Monthly Archives: April 2013

What Image Type is Best?

Picture of cute dog

Obligatory cute dog

In the last post, we learned some reason why your computer saves images in different formats. But that doesn’t help us do anything about it. This post will be short and sweet — a table of the different file types we’ll cover in future posts, when you want to use them, and when they fall short. I’ll even give you the tl;dr version: use JPEG to send pictures of your cute dog to Aunt Sally.

File Type Strength Weakness
JPEG Photos, especially for viewing on screens Line art and high-resolution printing
GIF Images with very few colors, such as logos and line art Photos, or anything that needs more than 256 colors
PNG Images where you want transparent areas Not good at photos, not all cell phones can display these
RAW Photos where you want loads of detail, such as printing poster-sized images Files are huge, often takes special software to display
TIFF Photos with lots of detail Files are huge, fewer and fewer photo sharing sites are supporting this format

 

Photos and Your Computer: The Basics

Besides surfing the web and sending email, one of the most common reasons for people to get a computer is pictures. Whether it’s scanning old photos to share, uploading digital pictures to an online photo album, or sending your camera phone pictures to Facebook, just about everyone has some use for digital pictures. There are a lot of good photo editing software packages out there that make common adjustments to photos easy to do. But with that software often comes a bewildering choice — what format to save the end result in?

First we need to know a little bit about digital photos. Digital photos are made up of a grid of little dots called pixels. If you’ve seen a photo say that it’s 400 x 300, that means it’s 400 dots across and 300 dots high. When the dots are small enough, our eyes blend it all into one smooth picture. Each of those dots has a number associated with it that also tells the computer what color the dot is and how bright that color is. There are different ways to code the color and brightness information, but it still comes down to storing a number for that pixel.

So why do we have different formats? It all comes down to size.

Let’s say you have a 5 megapixel camera. Not very large as cameras today go. 5 megapixels is 5 million pixels. Each of those pixels has a number associated with it. My digital camera stores the color information in about 2 bytes of data per pixel, which means each picture is about 10 megabytes in its raw format. If I want to email a dozen pictures to a friend, especially a friend with a slow internet connection, they aren’t going to be very happy about the size of those photos.

What can be done? Well, a lot of pictures have relatively large patches of the same color. Your computer might notice that there are 100 pixels in a row of blue sky. So instead of storing the number for sky blue 100 times, it make a notation of the color and that it will be repeated 100 times — storing just two pieces of information instead of a hundred. This is called compression and it makes the file smaller, making everyone is happier.

Naturally, it’s not quite that easy in real life. We might think the sky is just blue, but each pixel might be just one shade of blue different from the next pixel. Now instead of saying we have 100 pixels of sky blue, your computer starts storing twice as much information as the original, because it is storing a color, saying it repeats for a single pixel, storing another color, saying that repeats for another pixel, etc.

What to do? This is where the different formats come in. Each format has strengths a weaknesses — one format may make the photo’s file size smaller, but at the cost of quality. Another format may have a special feature or two that are really useful in some situations and not others. In the next few posts we’ll go over some of the common formats, where they excel, and where they fall short. Then when you are faced with a choice of formats, you’ll be confident you’re choosing the best one for your needs.

Web 101: When Cookies Go Bad

We learned in the last post that cookies can make the web more useful and more fun. But cookies can have a darker side, too. Here we’ll learn about the seedier uses of cookies and what you can do about them.

If you already have a cookie from a website and you revisit that website, your browser only sends the information for that website’s cookie. So if you’re at Amazon, your browser only sends the Amazon cookie information and not the Ebay cookie information. There are a couple of exceptions to that rule, and this is where cookies cause problems for most people.

Lots of web sites contain advertisements. This isn’t normally a bad thing — the ads pay for the costs associated with the web site and make it possible for lots of free content to be out there for you. However, those ads are served up by a different domain than the site you’re on. If you’re visiting example.com, the ads might come from advexample.com and spamsalot.com. Both of those advertising domains can then put what are called “third-party cookies” into your browser. Later on, when you go to anotherexample.com, which also has an ad from advexample.com, that advertiser not only knows it’s you, but knows you recently visited example.com. These advertising cookies can track you across the web, and are the reason why after visiting a site selling shoes you suddenly start seeing lots of ads for shoes on other sites.

Some people really like having more targeted ads — if you have to see ads anyway, they may as well be for something you’re interested in. Other people find this tracking to be a bit creepy. If you’re in the latter group, there’s an easy fix. All the major browsers let you block any third-party cookies. (You can also use these same instructions to block all cookies.)

You probably already have a lot of tracking cookies stored in your browser. If you want to get rid of those, too, there are a couple of ways to do it. You can either go through your existing cookies one by one, or you can delete all your existing cookies. Deleting all your cookies is a lot faster than trying to figure out which ones you want and which ones you don’t, but it does mean you will need to sign in to any web sites again.

Deleting tracking cookies doesn’t stop all forms of tracking, but currently this is the most common form used. And now you have some control over the process.