alpha_channel clarification

In category: Tag/Wiki Projects and Questions

Suppose there were a bot that went around automatically tagging certain properties of images that could reliably be determined by a computer: alpha_channel, greyscale, monochrome, black_and_white, etc.

Specifically regarding alpha_channel, should a bot explicitly follow the rules laid out in alpha_channel (an image with any transparent pixels should be tagged with alpha_channel)? Or should it only include images that are "visibly" transparent?

Case in point: post #1300343. This image has 5082 pixels with an alpha value of 246 (aka most of the border is lightly transparent). All other pixels are fully opaque. Technically this image should be tagged alpha_channel, but nobody looking at this image would know it was transparent. It's also probably safe to assume the artist didn't even intend to make this image transparent.

disclaimer: no bot(s) will be unleashed upon the site without clearing it with the admins/mods first


to be honest the wiki would need a small edit because there is no way of telling if a image is semi-transparent or not without being able to move the image over text or a button to see if they show thru, full transparency can be seen because backgrounds in thumbnails on e621 are always black while on the post page the sites primary blue background layer is seen as the backdrop.

It would have to be visibly transparent if the tag was to be useful, we care that it has a visible transparant background, not pixels coded for transparency but arnt apparent.


Alpha channel should only be tagged if any pixel contains a value other than 255 on the alpha channel. The purpose of the tag is to indicate the alpha channel is used, not just present.
We may add mode:<RGB|RGBA|Indexed|grey|1> in the future if we wish to allow searching by image mode, but this is not planned right now, and would require indexing of all existing images.

In a perfect world, all pngs would be optimized and stripped of the alpha channel if it is unused.


Chaser said:
Alpha channel should only be tagged if any pixel contains a value other than 255 on the alpha channel. The purpose of the tag is to indicate the alpha channel is used, not just present.
We may add mode:<RGB|RGBA|Indexed|grey|1> in the future if we wish to allow searching by image mode, but this is not planned right now, and would require indexing of all existing images.

In a perfect world, all pngs would be optimized and stripped of the alpha channel if it is unused.

Two problems: images which are clearly using alpha channel almost fully, but may not have full transparency anywhere and then I have bumped into two images which do have full transparency, but it's little tiny dot, almost like it was mistakenly made by artist with eraser tool (post #794587, didn't find other example I was thinking.)

I would almost like to say that any image with any level of visible transparency should be tagged, but that would go into insanely subjective territory and then stuff like I linked above, that's something I would never ever be searching with the tag.

Also reminder, we do also have transparent background which does imply that whole background is transparent.


Thanks for the input.

At the risk of sounding thick, does this mean there's a consensus to tag anything with any pixels < 255 as alpha_channel? So far (from staff anyway) I see 1 vote for "yes" and 1 vote for "maybe", if I'm understanding you guys correctly.

Also, another fun example of how useless this tag might be if it's applied exactly as the wiki says: post #1302278 has just a single pixel with an alpha of 254.


I don't know about no bot...who is going to make this bot? You? Or is this purely hypothetical?

Personally I think it would be dumb to tag a picture with one transparent pixel with alpha_channel...that would just lead to confusion. Users would bring up the image and be like "what the heck? I don't see any transparency! This is mistagged!" Ultimately every tagging decision should be done with the end user in mind, and this would just frustrate them.


I've already made the bot. This is just a discussion about tuning.


asw_xxx said:
I've already made the bot. This is just a discussion about tuning.

I would suggest not even releasing it without the staff's sayso.


Furrin_Gok said:
I would suggest not even releasing it without the staff's sayso.

asw_xxx said:
disclaimer: no bot(s) will be unleashed upon the site without clearing it with the admins/mods first