- From: Eric Portis via GitHub <sysbot+gh@w3.org>
- Date: Wed, 25 Mar 2020 21:38:58 +0000
- To: public-css-archive@w3.org
> Is it EXIF-based resolution-x/resolution-y […] Format specific?
I think it can be anything: format/implementation-specific. It's been intentionally unspecified.
See this discussion [(source)](https://lists.w3.org/Archives/Public/www-style/2012Jan/0573.html), re: `image-orientation`:
```
<tantek> or image-orientation: exif ?
<tantek> why not be specific and say exif rather than auto?
<fantasai> tantek, because it might be done via some other technology
in some other image format
<fantasai> CSS keywords are format-agnostic
```
For instance, [PNGs have a dedicated piece of metadata for this](http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#C.pHYs), that isn't EXIF.
There were a [couple](https://lists.w3.org/Archives/Public/www-style/2013Jul/0566.html) of [discussions](https://lists.w3.org/Archives/Public/www-style/2014Apr/0209.html) about how “inches” and “centimeters” in metadata – which may have initially been intended to affect printing – should be interpreted, in CSS. It was [ultimately resolved](https://lists.w3.org/Archives/Public/www-style/2013Aug/0001.html) that they should be interpreted as CSS `in` and `cm` (so, visual angles instead of physical units), but this doesn't appear to have made it into [the spec](https://drafts.csswg.org/css-images-4/#valdef-image-resolution-from-image).
> How does it work when they're not 1:1?
There was also [a discussion](https://lists.w3.org/Archives/Public/www-style/2013Jul/0568.html) about this, which [resolved](https://lists.w3.org/Archives/Public/www-style/2013Aug/0001.html) on:
1. Giving `image-resolution` the ability to take two (X+Y) values.
2. Distorting the image when they aren't the same.
However, this also doesn't appear to have made it into [the spec](https://drafts.csswg.org/css-images-4/#valdef-image-resolution-from-image).
(Note! That while the primary use case discussed the old mailing list posts about this was weird content from weird scanners and/or [fax machines](https://lists.w3.org/Archives/Public/www-style/2013Jul/0573.html), I actually have a reasonable, modern, use case for this, now, I think: [low-resolution image placeholders](https://github.com/httpwg/http-extensions/issues/1102#issuecomment-594972732))
--
GitHub Notification of comment by eeeps
Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/4881#issuecomment-604101751 using your GitHub account
Received on Wednesday, 25 March 2020 21:39:01 UTC