How to Compress an Image Without Losing Quality
A photo straight off a phone is often three or four megabytes, and almost none of that is doing anything useful on a web page. Compressing it to under a megabyte usually changes nothing you can see. The Bulk Image Compressor takes up to twenty images at a time and hands them back as a single ZIP.
Why a photo can shrink by half and look the same
JPEG compression works by discarding detail the eye is poor at noticing, starting with fine variations in colour. Your eye is very sensitive to changes in brightness and much less so to changes in hue, so a JPEG keeps the brightness information and throws away a surprising amount of the colour information. At moderate settings you genuinely cannot see the difference at normal viewing size.
What you can see, eventually, is blocking - faint square patches in smooth areas like skies and skin. That is the point at which you have gone too far, and it is the thing to look for when judging a setting rather than watching the file size alone.
What setting to use
Around fifty per cent is the usual sweet spot for photographs. It is low enough to cut the file size dramatically and high enough that nothing visible goes missing. Screenshots and graphics with flat colour and sharp text behave differently and often look better saved as PNG, or converted with the Image Format Converter, because JPEG blurs hard edges.
The compressor applies one percentage proportionally rather than forcing every file to the same size, so a 100 KB image and a 200 KB image at fifty per cent come out at roughly 50 KB and 100 KB. A batch of mixed photos stays in proportion instead of the small ones being wrecked to match the big ones.
Compress once, from the original
Every JPEG save discards a little more detail, and the loss is permanent. Compressing an already-compressed file compounds the damage, which is how a photo slowly turns mushy over a few rounds of editing and re-saving. Keep the original somewhere, compress a copy, and if you need a different setting later go back to the original rather than squeezing the squeezed version.
Common questions
Will compressing hurt how my site ranks?
The opposite. Page speed is a ranking signal and oversized images are the commonest reason a page is slow, so a smaller file helps. What would hurt is compressing so hard the pictures look bad.
Are my photos uploaded anywhere?
No. The compression happens in your browser on your own device, which is also why a batch of twenty finishes without an upload wait.
Can I compress a PNG?
Yes, though PNG compression is lossless and works differently - it finds repeated patterns rather than discarding detail. Photographs saved as PNG will shrink far more if you convert them to JPEG first.
How small should a web image be?
Under 200 KB is a reasonable target for a photograph on a page, and under 100 KB for anything that appears several times, like a thumbnail. Exact numbers matter less than not serving a four-megabyte file.
Does compressing remove the location data in a photo?
Not reliably, and you should not count on it. If that is what you are after, strip it deliberately with the EXIF Data Viewer and Remover.
Ready to make a folder of photos web-ready?