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Optimization levels
Four presets rather than a row of sliders you have to guess at. The numbers come from encoding a real 2048×1367 photograph of 721,366 bytes.
| Level | WebP | AVIF | Typical saving |
|---|---|---|---|
| Conservative | q90 | q68 | ~28% / ~53% |
| Balanced (recommended) | q82 | q58 | ~45% / ~66% |
| Aggressive | q75 | q50 | ~59% / ~78% |
| Custom | yours | yours | — |
Balanced unless you have a reason not to. It is the setting where a photograph is indistinguishable from the original at normal viewing sizes while weighing a third of what it did.
Conservative for photography and portfolio sites where the images are the product, and where a client may pixel-peep. You give up roughly a third of the possible saving.
Aggressive when you have thousands of images and page weight is the problem you are actually solving. Fine texture and smooth gradients can show artefacts at AVIF q50; flat colour and photographic subjects hold up well.
Custom once you have used the levels enough to know what you want to change.
A derivative that is not smaller is deleted. Icons, logos and already-optimized PNGs frequently encode larger than the original. Those are recorded as skipped — a normal outcome, not an error — and are not retried on every pass.
Images too large for memory are skipped, not attempted. A 34-megapixel original needs around 136 MB just to hold the pixels. Rather than let that kill the request, it is recorded and passed over.
Animated GIFs and APNGs are left alone, because converting them would drop every frame but the first.
Transparency is preserved. Both WebP and AVIF keep the alpha channel.
The plugin sets the quality WordPress uses when it creates thumbnails, so they are born optimized. It does not recompress existing thumbnails in place, which would mean a second round of loss on an already-lossy file.
For images already in your library, bulk conversion works from the untouched original. That gives better quality than recompression — and it is only possible because originals are never modified.
Separately, if your server has a genuine lossless tool (jpegoptim, jpegtran,
optipng, gifsicle), the Advanced tab can enable in-place lossless
optimization of thumbnails. Where no such tool exists the option is greyed out
and the Diagnostics screen names the package to request. No PHP library can
losslessly recompress a JPEG, so the plugin does not pretend otherwise.
Changing the level and re-running bulk conversion rebuilds only what was produced at a different setting. Each row records the quality it was built with, so nothing is redone unnecessarily.