Re: JPEG-XL as Content-Encoding?

Mark Nottingham <> Mon, 24 August 2020 00:07 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id 7845A3A0475 for <>; Sun, 23 Aug 2020 17:07:17 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -0.849
X-Spam-Status: No, score=-0.849 tagged_above=-999 required=5 tests=[DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HEADER_FROM_DIFFERENT_DOMAINS=0.249, MAILING_LIST_MULTI=-1, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (2048-bit key) header.b=WxMYdrEl; dkim=pass (2048-bit key) header.b=J4GmRWHn
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id dbaAQ3q4Equs for <>; Sun, 23 Aug 2020 17:07:15 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id AC3A53A046E for <>; Sun, 23 Aug 2020 17:07:15 -0700 (PDT)
Received: from lists by with local (Exim 4.92) (envelope-from <>) id 1k9zym-0003hC-NL for; Mon, 24 Aug 2020 00:04:53 +0000
Resent-Date: Mon, 24 Aug 2020 00:04:52 +0000
Resent-Message-Id: <>
Received: from ([]) by with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from <>) id 1k9zyl-0003fA-72 for; Mon, 24 Aug 2020 00:04:51 +0000
Received: from ([]) by with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from <>) id 1k9zyI-0004CQ-P9 for; Mon, 24 Aug 2020 00:04:51 +0000
Received: from compute4.internal (compute4.nyi.internal []) by mailout.nyi.internal (Postfix) with ESMTP id 4EFA25C00C8; Sun, 23 Aug 2020 20:04:09 -0400 (EDT)
Received: from mailfrontend2 ([]) by compute4.internal (MEProxy); Sun, 23 Aug 2020 20:04:09 -0400
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; h= content-type:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; s=fm3; bh=m 9dq+M3Gu36H4rek/UxZN3tLThlaIjJoPLZHD6L19+U=; b=WxMYdrEl/pa19HDIc HVXg3d5Q5GbDRxjNGqa+2b5/noSy2m0NK0dtH2DUL/OMvIh/S32YNfIS791ljiIB oqACYuR8pFsC3ZGvVhQ6++5NUJBBW8Hap/+2+hrALUaiT4IwUKY5OVi92FPylgFw XhOH5EEG1UeI1FlZ/zq5Rxedhu21lRoK7Ke5W7h4YSpjSEJb3SdBHRkMgwOrish8 cfytZ6fB/xFwY2zsLLQCY6OWotKFRWf44eSMUvvzhHRg1F+Pxhx6C6rNHY8C0Nat U1ABEu4mM2doGJ7QLmLnanc9pXWfyluypMEaEcrWHb5nqBsDAQos7TpjA8ZxPTyh UHCYA==
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=; h=cc:content-transfer-encoding:content-type :date:from:in-reply-to:message-id:mime-version:references :subject:to:x-me-proxy:x-me-proxy:x-me-sender:x-me-sender :x-sasl-enc; s=fm3; bh=m9dq+M3Gu36H4rek/UxZN3tLThlaIjJoPLZHD6L19 +U=; b=J4GmRWHneaFu2BeMGtb2+bS3y4bfsSWbIpHm18AVBMxK6UPzzlsZyKz7B ZMDoDUlytVN+fNQNyVnv/WGulOU5rOHRealaicpJcMXIrYuqwC22oN2qdoLppK3+ Mj9J1mTCf93VKkIleZnKQQa2n06cLkdl9us0Z2Ugu/xVOMKTiRbUEjHItJ4fFkAB LVnfjZY8+1z5nHvn7Epyi8saY+PcI0qFe+L46NePCjyjnx6IqhzYpXppI2YxEgZ+ Np4iOvakHgvX9hCMoCPg8zYGoSCnw89fmKM9EhPq1jHmWb65P5Unc00tdqmmiBdK PE0ha2KDP18d4mpMIXAG0N/CsY5og==
X-ME-Sender: <xms:-ANDX2U2IDq8WlKdMqF1P33a9vFJ5LaVL6Spw72szoWv0bgxRo3DrQ>
X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeduiedruddujedgudekucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne gfrhhlucfvnfffucdlvddtmdenucfjughrpegtggfuhfgjfffgkfhfvffosehtqhhmtdhh tdejnecuhfhrohhmpeforghrkhcupfhothhtihhnghhhrghmuceomhhnohhtsehmnhhoth drnhgvtheqnecuggftrfgrthhtvghrnhepteefleffjeffhfehheeffeegudelgfeujedu keeigedvgeehffefvdehffeileeknecuffhomhgrihhnpehmnhhothdrnhgvthenucfkph epudduledrudejrdduheekrddvhedunecuvehluhhsthgvrhfuihiivgeptdenucfrrghr rghmpehmrghilhhfrhhomhepmhhnohhtsehmnhhothdrnhgvth
X-ME-Proxy: <xmx:-ANDXykDqLPyDcwMZmpvoAWWJ0OLkUCpbWwN7bWpw4hHmPBSJedcpg> <xmx:-ANDX6aGjOCd-5LF9sh5TxPUVs7IBtOcgSWZYyQouolVTbHeHoCq8Q> <xmx:-ANDX9XkuTbOavHq5IC65cRUwpUSdHcBQmwH-uv9p-VBuf4Fr_iXMg> <xmx:-QNDX8vVNvyRSg1OrgB0uDHMgutfaodY_D0papZI-FDWG16Q7JZ2Gw>
Received: from [] ( []) by (Postfix) with ESMTPA id 98D273060272; Sun, 23 Aug 2020 20:04:07 -0400 (EDT)
Content-Type: text/plain; charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.\))
From: Mark Nottingham <>
In-Reply-To: <>
Date: Mon, 24 Aug 2020 10:04:05 +1000
Cc: " Group" <>
Content-Transfer-Encoding: quoted-printable
Message-Id: <>
References: <>
To: Yoav Weiss <>
X-Mailer: Apple Mail (2.3608.
Received-SPF: pass client-ip=;;
X-W3C-Hub-Spam-Status: No, score=-9.8
X-W3C-Hub-Spam-Report: BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001, W3C_AA=-1, W3C_DB=-1, W3C_IRA=-1, W3C_IRR=-3, W3C_WL=-1
X-W3C-Scan-Sig: 1k9zyI-0004CQ-P9 f2651d85ad777eb2bda76cc85c3bdc76
Subject: Re: JPEG-XL as Content-Encoding?
Archived-At: <>
X-Mailing-List: <> archive/latest/37955
Precedence: list
List-Id: <>
List-Help: <>
List-Post: <>
List-Unsubscribe: <>

