• a man with a pencil
• lab home page
• experiments
  • browser bugs
    • conditional comments bug
    • Firefox DHTML bug
  • centre a page
  • cross-browser PNG alpha
    • introduction
    • JavaScript: image swap
    • JavaScript test page
    • PHP: targeted content
    • PHP test page
    • conclusion
  • IE: opacity and image loader filters
  • dynamic form elements
  • forms without tables
  • IE tool tips
• musings
  • blinkin' Firefox
  • HTML email in Apple's Mail
• background
  • browser detection
  • conditional comments
  • trinity

Comments or questions?
Please contact me.

©2006, Nigel Moore.

Conclusion

• Introduction
|
• JavaScript: image swap
|
• JS test page
|
• PHP: targeted content delivery
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• PHP test page
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• Conclusion

Two methods have been presented for supporting 24-bit PNG images with alpha transparency in Internet Explorer versions 5.5 and 6.

Both of these methods assume that if a browser is not IE5.5 or IE6 then it can handle PNG alpha transparency correctly. This is true for modern browsers, but some other older browsers (e.g. IE4) will not show the images as intended. The scarcity of these browsers means that ths is probably a minor issue for most cases. However, where this is not the case, the PHP script could be adapted to search more extensively within the user agent string, and deliver GIF images to those browsers.

The choice of method will depend upon the circumstances in which it's deployed:

• Support for server-side scripting
• Reqirement for client-side JS support
• Need to support IE5.0 for Windows (favours the PHP approach)
• Need to serve alternative image formats to other browsers (favours the PHP approach)
• Balancing download speed against delay in screen display (favours the PHP approach)