Glyphs are drawn on the screen using an anti-aliasing technique that can make curves and diagonal lines look smooth, avoiding the jagged look caused by the individual pixels. This is acheived by adding shaded pixels to the glyph to give the illusion of partial pixels, but this also reduces the perceived sharpness of the glyph. Therefore, for a given pixel size, increased sharpness is gained only by a reduction in smoothness, and vice versa.
The TypeGenius feature allows the weight and sharpness of each font to be adjusted. (See the
`Freedom to advanced font controls` patch to enable TypeGenius for sideloaded fonts.) Adjustng the sharpness allows the ideal balance of smoothness vs sharpness to suit individual preferences.
The table in the following screenshots (Glo 3.15.0) shows the range of weight and sharpness values that can be set from the slider. This is only a sample of the possible values, the slider actually allows much finer adjustment. (These screenshots were created from this
demonstration kepub using the built-in Georgia and sideloaded Tex Gyre Bonum fonts, and are best viewed at 100% zoom to see the increase in sharpness from left to right):
In firmware versions up to 3.1.1 the advanced fonts menu had separate sliders for weight and sharpness which allowed any combination of values to be selected. But from firmware version 3.2.0 there is only one slider which sets both weight and sharpness, so an increase in weight results in an increase in sharpness too. In effect this means only the combination of values along a diagonal from the lower left to upper right of the above table can be selected.
The
`ePub fixed font sharpness` and
`KePub fixed font sharpness` patches allow a fixed sharpness value to be chosen, e.g. 0.0, 0.1, or 0.2, so that the sharpness value selected by the adjustment slider is ignored and only the weight value used. In effect this means that the slider can be used to select combinations from a vertical column instead of from the diagonal of the table above.
It is also possible to set the weight and sharpness independently without patching by editing the device's configuration file and changing the values of readingFontWeight and readingFontSharpness in the [Reading] section. While these patches only allow one fixed sharpness value to be selected, they avoid the need to re-edit the configuaation file after adjusting the weight via the slider.