PNG image writing: memory inefficiency?

[Daniel Gredler]

Thanks for the confirmation!

I went ahead and made some measurements, and the improvement possibilities
really are quite good -- in a local test PNGImageWriter.write( ) and
callees were initially showing up as an allocation hotspot (~400k objects /
~65 MB allocated), but after some optimizations I'm seeing much better
numbers (~400 objects / ~740 KB allocated).

I also spent some time creating regression tests for different combinations
of alpha pre-multiplied vs. not, BufferedImage vs. other image types,
untiled vs. single-tile vs. multi-tile, custom source bands vs. none, etc.

I've filed a bug (internal review ID 9077379), but do not have a bug number
yet. Once I have a bug number I'll submit a PR for review.

Take care,

Daniel


On Wed, Jul 31, 2024 at 8:13 PM Philip Race <philip.race at oracle.com> wrote:

> I think yes.
> Whereas JPG grabs the raster for the whole image whereas as you noted,
> PNG is looping row by row,
> so there might need to be some updates in the handling of the child
> raster needed.
>
> -phil.
>
>
> On 7/31/24 10:02 AM, Daniel Gredler wrote:
> > Hi all,
> >
> > I'd like a quick sanity check on a possible memory inefficiency in
> > PNGImageWriter.
> >
> > Some of the other image writers, like JPEGImageWriter, do their best
> > to avoid duplicating the image raster + data buffer [1]... although it
> > doesn't look like this was always the case [2].
> >
> > The PNGImageWriter, on the other hand, always makes a new raster +
> > data buffer copy for each row [3]. It *is* per-row, so the data isn't
> > all duplicated in one go, but even on a row-by-row basis, it ends up
> > being quite a bit of unnecessary allocation and subsequent garbage
> > collection.
> >
> > Can somebody confirm if I'm reading things right, and whether
> > PNGImageWriter would benefit from a similar BufferedImage + single
> > tile check, such as already exists in JPEGImageWriter?
> >
> > Thanks!
> >
> > Daniel
> >
> > [1]
> >
> https://github.com/openjdk/jdk/blob/e4c7850c177899a5da6f5050cb0647a6e1a75d31/src/java.desktop/share/classes/com/sun/imageio/plugins/jpeg/JPEGImageWriter.java#L415
> > [2] https://bugs.openjdk.org/browse/JDK-6266748
> > [3]
> >
> https://github.com/openjdk/jdk/blob/e4c7850c177899a5da6f5050cb0647a6e1a75d31/src/java.desktop/share/classes/com/sun/imageio/plugins/png/PNGImageWriter.java#L923
> >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/client-libs-dev/attachments/20240801/1caf9b96/attachment.htm>