GeezerVison

What you're seeing is the effect of "soft hinting" where it hints to subpixels in the x direction. Years ago we did a sort of survey on the mailing list of which kind of hinting looked best and that's what we determined. Of course, it doesn't have to be hardcoded, so I've attached some changes that make the amount of softness tweakable with an rcParam. Can you try this out (setting "text.hinting_factor" to 1) and let me know if this resolves your issue? I'm hesitant to change the default as many users (and the testing framework) are relying on the present behavior.

Attached is a pull request that makes the "hinting factor" tweakable at runtime.

The hinting factor is the amount of softness in hinting is applied in
the horizontal direction.  For years, matplotlib has hinted to 1/8
pixels in the horizontal direction and whole pixels in the vertical
direction.  This results in text that is often more
legible (particularly at smaller sizes) than standard 1:1 hinting.
This is based on idea from this paper from the author of Agg:

    http://www.antigrain.com/research/font_rasterization/

However, sometimes the user may want full-on hinting, so this value is
now tweakable using the `text.hinting_factor` rcParam.

Thanks for the patch! It does improve things, but the hinting still leaves a bit to be desired, at least compared to the Cairo backend. I've updated the images at http://jim.sh/~jim/tmp/matplotlib-font to show how the text.hinting_factor = 1 changes things. I also included a plot that attempts to force hinting with text.hinting = True, but that doesn't seem to make a difference. Notice how vertical letters like the Ls are now sharper horizontally, but still don't fully snap to pixels like in the Cairo case.

Regarding the default, I agree that the present behavior shouldn't be changed at this point. I'm fine with setting a variable in my own scripts.

I think I figured it out: currently, text.hinting can choose between the FreeType options LOAD_NO_HINTING or LOAD_FORCE_AUTOHINT. The option I need is LOAD_DEFAULT -- use the font's native hinting if available. If I hack lib/matplotlib/backends/backend_agg.py so that _get_hinting_flag always returns LOAD_DEFAULT, then the Agg font rendering matches Cairo exactly.

Maybe text.hinting could be extended in a compatible way, e.g.:

{
False: LOAD_NO_HINTING,
True: LOAD_FORCE_AUTOHINT,
"auto": LOAD_FORCE_AUTOHINT,
"native": LOAD_NO_AUTOHINT,
"either": LOAD_DEFAULT,
}

Ok. I've incorporated this.

Works perfectly. Now text.hinting_factor: 1 and text.hinting: native gives me exactly what I wanted. Thanks so much!

Great! Merging...