JPEG uses lossy compression that discards data based on what the human eye is least likely to notice. It works by dividing the image into blocks, applying a discrete cosine transform, and quantizing the results. PNG uses lossless DEFLATE compression, which finds repeating patterns and encodes them efficiently. WebP uses predictive coding and advanced entropy encoding, giving it superior compression for both lossy and lossless modes. TIFF can use various compression methods including LZW (lossless) and JPEG (lossy) within the same file.

The same quality setting produces different results depending on image content. Photos with smooth gradients and natural textures compress well at lower quality settings. Images with sharp edges, text, or solid color blocks show artifacts more readily and need higher quality. High-frequency detail like grass, hair, and fabric patterns are the first to degrade. When compressing, look at these challenging areas to judge quality, not smooth sky or blurred backgrounds.

Our Image Compressor offers two modes. Quality mode lets you set a percentage and see the resulting file size. Target size mode lets you specify an exact file size (like 100KB) and the tool automatically finds the best quality setting to hit that target. Target size mode is perfect when you have strict requirements — job application portals, form uploads, or email attachments with size limits. Quality mode is better when you want manual control over the visual result.

JPEG compression uses chroma subsampling, which reduces color detail more than brightness detail. This works because human eyes are more sensitive to brightness changes than color changes. 4:2:0 subsampling (the default) keeps full brightness detail but halves color detail both horizontally and vertically. For most photos, this is invisible. For images with fine colored text or sharp color transitions, 4:4:4 (no subsampling) preserves better quality at the cost of larger files. Our compressor uses 4:2:0 for the best balance.

Start by resizing to your target display dimensions — never compress a 4000px image that will only display at 800px. Choose the right format: WebP for web, JPEG for general use, PNG for graphics with transparency. Set quality to 80% as a starting point. Preview the result and check challenging areas. If artifacts are visible, increase quality by 5-10%. If the file is still too large, consider reducing dimensions further. Use our target-size mode for strict file size requirements. Always keep your original uncompressed file as a master.