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Date: Fri, 17 Jun 2016 12:11:08 -0700
Message-ID: <CANaX5ne_oQr6m1vvgyS2L+BQYBg24gUh+_ch2gm=ugcp22-=Sw@mail.gmail.com>
To: Pierre Joye <pierre.php@gmail.com>
Cc: Christoph Becker <cmbecker69@gmx.de>, PHP internals <internals@lists.php.net>, 
	PHP Quality Assurance Team Mailing List <php-qa@lists.php.net>
Content-Type: multipart/alternative; boundary=94eb2c070e1a0a60bb05357e1eea
Subject: Re: [PHP-DEV] Re: Improve GD test suite
From: davey@php.net (Davey Shafik)

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I would love to see a native ssim/dssim implementation in PHP=E2=80=A6

On Fri, Jun 17, 2016 at 6:54 AM, Pierre Joye <pierre.php@gmail.com> wrote:

> Hi
> On Jun 17, 2016 8:18 PM, "Christoph Becker" <cmbecker69@gmx.de> wrote:
> >
> > Hi!
> >
> > I like to suggest to improve the current test suite of the gd extension=
.
> > The main issue I see with the current suite is that many (~ 28) tests
> > use md5() to verify that a drawn image is correct.  However, as Pierre
> > mentioned long ago[1], md5() does not work (reliably) for this purpose.
> >
> > An alternative would be to have prepared images, and to compare these
> > with the actual resulting images pixel by pixel.  While that might work
> > fine for lossless compression, it still can result in failing tests,
> > which would be hard to track down, and obviously a pure PHP
> > implementation is slow.
> >
> > Especially, when it comes to verify lossy image compression a more
> > sophisticated approach is required.  Due to the necessity to test
> > imagewebp() I had committed a very simplistic calc_image_dissimilarity(=
)
> > a while ago[2].  Obviously, this should be improved either regarding th=
e
> > algorithm as well as the performance.
> >
> > libgd already has a much better testing library written in C[3], which
> > generates image diffs for failing tests, and we may consider to use
> > parts of it for PHP.  I can't see any issues regarding the license.
> >
> > Thoughts?
>
> The current testing code is under new bsd, so there is no license issue
> here.
>
> I plan to improve the current code to be more useful as well as adding
> perceptual diff. My initial idea was to use pdiff. It is under gpl but as
> it uses only for the tests suite it is ok. Sadly not for php. Alternative=
ly
> the cmd pdiff can be used but it is then slower.
>
> In any case we can expose the image diff functions in ext/gd but it will
> need some work on the results to be useful in the wild.
>
> It should also be easy to write a script to port test from c to/from  php
> to complete both side testing.
>
> Thanks for bringing that up :)
>
> Cheers
> Pierre
>

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