Can opacity of images be considered to be well supported in almost all browsers?

There is a design where a button need to be made "more invisible", either by creating another image with brightness +192 or +212, or we can use CSS's opacity to simulate the same effect.

It seems that with the special situation of IE (6, 7, and 8+), the fol开发者_开发技巧lowing:

opacity:0.2; filter:alpha(opacity=20)

can make the opacity happen in almost all browsers, including IE 6? So really, there is no need to add one more image, but just using CSS is good enough?

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According to this example you can do more. Especially for IE8:

/* IE 8 */
-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";

More info why MS did it this way in article Opacity rettuns to IE8