Don't stop at transparancy

4 views
Skip to first unread message

Pheterson

unread,
Oct 1, 2010, 3:36:03 PM10/1/10
to WebP Discussion
Support translucency so that variable levels of opacity are able to be
saved and viewed.

I always say set a goal and double it. This should be a sufficient
challenge beyond simple "color or transparent" pixels.

Russell

unread,
Oct 2, 2010, 8:28:42 PM10/2/10
to WebP Discussion
You mean like the 32bit ARGB model that you'll find in PNG, rather
than the "transparent colour" feature in GIF? Good idea.

Being a lossy format, I think the ARGB model is very achievable. As
the transparent colour in GIF is based on a 256 colour palette (which
VP8 wouldn't support), it wouldn't work. Especially because WebP is a
lossy format.

I've never seen a lossy ARGB model before. It would be interesting to
see one in action. It would also solve the problem on the Web where
developers need to refrain from using transparency on large images
(such as banners), because PNG sucks up far too much bandwidth.

The fun part would be applying compression based on opacity. A block
that's 90% transparent should have far higher compression applied to
RGB values than something that's opaque.

Jari Pennanen

unread,
Oct 3, 2010, 2:33:35 PM10/3/10
to WebP Discussion
\o_

We should gather more support for this, it's important.

MaxSt

unread,
Oct 4, 2010, 6:06:52 AM10/4/10
to WebP Discussion
Flash can use a combination of JPEG for rgb channels plus PNG for
alpha channel. I think it's generally a good idea for alpha channel to
be compressed losslessly.

Pierre Joye

unread,
Oct 4, 2010, 10:32:52 AM10/4/10
to webp-d...@webmproject.org
hi,

Good point, if webp supports transparency at some point then it should
have an option to store in a loss-less manner. Alpha is often used to
smooth images (anti aliasing using alpha channel only) or similar
usages. A destructive compression can have dramatic visual artifacts
(a good example are texts).

> --
> You received this message because you are subscribed to the Google Groups "WebP Discussion" group.
> To post to this group, send email to webp-d...@webmproject.org.
> To unsubscribe from this group, send email to webp-discuss...@webmproject.org.
> For more options, visit this group at http://groups.google.com/a/webmproject.org/group/webp-discuss/?hl=en.
>
>

--
Pierre

@pierrejoye | http://blog.thepimp.net | http://www.libgd.org

Gynvael Coldwind

unread,
Oct 4, 2010, 10:45:35 AM10/4/10
to webp-d...@webmproject.org
Hi,

If transparency (ARGB model) support would be included, maybe a good
way to save some space would be to not store the RGB data for places
(pixels, 8x8 groups of pixels, etc) which are totally transparent
(i.e. alpha = 0).
E.g. PNG stores the RGB data in such places, resulting some space
being lost for RGB(0,0,0) color (this is the best scenario, which not
always is the case) or some artifacts left by the artists under the
transparency layer or other artifacts generated by the graphical
program at coding.

Not sure how the above idea would work out, but imo it would be OK to
consider it.

Good luck,

--
gynvael.coldwind//vx

Reply all
Reply to author
Forward
0 new messages