(epspdf.info)Bitmapped and vector

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3.1 Bitmapped and vector
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Pictures can be described either in terms of pixels, or more abstractly,
in terms of geometric shapes, fonts and text.

Bitmapped or pixel-based graphics are appropriate for photographs and
screenshots, but less so for diagrams and spreadsheet-generated
graphics.

A file in PostScript- or pdf format can contain both types of graphic
data.

Vector graphics can be freely scaled without losing sharpness or
becoming pixellated.  If bitmapped graphics are enlarged too much,
individual pixels become apparent.  With low-resolution bitmaps this
happens sooner than with high-resolution bitmaps, but high-resolution
bitmaps have (much) larger file sizes, and take longer to process.

So avoid converting vector to bitmap.  However, converting from bitmap
to vector is also best avoided, since it is very hard to do well.

Epspdf usually avoids conversion from vector to bitmap and never
converts the other way.  With the screen- and ebook "Target use" option,
included bitmaps tend to be downsampled, i.e.  reduced to a lower
resolution.