WML
Images
Wireless
Bitmap (WBMP)
WML
cards can contain images. In the early days, WAP-enabled wireless
devices only supported the Wireless Bitmap (WBMP) image format. WBMP
images can only contain two colors: black and white. Also, WBMP is
not a compressible format, since the processor of wireless devices in
the old days did not have enough computation power and decompression
would result in a long delay. The file extension and the MIME type of
WBMP are ".wbmp" and "image/vnd.wap.wbmp"
respectively.
To
draw WBMP images, a WBMP image editor is needed. The Nokia Mobile
Internet Toolkit comes with a WBMP image editor that you can use.
Besides drawing WBMP images, you can use it to convert other image
formats to WBMP. Just open a GIF or JPG image file with the editor
and it will be converted automatically. Free tools such as
ImageMagick
can also do such kind of thing. However, remember that WBMP images
can only contain black and white colors, which means there will have
detail loss during the conversion of a colorful image to the WBMP
format.
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A
colorful picture before conversion to WBMP.
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The
picture after conversion to WBMP.
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Can a WML Browser
Display Color Images?
A
WML browser can display color images if the image format used is
supported by the wireless device. Currently, most mobile phone models
on the market have color screens and support color images. Commonly
supported image formats are GIF 87a, GIF 89a (animated GIF), JPG and
PNG. Note that the image formats supported are device-specific. Some
wireless devices can only support a subset of the above image
formats.
One
simple way to find out whether a particular image format can be
displayed on a WML browser is to check the accept HTTP header, like
what we have done in the "Choosing
MIME Types Dynamically" section of our XHTML
MP tutorial. For example, if "image/gif", "image/jpg"
and "image/png" are found in the accept HTTP header, it
means the WML browser can display the GIF, JPG and PNG image formats.
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