Why am I seeing colour fringing

Frode Bo Helland's picture

Screenshot from Firefox on a Mac.

Enlarged by 400 %

All these stems (and even the round edges in o) are landing 100% on the pixel, but the Quartz rendering still manage to throw them off. My em is 1100, all stems are 100 units and all character widths are multiples of 100. The CSS font size is 11 px. Any idea why this is happening? Also, see "ploughline" which is all fuzzed up. Am I doing something wrong in the font settings?

Frode Bo Helland's picture

Just to explain: I do expect some colour fringing, but I’d expect it to be the same all over.

Frode Bo Helland's picture

Here, with a pixel font, the colour fringing is far from what I’m getting. Remember, I’m only comparing the stems.


Unibody, a pixel font by Underware rendered under the same conditions

k.l.'s picture

(Provided I get the idea:) Tiny error in your metrics?

Frode Bo Helland's picture

Nope, but I tried exporting postscript outlines, and suddenly everything looked way better. Still don’t understand why, and I’m not sure if I can rely on postscript for this project. Btw, if you notice some different letters it’s just revisions as I go. It’s still the same font.


Postscript outlines


Postscript outlines, 400 % zoom

Rob O. Font's picture

Is the word space unitized?

Frode Bo Helland's picture

Yes. Everything is a multiple of 100 units. I’ve been working on a ps version of it in another font file as well, and when exporting it to ttf everything seems to be working fine. No idea why …

Mark Simonson's picture

Have you made sure that no autohinting is being applied?

Frode Bo Helland's picture

I thought I had, but I'm not well versed in these areas. Under "font info" (I assume), which exact parts do I need to check/uncheck and which values might affect this?

Mark Simonson's picture

You can control the default autohinting settings in: Preferences > Generating OpenType & TrueType > TrueType/OpenType TT (.ttf)

You can override the default autohinting settings per font in: Font Info > TrueType-specific settings > OpenType export

John Hudson's picture

My guess is that this is a raster-side by-product of colour filtering resulting in colour bleed. I made a similar test in Windows some months back, and found that even when outlines and metrics were snapped to a grid, as in your 'pixel font' example, there was a small amount of pale yellow and blue bleed.

See the images and comments I posted in this thread:
http://www.typophile.com/node/71019

Rob O. Font's picture

>Yes. Everything is a multiple of 100 units

Well, you said you understood the light fringing occurring. The feature alignment is definitely going out of phase with the grid, so it's either the advance widths, or the composition ignoring them for some adjustment...

Thomas Phinney's picture

Also, this is being rendered by Mac OS, so hinting (or lack thereof) is irrelevant. Mac OS ignores hinting built into the font.

aluminum's picture

Isn't that the OS's sub-pixel font smoothing?

Frode Bo Helland's picture

Rendering control where hinting has no effect is the whole point here, Thomas. Both binary rendering and Quartz rendering works like a charm (with this first issue resolved). The troublemaker is actually Cleartype, especially diagonals.

Rob O. Font's picture

I don't understand that? Normal diagonals are about the same as normal.vertical stems in CT. It is thin diagonals and thin verticals where it fails miserably.

Rob O. Font's picture

>Also, this is being rendered by Mac OS, so hinting (or lack thereof) is irrelevant. Mac OS ignores hinting built into the font.

you keep repeating this, over and over, thread to thread, as if ithat would make it true.;)

Frode Bo Helland's picture

Me neither, David. My diagonals are almost as sexy as my curves in 0101, but CT sure adds some weight to those thighs.

Thomas Phinney's picture

DB: I assume that is supposed to be a comment on this fact not being widely understood, not that you actually disagree with me?

Cheers,

T

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