Image Resizer

What the Image Resizer Does

Sometimes an image is simply the wrong size in pixels — a 6000-pixel photo where a 1200-pixel one would do, or an upload that must fit specific dimensions. This tool redraws the image at the width and height you set, so you get exactly the pixel size you need.

By default it keeps the proportions: change the width and the height adjusts to match, so nothing looks stretched. Uncheck the aspect lock if you deliberately want to set both sides independently.

How It Works

When you load an image, the tool fills in its current width and height and remembers the ratio between them. The presets and the aspect-lock both work from that ratio, so a 16:9 photo stays 16:9 when you pick 1280.

Your chosen dimensions become a new canvas, and the image is drawn into it at that size using the browser's built-in image smoothing. The canvas is then saved as a PNG — a lossless format — so the only change is the pixel count, not the encoding.

Processing pipeline

1. Step 1. Drop in an image — it is decoded locally, never uploaded.
2. Step 2. The current width and height are filled in; the aspect ratio is locked by default.
3. Step 3. Type a new width or height (the other follows), or tap a preset: 1920, 1280, or 800.
4. Step 4. The image is redrawn at the new size on a canvas with the browser's smoothing.
5. Step 5. Download the result as a lossless PNG.

Privacy

Resizing happens entirely on your device. The image is read from disk, redrawn in the page's memory, and the PNG is produced locally — no upload, no server copy.

Nothing is stored and there is no account. Close the tab and both images leave memory, so it is fine for private photos and assets.

Technical Details

Standards & references

• HTML Canvas API — drawImage scales the picture to the target size; imageSmoothingEnabled is on by default (bilinear), so pixels are interpolated rather than duplicated.
• ISO/IEC 15948 (PNG) — the lossless output format, so the resize itself adds no compression artefacts.

Accuracy & Limitations

Downscaling is where this shines — making an image smaller throws away pixels cleanly and usually looks great. The tool uses the browser's default smoothing (bilinear interpolation), which is fine for typical reductions; shrinking by a very large factor in one step can look a little soft compared with a dedicated multi-step or bicubic resampler.

Upscaling cannot create detail. If you set dimensions larger than the original, the tool interpolates new pixels, so the image gets bigger but not sharper — it will look softer or blockier. Enlarging works best for small bumps, not for rescuing a tiny image.

Aspect ratio is protected by default. With the lock on, the opposite dimension is computed for you so nothing distorts; turn it off only if you intend to stretch the image to exact, non-proportional dimensions.

Output is a lossless PNG, so no JPEG-style artefacts are introduced by resizing. Note that a photo saved as PNG can be larger than the same photo as JPEG — if file size is the goal, compress the resized image afterwards.

Real-World Use Cases

When to use it — and when not to

To cut file size, compress the resized image; to keep a region at full size rather than scale, use an image cropper.

Frequently Asked Questions

References

• CanvasRenderingContext2D.imageSmoothingEnabled — MDN
• ISO/IEC 15948:2004 — Portable Network Graphics (ISO)
• Image file type and format guide — MDN

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