Detecting Quality that was used to encode to a lossy webp

[Aarti Parikh]

Hello,

How can I extract the quality from a given lossy webp image? 

Thanks

Aarti

[Pascal Massimino]

Hi Aarti,

On Mon, Jul 18, 2016 at 1:19 PM, Aarti Parikh <aarti....@gmail.com> wrote:

Hello,

How can I extract the quality from a given lossy webp image? 

it's quite difficult to summarize all to possible lossy-encoding parameters in just one quality number.

The mapping is not 1:1 (JPEG has the same problem, note, but to a lesser extent).

Sorry for not having a better answer to offer!

Still, i'll try to see if one could get an estimation (and how bad this estimation would be) based on the

quantizer steps signaled in the bitstream. I'll update this thread, should there be some usable results...

hope it helps,

skal/

[Pascal Massimino]

Hi Aarti,

so i went ahead a submitted[*] a small tool/API to try and reverse-guess the encoding quality.

It's on the tip of the tree:

git pull

./autogen.sh

./configure --enable-everything

make -j4 all

-> you should get a extras/webp_quality binary, that will attempt to guess a rough value

of the encoding quality (try './extras/webp_quality my_file.webp'). Not guarantee! :)

hope it helps,

skal/

[*] https://chromium-review.googlesource.com/#/c/362030/ commit e8ab6a825a86ed77f0b148645fa7ce3aa25ec216