Re: CfC: to publish "The srcset attribute" specification as a First Public Working Draft (FPWD)

On Monday, Feb 4, 2013, at 11:11 PM, Fred Andrews wrote:

> > From: mat@matmarquis.com
> > Date: Mon, 4 Feb 2013 22:00:00 -0500
> 
> > The relationship between the sizes is communicated by the same criteria used to determine which should be served. It�s not necessary for the UA to know the exact dimensions of the image�if the author has flagged an image source as only being appropriate for high-resolution screens, it is the larger image. Given `sd.jpg 1x, hd.jpg 2x,` it�s clear to the UA which of these will be the larger image. If the concern is that the author will specify these incorrectly, there isn�t much we can do syntactically to avoid that.
> 
> Lets boil it down to a simple example that you can not refute.
> 
> Let there be two images:  image_200x100.jpg and image_400x200.jpg with resolutions 200x100 and 400x200 pixels respectively.
> 
> Let the author hint to the UA to use image_200x100.jpg on low density 1x devices and image_400x200.jpg on high density 2x devices.
> 
> Let the author hint that the UA should upscale the images to fit a larger image box.

> <img style="width: 800px; height: 400px: "srcset="image_200x100.jpg 1x, image_400x200.jpg 2x">

Upscaling either source, in this case, would result in a distorted image. For any user with a standard resolution display, the image will be scaled up four times by the CSS and heavily distorted. For any user with a high resolution but qualified context, the image will be scaled up twice by the CSS and less distorted. For a user with a high-resolution display but unqualified context�low bandwidth, for example�the image will be scaled up four times by the CSS and heavily distorted. This isn�t something authors would reasonably do, but in this scenario the existing syntax does what you describe below.

> Let the UA make a choice and let the choice be to select the smallest image that yields sharp image presentation - a reasonable use case.

In the example you provide, *this is precisely what happens*. The only reason this wouldn�t be the case is if the larger image were specified as `1x` and the smaller as `2x`�which would be a very obvious authoring error.

> The UA does not know the image sizes, it does not know that image_200x100.jpg is 200x100 pixels, or that image_400x200.jpg is 400x200 pixels so it can not solve this technical problem.  The UA does not know if the author hinted to upscale or downscale the images.

> If you can refute this then please prove it or otherwise please withdraw your proposals.

I appreciate your feedback and welcome you to file bugs against either/both extension specifications, and regret that we couldn�t come to an understanding on this.

> cheer
> Fred