WebPImagePlugin.py decodes webp in open()

[christophegithubtts]

What did you do?

Calling Image.open() on a webp file

What did you expect to happen?

The call should be quick

What actually happened?

open() for a webp image actually decodes the webp into rgb !
So open() for a webp image is much slower than open() for a png for instance

The implementation in WebPImagePlugin.py is not efficient at all.
open should call WebPGetInfo or WebPGetFeatures but not WebPDecode !

What versions of Pillow and Python are you using?

Latest pillow (4.1) and python 2.7

[hugovk]

PRs welcome.

Have a look at:

• https://pillow.readthedocs.io/en/latest/handbook/writing-your-own-file-decoder.html
• https://github.com/python-pillow/Pillow/blob/master/PIL/WebPImagePlugin.py
• https://github.com/python-pillow/Pillow/blob/master/_webp.c

[wiredfool]

There is actually a pr languishing that totally rewrites webp support.

[hugovk]

• Add WebP decoder #1122: "Add WebP decoder"
• Add WebP advanced options #1263: "Added WebP advanced options."

[christophegithubtts]

wiredfool : do you mean pr #1122 has some problems and will not be checked in ?

[wiredfool]

No. I mean that there is a PR, and that it appeared to be a ground up rewrite which may or may not have the same issues as the current version of the webp plugin. IIRC, there was discussion around that PR, and then it went nowhere because it's a huge code drop that replaced existing functionality without ever discussing the differences between it and the current code.

[radarhere]

#2761 being merged in on 6 Nov 2017 meant that WebPDecode is no longer called for newer versions of libwebp. Testing, if I force the legacy mode to be used, it is 424% of the time of PNG open. Testing the normal version of WebP open, I get 188% of the time of PNG open.

Is that speed up sufficient for this issue to be closed?

[christophegithubtts]

That's better for sure
I guess the following line
self._decoder = _webp.WebPAnimDecoder(self.fp.read())
is responsible for 88% additional time compared to png ?

I let you close the ticket

[radarhere]

No, self._decoder = _webp.WebPAnimDecoder(self.fp.read()) is only responsible for about 13% of the additional time compared to PNG.