Raster and Vector
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Definition
Section titled “Definition”Raster content is a grid of pixels: a photograph, a scan, a rendered image. Vector content is a set of drawing instructions: shape paths and glyph placements the reader executes at any size. Text in a born-digital PDF is vector, which is why it stays sharp at any zoom and why it can be selected. A page rendered to an image is raster, which is why converting a PDF to pictures makes the text unselectable and the file resolution-dependent.
Example
Section titled “Example”The same invoice as two files. In the original, received from the billing system, the invoice number can be selected, copied into a ledger, and searched for. In a photograph of the same invoice taken on a phone, the number is visible but unreachable — a picture of text is not text, and no amount of zooming makes it selectable. OCR is the bridge that adds text back to a raster page.
In the PDFLean tools
Section titled “In the PDFLean tools”- convert PDF to JPG — the rasterizing direction; each page becomes an image
- convert SVG to PDF — the vector-in direction, rendered by the browser
Related reading
Section titled “Related reading”- OCR Text Layer — how text is added back to a raster page
- Lossless and Lossy Compression — why raster pages behave so differently under compression
- How to Convert PDF Files — where appearance-faithful and text-level conversions diverge