Refactor optimize_raw

[andrews05]

Code always tends to get messy over time. I've found the optimize_raw function increasingly harder to read, particularly after the addition of fast mode, so I've taken some time to refactor and simplify it.

One change of note here is the main compression trials now use the Evaluator. This means verbose output is a little different which is shown below.

There is no change to performance or output size.

-vvo2: master

Processing: tests/files/rgba_8_should_be_palette_4.png
    500x400 pixels, PNG format
    8-bit RGB + Alpha, non-interlaced
    IDAT size = 2757 bytes
    File size = 18109 bytes
Eval: 4-bit Indexed (5 colors)      None       1837 bytes
Eval: 8-bit Indexed (5 colors)      None       1988 bytes
Eval: 4-bit Indexed (5 colors)      Bigrams   >1837 bytes
Eval: 8-bit Indexed (5 colors)      Bigrams   >1837 bytes
Transformed image to 4-bit Indexed (5 colors), non-interlaced
Evaluating: 2 filters
Eval: 4-bit Indexed (5 colors)      Sub       >1810 bytes
Eval: 4-bit Indexed (5 colors)      Entropy   >1810 bytes
Trying: None
    zc = 11  f = None      1583 bytes
Found better combination:
    zc = 11  f = None      1583 bytes
    IDAT size = 1583 bytes (1174 bytes decrease)
    file size = 16962 bytes (1147 bytes = 6.33% decrease)
16962 bytes (6.33% smaller): Running in pretend mode, no output

-vvo2: PR

Processing: tests/files/rgba_8_should_be_palette_4.png
    500x400 pixels, PNG format
    8-bit RGB + Alpha, non-interlaced
    IDAT size = 2757 bytes
    File size = 18109 bytes
Eval: 4-bit Indexed (5 colors)      None       1837 bytes
Eval: 8-bit Indexed (5 colors)      None       1988 bytes
Eval: 4-bit Indexed (5 colors)      Bigrams   >1837 bytes
Eval: 8-bit Indexed (5 colors)      Bigrams   >1837 bytes
Transformed image to 4-bit Indexed (5 colors), non-interlaced
Evaluating 2 filters
Eval: 4-bit Indexed (5 colors)      Sub       >1810 bytes
Eval: 4-bit Indexed (5 colors)      Entropy   >1810 bytes
Trying filter None with zc = 11
1610 bytes
Found better result:
    zc = 11, f = None
    IDAT size = 1583 bytes (1174 bytes decrease)
    file size = 16962 bytes (1147 bytes = 6.33% decrease)
16962 bytes (6.33% smaller): Running in pretend mode, no output

-vvZo5: master

Processing: tests/files/rgba_8_should_be_palette_4.png
    500x400 pixels, PNG format
    8-bit RGB + Alpha, non-interlaced
    IDAT size = 2757 bytes
    File size = 18109 bytes
Eval: 8-bit Indexed (battiato sort) None       1821 bytes
Eval: 4-bit Indexed (5 colors)      None       1657 bytes
Eval: 8-bit Indexed (mzeng sort)    None       1821 bytes
Eval: 8-bit Indexed (5 colors)      None       1821 bytes
Eval: 8-bit Indexed (battiato sort) Bigrams   >1821 bytes
Eval: 4-bit Indexed (5 colors)      Bigrams   >1657 bytes
Eval: 8-bit Indexed (mzeng sort)    Bigrams   >1657 bytes
Eval: 8-bit Indexed (5 colors)      Bigrams   >1657 bytes
Transformed image to 4-bit Indexed (5 colors), non-interlaced
Trying: 8 filters
    zc = zopfli  f = Brute     1562 bytes
    zc = zopfli  f = Sub      >1562 bytes
    zc = zopfli  f = Bigrams  >1562 bytes
    zc = zopfli  f = None      1407 bytes
    zc = zopfli  f = Up       >1407 bytes
    zc = zopfli  f = MinSum   >1407 bytes
    zc = zopfli  f = BigEnt   >1407 bytes
    zc = zopfli  f = Entropy  >1407 bytes
Found better combination:
    zc = zopfli  f = None      1407 bytes
    IDAT size = 1407 bytes (1350 bytes decrease)
    file size = 16786 bytes (1323 bytes = 7.31% decrease)
16786 bytes (7.31% smaller): Running in pretend mode, no output

-vvZo5: PR

Processing: tests/files/rgba_8_should_be_palette_4.png
    500x400 pixels, PNG format
    8-bit RGB + Alpha, non-interlaced
    IDAT size = 2757 bytes
    File size = 18109 bytes
Eval: 8-bit Indexed (battiato sort) None       1821 bytes
Eval: 4-bit Indexed (5 colors)      None       1657 bytes
Eval: 8-bit Indexed (mzeng sort)    None       1821 bytes
Eval: 8-bit Indexed (5 colors)      None       1821 bytes
Eval: 8-bit Indexed (battiato sort) Bigrams   >1657 bytes
Eval: 4-bit Indexed (5 colors)      Bigrams   >1657 bytes
Eval: 8-bit Indexed (mzeng sort)    Bigrams   >1657 bytes
Eval: 8-bit Indexed (5 colors)      Bigrams   >1657 bytes
Transformed image to 4-bit Indexed (5 colors), non-interlaced
Trying 8 filters with zopfli, zi = 15
Eval: 4-bit Indexed (5 colors)      Brute      1589 bytes
Eval: 4-bit Indexed (5 colors)      Bigrams    1641 bytes
Eval: 4-bit Indexed (5 colors)      Sub        1711 bytes
Eval: 4-bit Indexed (5 colors)      None       1434 bytes
Eval: 4-bit Indexed (5 colors)      Up         1764 bytes
Eval: 4-bit Indexed (5 colors)      MinSum     1760 bytes
Eval: 4-bit Indexed (5 colors)      BigEnt     1742 bytes
Eval: 4-bit Indexed (5 colors)      Entropy    1748 bytes
Found better result:
    zopfli, zi = 15, f = None
    IDAT size = 1407 bytes (1350 bytes decrease)
    file size = 16786 bytes (1323 bytes = 7.31% decrease)
16786 bytes (7.31% smaller): Running in pretend mode, no output

[andrews05]

@AlexTMjugador Thanks for merging the APNG update, hope you're ready for another one 😄

I've got one minor fix which I'll post after this and then we can probably do another release.

[ace-dent]

Thanks @andrews05 - I do (slightly) prefer the original verbose output. I occasionally write scripts to extract a result (e.g. filter tested), so for some these changes may break their workflow. If no one speaks up, I'm sure it's absolutely fine. 👍

Oh- and if you are adding zopfli iterations, as per #658 (comment), that would be an awesome addition!! 🤞

[andrews05]

Thanks @andrews05 - I do (slightly) prefer the original verbose output. I occasionally write scripts to extract a result (e.g. filter tested), so for some these changes may break their workflow. If no one speaks up, I'm sure it's absolutely fine. 👍

Is there something in particular you think could be improved, or is it just a matter of updating the script to handle the new output? I’m afraid the output isn’t something the user can rely on to be “stable” and changes between versions (even minor versions) can be expected.

Oh- and if you are adding zopfli iterations, as per #658 (comment), that would be an awesome addition!! 🤞

Unfortunately no, this is just showing the value of the zi parameter which defaults to 15. As noted in that thread though, you can parse zopfli’s debug output to try and find what you’re looking for.