Image compression is not just “lower quality”: JPG, PNG, WebP and resizing

When an image is too large, reducing the quality slider is not always the best first step. File size depends on pixel dimensions, image format, compression settings, transparency and the type of visual detail. Matching the image to its final use usually gives better results.

Start with the required display dimensions

If a 4000 × 3000 photo will only appear in an 800-pixel-wide web card, resizing the dimensions can save more data than aggressively lowering JPEG quality. If the image is intended for print or zooming, keeping more resolution may be necessary.

JPG, PNG and WebP in practice

• JPG: good for photos and gradients; does not support transparency.
• PNG: useful for transparency, interface screenshots and graphics with sharp edges; photos are often larger.
• WebP: useful for web delivery and can provide smaller files at acceptable visual quality, including transparency support.

Quality numbers are not universal

Two images at the same quality setting may look very different. Fine text, skin tones, skies and high-contrast edges respond differently to compression. Always compare the actual preview with the resulting file size.

A useful web-image sequence

Resize to the dimensions actually needed, convert to an efficient format such as WebP when appropriate, choose a reasonable quality, then set explicit width and height in HTML. This reduces downloads and also helps prevent layout shifts during page loading.

Be careful with screenshots containing text

Heavy lossy compression can make small text blurry. Compare PNG and high-quality WebP instead of automatically using low-quality JPG for screenshots.

WUCJ Image Tools can quickly compress, resize and convert everyday images. Keep original files when working with photography, print color or other professional image requirements.