Image Compression & Formats
Every image on a web page is a trade between how good it looks and how long it takes to arrive, and almost nobody gets to make that trade deliberately — you export at whatever the camera or the design tool offered, and find out later that the page takes six seconds to load on a phone.
These guides cover the trade itself. What lossy compression actually throws away and why you cannot see most of it. Which of JPG, PNG, WebP and AVIF suits which kind of picture, with the published figures rather than folklore. Why pixel dimensions matter more than the quality slider for most oversized files. And what to do when a file has been compressed twice and is still too large for the form that keeps rejecting it.
The practical claims here are checked against how ToolForge's own compressor behaves, which is occasionally less flattering than a marketing page would be — quality settings do nothing at all to a PNG that stays a PNG, and re-compressing an already-optimised file usually makes it bigger. Both are worth knowing before you blame the tool.
Start with the guide
GuideHow Image Compression Works
Why a photo can lose 80% of its bytes and look identical: what lossy compression discards, how quality settings behave, and why PNG ignores them entirely.
Tools for this
The tools these guides refer to, most relevant first.
Image Compressor
Compress JPG, PNG, WebP by quality or target file size
Image Format Converter
Convert between JPG, PNG, WebP, AVIF, and HEIC
Image Batch Resizer
Resize multiple images at once online for free
Image Metadata Remover
View and remove EXIF, GPS, and hidden data from images
Social Media Image Resizer
Resize one image to every social platform size at once
Image Cropper
Crop and resize images with custom aspect ratios
Guides & tutorials
How to Compress an Image
Compress JPG, PNG or WebP files in your browser: which preset to use, when to set a target size in KB, and the order of operations that saves the most.
How to Compress Images Without Losing Quality
Truly lossless compression, and visually lossless compression, are different things. Which to use per image type, and where the quality thresholds actually sit.
Image Optimization Best Practices
The nine things that actually make images fast, in order of impact — right dimensions, right format, lazy loading everything except the one image you must not.
Explainers
What Is the Difference Between Lossy and Lossless Compression?
Lossless keeps every pixel; lossy discards what you cannot see. What each one actually promises, why lossless is not "better quality", and which to pick.
What Image Size Should You Use on a Website?
Pixel dimensions, file size and DPI are three different things, and only two of them matter on the web. The sizes to use, and why 300 DPI is meaningless here.
Comparisons
Troubleshooting
Frequently asked questions
What is the best image format for a website?
WebP for almost everything, with JPG as the fallback for older browsers and PNG reserved for screenshots, line art and anything needing sharp edges. Google puts WebP at 25–34% smaller than JPEG at equivalent visual quality and 26% smaller than PNG losslessly, which is a large saving for a format every current browser reads.
How much can I compress an image before it looks bad?
For photographs, around 80% quality is where most people stop being able to tell — the artifacts exist but need a side-by-side comparison and a hard look to find. Below roughly 60% they become visible in skies, gradients and flat colour. Line art, text and screenshots behave completely differently and show damage almost immediately.
Does compressing an image reduce its dimensions?
Not unless you ask. Compression and resizing are separate operations: compressing re-encodes the same pixel grid more economically, while resizing removes pixels. Most oversized web images need the second one, which is why a 4000-pixel-wide photo displayed in a 800-pixel column is wasting most of its bytes regardless of quality setting.
Is compressing an image online safe for private photos?
Depends entirely on the site. Every image tool on ToolForge decodes and re-encodes in your browser — the files never leave your device, and even the background worker script is served from this domain rather than a third-party CDN. Before uploading personal photos anywhere else, check whether processing happens on their servers.
