You can convert images in a browser without installing anything, and for most everyday jobs it is the shortest route. The browser already ships with the codecs for JPEG, PNG and WebP, plus a canvas that can resize and re-encode pixels. What it cannot do is decode every exotic format, and that single limitation explains almost all the confusing advice online. This guide gives seven concrete ways to get from the file you have to the file you need, says which ones work locally, and flags the cases where a desktop application is still the honest answer.
Why convert an image in the first place
Format, dimensions and file size are three separate properties, and people often try to fix one by changing another. A photo rejected for being 6 MB needs re-encoding, not a smaller width. A form demanding 600 by 600 pixels needs resizing, not a different format. A printer refusing a WebP file needs a format change, not compression. Deciding which problem you have first turns a frustrating afternoon into two clicks.
| Symptom | Real problem | Fix |
|---|---|---|
| Upload form says file too large | Too many bytes | Re-encode at a lower quality |
| Form says wrong dimensions | Too many pixels | Resize to a maximum box |
| Software will not open the file | Unsupported format | Convert to JPEG or PNG |
| Website loads slowly | Heavy assets | WebP plus resizing to display width |
1. Convert between JPEG, PNG and WebP
This is the workhorse. The Image Converter takes a batch of images and writes each one in the format you choose, using the codecs already built into your browser. WebP is typically 25 to 35 percent smaller than JPEG at comparable quality and works in every current browser, so it is the default for anything shown on a web page. JPEG remains the safest choice for email, print shops and older desktop software. PNG is the right answer when transparency or crisp edges matter.
One trap: converting a JPEG to PNG rarely makes it smaller. PNG is lossless, so it often inflates a photograph substantially. If the goal is fewer bytes, WebP or JPEG is the direction to go.
2. Re-encode to hit a byte limit
When a portal says 2 MB maximum, quality is the dial that matters. The Image Compressor re-encodes JPG, PNG and WebP at a slider value you pick, and around 70 to 80 percent is visually indistinguishable on photographs. Start there, check one file at full size, then process the whole folder. Keep your originals in a separate directory and compress a fresh copy each time; stacking repeated lossy saves is what actually degrades a picture.
3. Resize to exact pixel dimensions
For avatars, ID photos and fixed-width layouts, use the Image Resizer. It scales each image to fit inside a maximum width and height while preserving the aspect ratio, so nothing is stretched or cropped. Leave upscaling off: enlarging a bitmap invents no detail and produces a soft, heavier file. Resize first, then compress, when a form gives you both a pixel requirement and a byte limit.
4. Deal with HEIC photos from an iPhone
HEIC is the case where a browser-only answer depends on which browser you have. Safari decodes HEIC natively, so those photos can go straight into a converter. Chrome and Edge on Windows generally cannot decode it, because the required codec is not shipped with them. The practical fix is to transfer the photos as JPEG using the phone's own share settings, or ask the Photos app to export a compatible copy. Once the file is a JPEG, every local tool works normally. No downloadable software is needed, but a conversion step on the device itself is.
5. Convert screenshots for the web
Screenshots are usually PNG because they contain sharp text and interface edges. That is the right source format, but a 2 MB screenshot on every documentation page is a slow site. A two-step pass works well: resize to the width the layout actually displays, then convert to WebP. The text stays crisp enough to read while the bytes drop sharply. Keep the PNG as the editable source in your repository.
6. Use your operating system's built-in tools
Sometimes the fastest converter is the one already installed. macOS Preview exports to JPEG, PNG and PDF and can change dimensions in one dialog. Windows Photos offers a resize option, and Paint can save a file as JPEG or PNG. These are local applications, so they do not upload anything, but they are manual and awkward for a batch of fifty files. Use them for one-off fixes; use a browser tool when the same operation has to happen to a folder.
7. Know when a real editor is required
Raw camera files, multi-layer designs, CMYK print workflows and colour-managed output all need a dedicated application. A browser canvas works in sRGB and flattens everything into a single raster layer. If a print shop asks for a specific ICC profile or a 300 DPI TIFF, that is not a job for a web page. Trying to force it through a free converter usually produces a file that technically opens and is quietly wrong.
A repeatable three-step workflow
- Name the constraint. Write down whether the blocker is bytes, pixels or format. This determines the tool and the order of operations.
- Work on one representative file. Convert or compress a single image, open it in the destination application, and confirm it is accepted before processing a batch.
- Keep the source. Save outputs under new names or into a separate folder. Lossy re-encoding cannot be undone, and a second pass on a copy is where quality is lost.
source photo (6.0 MB, 4000x3000)
-> resize to 1600px wide -> 1.8 MB
-> convert to WebP at quality 78 -> 620 KB
-> still too big? compress again from the resized source, not from the WebPThe arrow diagram above is the whole logic: change dimensions before changing encoding, and always start a new lossy pass from the cleanest available source. Working from an already compressed copy is the most common way people end up with muddy images.
Common questions
Will converting lose quality?
JPEG and WebP at moderate settings are lossy, so one conversion discards some detail. The loss is normally invisible at 75 to 85 percent. Working from the original each time keeps that loss to a single pass; repeatedly saving the same file compounds it.
Can I do a whole folder at once?
Yes for the three browser tools linked here: they accept multiple files in one drop and produce a corresponding set of outputs. Format, quality and dimension settings apply to the whole batch, which is exactly what you want when preparing a consistent set of product photos.
Is anything uploaded during conversion?
No. The browser reads the file from your disk, decodes it in memory, re-encodes it with its own codecs and hands the result back as a download. The Network panel in developer tools will show no request containing your image bytes.
Tools on this site
Image Converter handles format changes in batches. Image Compressor brings a file under a byte limit. Image Resizer fixes dimension requirements without distorting the picture.