Image compression reduces the amount of data needed to store or deliver a picture. It is useful when a website loads slowly, an upload form has a file-size limit, or you need to send images over a limited connection. The aim is not always the smallest possible file; it is a useful balance between dimensions, visual quality and file size.
Lossy and lossless compression
Lossy compression discards some image information to reduce file size. JPEG and many WebP settings use lossy compression. Moderate settings can look good, but repeated re-saving may introduce artifacts. Lossless compression reduces file size without discarding pixel information. PNG commonly uses lossless compression and is useful for screenshots, diagrams and transparent graphics.
Choose the right format
- JPG: photographs and images where compact size matters.
- PNG: logos, screenshots, diagrams and transparency.
- WebP: web images; supports lossy and lossless compression and transparency.
Compress an image step by step
- Keep an untouched copy of the original.
- Resize excessive dimensions first. A 4,000-pixel photo may be unnecessary in a 900-pixel content column.
- Choose a format suited to the image.
- Start with moderate quality and compare the output at normal viewing size.
- Inspect text, edges, gradients and faces for artifacts before publishing.
Example: preparing a blog photo
A 4,000 × 3,000 photo displayed at 1,000 × 750 pixels contains far more pixels than the page needs. Resizing to the display dimensions can reduce data before compression. The final file size depends on image detail, format and quality; there is no universal reduction percentage.
Use the Tolvix Image Compressor
Open the Image Compressor, select a supported image, choose the available settings and compare the output before saving. Processing is performed in your browser for supported formats. Large images can use substantial device memory.
Common mistakes
- Compressing an already compressed image repeatedly.
- Reducing quality until text and edges look damaged.
- Ignoring pixel dimensions and relying only on quality reduction.
- Overwriting the original instead of keeping a backup.
How to compare compression results
Compare the original and compressed files at the size they will actually be displayed. A file-size reduction is useful only if the image still communicates clearly. For a photograph, inspect skin tones, fine textures and gradients. For a screenshot or chart, zoom in on small labels, thin lines and sharp edges. If visible artifacts appear, raise the quality setting or choose a lossless format.
Choose settings for the job
- Website thumbnail: resize to the displayed dimensions first, then use a web-friendly format.
- Transparent logo: keep transparency and use PNG or a supported lossless WebP workflow.
- Photograph: compare JPG and WebP output at moderate quality rather than selecting the lowest file size automatically.
- Archive or original: keep an untouched copy; lossy compression permanently discards detail.
Compression results vary with image content. A flat illustration and a detailed photograph of the same dimensions can produce very different file sizes, so test representative images rather than relying on a fixed percentage.
Frequently asked questions
Does compression always reduce quality?
Lossy compression can reduce detail; lossless compression preserves pixel information. Resizing removes pixels, so keep the original when full resolution may be needed.
Is WebP always smaller than JPG?
No. Compare the actual files at a visually acceptable quality level.
Can I compress a PNG photograph?
Yes. A photograph may become smaller as JPG or WebP, but retain PNG if transparency or lossless pixel preservation matters.
Why did the output become larger?
Re-encoding a small optimized image or changing formats can add overhead. Try another format or keep the original.
Educational guide. Supported formats and results may vary by browser and device. Keep an original copy of important files.
Guide content reviewed: 5 November 2026.