Frequently Asked Questions

Lossless compression rewrites the file's data more efficiently without discarding anything — the decoded pixels are identical to the original. Lossy compression permanently discards information the human eye is unlikely to notice (subtle color variations, high-frequency detail), which is why it achieves far smaller files. Photos are usually compressed lossily because the savings are large and the artifacts are invisible at sensible quality levels; screenshots, line art, and images with sharp text edges benefit from more careful handling.

The quality value (0–100) controls how aggressively the encoder is allowed to discard detail. At 80–90, most photos look essentially identical to the original while shrinking dramatically. Below 60, you start to see blocking and blurred edges. The best approach is empirical: start high, look at the before/after comparison, and step down until you can just barely see a difference — then step back up one notch.

It depends entirely on the source. Camera photos straight from a phone often shrink to 20–40% of their original size with no visible change, because cameras apply minimal compression to preserve editing headroom. Already-optimized images (exported from a website or previously compressed) have far less redundant data and may only shrink slightly. PNG screenshots with large uniform areas convert to JPG or WebP very efficiently.

No. Lossy compression is irreversible — once detail is discarded, it cannot be reconstructed. That's why you should always keep your originals and compress copies. If you compress an image and later need a higher-quality version, go back to the original rather than re-compressing the compressed file, which compounds quality loss.

Yes — this is called generation loss. Every lossy re-compression discards a little more information, and artifacts accumulate. Avoid chains like export → compress → edit → compress → upload. Instead, edit from the original in a single pass and compress once at the end.

Visual complexity determines compressibility. An image with smooth gradients, sky, or flat backgrounds compresses far better than one packed with fine detail — foliage, crowds, noise. A noisy low-light photo may barely shrink at all, because the noise is effectively random data that cannot be represented more cheaply.

Use JPG for photographs and natural imagery with smooth gradients — it compresses them dramatically with invisible quality loss. Use PNG when you need transparency, sharp text, line art, or screenshots with crisp edges — PNG is lossless and preserves exact pixels, at the cost of much larger files for photographic content. See our detailed comparison in PNG vs JPG: when a format switch saves you 80% of the file size.

WebP is a modern format from Google that supports both lossy and lossless modes plus transparency, and typically produces files 25–35% smaller than JPG at equivalent quality. Every modern browser supports it now, so it's the default best choice for web images. The main reason to convert WebP back to JPG is compatibility with older software or platforms that require it. We cover the trade-offs in WebP vs PNG: which format should you use?

Since iOS 11, Apple saves photos as HEIC (High Efficiency Image Container), which stores the same quality at roughly half the size of JPG. The problem is compatibility: many websites, Windows PCs, and older apps can't open it. Converting HEIC to JPG before sharing avoids the issue — our HEIC to JPG converter does this locally in your browser, so your photos are never uploaded anywhere.

SVG is a vector format — instructions for drawing shapes rather than a grid of pixels — so it scales to any size perfectly and is ideal for logos, icons, and illustrations with flat colors. It's a poor fit for photographs, which would need to be embedded as raster data anyway and make the file huge. Read more in SVG vs PNG: raster or vector for your project?

Our Image Converter handles JPG, PNG, and WebP conversions entirely in your browser: drop the files in, pick the target format and quality, and download the results. Nothing is uploaded, so it's safe for private photos. For Apple HEIC files, use the dedicated HEIC to JPG converter.

No. All SlimImg tools run entirely in your browser using the standard Canvas API. Your files are read locally, processed locally, and handed back to you locally. There is no upload step, no processing queue, and no storage — you can verify this yourself by opening your browser's network inspector while using any tool: no image data ever leaves your device.

Yes, once the page has loaded. Because processing happens on your device rather than a server, a dropped connection doesn't stop you from finishing your work. This also means the tools work at the speed of your own hardware, even on slow connections.

EXIF data embedded in photos can include GPS coordinates, the exact date and time, camera model, and lens settings. When you upload photos to websites or send them to strangers, that information travels with the file unless it's stripped. Our compression and conversion tools re-encode images, which drops most EXIF metadata along the way. For a full walkthrough of what EXIF contains and how to strip it before sharing, see our guide to EXIF data and privacy.

Browser-based processing has almost no marginal cost per user — there are no servers doing the compression and no storage bills for your files. The site is supported by advertising, the same way most free web tools are. No accounts, no watermarks on output, no daily limits.

No. There is no registration, no email capture, and no login anywhere on the site. Open a tool, use it, close the tab.

You can add as many images as your device's memory comfortably allows — typically dozens at a time. They are processed in parallel, each with its own quality setting if you want fine control, or all at once with the global slider. You can download results individually or all together.

Each image can be up to 10 MB. This limit exists because the entire processing pipeline runs in your browser, and memory-hungry operations on very large files can slow down or crash a tab. If you have larger files, resizing them down first usually brings them under the limit.

Any modern browser — Chrome, Edge, Firefox, Safari, and their mobile counterparts. The tools rely on standard web APIs (Canvas, FileReader, drag-and-drop) that have been stable for years. Older browsers like Internet Explorer are not supported.

Yes. The tools are fully responsive and touch-friendly. On iOS, you can even paste screenshots directly from the clipboard. Processing speed depends on your device, but modern phones handle typical photo compression easily.

On the main compressor, Smart Adaptive mode automatically recommends a setting based on the image type, and you can adjust per-image or globally. For a precise target, step the quality down while watching the live size readout — with the before/after comparison visible, converging on an acceptable size takes seconds.

The Social Resizer has preset dimensions for every major platform — Instagram, Facebook, Twitter/X, LinkedIn, and more. Pick the platform and placement, and your image is resized with the correct aspect ratio. For complete dimension reference tables, see our guide to social media image sizes.

The Image Cropper lets you crop freely or lock to a fixed aspect ratio (1:1, 16:9, 4:3, and platform presets). Pixel dimensions are shown live as you drag, so you can hit exact targets. Our crop guide covers composition basics like the rule of thirds.

Yes — the Rotate & Flip tool rotates by any angle or straightens in 90° steps, plus horizontal/vertical flips. Sideways phone photos are usually caused by EXIF orientation tags that some apps ignore; rotating visually fixes it permanently.

The Watermark tool overlays a text or logo watermark with a 9-position grid, adjustable opacity and size, and batch support. For placement and opacity recommendations, see our guide to adding watermarks.

The Color Picker extracts colors from any image — click a pixel to get its HEX, RGB, and HSL values, and build palettes from the results. Our color picker guide explains how to use the values in your designs.

The SVG to PNG tool rasterizes vector graphics at any resolution, with custom background color and scale — useful when a target platform doesn't accept SVG. For when SVG is the right choice in the first place, see SVG vs PNG.

Yes. The QR Code Generator creates codes from plain text, URLs, email addresses, and phone numbers, downloadable as PNG or SVG. A popular use case is a QR code that joins your Wi-Fi network — we explain the format in our Wi-Fi QR code guide.