Re: PNG support in IE4

Ken Sykes (
Wed, 27 Aug 1997 15:14:53 -0700

Message-ID: <>
From: Ken Sykes <>
Date: Wed, 27 Aug 1997 15:14:53 -0700
Subject: RE: RE: PNG support in IE4

One correction: I misread the HTML below.  It will still fail as is.  I
was thinking the internal <IMG> tag had a .png file in it as well.


> -----Original Message-----
> From:	Ken Sykes 
> Sent:	Wednesday, August 27, 1997 3:09 PM
> To:	''; ''
> Subject:	RE: PNG support in IE4
> See comments below
> 			-----Original Message-----
> 			From: Lee Daniel Crocker <
> <>>
> 			To: <> <
> <>>
> 			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 years).
> 			>
> 			>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 thing.
> 			>
> 			>  This fails on IE4:
> 			>
> 			>  <object type="image/png"
> src="/images/test1.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
> correct.  
> 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
> modified
> >for any purpose, without permission, attribution, or
> notification."--LDC