Actually, subj.

This would probably be better as an Alias.

Alpha channel is transparency with some kind of gradient possible on a PNG file while the transparency from a gif/non alpha channel PNG is only one color that is transparent ; Alpha channel should imply transparent background

Neitsuke said:
Alpha channel is transparency with some kind of gradient possible on a PNG file while the transparency from a gif/non alpha channel PNG is only one color that is transparent ; Alpha channel should imply transparent background

transparent_background should imply alpha_channel, not the other way around. transparent_background describes the look of the image (the background or backdrop) and requires + implies alpha_channel. alpha_channel describes the actual file, and would be reserved for describing some small elements in the image that are made transparent as a gimmick, like eyes or a window or something. GIF effectively has a 1-bit alpha channel while PNG can have up to 16-bit, usually 8-bit, so all uses of transparency should be tagged alpha_channel.

trfg7xz2oxps said:
transparent_background should imply alpha_channel, not the other way around. transparent_background describes the look of the image (the background or backdrop) and requires + implies alpha_channel. alpha_channel describes the actual file, and would be reserved for describing some small elements in the image that are made transparent as a gimmick, like eyes or a window or something. GIF effectively has a 1-bit alpha channel while PNG can have up to 16-bit, usually 8-bit, so all uses of transparency should be tagged alpha_channel.

Wow. Learn something new every day. o-o

Wouldn't that mean that all cases of alpha channel involve a transparent background, though, trfg?

123easy said:
Wouldn't that mean that all cases of alpha channel involve a transparent background, though, trfg?

no.
this, for example does not have a transparent background, but utilizes the alpha_channel effect
post #55954

... 'Effectively', maybe -- but it's not a 1-bit channel / mask in a GIF; GIF transparancy is applied using a specific value in the existing 'channel'/index of the (up to) 8-bit color table -- not a separate element of the image. From a technical standpoint there is most definitely no alpha channel possible in a GIF. From a content / tagging standpoint what would be described by alpha_channel would logically (to me, anyways) be things that require more than a 1-bit mask (or equivalent) anyways, like what Neitsuke said -- things where the image file itself contains partial transparency.

As such, I don't really think either should be aliased or implicated from the other. The only problem I see with how it currently is would be that IIRC 'transparency' is a tag used to denote clothes / etc being partially transparent or translucent, leaving no good existing tag for images like what ippiki linked (that I know of).