A web page with images is almost always more attractive that one with just words. People just love pictures!
Web pages use images in a number of ways:
However, there is a trade-off. The more images on the page and the larger the images are, the longer it will take the browser to show the whole page.
There is a limit to how long people will wait. 30 seconds is an eternity when you are staring at a blank page!!
As a web page author, you must carefully consider the number of images to include, how large they should be, and what image file format to use.
There are three file formats in general use for images on web pages: GIF, PNG, and JPEG. All modern browsers can display these formats. All three compress the file, making the file smaller and thus faster to download. They use different methods so each one is best for a certain type of image.
Uses extension gif. Good for drawings and clipart.
Transparent GIF - Has one color set to "transparent". The page background will show
wherever that color is in the image.
Animated GIF - A sequence of gif images in one file that creates the illusion of motion
Examples of transparent, animated gifs :
The border around the yellow diamond animation shows its actual size. The transparent part of the image lets the page background show through.
Uses the extension png. This is a relatively new compressed image format. It was created to avoid licensing problems involved with the GIF format. PNG images can have more colors than the 256 that GIF images can handle.
Images turn out much like
GIF images do but often have smoother colors and shading.
Can you tell the difference between these two images?
One is in PNG format and one is in GIF format. The PNG image is 801 bytes in size but the GIF is 1740 bytes, twice the size. That is not necessarily true all the time, but it points out that the choice of format can affect file size drastically.
Uses extension jpg or jpeg. Good for photographs.
Not recommended for web use because the image file is large. Browsers can display these images, but you do not normally want to use this format on a web page.
A vector file can display smoothly at any size! Current browsers [May 2014] support this format (IE, Chrome, Firefox) but IE8 and earlier do not.
Examples: The images below use the same original file with different width and height. The apples in SVG format look nice and smooth at any size. The lions in GIF format do not!
SVG Example - Apples: Screenshot below shows one SVG image with displayed different dimensions.
(Some browsers do not display SVG images so the image below is a PNG copy of a screenshot)
Apple: Image courtesy of BeaOriginal
GIF Example - Lions: Enlarging the image by increasing the width and height of the original image works, sort of. But the image is not smooth.
Most images on the web are in color. If you are an artist, you may be disappointed with how your work displays on other computers. The colors will not be quite the same, at best.
Factors affecting color:
Your wonderful graphics, text colors, and background colors will not look exactly the same on different computers. They may not look much like what you intended at all!
Some hand-held or palm-size computers show only gray scale (256 shades from black to white). In the olden days, computers used to show just 256 colors. Sometimes it was just that the owner does not know that the color depth could be changed!
When a browser has to display an image that has more colors than the system can display, it has two choices.
Use the nearest available color.
(This won't quite work if your monitor is using less than True Color.)
Compare the photos below. 256 colors (on the right) just isn't enough to do the job for a photo!
Windows and Mac do not the same 256 colors when set for that number. I expect that this is not often a problem anymore but it certainly used to be a big pain.
The colors that Windows and Mac do share are sometimes called the browser safe colors. Drawings and clipart that use just those colors will look very much the same on different computers. (Artists may not agree, but the rest of us would not notice much difference.)
Photos, however, simply will not display correctly in only 256 colors. They often look like some kind of modern art instead of a photo of reality.
To insert an existing image into a web page:
To create or change an image, or to change the file format of the image:
If you work with web pages a lot, you will want to get a graphics program so you can make changes in your images or even create your own. No matter how many images you have to choose from, none ever seem to be exactly what you had in mind!
A good graphics program will be able to open and save in many image formats, has tools that save you time, and can create advanced effects.
PaintShopPro Does most of what Photoshop does, for a
fraction of the cost. Now owned by Corel.
[It's what I use for images for this site.]
GIMP A freeware graphics program.
Windows Paint: Included with Windows but a bit different for each version of Windows. Limited and a bit awkward but good enough for many situations. Different versions allow different formats.
If all you need to do is change the file format, you can use a graphics conversion program. There are many shareware and freeware programs for this, like Irfan Viewer, which lets you view and then convert images in many different formats. Irfan Viewer is free for educational use. Some of these programs even let you make certain changes like adding text or changing colors. Most will let you assign a transparent color for a GIF or PNG file. You will not be able to make as many changes as you can with a regular graphics program. A simple converter program won't let you create a new image.
The HTML tag for an image is not paired with a closing tag. It has several attributes that are required and others that are optional. The tag below shows the attributes that should always appear: source, width, height, alternate text.
<img src="baseball.gif" width="150" height="157" alt="My
son playing baseball">
This tag has several attributes: SRC, WIDTH, HEIGHT, ALT. The values are the parts between double quote marks. This tag illustrates several of the punctuation rules for all tags.
Quotes: In HTML 4.01 quotes were not required around numbers or values that are chosen from a limited list of values that the standard allows. But, in XHTML and HTML5 quotes are required around all the values. Start a good habit now! No one knows when browsers will fail to render or will even choke on obsolete code.
Ending slash / in a stand-alone tag: This is required for XHTML but not for HTML. Many online documents are required to follow the XHTML rules by companies and governments. Are we ready to be confused??
Deprecated attributes: Some attributes like ALIGN for all tags and BORDER, HSPACE, and VSPACE for an IMG tag were deprecated in HTML 4.01, and are not supported at all in HTML5. These features should be controlled with style sheets.
Losing part of the page: Leaving out punctuation, like a " or < or >, can make part or all of your page disappear from the browser!
Path to the source file for the image. This can be a full path, a relative path, or just the filename.
Full path, like "http://www.worldtravelinc.net/island.gif"
Filename only, like "island.gif". Image must be in the same folder as the HTML page
Should always be the actual size of the image, in pixels.
If you are typing the tag yourself, you will need to find out the true dimensions of the image from Windows Explorer or a graphics program.
Why use actual size?
= a description of what the image is for
Ways ALT text is helpful:
Your ALT text can be very annoying or very helpful. It's your choice.
= Text that will show as a screen tip when the mouse hovers over the image, like title="Example of correct code". Hover over the the butterfly picture to see the title attribute in action.