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lil cactus

How to pixelate an image

Beginner4 minutesUpdated

Quick answer

In Lil Cactus, choose Filter then Pixelate then Pixelate… Cell Size sets each block’s width and height in image pixels; 48 px gives 32 blocks across a 1536 px-wide photo. Click Apply. To pixelate only part of an image, select that area with Marquee Select before opening the filter. Export the result through File then Export then PNG…

A coffee cup and orange tabletop before and after the whole photo is replaced by 48-pixel square mosaic blocks
Cell Size 48 px turns the whole sample into a coarse mosaic. The image stays 1536 × 1024 px. Drag the handle to compare.
Time
4 minutes
Level
Beginner
You need
A photo and the block size you want
Works with
JPEG, PNG, WebP and other images Lil Cactus opens; the active layer must be an image layer
Open the sample in Lil CactusUse your own photo

Free, no sign-up. Your photo stays on your computer.

Pixelating replaces groups of pixels with flat blocks of their average color. A larger block removes more fine detail. You can use the effect across a photo for a mosaic look, or contain it inside a selection.

Pixelate the whole photo in five steps

  1. Open the photo and duplicate its layer

    Open the sample, or choose File then Open… for your own image. Choose Layer then Duplicate Layer. In Layers, double-click the copy’s name, type Mosaic and press Enter.

    Leave Mosaic selected above the original Background layer.

    Layers showing the selected Mosaic copy above the original Background photo
    Apply the effect to Mosaic; keep Background for comparison.

  2. Open Filter › Pixelate › Pixelate…

    If a dashed selection border shows, choose Select then Deselect first. Then choose Filter then Pixelate then Pixelate… With no selection, the filter covers the whole active image layer.

    Filter menu with its Pixelate submenu open and Pixelate… ringed
    The Pixelate filter is inside the Pixelate submenu.

  3. Choose the cell size and apply it

    Cell Size is the width and height of a square block in image pixels. Set it to 48 for this sample. Keep Preview on to see the result; turn it off and on to compare before committing the change. Click Apply.

    Pixelate dialog with Cell Size 48 px, Preview checked and Apply ringed
    Larger Cell Size values make fewer, larger blocks.

  4. Compare with the original

    Click the ringed eye beside Mosaic to hide it and see Background. Click the same spot again to show the mosaic.

    Mosaic above Background in Layers, with the Mosaic eye button ringed
    Use Mosaic’s eye for a before-and-after comparison.

  5. Export the mosaic

    Choose File then Export then PNG…, then click Export. PNG stores every block exactly.

    To keep both layers, choose File then Save As then Lil Cactus Project… File then Save then updates that project. Before you save a project, File then Save writes back into the opened JPEG as one flat image; the first time, it opens the Save Image dialog.

Pixelate only part of the photo

For a selected-area version, open the sample from this page again, or use File then Open… to reopen your own original photo. Choose Layer then Duplicate Layer and rename the copy Cup mosaic.

  1. Right-click the selection button just below Move in the toolbar, or press and hold it, and choose Marquee Select.
  2. Keep Shape on Rectangle. Feather softens a selection’s edge; leave it at 0 px for a sharp boundary. Keep Style on Free so the rectangle follows your drag.
  3. Start in the orange above the cup’s rim, lined up just left of the saucer’s widest edge. Drag to below the saucer, just past the handle’s right edge. Leave a narrow margin of orange around the cup and saucer, as shown by points 1 and 2.
  4. Choose Filter then Pixelate then Pixelate…, set Cell Size to 48 and click Apply. Choose Select then Deselect to remove the selection border.

Only the rectangle changes. The surrounding tabletop keeps its original detail.

To hide faces, plates or text before sharing, follow blur or pixelate faces: it covers block size for faces and when to cover an area instead.

Selection toolbar group with the group button and Marquee Select choice ringed, with neighboring tools visible
Choose Marquee Select from the button below Move; enlarged view.
Marquee Select options showing Shape Rectangle and Feather 0 px
Rectangle and 0 px Feather give a hard-edged selection.
Marquee Select options showing Style Free beside the disabled Anti-alias checkbox
Free lets you choose the rectangle’s proportions by dragging.
A rectangular marquee around the cup and saucer, with points beside its upper-left and lower-right corners
Leave a little tabletop inside the rectangle on every side.
  1. Start above the cup, left of the saucer
  2. Finish below the saucer, right of the handle
Pixelate dialog with Cell Size 48 and the note Applies within the selection
The selection note confirms that the filter has a limited area.
The cup and saucer pixelated inside a rectangle, with the orange tabletop outside it still detailed
A crop of the selected-area version after deselecting.

What to do next

Coming from another editor

Photoshop
Filter › Pixelate › Mosaic…
GIMP
Filters › Blur › Pixelize…

Pixelating images: questions and answers

Does pixelating an image change its dimensions?

No. In Lil Cactus, Pixelate changes the colors inside the image, not its width or height. A 1536 × 1024 px photo stays 1536 × 1024 px.

How large can the Pixelate blocks be?

Lil Cactus accepts a Cell Size from 2 to 100 image pixels. The same value looks finer on a larger photo because more blocks fit across it; screen zoom does not change that value. Blocks at an image or selection edge can be cut short.

Can I undo pixelation?

Yes. In Lil Cactus, Edit › Undo steps back through edits while the document is open. If you made other changes after applying Pixelate, undo those first to reach the filter step.

Is pixelating a photo the same as drawing pixel art?

No. Lil Cactus’s Pixelate filter groups colors from an existing image into blocks. Pixel art is drawn by placing individual cells to create a new design.

What is the difference between pixelation and blur?

In Lil Cactus, Filter › Pixelate › Pixelate… produces distinct square blocks; Filter › Blur › Gaussian Blur… blends detail into a soft result with no grid.

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