Passthrough <filname>.png to <filename>8.png if IE<=6 and <filename>8.png exists

Question

I just found out that by converting PNG32 to PNG8 via Photoshop will fix the PNG transparency bug in IE<=6.

So I had this thought that instead of serving PNG32 to all browser, why not serve PNG8 if the client is using IE<=6.

I'm not really an expert when it comes to htaccess/httpd directives so I'm here for help.

The title is the psuedocode itself.

Answer 1

Put this in your .htaccess

RewriteEngine on
RewriteRule ^/(.*)\.png$ /$18.png [L,QSA]

Should work.

Answer 2

I haven't actually tried this, but I think it should work:

RewriteEngine on
RewriteCond %{HTTP_USER_AGENT} ^Mozilla/4.0\ \(compatible;\ MSIE\ [1-6]\.
RewriteCond %{REQUEST_FILENAME} ^(.+)(\.png)$
RewriteCond %18%2 -f
RewriteRule ^(.+)\.png$ $18.png [L,QSA]

The first line turns mod_rewrite on (and can be omitted if you've already done that). The second does the IE <= 6 filter. The third is mainly to split the filename for the fourth line, which checks to see if <filename>8.png exists. The fifth line actually does the redirect.