Consider applying ipd or bpd to content images

[plehegar]

It's reasonable to apply ipd and bpd to image and have an implied scaling semantic. People are already used to that concept in HTML.

(raised by Glenn Adams on 2015-04-10)
From tracker issue http://www.w3.org/AudioVideo/TT/tracker/issues/387

[nigelmegitt]

I cannot see any specification now for what happens if an image is placed in a span that specifies ipd and bpd, and the extent of the image is not equal to that specified size. I agree that it seems reasonable to specify an implied scaling semantic in that case.

[skynavga]

@nigelmegitt regarding #140 (comment), this was (originally) about using ipd/bpd on <image> in an inline context, and not about using ipd/bpd on <span>. However, at this point we have already specified the ability to use tts:extent on <image> in both block and inline contexts, so we have already satisfied the original request and can close this issue.

[nigelmegitt]

@skynavga I'm still not clear from the current ED what the image presentation semantic is though:

§9.1.5 image includes:

An image element may specify an tts:extent style attribute in order to specify the presentation width or height of the image when intrinsic width or height information is not available or is intended to be overridden. If this attribute is specified on both an image element in an image presentation context and on the image element in an image defining context to which the former refers, then the attribute specified on the former takes precedence over the one specified on the latter.

And §10.2.16 tts:extent says:

If a tts:extent attribute is specified on an image element, then its computed value determines the width and height of the image.

So we see that the width and height of the image are overridden or determined by setting tts:extent and that results in a computed extent value, but we do not define what the presentation behaviour should be when the computed extent does not equal the intrinsic size of the image, for example all of the following appear to be conformant:

1. scale the image anamorphically to fit the exact dimensions,
2. scale the image to fit in the largest dimension,
3. (if larger than the computed extent in either dimension) crop the image to fit,
4. (if smaller than the computed extent in either dimension) locate the image at some position (which?) within the area that has the computed extent and fill the rest with some background colour (which?),
5. (if smaller than the computed extent in either dimension) repeat the image to fill the area that has the computed extent.

Possibly there are other options! I think we need to be specific, probably that we mean option 1. Or please point me to the existing text that I've failed to find...

[skynavga]

Add note in c14d76a regarding anamorphic scaling.

[nigelmegitt]

Why is the anamorphic scaling semantic defined only in a note and not made normative? Probably this is something we should discuss. I was not expecting a non-normative resolution to this issue, so in my view it is not yet closed.

[skynavga]

Addressed in afead4c.