[okular] [Bug 408222] Okular is bad in displaying of scanned PDF ! Please fix this !

[Tobias Deiminger]

https://bugs.kde.org/show_bug.cgi?id=408222

--- Comment #23 from Tobias Deiminger <haxtibal at posteo.de> ---
(In reply to Tobias Deiminger from comment #22)
> $ compare -metric SSIM test-1-original.jpg test-1-cairo-200dpi.png null: 2>&1
> 0.826331
There was a mistake in the example. The compare tool needs two identical sized
images (it works otherwise, but does a completely different thing then). So now
I scale up poppler output back to original size with a high quality filter
before comparing images.

Here are some first test results:

|       Test conditions    | avg. SSIM (higher is better) |
orig_size  new_size   scale  Splash    Cairo     Lanczos(*)
1894x2798  1799x2658  0.95   0.894696  0.97901   0.986598
1894x2798  1704x2518  0.90   0.940628  0.975257  0.961978
1894x2798  1609x2378  0.85   0.939805  0.972347  0.961621
1894x2798  1515x2238  0.80   0.896754  0.965689  0.972571
1894x2798  1420x2098  0.75   0.944005  0.955174  0.969092
1894x2798  1325x1958  0.70   0.944173  0.954734  0.966077
1894x2798  1231x1818  0.65   0.913747  0.959678  0.963164
1894x2798  1136x1678  0.60   0.932564  0.939862  0.959964
1894x2798  1041x1538  0.55   0.945498  0.926968  0.948855
1894x2798   947x1399  0.50   0.888512  0.951904  0.952485
1894x2798   852x1259  0.45   0.893747  0.944982  0.942065
1894x2798   757x1119  0.40   0.926194  0.938078  0.936967
1894x2798   6620x979  0.35   0.908621  0.928839  0.929847
1894x2798   568x 839  0.30   0.871821  0.9177    0.9235
1894x2798   473x 699  0.25   0.909859  0.903451  0.909088
1894x2798   378x 559  0.20   0.894681  0.88581   0.894793
1894x2798   284x 419  0.15   0.869878  0.879541  0.876719
1894x2798   189x 279  0.10   0.861054  0.858674  0.863767

If there were no further mistakes, that was a quite significant win for Cairo
over Splash. I'm planning to publish my test methods and open an issue at
poppler. There we can discuss if we take action.

(*) Lanczos downsampling (with IM7) is included for reference and plausibility.

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