test suite; generalize past 8x8

[camilleg]

Github user zvezdochiot suggests block sizes other than 8x8.
This change would be invasive, because 8x8 is hardcoded in loops such as costella/costella_unblock.c lines 1060-1300, 1500-1750, 2020-2170, 2260-2400, 2590-2780... .
This would first need some test cases to ensure that all the 8's were caught.

[zvezdochiot]

cjpeg -quality 30 -outfile lena256.jpg lena256.ppm

Decode

Upscale x2 (cubic)

[camilleg]

Is this right?

• Lena is the starting point. cjpeg's deliberately blocky output, converted to bmp (and to png) is the test case's input. unblock's output as of 2021 Jan 28 is the test case's expected output. That reassures us that the 8x8 case hasn't been broken.
• The upscale x2 is a separate test case, for 16x16. That lets us check if 16x16 outperforms 8x8, as it should.

[zvezdochiot]

Right.

[camilleg]

Good! I'll build that. But instead of Lena, Jelly Beans http://sipi.usc.edu/database/download.php?vol=misc&img=4.1.08 (smooth gradients) and Mandrill http://sipi.usc.edu/database/download.php?vol=misc&img=4.2.03 (high frequency fur). By now, major journals are refusing articles that use Lena, https://en.wikipedia.org/wiki/Lenna#Criticism.

[camilleg]

Committed test cases for 8x8.

[zvezdochiot]

Source: in2.png

Upscale x2: in2.x2.png

Unblock: ./unblock in2.x2.png out2.x2.png

No good.

[zvezdochiot]

Build:

Replace

CFLAGS = -O3 -Wall -W

to

CFLAGS = -O3 -Wall -W -std=c++11

[camilleg]

What's your question about ./unblock in2.x2.png out2.x2.png? I haven't yet implemented 16x16; that's why this issue is still open. I've only committed some 8x8 test cases.

[camilleg]

https://ffmpeg.org/ffmpeg-filters.html#deblock allows block sizes from 4 to 512 with a default of 8. Although ffmpeg is related to avisynth, its deblock filter didn't come from Costella, but from "Ramkishor, K., Karandikar, P.: A simple and efficient deblocking algorithm for low bit-rate video coding. In: IEEE Inernational Symposium on Consumer Electronics (December 2000).".

That filter would provide another way to test and compare the performance of this repo.