Re: PNG support in IE4

Ken Sykes (
Wed, 27 Aug 1997 15:09:09 -0700

Message-ID: <>
From: Ken Sykes <>
Date: Wed, 27 Aug 1997 15:09:09 -0700
Subject: RE: PNG support in IE4

See comments below
				-----Original Message-----
				From: Lee Daniel Crocker < <>>
<> < <>>
				Date: Friday, August 22, 1997 4:56 PM
				Subject: PNG support (was Entities)
				>> Side question: will PNG images be
added to MSIE so they can be 
				>> included using <IMG> or does one have
to rely on plugins and the use 
				>> of <OBJECT> which is handled in a
buggy manner by most browsers 
				>> (enough to make me avoid using it for
				>The current release of IE4 that I have
supports PNG only in a
				>perfunctory buzzword-on-the-box sense,
but fails to support it in
				>the most natural, useful ways.  In
particular, an <IMG> tag with a
				>PNG src will work with built-in
support, but an <OBJECT> tag will
				>look for a plug-in, even though PNG
support is built in, so you
				>can't do the nested object fallback
				>  This fails on IE4:
				>  <object type="image/png"
				>    <img src="/images/test1.gif">
				>  </object>

The syntax above works properly in current builds but was broken in PP2.
Looking for the plugin is the correct thing to do here as the site
author may want custom behavior for the data.  This is similar to how we
deal with suggested MIME types from the server: if the server specifies
the MIME type we don't second guess based on sniffing.  If the OBJECT
tag doesn't find a plugin the builtin support will take over and render
the image.

>Also, IE4 does not send image/png in its HTTP-Accept headers, so
>you can't do content negotiation either.  Finally, neither gamma
>correction for color matching or partial transparency is supported.
>In short, IE4 may claim to "support" PNG, but the claim is hollow.

We send */* at the end of our accept header list so there shouldn't be
anything preventing PNG files from being sent.  I'm not familiar with
all the issues here but our current list is the result of compatibility
testing over the last 6-12 months.  My understanding is the accept
headers are generally ignored.  We won't be changing the list for IE4,
but if you have comments on accept header processing please pass them on
so we can consider them for IE5.

Gamma correction is supported, go to  PP2 had a bug with greyscale
gamma correction but the current builds render this page completely

We support color-index alpha channel, converting the alpha to 0/non-0
values.  We will also alpha blend against the preferred background color
if it exists.  We do not do general alpha blending.  As all of you are
aware this is not required by the PNG spec - it makes that very clear:

			10.8. Alpha channel processing
			In the most general case, the alpha channel can
be used to composite a foreground image against a background image; the
PNG file defines the foreground image and the transparency mask, but not
the background image. Decoders are not required to support this most
general case. It is expected that most will be able to support
compositing against a single background color, however. 

We recognize the usefulness of full alpha blending and will incorporate
that into our next version of the browser.  Our only concern right now
is finishing the one we are working on.  When that is out I will worry
about full alpha.

>Lee Daniel Crocker < <>> <
>"All inventions or works of authorship original to me, herein and past,
>are placed irrevocably in the public domain, and may be used or
>for any purpose, without permission, attribution, or