Sharpen an image

Increase local edge contrast with a 3×3 convolution while preserving image dimensions.

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ToolSharpen Filter
Input
Output
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Preview

How it works

A 3×3 kernel gives the centre weight 1 + 4a and four neighbours −a, with diagonal weights zero. Coordinates outside the image clamp to the nearest edge before RGB channels are accumulated.

  • Amount 1 is the initial high-pass strength.
  • Alpha is copied from the centre pixel.

Worked example

Sharpen a test tile
Input
											Input: data:image/png;base64,iVBORw0KGgo=
Amount: 1
Output
												PNG data URL with edge-enhanced RGB pixels

When to use this

Scanned documents increase crispness, photo pipelines sharpen before export, and graphics lessons demonstrate convolution kernels.

Edge cases

  • Strong amounts create halos and clipped highlights.
  • Edge pixels reuse border samples rather than wrapping.
  • Noise is high-frequency detail and can be amplified.

References