Bug#862286: zoplipng produces unnecessary large files for small grayscale images

[Sebastian Noack]

I just recently switched from pngout (non-free) to zopflipng. So I
kinda use it almost daily now, but not for a very long time. I also
evaluated pngcrush and optipng (which are included in Debian as well)
but except when zopflipng is messing with the color mode, it always
produces smaller files than the other tools.

While you are asking, there seems to be a similar issue when you have
some special kind of palette [1], preventing zopflipng from optimizing
the image. My fix doesn't help there, and I didn't look into it yet.

There are more issues on GitHub that haven't been addressed by
upstream. But so far none, that I personally care too much about.

[1]: https://github.com/google/zopfli/issues/75

On Wed, May 10, 2017 at 7:29 PM, László Böszörményi (GCS)
 wrote:
> Control: merge 862286 862287
>
> Please file bugs only once.
>
> On Wed, May 10, 2017 at 6:07 PM, Sebastian Noack
>  wrote:
>> Thanks for adding zopflipng to the package. However, I just found one
>> scenario in which it gives undesirable results.
> [...]
>> So I wonder if you would consider adding patches to fix bugs like this
>> to the Debian package? For this particular bug, you find the patch (it
>> is a tiny change) inline in my comment on the upstream issue.
>  I had the impression you use zopflipng daily before asking for its
> inclusion. OK, never mind. Do you have any bugs that needs to be
> fixed? It would be nice to include all in one shot and not one after
> another.
>
> Regards,
> Laszlo/GCS

Bug#862286: zoplipng produces unnecessary large files for small grayscale images

[GCS]

Control: merge 862286 862287

Please file bugs only once.

On Wed, May 10, 2017 at 6:07 PM, Sebastian Noack
 wrote:
> Thanks for adding zopflipng to the package. However, I just found one
> scenario in which it gives undesirable results.
[...]
> So I wonder if you would consider adding patches to fix bugs like this
> to the Debian package? For this particular bug, you find the patch (it
> is a tiny change) inline in my comment on the upstream issue.
 I had the impression you use zopflipng daily before asking for its
inclusion. OK, never mind. Do you have any bugs that needs to be
fixed? It would be nice to include all in one shot and not one after
another.

Regards,
Laszlo/GCS

Bug#862286: zoplipng produces unnecessary large files for small grayscale images

[Sebastian Noack]

Package: zopfli
Version: 1.0.1+git160119-2

Thanks for adding zopflipng to the package. However, I just found one
scenario in which it gives undesirable results. That is with small
images (<4K of uncompressed image data) that only use shades of gray
(and optionally an alpha channel). There is an optimization in the
code for such small images, however that optimization enforces RGB(A)
color mode, which therefore causes unnecessary large files if there
are only shades of gray in the image. I already reported this bug
upstream [1]. However, upstream development seems to be stalled. The
last commit was a year ago, while the numbers of issues are growing.
So I wonder if you would consider adding patches to fix bugs like this
to the Debian package? For this particular bug, you find the patch (it
is a tiny change) inline in my comment on the upstream issue.

[1]: https://github.com/google/zopfli/issues/34#issuecomment-300523295