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How to upscale an image without it turning blocky

Beginner4 minutesUpdated

Quick answer

Choose Image then Image Size…, set the units to Percent (or keep Pixels), type the new width, keep Resample on, choose Bicubic Sharper and click Resize. Then choose Filter then Sharpen then Smart Sharpen… and click Apply to firm up the edges. Enlarging spreads the existing detail over more pixels; it can’t add detail that was never captured.

Three enlarged crops of the cat’s eye: blocky squares on the left, a smooth but slightly soft eye in the middle, and a crisper eye with fine fur on the right
The same eye enlarged from 640 px to 1536 px with Nearest Neighbor (left) and Bicubic Sharper plus Smart Sharpen (middle), next to a photo taken at 1536 px (right).
Time
4 minutes
Level
Beginner
You need
A small image you need at a larger size
Works with
JPEG, PNG, WebP, HEIC, PSD and other images
Open the sample in Lil CactusUse your own photo

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

A digital image is a grid of pixels. To make it bigger, the editor has to invent the new pixels in between, a step called resampling. Good resampling blends neighboring pixels smoothly, so the picture gets bigger without turning into visible squares, but the extra pixels carry no new information: fine detail such as fur or text that was too small to record stays soft.

In this tutorial you enlarge a 640 px photo of a cat to 1536 px, sharpen it, and compare it with the same photo taken at full size, so you can see what to expect.

Upscale an image in five steps

  1. Open the image

    Go to lilcactus.app and choose File then Open…, or drag the image onto the window. To follow along exactly, open the sample photo from this page.

  2. Open Image Size

    Choose Image then Image Size… The top of the dialog shows the current size (640 × 426 for the sample) and, when you press Tab after typing, the new one.

    The Image menu with Image Size… ringed
    Image then Image Size…

  3. Enter the new size

    Set Units next to Width to Percent and type 240 for Width, then press Tab: the height follows, because the link between them keeps the proportions. The summary now reads 640 × 426 → 1,536 × 1,022 px. If you need an exact size, keep Pixels and type the width instead.

    Keep Resample ticked and choose Bicubic Sharper, then click Resize.

    Tip The method starts on Bilinear; switch it, or the result comes out softer.

    The Image Size settings: 640 × 426 → 1,536 × 1,022 px, Width and Height 240, Units Percent, Resolution 72, Resample ticked with Bicubic Sharper, and Units, Width and Bicubic Sharper ringed
    Percent, 240 and Bicubic Sharper.

  4. Sharpen the enlarged image

    Enlarging leaves edges a little soft. Choose View then Actual Size (100%) first, so you judge it at real size, then Filter then Sharpen then Smart Sharpen… Its starting settings (Amount 150%, Radius 1 px) suit this photo: untick Preview and tick it again to compare, then click Apply. Edges such as the eyelids and the dark fur stripes look firmer. Sharpening a photo explains the settings.

    Two enlarged crops of the cat’s eye: on the left after Bicubic Sharper, on the right after Smart Sharpen, with firmer edges
    Before and after Smart Sharpen, enlarged.

  5. Export the bigger image

    Choose File then Export then JPEG… (or PNG) and click Export to download the enlarged copy; the file you opened keeps its size. File then Save writes the larger version back into the file you opened instead; for a JPEG the first save opens the Save Image settings.

Which resampling method to choose

  • Bicubic Sharper: the best choice for photos. It blends smoothly and keeps edges a little crisper.
  • Bilinear: a simpler blend that comes out softer.
  • Nearest Neighbor: copies pixels without blending, so a photo turns into visible squares. Use it for pixel art, icons and screenshots of text, enlarged by whole multiples (200%, 300%), to keep their edges hard.
Three enlarged crops of the cat’s eye: blocky squares with Nearest Neighbor, a soft eye with Bilinear, and a slightly crisper eye with Bicubic Sharper
Nearest Neighbor, Bilinear and Bicubic Sharper, enlarged.

How far you can enlarge

A small enlargement is usually hard to notice at normal viewing size. At 240%, as here, the image looks fine at a glance but soft up close: fur that was a pixel wide in the small photo can’t come back as separate hairs. Measured on the sample, only about a quarter of the full-size photo’s finest texture is there, with or without sharpening. Sharpening makes edges more contrasty (from about 63% to about 75% of the original’s edge contrast), not more detailed.

So enlarge as little as the job needs, and start from the largest copy you have.

Two enlarged crops of the eye: on the left the upscaled and sharpened eye, smooth but without fine hairs; on the right the full-size photo with individual hairs and a sharp catchlight
Upscaled and sharpened (left) next to the photo taken at full size (right).

Bigger for printing, without adding pixels

For a print, multiply its size in inches by about 300 to get the pixels you need. In Image then Image Size…, untick Resample and type a Resolution: the print size changes and the pixels stay as they are. Enlarge only if the print is still too small. More in how to resize an image.

Fix common problems

The enlarged image looks blocky

Nearest Neighbor was chosen. Choose Edit then Undo and resize again with Bicubic Sharper.

Sharpening made bright outlines along edges

The sharpening is too strong for the enlarged image. Undo it and apply it again with a lower Amount, 100% or less.

The image didn’t get any more pixels

Resample was unticked, so only the print size changed. Undo, tick Resample and resize again.

Coming from another editor

Photoshop
Image › Image Size…, with Resample and a resampling method such as Bicubic Smoother.
GIMP
Image › Scale Image…, with Interpolation.
Mac Preview
Tools › Adjust Size…

Enlarging images: questions and answers

Can I upscale an image without losing quality?

Not completely. In Lil Cactus, Image Size with Bicubic Sharper enlarges smoothly, and a light Smart Sharpen firms up edges, but fine detail that the small image never had stays soft.

Does Lil Cactus have AI upscaling?

No. Lil Cactus enlarges by resampling (Bicubic Sharper, Bilinear or Nearest Neighbor), which keeps the picture faithful but doesn’t invent new detail.

What size should I upscale to for printing?

About 300 pixels per inch of print: a 6 × 4 in print needs about 1800 × 1200 px. In Lil Cactus, untick Resample in Image › Image Size… and set Resolution to 300: the size shown is how large the image already prints.

How do I make pixel art bigger without blurring it?

In Lil Cactus, choose Image › Image Size…, set Units to Percent, type 200, 300, 400 or another multiple of 100, and choose Nearest Neighbor.

Is my image uploaded when I upscale it in Lil Cactus?

No. Everything runs in your browser, on your own device. When statistics are on, the editor records which tools are used, never the image, as the privacy policy explains.

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