[mediaqueries-5] image backgrounds vs transparency

[fantasai]

Given the name of prefers-reduced-transparency, I would expect it to be "transparency is bad, but complex backgrounds are totally fine". However, I wanted to check if that's actually a correct interpretation of the accessibility requirement.

(@cookiecrook mentioned that prefers-reduced-transparency derives from a MacOS setting in a context where transparency is often used but background images aren't a thing; but on the Web, they definitely are. So we have this additional thing to consider.)

So the question is, is the requirement that generated prefers-reduced-transparency really about wanting reduced transparency e.g. because of some confusion over whether the obscured content is still relevant, or is it also about reducing decorative visual complexity--including both the use of transparency but also complex background images, such that authors should not be using complex opaque backgrounds either?

If the former (really only about transparency), do we also need an MQ for reducing e.g. patterned or image backgrounds to more subtle or solid effects? (And if so should that really be a separate MQ, given that adding one adds authoring complexity and fingerprinting surface?)

[cookiecrook]

derives from a MacOS setting

All four major Apple platforms support this, not just macOS.

in a context where transparency is often used but background images aren't a thing;

Background images happen in native UI, but aren’t as common as on the Web.

is it also about reducing decorative visual complexity […] such that authors should not be using complex opaque backgrounds either?

I agree that this one is much more related to reduced visual complexity than the contrast issue in #5433. I would not go as far as to say authors should not be using any complex backgrounds, but they should not be using those complex backgrounds (opaque or otherwise) behind text and other content where the background visual can be distracting or reduce readability/understandability.

The main reason the native API includes transparency in the name is because 1) use of transparency is very common in modern UI starting with iOS 7 when this API shipped, and 2) users understand what the setting does and engineers understand what they should do to react to it.

[Crissov]

(Partial) transparency is also something that is really only noticeable within interactive media, e.g. while scrolling or dragging, and not in paper print-outs in particular. (Are there printers that can produce white ink for transparency slides?)

That being considered, can prefers-reduced-transparency be altered to also cover the browser setting to suppress background images (and colors) when printing?

[Myndex]

A principal goal behind "reduce transparency" is to have text rendered on a plain, untextured, non-image background.

It might be better to have: prefers-plain-background

[cookiecrook]

It’s not always about text and texture.

Another principle goal is to avoid vestibular discomfort associated with UI that uses transparency to simulate depth.