Blur Image

Each output pixel is replaced with a weighted average of the pixels around it, with nearby neighbours counting for more than distant ones. The weighting follows a bell curve, which is where the name comes from, and it is what makes the result look naturally soft rather than smeared in a particular direction.

The radius controls how far that averaging reaches. A small radius mixes only immediate neighbours and takes the edge off; a large one pulls in pixels from across the frame and dissolves the image into colour fields. The relationship is not linear — doubling the radius does considerably more than double the visual effect.

Because the operation replaces pixel values rather than covering them, it is destructive by nature. That is a drawback when you are softening a photograph for effect and precisely the point when you are hiding something.

Drawing a black box over a bank account number in an editing application feels like redaction, but if the file keeps layers the box can be moved, and even flattened it advertises that something was concealed. Blur removes the information instead of hiding it: after export, the characters are not recoverable because they are no longer represented in the pixels.

The practical rule is to judge the result at full zoom, not in a preview. A blur that looks convincing at thumbnail size can leave text perfectly legible when someone opens the image properly. If you can still make out what it said, so can anyone else.

For redacting a specific area rather than the whole picture, the Blur Face tool lets you draw regions and leave everything else sharp — usually what you want when only one part of a screenshot is sensitive.

Text laid over a photograph is often hard to read, because the image underneath has edges and contrast competing with the letterforms. Blurring the background is the standard fix — the photograph still provides colour, mood and context, but nothing in it fights the type.

This is why blurred imagery is everywhere behind headlines, login screens, hero sections and presentation title slides. The blur wants to be heavier than instinct suggests: if any recognisable edge survives, it will find its way behind a letter and make it harder to read.

Blurring also shrinks the file, which is a useful side effect for a full-width background image that would otherwise be one of the heaviest things on the page.

A camera with a wide aperture throws the background out of focus and makes the subject stand out. Phone cameras approximate this with portrait mode, and it can be approximated further after the fact by blurring an image and compositing a sharp subject back over it.

The honest caveat is that a uniform blur is not what a lens does. Real optical defocus increases with distance, so a true shallow-depth photograph is progressively softer toward the back of the scene, while a uniform blur is equally soft everywhere. Keep the effect light and it reads convincingly; push it hard and it looks like what it is.