Use mozjpeg instead of libjpeg-turbo

[atjn]

Hello again :)

I would strongly recommend using mozjpeg for JPEG encoding. It is identical to libjpeg-turbo, but has some added patches that significantly improves compression without sacrificing image quality. It is used in many popular image suites, including other ports of libvips.

If you need to use libjpeg-turbo to test bleeding-edge updates, it is very easy to change back to. I can even add a flag to automatically switch between the two if you'd like.

[kleisauke]

Hi @atjn,

Thanks for the PR! The reason that I used libjpeg-turbo instead of mozjpeg was that the latest version of mozjpeg (4.0.3) was a bit out-of-sync. But you're right, we could just build against mozjpeg's master branch instead (which is based upon libjpeg-turbo 2.1.3).

Note that libvips resets to libjpeg-turbo's JCP_FASTEST defaults so this can be considered a "no-op" unless mozjpeg features are explicitly set, see: lovell/sharp-libvips#89.

This will be in v0.0.4.

[kleisauke]

FWIW, the Windows CI failure is unrelated to this and should be fixed with commit 5823efb.

[atjn]

Cool!

The reason that I used libjpeg-turbo instead of mozjpeg was that the latest version of mozjpeg (4.0.3) was a bit out-of-sync.

Yeah that is a bit weird.

Note that libvips resets to libjpeg-turbo's JCP_FASTEST defaults so this can be considered a "no-op" unless mozjpeg features are explicitly set, see: lovell/sharp-libvips#89.

Good to know, thanks!
Would it make sense for this port to enable some mozjpeg features by default? I would be happy to play around with it, if you are open to it.

[kleisauke]

Would it make sense for this port to enable some mozjpeg features by default?

Good question. I think we shouldn't deviate too much from libvips default settings. The mozjpeg settings can be controlled with these options:

wasm-vips/lib/vips.d.ts

Lines 7316 to 7331 in a51b0e2

	/**
	* Apply trellis quantisation to each 8x8 block.
	*/
	trellis_quant?: boolean
	/**
	* Apply overshooting to samples with extreme values.
	*/
	overshoot_deringing?: boolean
	/**
	* Split spectrum of dct coefficients into separate scans.
	*/
	optimize_scans?: boolean
	/**
	* Use predefined quantization table with given index.
	*/
	quant_table?: number

Which are guarded in libvips with the HAVE_JPEG_EXT_PARAMS condition:
https://github.com/libvips/libvips/blob/7e961b46718b32d654a1c10e9261cdbbd5ccb9b6/libvips/foreign/vips2jpeg.c#L613-L670

I'm aware that sharp has a shortcut option that would enable these settings at once (it also enables optimize_coding by default), see:
https://sharp.pixelplumbing.com/api-output#jpeg

A better option would be to provide a polyfill for sharp, based on wasm-vips, as discussed in this Twitter thread:
https://twitter.com/lovell/status/1395710714799665163