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

[Thomas Caswell]

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

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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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