Rasterization
Converting vector content (text, shapes, lines) into a grid of pixels — a raster image. Often a deliberate step for redaction or compression; sometimes an unwanted side effect.
Rasterization is the conversion of vector-based content (text, lines, shapes defined as mathematical instructions) into raster content (a grid of colored pixels). Vector content scales cleanly to any size; raster content is fixed at its pixel resolution.
When rasterization happens
- PDF to image conversion. When you export a PDF page as a JPG or PNG, every element on the page is rasterized to pixels at a chosen DPI.
- Aggressive compression. Very high compression levels may rasterize text into images to save space — this loses searchability but maximizes size reduction.
- True redaction. Redacting a PDF properly often involves rasterizing the affected page so the hidden text literally ceases to exist.
- Printing. Even when printing a PDF, the printer ultimately rasterizes everything to its native resolution.
Rasterization trade-offs
Gained:
- A page becomes a single image, which cannot reveal hidden content (important for redaction)
- Guaranteed identical rendering everywhere — no font substitutions, no reflow
Lost:
- Text becomes pixels, so search and copy-paste no longer work
- File size usually grows if the original was text-heavy (text compresses extremely well; images don't)
- Editing becomes harder — you can no longer click a word and change it
Tools that use rasterization
- Redact PDF rasterizes pages containing redactions to guarantee the hidden text is gone
- PDF to JPG and PDF to PNG rasterize every page
- Compress PDF may rasterize heavily at the Extreme setting