optipng (vs|+) pngout

[Alysko]

Hi,

It's just a note.

optipng doesn't strip useless txt - let by software like Adobe Photoshop - in PNG. pngout does.

pngout compress better but you have tell him what kind of png is there (color+alpha, greyscale+alpha, etc.), otherwise he's doing wrong.
optipng knows what type of png should be used.

So, if I want a real optimised PNG (for example to convert in base64 for dataURI), I use optipng then pngout (in that order).

[paulirish]

hmm we want to move to "improved pngquant".. do you know what its behavior is?

[craigbarnes]

The following is about as good as lossless compression gets for PNGs:

optipng -o7 *.png && advpng -z4 *png && advdef -z4 *.png

PNGOUT is closed source, it's license prohibits bundled distribution and it's development is completely mothballed.

[nimbupani]

Looping in @pornel! Do you have a recommendation for using pngquant with H5BP build script?

[kornelski]

pngquant removes all optional chunks. Files reduced with pngquant can be further optimised with optipng & co.

Beware that some png's might not take conversion to png8 well, so this can't be blindly applied to all of them (I plan to include dssim tool with pngquant to detect this case and skip conversion automatically.)

[Alysko]

"improved pngquant" is not a tool to optimize png, but to "Quantizes one or more 32-bit RGBA PNGs to 8-bit (or smaller)" (which is done very well). But it's not the same.

Metadata stripping is planned for v0.7 of OptiPNG, but there's no release date.

pngcrush is also a very good alternative. There is a "prod option", -brute, which test all the different optimization to determine the best. But it's verrryyyy slow (6s ans (gain 2.6%) for the default on a 140k/24b png ; 46s (gain 4%) for with the -brute option). But it doesn't strip comment too.

And yes, PNGOUT is closed source, but it's one of the few to strip comment.

[craigbarnes]

"improved pngquant" is not a tool to optimize png, but to "Quantizes one or more 32-bit RGBA PNGs to 8-bit (or smaller)" (which is done very well). But it's not the same.

I'm pretty sure @pornel already knows what it does ;)

[Alysko]

This was a reply to Paul :) "improved pngquant" should not replace optipng because it's a different tool.

[Vyeche]

I find PNGout doing way more compression then optiPNG. I did some tests on 32 bit depth and they compressed down to the same file size, as compared to using PNGout. Damns, so much for automating the png's in HTML5 boilerplate.

[tchalvak]

So no consensus on this one, then?

[Alysko]

Yes : wait for optipng v.0.7 (Plans for version 0.7: Metadata editing -- including the highly-anticipated metadata stripping capability :-))

[necolas]

Closing this because the plan seems to be "update optipng when there's a new release". If this needs to be reopened, please do it at the ant build script repo with a cross-repo link back to this issue. Thanks

[ghost]

So I've mentioned 2 years ago that automatic conversion to png8 might be risky. Well, it's fixed now:

pngquant --quality=90-99 --force --ext .png file.png

This will overwrite the file.png only if conversion doesn't lose more than 10% of quality (quality is min-max format) and makes pngquant automatically choose number of colors aiming for only 1% quality loss.

Still, file size can be reduced afterwards with lossless optimizers like optipng or pngout.

[roblarsen]

I'm already on this over at the ant build script repo.

[necolas]

Thanks guys. Closing as this is an issue for the build script. But good to know.