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

Le 26/07/2013 17:39, Tab Atkins Jr. a écrit :
> 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.

I disagree. "Real" physical units shouldn’t be involved, for the same 
reason we don’t have them in CSS <length>: they’re just not what you 
want when you don’t know the viewing distance, which can vary a lot 
between, say, a phone and a projector.

Also, images with "image-resolution: from-image" should definitely be 
affected by both CSS transforms and user zoom, just like any other 
content. And I find "physical units when used at default zoom and unit 
transform" terrible as a concept.

-- 
Simon Sapin

Received on Friday, 26 July 2013 16:56:12 UTC