What Is Image Compression?
Compression reduces the number of bytes needed to store an image file. Fewer bytes means a smaller file, which downloads faster and uses less storage. When you share photos by email, upload images to a website, or post on social media, the files go through some form of compression.
There are two types: lossy and lossless. Understanding which one applies to your situation helps you get smaller files without sacrificing more quality than necessary.
Lossy Compression
Lossy compression permanently removes image data that the human eye is unlikely to notice. JPEG and WebP both use lossy compression. A JPEG at quality 80 looks nearly identical to the original to most people, but the file can be 60–80 percent smaller.
The trade-off: every time you open and save a JPEG, you lose a little more quality. If you need to edit an image repeatedly, keep the original and only export a compressed JPEG when you are finished editing.
Best for: Photographs, product images, food photos, travel images, social media content.
Lossless Compression
Lossless compression removes redundant data without discarding any image information. PNG uses lossless compression. The file is always a perfect copy of the original — you can open, edit, and re-save a PNG as many times as you like without any quality loss.
The trade-off: PNG files are usually larger than JPEG for photographs. For a photo with thousands of similar-colored pixels, JPEG's lossy approach produces a much smaller file.
Best for: Logos, icons, screenshots, UI graphics, images with sharp text or flat areas of solid color.
How to Choose a Quality Setting
When compressing a JPEG or WebP, a quality setting between 70 and 85 is the practical range for most situations:
- Quality 85–95: Near-original quality. Use for large prints, high-end portfolios, and professional delivery files.
- Quality 70–84: Good for web photos, blog images, product photos, and social posts. File is noticeably smaller, quality is still clean.
- Quality 50–69: Use for thumbnails and preview images where detail is less important.
- Below 50: Visible artifacts, blocky shadows, and soft text. Avoid unless file size is the only priority.
Always preview the result before downloading. Pay close attention to faces, product labels, fine text, and gradients — these areas show compression artifacts first.
Compress Before Resizing or After?
Resize first, then compress. Compressing a 4000 × 3000 px image at quality 80 still gives you a large file because there are millions of pixels. Resize it to 1200 × 900 px first, then compress — the combination gives much better file-size results.
Batch Compression Tips
If you are preparing multiple images for a website or product catalog:
1. Decide on a consistent output format (WebP for modern browsers, JPEG as a fallback).
2. Resize all images to the target display width before compressing.
3. Use a consistent quality setting across the set so all images look uniform.
4. Check the largest and most complex image in the batch — if it looks acceptable, the rest usually will too.
When Not to Compress
Some situations call for keeping the original file intact:
- Source files for future editing: Keep originals as PSD, PNG, or high-quality JPEG.
- Legal or medical documents: Compression artifacts can create problems with printed documents, signatures, or diagnostic images.
- Images for print: Print files need high resolution and minimal compression.
Summary
Use lossy compression (JPEG or WebP) for photographs and web images. Use lossless compression (PNG) for graphics, logos, and screenshots. A quality setting of 75–85 covers most everyday needs. Always preview before downloading, and always compress from the original — not from an already-compressed file.