Cropping in macOS Preview is a pixel-perfect rectangular cut using the Rectangular Selection tool inside the Markup toolbar, and it works on any image Preview can open — JPG, PNG, HEIC, TIFF, and most common formats. The app reads your selected rectangle, removes everything outside it, and saves the trimmed image back to the same file format. Because Preview is built into every Mac and uses the macOS-native rendering pipeline, the crop is byte-accurate: every pixel inside the box is identical to the source, with no resampling or extra compression added by the app itself. That makes Preview a perfectly reasonable tool for one-off crops, screenshots, and quick sharing. The catch is that Preview is locked to a single Mac, requires the file to be opened from disk or a compatible app, and overwrites the original unless you duplicate it first. A browser-based cropper such as Image Cropper sidesteps both limits by running the same pixel-accurate cut on any operating system, never touching a server.
What Cropping an Image in Preview Actually Does
Preview is not a full photo editor. It does not add filters, layers, or non-destructive history. What it does offer is a fast, reliable rectangular crop that mirrors the way image files actually store pixel data: a width, a height, and the pixel values inside. When you select an area and confirm the crop, Preview simply rewrites the file so its visible region matches your rectangle. The pixels inside that rectangle are untouched, and every pixel outside it is dropped from the saved file.
This is why a Preview crop keeps the original image quality inside the kept area. There is no re-rendering, no scaling, and no re-encoding when the format stays the same. If the source is a PNG and you crop within Preview and re-save as PNG, the cropped image is lossless. If the source is a JPEG, Preview re-encodes the cropped rectangle as JPEG and the usual compression artifacts apply — the cropped region stays sharp at the same resolution, but the file is recompressed slightly during the save. For most everyday work, including screenshots, scanned receipts, ID photos, and social media posts, the difference is invisible.
The main thing Preview does not give you is a circular crop, a free-form crop, or a precise aspect-ratio lock beyond what you draw by hand. It also cannot lock a ratio while you drag — the rectangle is always free-form. That is one of the practical reasons people look beyond Preview for more demanding crops, especially anything that has to match a platform's exact dimensions.
How to Crop an Image in macOS Preview
Preview's crop lives behind the Markup toolbar, which is hidden by default in recent versions of macOS. The full sequence takes only a few clicks once the toolbar is visible.
- Open the image in Preview by double-clicking it in Finder, or right-clicking and choosing Open With → Preview. PNG, JPG, HEIC, and TIFF files all open natively.
- Show the Markup toolbar if it is not already visible: click the small Markup button (a pen tip inside a circle) in the top-right of the Preview window, or use View → Show Markup Toolbar from the menu bar.
- Click the Rectangular Selection tool in the Markup toolbar — it looks like a dashed rectangle with a corner handle.
- Click and drag across the image to draw a box around the area you want to keep. You can adjust the box by dragging any edge or corner, or by clicking inside it and dragging the whole selection to a new position.
- Click the Crop button in the Markup toolbar (the icon shows two overlapping right-angle corners), or choose Tools → Crop from the menu bar. The area outside your selection disappears immediately.
- Save the result. Press ⌘S to overwrite the original, or use File → Duplicate (⌘D) first to keep both versions, then save the duplicate under a new name. File → Export As lets you pick a specific format and quality for the cropped file.
A quick habit worth keeping: always duplicate the image before cropping when you might want the full version later. Preview's ⌘S writes directly to the source file with no undo across app restarts, so a stray crop on an original is permanent unless the file is backed up elsewhere. The Duplicate command gives you a clean safety net.
Why a Browser Cropper Is Often Easier
Preview is fast on the Mac where the file lives, but it has friction in common situations. If you want to crop a screenshot you just took on another device, an image emailed to you on a Windows PC, or a photo stored in a web-only service like Google Photos, you cannot open it in Preview without first downloading the file and moving it to a Mac. The crop also has to happen on the original machine, with no way to delegate the work to a quick drag-and-drop page.
A browser cropper removes that friction. You open a single page, pick the file from your device, frame the crop, and download the result. Nothing leaves your computer — the file is decoded locally, the crop runs in the browser's Canvas API, and the output PNG is handed back as a download. For screenshots, ID photos, receipts, and other private images, this matters because the file never reaches an upload server, a queue, or a third-party storage bucket.
The other advantage is repeatable ratios. Preview's selection box is always free-form, which is great for one-off framing and terrible for anything that needs to match a target platform. A dedicated browser cropper such as Image Cropper ships with the four ratios that cover almost every common job — 1:1, 4:3, 16:9, and 3:2 — and locks them while you drag the corner handles.
How to Crop an Image in Your Browser With Image Cropper
Image Cropper runs the entire crop locally, which is why it works for sensitive images as well as everyday ones. The interaction is built around a single visible selection box, a small set of controls, and a one-click crop button.
- Click Browse and choose the image you want to crop — it loads instantly and stays on your device.
- Drag the selection box to frame the area you want to keep, resize it from the corner handles, or pick a 1:1, 4:3, 16:9, or 3:2 aspect-ratio preset to lock the proportion. The live readout shows the exact output pixel dimensions as you drag.
- Click Crop image to cut out that region and download it as a lossless PNG. The original file is never modified; the cropped result is a brand-new PNG.
Because the crop is a single pixel-accurate cut — the tool maps the on-screen selection back to the original image's true pixel coordinates and copies the sub-rectangle at 1:1 scale — every pixel inside the box is byte-for-byte identical to the source. The cropped image is a lossless PNG by default, which is the safest format for sharp edges, text, and fine detail. There is no scaling, no resampling, and no server round-trip in the path.
Choosing the Right Aspect Ratio for Your Crop
Aspect-ratio presets are the single biggest time-saver in any crop workflow. Picking the right one up front means the result matches the target platform without trial and error. The table below summarizes the four built-in presets in Image Cropper, plus the Free option for fully custom rectangles.
| Preset | Ratio | Best for |
|---|---|---|
| Free | Any rectangle | Custom framing where no specific ratio matters |
| 1:1 | Square | Profile pictures and avatars, especially where platforms mask to a circle |
| 4:3 | Classic camera | Older displays, slideshows, and traditional compact-camera frames |
| 16:9 | Widescreen | YouTube thumbnails, slide decks, modern monitors, and video covers |
| 3:2 | Native DSLR | DSLR and mirrorless photo crops that keep the natural camera framing |
When a ratio is locked, the corner handles resize the box while holding the exact proportion, and the live readout updates the output pixel dimensions in real time. That makes it simple to land on the exact pixels a target platform expects — for example, a 1080×1080 1:1 for an Instagram profile picture or a 1920×1080 16:9 for a YouTube cover — without measuring by hand.
After the Crop: Resize, Convert, or Compress
A crop only removes the pixels outside the selection. It does not resize what remains, change the color, or compress the file. If the cropped image still needs to land at a specific pixel size or a smaller file footprint, the right next step depends on the goal.
For exact pixel dimensions — say a 400×400 avatar or a 1200×630 Open Graph image — run the cropped PNG through the Image Resizer, which scales to the requested size without uploading. For a smaller file while keeping the same dimensions, drop the result into the Image Compressor. For a photo-friendly format with much smaller files than PNG, convert the cropped result with the PNG to JPG tool. Doing those steps in the same browser keeps the original file private end-to-end, and each tool is focused on one job.
If a circular crop is what was actually needed — an avatar that already matches a 1:1 square but should not show its corners — start from a square crop in the Image Cropper and then hand the PNG to the dedicated Circle Crop tool, which outputs a transparent PNG with a centered circle.