[Matplotlib-devel] [Matplotlib-users] paletted PNG backend

[Jesper Larsen]

Hi Thomas

Thanks for your reply. The pull request by mdboom actually led me to find
an undocumented option in Pillow to set the compression level (we now use
compress_level=7). This reduced the cost of producing the paletted PNG very
much with very little effort.

We are however still interested in improving the performance further. And
the information that you have provided is definitely useful for this

Best regards,
Jesper

2016-02-15 16:43 GMT+01:00 Thomas Caswell <tcaswell at gmail.com>:

> Jesper,
>
> That is a cool application!
>
> I am not sure doing this directly in Agg would be the best place (as I am
> not sure how to conceptually combine anti-aliasing + compositing + color
> pallet).  I think a better place to extend would be the png writer to
> directly export a palleted png (
> https://github.com/matplotlib/matplotlib/blob/master/src/_png.cpp#L123)
> from the Agg RBGA buffer.
>
> You might also be interested in
> https://github.com/matplotlib/matplotlib/pull/5389 where Mike did some
> work to sort out which png settings are fastest.
>
> Tom
>
> PS The mailing list has moved to matplotlib-devel at python.org  please
> re-subscribe and send future emails there.
>
> On Mon, Feb 15, 2016 at 3:19 AM Jesper Larsen <jesper.webmail at gmail.com>
> wrote:
>
>> Hi Matplotlib users,
>>
>> We are using Matplotlib for a web service which makes PNG images on the
>> fly for presentation on a map (web site using the web service is here:
>> https://ifm-beta.fcoo.dk)
>>
>> Performance and image size are two major concerns for us. We therefore
>> save the resulting RGBA PNG to a buffer and afterwards use Pillow (PIL) to
>> convert it to a P PNG (paletted PNG) to reduce the image size dramatically.
>>
>> This procedure does however use a significant amount of our total
>> processing time per image. I would therefore be interested in extending
>> e.g. the AGG backend to produce paletted PNGs directly. I am of course
>> aware that this might not be useful for many others since one would have to
>> provide some extra information when rendering with this backend (possibly
>> output palette and quantizing method). But on the other hand it might be
>> useful for others doing web services using matplotlib.
>>
>> My questions are:
>>
>> 1) Is it possible to extend the AGG backend for this and how?
>>
>> 2) Is it better to make a separate Pillow based backend for this (Pillow
>> is probably not as fast as AGG)?
>>
>> Best regards,
>> Jesper
>>
>>
>>
>>
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