> Hi Jan,
>
> On Thu, Jul 12, 2012 at 4:05 PM, Jan Niklas Hasse <
jha...@gmail.com> wrote:
>>
>> I am currently using ImageMagick with Lanczos resampling
>> (
http://en.wikipedia.org/wiki/Lanczos_resampling) to scale my images. Which
>> algorithm is libwebp using for rescaling?
>
>
> the algorithm used is based on summed area (i.e.: box-filtering). It is
> geared toward large _shrinking_
> ratio. It will work for upsampling too, but that really not recommended. The
> primary use-case for
> this built-in rescaling capability is when you have a very large image to
> display on a small screen
> (phone?), or as a thumbnail.
>
> (Lanczos is indeed a good choice if the rescaling ratio is close to 1.0: it
> preserves the crispness
> better).
>
> Note that since this rescaling is tightly integrated into the decoding
> pipeline, memory (and CPU, somehow)
> consumption is proportional to the output resolution, not the input's.
> Basically, to downscale a large
> panorama into a small thumbnail, you won't have to use gigs of memory to
> store the intermediate
> non-rescaled image. The output is directly at thumbnail's resolution.
>
> hope it helps,
> skal
that sounds pretty good! I'm doing shrinking only (e.g. 1080p to 720p).