Image resizing scales the picture itself. Changing canvas size changes the space around the picture without scaling it. These are useful for different jobs: resizing a photo for a website, adding a border around a logo, or trimming excess space.
Use custom resizing to scale the image
A 1000 × 500 image resized to 500 pixels wide becomes 500 × 250 when its proportions are preserved. The picture occupies fewer pixels. Enter one dimension and leave the other blank for automatic sizing, or enter both and choose fit, crop, stretch or padding.
Use canvas size to add space without enlargement
Select Change canvas size — no scaling. If the source is 1000 × 500 and the new canvas is 1200 × 700, the picture stays 1000 × 500 and gains 100 pixels of space on every side. The tool centres the image automatically.
Choose transparent padding for a PNG or WebP, or choose white or black. Transparent padding becomes white when exported as JPG. If you leave a dimension blank in canvas mode, that axis keeps its original size.
A smaller canvas crops the original
Changing that 1000 × 500 image to an 800 × 500 canvas removes 100 pixels from the left and 100 from the right. The subject is not shrunk to fit. If you need the whole picture visible, use custom resizing with fit or padding instead.
How canvas mode differs from padding
The custom resize padding option first scales the complete image to fit the target rectangle, then fills any unused space. Canvas mode does not scale the image. If a logo must retain its original pixel dimensions while gaining a border, choose canvas mode.
Save a copy of the source and inspect the result before replacing any files. In a batch, the same canvas dimensions are applied to each image, so differently sized originals may gain different borders or lose different amounts at the edges.
Behind the result
Resampling changes the subject’s pixel dimensions. Canvas-size changes alter its surrounding frame without scaling the subject. A smaller canvas clips the image; a larger canvas adds space.
How dimensions are calculated
A decoded image is drawn onto a new canvas. With one dimension blank, the other is calculated from the original aspect ratio. Fit inside uses the smaller of the width and height scale factors; centre crop uses the larger and clips the excess. Stretch uses separate horizontal and vertical scales. Padding keeps the subject proportional and fills the remaining canvas area.
Resampling versus canvas size
Resizing resamples pixels through the browser’s canvas drawing implementation with smoothing enabled. Reducing dimensions removes spatial detail. Enlarging interpolates pixels and cannot recover missing photographic detail. Change canvas size keeps the image at its original pixel size and adds space or clips edges around it. Maximum-long-edge mode only reduces dimensions, while custom dimensions can enlarge.
What does encoding mean?
Decoding turns the bytes in an image file into pixels that a browser can display. Encoding turns pixels back into a file, using the rules of JPG, PNG or WebP. It is not encryption. Our compression and conversion tools decode locally, draw the image onto a canvas and call the browser’s canvas.toBlob encoder. The browser supplies the codec, so results can vary between browsers.
Why size and quality are different
Pixel dimensions describe the image grid; file size measures encoded bytes. A 600 × 600 image has 360,000 pixels, but its byte size depends on format, visual complexity and quality. PNG preserves transparency; JPG requires an opaque background.
Where processing happens
Your selected image is processed on your device, without an image upload. Canvas exports are new files and may change embedded metadata or colour information. Keep a master copy for archival work. Animated PNG and animated WebP are rejected; these tools handle static images.
How target-size compression works
Choose 100 KB, 200 KB, 500 KB or a custom decimal-KB limit. For JPG/WebP, the tool tries quality values from your selected maximum down to 10% and refines a successful bracket with a bounded binary search. When you explicitly allow smaller dimensions, it can also try up to eight downsizing steps. PNG ignores quality. Exact resizer dimensions are preserved. Only a measured output within the byte limit is marked Target met; otherwise the smallest tested candidate is marked Above target. This is a bounded search, not proof of a globally optimal result.
Metadata choice
Preserve supported metadata is the default: EXIF dates, camera and GPS fields are copied, with orientation reset after decoding and dimensions updated. PNG text/dates and JPG comments stay within their format. XMP, IPTC and original colour profiles are not transferred; embedded preview links are cleared. Retained metadata is included in target-size measurements. Remove metadata omits source metadata and disables the original-file fallback. Filesystem download dates are separate.
Explore the details: Browser encodingImage formats — MDN