Resize image

Steps

1. Drop a JPEG, PNG, WebP, HEIC, or AVIF, or click the zone and choose one. Resize stays disabled until a file is chosen. Choosing a file only reads it into this tab. Files above 80 MiB (83,886,080 bytes) are refused. Each edge must be 1 to 16,384 px.
2. Type a width and height, or switch to Long edge and type one pixel size for the longer side. Keep aspect is on by default, so one edge fills the other. Unlock it only if you intend to stretch.
3. Press Resize. JPEG, PNG, and WebP decode with this browser. HEIC loads libheif-js from /assets/libheif/ on that press. AVIF uses the browser decoder; if this tab cannot open it, the page stops. The photo is not uploaded.
4. Read the status line. It prints input pixels, output pixels, and the measured byte size of the download. PNG stays PNG. JPEG, WebP, HEIC, and AVIF download as JPEG at quality 0.92. Then download from a local blob: URL.

How it works

Choosing a file reads it into memory in this tab, up to 80 MiB (83,886,080 bytes). Nothing is posted to LocalPix. Resampling is canvas.drawImage with imageSmoothingQuality set to high when the browser exposes it. New pixels are interpolated. This page does not invent photographic detail, and it does not search JPEG quality for a kilobyte cap. A named KB or MB cap is a second step on Compress to KB.

JPEG, PNG, WebP. This browser decodes the still. PNG downloads as PNG so alpha stays. JPEG and WebP download as JPEG at quality 0.92, the same encode as convert. WebP animation becomes one still. Canvas JPEG has no alpha and no EXIF.

HEIC. The first still is decoded with libheif-js 1.23.5 (1,463,506 bytes, LGPL-3.0) from /assets/libheif/, the same decoder as HEIC to JPG, then resampled and written as JPEG at quality 0.92. libheif loads on Resize, not on file pick. Accepted brands are heic, heix, hevc, hevx, mif1, and msf1. Live Photo motion and extra stills are not in the download.

AVIF. Decode uses this browser. There is no fallback decoder. If decode fails, the status says so and the file stays on disk. A still that this browser can open downloads as JPEG at quality 0.92. Convert-only is also on AVIF to JPG.

GIF, TIFF, BMP, and other containers are refused. Upscaling is allowed; the extra pixels are interpolated. Same-size runs still re-encode.

What the status line says

Read this line before you send the file. Kilobytes are blob.size / 1024, one decimal place. The download name ends in -{width}x{height} plus the output extension.

• Before a file. “Waiting for an image.” Resize stays disabled.
• After you choose a file. “Ready: ” plus the file name, the pixel size when this tab can read it, and the input kilobytes. A file above 80 MiB prints that byte count and stays disabled.
• While it runs. “Resizing to {w}×{h} px…” {w} and {h} are the integers that will be written.
• When encode finishes. “Done: {sw}×{sh} → {w}×{h} px · {kb} KB {kind} ({bytes} bytes).” {kb} and {bytes} are measured from the result blob, not invented. HEIC, WebP, and AVIF add that the download is JPEG.
• This browser cannot open the file. JPEG/PNG/WebP: “Browser could not decode this image.” AVIF: “This browser could not decode AVIF.”
• Not an image this page reads. “This file is not a JPEG, PNG, WebP, HEIC, or AVIF this page can read.”

Limits

• 80 MiB in memory. 83,886,080 bytes. The whole file is read into the tab.
• 1 to 16,384 px on each edge. The same HEIC ceiling used on convert.
• Pixel size, not a KB cap. The status prints the real output bytes after encode. It does not search quality toward a number you type. That job is Compress to KB.
• JPEG quality is 0.92 for JPEG output. PNG is re-encoded as PNG at the new pixel grid. A photo that was already JPEG is re-encoded; the download is not the original bits.
• HEIC and AVIF become JPEG. Extra HEIC frames are dropped. AVIF has no extra decoder here.
• No account and no model for JPEG/PNG/WebP/AVIF. HEIC uses the same on-demand libheif download as convert. This page does not use the background-removal allowance.

Sources

• CanvasRenderingContext2D.drawImage() on MDN — the resample call.
• imageSmoothingQuality on MDN — set to high when the browser exposes it.
• HTMLCanvasElement.toBlob() on MDN — PNG or JPEG encode after resample.
• Blob on MDN — blob.size is the byte count the status prints, divided by 1024.