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Re: [css3-images] Units for `image-resolution: from-image`

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Fri, 26 Jul 2013 09:39:51 -0700
Message-ID: <CAAWBYDC5605K=-AF944M5qyFhv6MqKWs5w2tCnQPUKoo_=6kEg@mail.gmail.com>
To: Simon Sapin <simon.sapin@exyr.org>
Cc: www-style list <www-style@w3.org>
On Fri, Jul 26, 2013 at 5:41 AM, Simon Sapin <simon.sapin@exyr.org> wrote:
> Hi,
>
> The 'from-image' keyword of the 'image-resolution' property is defined as
>
>     The image's intrinsic resolution is taken as that specified by the image
> format. If the image does not specify its own resolution, the explicitly
> specified resolution is used (if given), else it defaults to ‘1dppx’.
>
> The only image formats that I found that have resolution metadata are JPEG
> and TIFF, where it is specified in "image pixels per inches" or "per
> centimeter".
>
> How should this be interpreted? I think it should map to CSS in and cm (and
> therefore the resolution is interpreted as dpi and dpcm) rather than
> physical inches and centimeters, which otherwise don’t exist in CSS.

I think this is quality-of-implementation.  If you know that an image
format means "real inches", and you know an accurate conversion ratio
between real inches and CSS px on the device you're running on, then
you should feel free to interpret the image format's resolution as
accurately as possible when converting into one of the CSS units.

If you don't have either of those pieces of information, then yes,
interpreting them as CSS units is perfectly appropriate.

~TJ
Received on Friday, 26 July 2013 16:40:46 UTC

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