The trick behind the blocky look
Pixelation is one of the oldest visual effects on the internet — a license plate, a face, a spoiler in a screenshot, all covered in the same chunky, hard-edged blocks. The effect looks complicated but works through a genuinely simple trick: the image is shrunk down drastically, so each remaining tiny pixel represents an average of a large chunk of the original, then scaled back up to full size with smoothing turned off. Normally, enlarging a small image blurs it smoothly; disabling that smoothing forces each of those averaged pixels to render as a hard, visible block instead — that's the entire effect, and it's why it looks so distinctly different from blur.
Blocky vs. smooth: picking the right obscuring effect
Pixelation and blurring both hide detail, but they read completely differently to a viewer. Pixelation's hard edges signal "this was deliberately censored" — it's the universally recognized visual language for "redacted," which is exactly why news broadcasts and reality shows use it for faces and license plates. Blurring reads as softer, more like an out-of-focus photo than an intentional edit, which can actually work against you if the whole point is to make it obvious that something was deliberately hidden rather than just poorly focused.
The privacy limitation almost nobody checks
Here's the part that catches people off guard: a light pixelation effect isn't always a one-way street. For simple, predictable content — especially text, where there's a limited set of characters it could plausibly be — a light pixelation can sometimes be partially reconstructed, since the averaged blocks still carry some statistical trace of the underlying content. This is a well-documented weakness of pixelation as a redaction technique, not a hypothetical concern. If you're hiding something genuinely sensitive — a document number, a password visible in a screenshot, anything that actually matters if exposed — a light pixel size isn't enough. Use a strong, heavy setting, or better yet, cover the area with a solid opaque block instead of a reversible effect.
Choosing the right pixel size for the job
The pixel size slider is the only real control here, and it's worth understanding what it actually changes: a small value averages a small cluster of source pixels, producing a subtle softening that barely reads as "pixelated" at all — useful for a gentle stylistic effect rather than obscuring anything. A large value averages much bigger blocks, producing the strong, unmistakable censored look most people actually want when hiding a face or detail. If your result looks like it barely did anything, the setting is too low for what you're trying to achieve, not a sign the tool isn't working.