Png quality doesn't work even with libimagequant

[PetrSnobelt]

What are the steps to reproduce?

export SHARP_DIST_BASE_URL=https://github.com/avishnyak/sharp-libvips/releases/download/v8.7.4/
npm install sharp
node png-test.js

(url from #1484)

png-test.js

const Sharp = require("sharp");

Sharp('./images/Accommodation.png')
  .resize(200)
  .png({quality:1})
  .toFile('./output/lowQ.png')
  .then(console.log)

Sharp('./images/Accommodation.png')
  .resize(200)
  .png({quality:99})
  .toFile('./output/highQ.png')
  .then(console.log)

output:

{ format: 'png',
  width: 200,
  height: 118,
  channels: 4,
  premultiplied: true,
  size: 28457 }
{ format: 'png',
  width: 200,
  height: 118,
  channels: 4,
  premultiplied: true,
  size: 28457 }

What is the expected behaviour?
pngs should have different sizes

Are you able to provide a standalone code sample, without other dependencies, that demonstrates this problem?

• see above
• I run it inside docker of ubuntu:bionic image, because I cannot find tar with libimagequant for mac

What is the output of running npx envinfo --binaries --languages --system --utilities?
ldd node_modules/sharp/build/Release/sharp.node:

	linux-vdso.so.1 (0x00007ffdbd9f1000)
	libvips-cpp.so.42 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libvips-cpp.so.42 (0x00007f4d2b960000)
	libvips.so.42 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libvips.so.42 (0x00007f4d2b328000)
	libglib-2.0.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libglib-2.0.so.0 (0x00007f4d2afb2000)
	libgobject-2.0.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libgobject-2.0.so.0 (0x00007f4d2ad5f000)
	libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f4d2a9d6000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f4d2a638000)
	libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f4d2a420000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f4d2a02f000)
	libpng16.so.16 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libpng16.so.16 (0x00007f4d29df6000)
	libz.so.1 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libz.so.1 (0x00007f4d29bdd000)
	libimagequant.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libimagequant.so.0 (0x00007f4d299d0000)
	libtiff.so.5 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libtiff.so.5 (0x00007f4d29757000)
	libjpeg.so.8 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libjpeg.so.8 (0x00007f4d294c2000)
	libgmodule-2.0.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libgmodule-2.0.so.0 (0x00007f4d292bf000)
	librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f4d290b7000)
	libexpat.so.1 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libexpat.so.1 (0x00007f4d28e8b000)
	libgsf-1.so.114 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libgsf-1.so.114 (0x00007f4d28c41000)
	libxml2.so.2 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libxml2.so.2 (0x00007f4d28958000)
	liborc-0.4.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/liborc-0.4.so.0 (0x00007f4d286c1000)
	liblcms2.so.2 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/liblcms2.so.2 (0x00007f4d28459000)
	libgif.so.7 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libgif.so.7 (0x00007f4d28250000)
	librsvg-2.so.2 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/librsvg-2.so.2 (0x00007f4d27995000)
	libgio-2.0.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libgio-2.0.so.0 (0x00007f4d275db000)
	libgdk_pixbuf-2.0.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libgdk_pixbuf-2.0.so.0 (0x00007f4d273af000)
	libcairo.so.2 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libcairo.so.2 (0x00007f4d270aa000)
	libwebpmux.so.3 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libwebpmux.so.3 (0x00007f4d26e9e000)
	libwebp.so.7 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libwebp.so.7 (0x00007f4d26c04000)
	libexif.so.12 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libexif.so.12 (0x00007f4d269be000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f4d2679f000)
	libffi.so.6 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libffi.so.6 (0x00007f4d26597000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f4d2bdc8000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f4d26393000)
	libcairo-gobject.so.2 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libcairo-gobject.so.2 (0x00007f4d2618b000)
	libresolv.so.2 => /lib/x86_64-linux-gnu/libresolv.so.2 (0x00007f4d25f70000)
	libpangocairo-1.0.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libpangocairo-1.0.so.0 (0x00007f4d25d62000)
	libpixman-1.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libpixman-1.so.0 (0x00007f4d25aa3000)
	libpangoft2-1.0.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libpangoft2-1.0.so.0 (0x00007f4d2588d000)
	libharfbuzz.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libharfbuzz.so.0 (0x00007f4d2556e000)
	libpango-1.0.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libpango-1.0.so.0 (0x00007f4d25324000)
	libgthread-2.0.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libgthread-2.0.so.0 (0x00007f4d25123000)
	libfribidi.so.0 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libfribidi.so.0 (0x00007f4d24f07000)
	libfontconfig.so.1 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libfontconfig.so.1 (0x00007f4d24cbb000)
	libuuid.so.1 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libuuid.so.1 (0x00007f4d24ab5000)
	libfreetype.so.6 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libfreetype.so.6 (0x00007f4d247f8000)
	libcroco-0.6.so.3 => /awsmodules/node_modules/sharp/build/Release/../../vendor/lib/libcroco-0.6.so.3 (0x00007f4d245bc000)

libimagequant is here

[PetrSnobelt]

It could be useful if .png({quality:99}) without libimagequant throws exception

[lovell]

https://sharp.pixelplumbing.com/en/stable/api-output/#png

To enable libimagequant at runtime use the palette option.

-  .png({quality:1})
+  .png({ palette: true, quality: 1 })

Set NODE_DEBUG=sharp to view libvips warnings about lack of palette support at runtime.

[PetrSnobelt]

It is unclear to me from docs, that I have to specify palette: true if I just want change quality, consider note it in docs.

Thanks a lot for a quick response and great library.

[PetrSnobelt]

BTW why libimagequant is not in default libvips?

[lovell]

The prebuilt binaries provided by sharp for libvips and its dependencies do not include GPL-licensed or patent-encumbered software.

[PetrSnobelt]

OK, thank you

[larryboymi]

Please include me in the group interested in why palette activates the quality setting for libimagequant ... I'm sure it's something I haven't studied up on yet, but if you're able to shed any light on it I'd appreciate it... Thanks!

[heikkipora]

libimagequant is only used in palette-based mode - i.e. when doing color quantization.
For "true color" PNGs libimagequant is not needed and thus the quality property has no effect.