I encountered a situation in the project that troubled me for a long time. Why did some icons of the same PNG8 image disappear in IE6? At that time, I suspected that it was a cache or hosts problem. Repeatedly opening and closing the browser still failed, and after repeated tests, I finally found the cause.
The problem lies in the PNG8 image itself. The following example simulates the situation. When browsing using IE6, you will find that the four icons in the second row are invisible. Demo
It turns out that the four icons below have been adjusted to 90% "Alpha transparency" (FW can retain "Alpha transparency" when exporting PNG8, but PS cannot do this).
The icons that are translucent by Alpha can be browsed normally in general browsing software or FF, Chrome, Safari, Opera, IE7 and above browsers, except IE6.
In fact, there is a way to make IE6 support PNG8's "Alpha transparency", the method is the same as the PNG32 IE filter. Demo
From the above results, we learned that it was png8 "Alpha transparency" that caused the problem. And this time PNG8 is different from png32 in that browsers that do not support png translucency (such as ie6) will automatically downgrade to fully transparent (like gif), instead of having a gray background like png32.