Instead of being linked to one
or two filename extensions, a perceived type key could be linked to dozens.
Say you just installed a new image-resizing utility that you??™d like to use with
a variety of photo formats. But rather than make it the default for those file
types, you decide to add a context menu item for each supported file format
(e.g., .jpg, .bmp, .png, and so on). Sure, you can do this for each of the 10 or
so graphic formats it supports, but it turns out that all you need to do is add
it to this key to affect all your image files at once:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\SystemFileAssociations\image\shell\my_
new_program
By default, the image key shown here is linked to all filename extensions
with a PerceivedType set to image, namely .bmp, .dib, .emf, .gif, .ico, .jfif, .jpe,
.jpeg, .jpg, .png, .rle, .tif, .tiff, .wdp, and .wmf.
Windows Vista comes with only five perceived type keys (audio, image,
system, text, and video) out of the box, but you can add your own to the
SystemFileAssociations branch at any time, provided you then link at least
one file extension to it by adding a PerceivedType value pointing to your new
key. The benefit is that you can use this key to add a custom context menu
item that affects a large number of different file types at once. The drawback
is that it??™s one more place you??™ll have to look to track down a misbehaving or
unwanted context menu item.
To break the connection between a filename extension and a perceived type,
just delete the PerceivedType value from the extension key.
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