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Re: [css3-images] What does image-resolution apply to?

From: Brad Kemper <brad.kemper@gmail.com>
Date: Tue, 24 May 2011 10:38:52 -0700
Message-Id: <F5555591-1EF0-4F8D-8DB2-069C24C2DC0E@gmail.com>
Cc: Alan Gresley <alan@css-class.com>, www-style list <www-style@w3.org>, MURAKAMI Shinyu <murakami@antenna.co.jp>
To: "Tab Atkins Jr." <jackalmage@gmail.com>

On May 24, 2011, at 10:23 AM, "Tab Atkins Jr." <jackalmage@gmail.com> wrote:

> On Tue, May 24, 2011 at 9:58 AM, Alan Gresley <alan@css-class.com> wrote:
>> On 25/05/2011 2:42 AM, Tab Atkins Jr. wrote:
>>> On Tue, May 24, 2011 at 7:24 AM, Brad Kemper<brad.kemper@gmail.com>
>>>> This is also a question about background size. Suppose that with
>>>> that same 400 x 400 raster image I have { background-image:
>>>> image('400x400.png' 10dpi); background-size: 1in 1in; }? What are
>>>> the final sizes of the rendered image pixels? 1/10" or 1/400"?
>>>> Perhaps in both cases, you are just adjusting a sort of "late
>>>> intrinsic" resolution that is then overridden by width and height
>>>> declarations? If so, I think you need to say so. (Apologies, if you
>>>> do somewhere already, and I just missed it.)
>>> I don't think it's clearly stated how this works, so I should fix
>>> that.  The intent is that it affects the intrinsic size.
>>> So, in your first example (400x400 pixel image at 72dpi, sized to
>>> 1in by 1in), you first apply the resolution.  This gives you a
>>> native image size of 533px (or 5.55in), which is then scaled down to
>>> 1in by 1in.  Your second example is similar, though more extreme
>>> given the tiny dpi.
>> What happens with a SVG background-image that has no intrinsic size or no
>> dimension?
>> background-image: image('basic.svg' 50dpi)
> For vector images, the "dot" in dpi is pixels in the outermost
> coordinate space.  So, that declaration simply means that the SVG's
> initial coordinate space is such that 1px in it is equal to 1/50th of
> an inch.
> In other words, if the SVG image had something like "<svg width='100'
> height='100'>" as the root element, then it would be scaled to be a
> 2in by 2in square.  Without that resolution declaration, the image
> would be just over 1in square instead.

Are SVG lengths alway unitless numbers? If not, I would expect an SVG measured in inches to be pixelated if given a low enough resolution (which might occasionally be a useful effect).  Forgive my ignorance of SVG, please. 
Received on Tuesday, 24 May 2011 17:39:30 UTC

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