Embedded bitmaps, metrics behave irregularly

Elias's picture

Hi

I have made a TTF with embedded bitmaps (at 19 ppm). The font is for an editor, where you write/edit with your "normal" TTF-beziers in order to generate a bitmap-image with your embedded bitmaps.

I have first made the strike and generated the .bdf in FontForge, then imported the bitmaps in Fontlab, copied them to background and then traced the pixels. Thus, the outlines are are just vectorized copies of the embedded bitmaps. I have set the spacing on each side of the glyph to one pixel:

However, when I test the font in Photoshop and in the editor, I get that the spacing behaves differently every time I type in the same word (the example shown is in a 96 dpi file, and the irregular spacing happens regardless if set the type in 14,25 pt or round it down to 14 pt). See attachment

Now my question is; what is causing this irregular spacing of the bitmaps, and how can it be corrected? Is the problem within the font or within a setting in the applications?

I am looking very much forward to getting your feedback. It will be much appreciated.

Best
Elias

AttachmentSize
Spacing example.jpg153.66 KB
Elias's picture

Ok, at least in Photoshop, the spacing now works as it should when fractional widths and optical kerning is turned off.

Frode Bo Helland's picture

I was not aware Photoshop used the embedded bitmaps. (Does it use them under all sharpness modes, as well?) Yes, with fractional widths and optical kerning, you are likely to get these rounding errors. I don’t know if Adobe Photoshop listens to x-direction TrueType hints either, but those could potentially provide better control in situations like these.

Elias's picture

Thank you, Frode.

No, anti-aliasing must be turned off as well, and so must ClearType, in case you have a PC.

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