Vector vs raster: why some images stay sharp and others go blurry
Zoom into one logo and it's crisp; zoom into another and it's a blocky mess. That's vector vs raster. Here's the difference and what it means for your PDFs and images.
You’ve seen it happen. You blow up a logo to put it on a banner and it turns into a staircase of blocky edges. Another logo, scaled to the side of a building, stays razor sharp. Same idea, totally different result. The reason comes down to two fundamentally different ways of storing an image: raster and vector. Knowing which is which saves you from blurry prints and bloated files.
Raster: a grid of dots
A raster image is a grid of colored dots, pixels. A photo is the classic example. Each tiny square holds a color, and together they make the picture. JPG, PNG, and most photos you take are raster.
The defining limit: a raster image has a fixed number of dots. Zoom in far enough and you run out, so the software has to guess what goes between the dots, and you get blur or blocky edges. This is why a small image looks terrible when you blow it up. The detail was never there to begin with; you can’t invent dots that don’t exist. How many dots an image has per inch is its resolution, or DPI, and it’s why print wants high-resolution originals.
Vector: instructions, not dots
A vector image doesn’t store dots at all. It stores instructions: “a circle this big, here, filled with this color; a line from here to there.” Because it’s math, not a fixed grid, it can be drawn at any size perfectly. The SVG format is the common one on the web.
That’s why a vector logo stays sharp on a business card and on a billboard. The instructions just get drawn bigger; there are no dots to run out of. Vectors are ideal for things made of clean shapes and lines: logos, icons, diagrams, type.
The trade-off: vectors aren’t good for photographs. A photo is too complex and organic to describe as shapes, so photos are raster, always.
The simple rule
- Logos, icons, line art, diagrams → vector, if you can. Scales to any size, stays crisp.
- Photographs → raster. Just start from a high enough resolution for how big you’ll use it.
The classic mistake is using a small raster logo where a vector belonged, then wondering why it’s fuzzy when enlarged. If you have the vector original, use it for anything that needs to scale.
What this means for your PDFs
PDFs can hold both kinds. A PDF exported from design software might keep your logo as crisp vector art; one built from photos or scans is full of raster images. This is also why scanned PDFs are big and don’t scale well, they’re raster, a grid of dots per page.
When you’re working with image-heavy PDFs, files.co has browser-based tools for it: turn images into a PDF with images to PDF, pull pages out as images with PDF to images, or shrink a heavy raster-filled file with compress. All of them run on your own device.
And that’s the privacy bit worth repeating: whether your images are a brand’s logo or personal photos, files.co processes them in your browser. Nothing is uploaded, which you can confirm with DevTools (F12) or by working offline.
So next time an image goes blocky when you enlarge it, you’ll know it was raster, and that a vector original, if one exists, is the fix. Sharp where it counts, and your files never leave your machine to sort it out.