Issues Concerning
Large Images in XHTML MP
Many
WAP browsers do not have horizontal scroll functionality. So, if the
width of an image is larger than that of the wireless device's
screen, many WAP browsers will crop off the image, which means your
XHTML MP page may not look nice and professional to your users. The
following example shows how an XHTML MP page with a large image will
look on some mobile phone browsers:
(imageEg2.xhtml)
<?xml
version="1.0"?>
<!DOCTYPE html PUBLIC
"-//WAPFORUM//DTD XHTML Mobile 1.0//EN"
"http://www.wapforum.org/DTD/xhtml-mobile10.dtd">
<html
xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Image
in XHTML MP</title>
</head>
<body>
<p>
<img
src="smileBig.gif" alt="Smile" height="159"
width="160" /><br/>
Welcome to our XHTML
MP tutorial.
</p>
</body>
</html>
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Sony
Ericsson T610
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Nokia
Mobile Browser 4.0
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Another
issue that you have to concern is that the image size will affect
your mobile Internet site's performance. Using the <img> tag's
height and width attributes to scale down an image does
not help improving the performance since the actual file size of the
image is still the same.
Also,
a larger image will cost more money for those who visit your mobile
Internet site using GPRS, since cellular network operators charge
their GPRS service subscribers by the amount of data transmitted
through their cellular network.
It
is essential to optimize the images in your XHTML MP pages so as to
keep the image size small. There are several ways to do so:
Using
an image manipulation program like GIMP and Photoshop to scale down
the images, instead of sending a large image to the wireless device
and reducing the image's rendering size with the height and
width attributes of the <img> tag.
If
the images are GIF files, you should use a small palette. A smaller
palette can mean lower image quality, so you have to take a balance
between the two.
If
the images are JPG files, you should save them in a suitable
compression ratio. A higher compression ratio will result in a
smaller file size but a lower quality. So, you have to take a
balance between the two.
Another
way that can help improving the performance of your mobile Internet
site is to use multipart messages. Normally when a user requests an
XHTML MP page that contains images, the WAP browser first loads the
XHTML MP document and then loads the images in separate requests.
This means to load the whole XHTML MP page, several requests have to
be made. Multipart messages allow you to place the XHTML MP document
and the images in the same response, which means the whole XHTML MP
page can be loaded with only one request. This minimizes the number
of trips to the server. The details about how to construct a
multipart message are out of the scope of this tutorial. You have to
find other sources on the web if you are interested in it.
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