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 Images Lesson

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PostSubject: Images Lesson   Thu May 20, 2010 7:33 pm

Lesson : Images


Wouldn't it be great if you could have an image of actor and music
legend David Hasselhoff right in the centre of your page?
That sounds like a bit of a challenge...


Maybe, but in fact it is pretty easy to do. All you need is an
element:

Example 1:

Code:

<img src="david.jpg" alt="David" />




would look like this in the browser:





All you need do is first tell the browser that you want to insert an
image (img) and then where it is located (src,
short for "source"). Do you get the picture?
Notice how the img element is opened and closed using
the same tag. Like the
tag, it is not tied to a
piece of text.
"david.jpg" is the name of the image file you want to insert in your
page. ".jpg" is the file type of the image. Just like the extension
".htm" shows that a file is an HTML document, ".jpg" tells the browser
that a file is a picture. There are three different types of image file
types you can insert into your pages:

  • GIF (Graphics Interchange Format)
  • JPG / JPEG (Joint Photographic Experts Group)
  • PNG (Portable Network Graphics)


GIF images are usually best for graphics and drawings, while
JPEG images are usually better for photographs
. This is for two
reasons: first, GIF images only consist of 256 colours, while JPEG
images comprise of millions of colours and second, the GIF format is
better at compressing simple images, than the JPEG format which is
optimized for more complex images. The better the compression, the
smaller the size of the image file, the faster your page will load. As
you probably know from your own experience, unnecessarily 'heavy' pages
can be extremely annoying for the user.
Traditionally, the GIF and JPEG formats have been the two dominant
image types, but lately, the PNG format has become more and more popular
(primarily at the expense of the GIF format). The PNG format
contains in many ways the best of both the JPEG and GIF format: millions
of colours and effective compressing
.

Where do I get my images from?


To make your own images, you need an image editing program. An
image editing program is one of the most essential tools you need to
create beautiful websites
.
Unfortunately, no good image editing programs comes with Windows or
other operating systems. Thus, you might consider investing in either
Paint Shop Pro, PhotoShop or Macromedia Fireworks, which are three of
the best image editing programs currently on the market.
However, as we said before, it will not be necessary to buy expensive
programs to complete this tutorial. For now, you can download the
excellent image editing program IrfanView
which is so-called freeware and therefore costs nothing.
Or you can just borrow images from other sites by downloading them.
But please be careful not to violate copyrights when downloading
pictures. Still, it's useful to know how to download pictures, so here's
how you do it:

  1. Right-click on an image on any image on the Internet.
  2. Choose "Save picture as..." in the menu that appears.
  3. Choose a location for the image on your computer and press "Save".


Do this with the image below and save it on your computer at the same
location as your HTML documents. (Notice that the logo is saved as a
PNG file: logo.png):



Now you can insert the image into one of your own pages. Try it
yourself.

Is that all I need to know about images?


There are a few more things you should know about images.
First, you can easily insert pictures located in other folders, or
even pictures that are located on other websites:

Example 2:

Code:

<img src="images/logo.png" />




Example 3:

Code:

<img src="http://www.html.net/logo.png" />




Second, images can be links:

Example 4:

Code:

<a href="http://www.html.net">
<img src="logo.png" /></a>




will look like this in the browser (try clicking on the image):





Are there any other attributes I should know about?


You always need to use the attribute src, which tells
the browser where the image is located. Besides that, there are a number
of other attributes which can be useful when inserting images.
The alt attribute is used to give an alternate
description of an image if, for some reason, the image is not shown for
the user. This is especially important for users with impaired vision,
or if the page is loaded very slowly. Therefore, always use the alt
attribute:

Example 5:

Code:

<img src="logo.gif" alt="HTML.net logo" />




Some browsers let the text of the alt attribute appear as a small
pop-up box when the user places their cursor over the picture. Please
note that when using the alt attribute, the aim is to
provide an alternative description of the picture. The alt
attribute should not be used to create special pop-up messages for the
user since then visually impaired users will hear the message without
knowing what the picture is.
The title attribute can be used to add information to
the image:

Example 6:

Code:

<img src="logo.gif" title="Learn HTML from HTML.net" />




Will look like this in the browser:





If you, without clicking, place the cursor over the image, you will
see the text "Learn HTML from HTML.net" appear as a pop-up box.

Two other important attributes are width and height:

Example 7:

Code:

<img src="logo.png" width="141px" height="32px" />




will look like this in the browser:





The width and height attributes can be used
to set the height and width of an image. The value that is used to set
the width and height is pixels. Pixels are the units of measurement used
to measure the resolution of screens. (The most common screen
resolution is 1024x768 pixels). Unlike centimetres, pixels are relative
units of measurement which depend on the resolution of the screen. To a
user with a high screen resolution, 25 pixels may correspond to 1
centimetre, while the same 25 pixel in a low screen resolution may
correspond to 1.5 centimetres on the screen.
If you do not set the width and height, the image will be inserted in
its actual size. But with width and height you can manipulate the size:

Example 8:

Code:

<img src="logo.gif" width="32px" height="32px" />




will look like this in the browser:





However, it is worth keeping in mind that the actual size in
kilobytes of the image file will remain the same so it will take the
same time to load the image as it did before, even though it appears
smaller on the screen. Therefore, you should never decrease the
image size by using the width and height attributes
. Instead,
you should always resize your images in an image editing program to make
your pages lighter and faster.
That said, it is still a good idea to use the width and height
attributes because the browser will then be able to detect how much
space the image will need in the final page layout before the image is
fully downloaded. This allows your browser to set up the page nicely in a
quicker way.
That's enough about David Hasselhoff and images for now.

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