Bug 216943

Summary:	Chroma subsampling based on encode quality
Product:	WebKit	Reporter:	Micah <micah.millereshleman>
Component:	Canvas	Assignee:	Nobody <webkit-unassigned>
Status:	NEW ---
Severity:	Normal	CC:	dino, sabouhallawa, sam, simon.fraser, webkit-bug-importer
Priority:	P2	Keywords:	InRadar
Version:	Safari 14
Hardware:	Mac
OS:	macOS 10.15

Description Micah 2020-09-24 14:36:28 PDT

Hi,

One unresolved browser inconsistency in the Canvas API is how image encoding quality affects chroma subsampling. 

In Firefox, chroma subsampling is turned off at quality >= 0.9, allowing crisp images to be exported from Canvas at relatively small file sizes (e.g. quality 92%). Chrome & Webkit only disable chroma subsampling at quality == 1.0 (100%), meaning that it's impossible to export a crisp canvas as a JPEG without also exporting a massive image.

I work at an online photo editor, and it means that we recommend Safari users save their images at 100% quality, and then use a different program to compress them (w/out chrome subsampling) before using them on a website. Other online photo editors bypass the browser altogether and load their own version of libjepg in WebAssembly. This seems a bit heavy-handed, and it'd be great if the browser default for Canvas produced images that were ready to use on the web.

Chrome recently opened a WHATWG issue for this, and it'd be great to hear from Safari. 
https://github.com/whatwg/html/issues/5395

Improving this small corner of the web platform would make Safari a better platform for our users. Thanks!

Comment 1 Radar WebKit Bug Importer 2020-09-27 10:06:46 PDT

<rdar://problem/69660091>

Comment 2 Micah 2021-01-28 14:58:08 PST

Any thoughts on this? It'd be great to hear from the Webkit team. Thanks!