I would love to see a native ssim/dssim implementation in PHP… On Fri, Jun 17, 2016 at 6:54 AM, Pierre Joye <pierre....@gmail.com> wrote:
> Hi > On Jun 17, 2016 8:18 PM, "Christoph Becker" <cmbecke...@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 the > > 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. Alternatively > 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 >
