trying to get your work published in a public forum, you will need to create a photography portfolio. So what's so important about a photography portfolio anyway?There are many reasons why having a portfolio of your work available for others to view. Take Spectacular Nighttime Photos with your Digital Camera - Part I Night photographs express a special something that cannot be seen in normal daytime photography. Whether it is a photograph of a moon and starlit sky over a windy deserted beach, the excitement of a downtown cityscape when the lights go on, or just a picture of you and some friends in front of a favorite hangout, nighttime photos, when done right, are sure to attract attention. Fuji Digital Cameras Fuji digital cameras entered the market in the late 90's. Started in Japan in 1934, Fuji has always tried to stay ahead of the pack. Cropping Digital Photos Into Shape Did you know that in many cases digital photos are cropped by the time they reach paper? If you have never "cropped" your photos manually, you may not be aware that it is happening.What is cropping?Cropping is the process of trimming portions of the digital image so it fits in the shape of the paper. Memories That Get Lost How many people have pictures in a shoe box? In a drawer? Inside a book? Sitting in the garage?Imagine 40 years from now. Someone will get those pictures and they will say: Who are these people? What are they doing in this boat?They won't have a clue about the stories that those pictures tell and they will probably throw part of your story away. Getting The Right Digital Camera For You There are really great advantages in digital photography:You can shoot till you dropTaking digital images on your camera has no implication other then you have captured the image. Then you can review each image on the small screen on the back of your camera. Magic and the Photograph It was widely reported in the press (15 September 1997) that a British tourist, who stole a lump of stone from the base of the Great Pyramid five years earlier, returned it to the Cairo Museum with a letter saying that 'it had brought him bad luck ever since'. The Museum authorities were not surprised; several such items had been returned by people who felt cursed {When the Luxor Casino was built in Las Vegas it moved on its foundation so the elevators had a lot of re-engineering to be done, while I lived in Las Vegas. Digital Cameras vs. Film Cameras- the debate goes on One of the biggest debates in the photography world is whether digital cameras are better or film cameras better? The answer to this question cannot be answered in a simple yes or no. There are several issues which need to be considered while answering this question. Tips for Purchasing a Digital Camera Lens Your lens is an essential element to good photographs. It's not just your camera. Pinhole Photography: Right Back to Basics Why Pinhole Photography?It's fun. It's creative. Digital Cameras & Resolution While analyzing any camera, one of the most important qualities of a photograph that a person seeks, is resolution. This word itself needs a brief discussion before progressing onto its implication upon a digital camera. The Mysterious Powerful Element of a Picture That Sells A photo buyer calls for a picture of pigs. It could be about anything.
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