Hi Yoav,

My personal .02 - 

The Intent to Prototype starts with the phrase 'JPEG XL is a next generation image format.' From the discussion, it seems like this is indeed a new format, and not a content encoding. If the proponents think that it will somehow ease the transition, that doesn't seem likely; it's more likely that they'll avoid well-understood problems introduced by format negotiation with brand-new problems related to format-specific content encoding. 

Just register a media type (or make it backwards-compatible to existing JPEGs).


> On 21 Aug 2020, at 12:11 am, Yoav Weiss <> wrote:
> Hey HTTPers!
> I was reviewing an intent to add JPEG-XL as a content-encoding for JPEG images, and thought I'd get some feedback from y'all regarding it.
> The team behind JPEG-XL think that since it can be used to seamlessly transform JPEGs, it might be interesting to enable that transformation to happen at the HTTP layer and get ~20% smaller images *automagically*, as compression would be done by supporting web servers and image compression providers.
> I'm slightly more skeptical about how automatic that would be, and find it somewhat strange to have image-specific content-encoding, while other image formats are served as separate mime types and negotiated with `Accept`.
> So, a few questions:
> 	• Would it make sense to have an image specific content-encoding?
> 	• Are web servers more likely to perform JPEG=>JPXL transformations if JPXL is a content encoding, compared to browser support for it as an image format?
> 		• Note that those transformations are CPU heavy, so will need to be cached, or done at "build" time.
> 	• Same question for CDNs
> 	• Finally for CDNs who already transform images - have you run into compatibility issues coming from web content manipulating raw image bytes directly, and failing to do that post-transformation?
> I'd highly appreciate y'all's opinions!
> Cheers :)
> Yoav

Mark Nottingham