Is resize_mobile_images enabled by default?

No. resize_mobile_images is not in CoreFilters, the default RewriteLevel; it runs only when you enable it by name with EnableFilters.

How do I enable resize_mobile_images on Apache and nginx?

Add ModPagespeedEnableFilters resize_mobile_images on Apache or pagespeed EnableFilters resize_mobile_images; on nginx. On IIS, add pagespeed EnableFilters resize_mobile_images to pagespeed.config.

filter · Image filters

Resize images for mobile (resize_mobile_images)

Q: What does the resize_mobile_images filter do?

resize_mobile_images serves smaller images to mobile devices based on the User-Agent header. Enabling it also enables inline_preview_images, which it depends on.

Category:: Image
CoreFilters:: No
OptimizeForBandwidth:: No
Risk:: Test first

resize_mobile_images serves smaller images to mobile devices based on the User-Agent header. Enabling it also enables inline_preview_images, which it depends on.

When to use it

Not in CoreFilters: it runs only when you enable it by name.
Risk rating on these docs: Test first.

Risks

Inlining increases HTML size. Inlined images are not cached separately by the browser. Set ImageInlineMaxBytes conservatively.
resize_mobile_images relies on User-Agent detection. Incorrect UA classification can serve wrong-sized images. It also pulls in inline_preview_images, so expect that filter’s placeholder-then-swap behavior when enabling it.

Configuration

Enable it in the module configuration, at server, virtual-host or location scope:

Apache

ModPagespeedEnableFilters resize_mobile_images

nginx

pagespeed EnableFilters resize_mobile_images;

IIS (pagespeed.config)

pagespeed EnableFilters resize_mobile_images

Parameter	Default	Description
`ImageInlineMaxBytes`	3072	Maximum image size in bytes to inline as a data: URI

Scoping, ForbidFilters and the thresholds filters read: Choosing filters .

Live example

Serves smaller low-quality placeholders to mobile browsers, then the full image.

This filter changes how the page is structured or delivered, not its size, so the example shows a source diff rather than a byte or request reduction.

See the before and after, with the source diff →

Frequently asked questions

What does the resize_mobile_images filter do?: resize_mobile_images serves smaller images to mobile devices based on the User-Agent header. Enabling it also enables inline_preview_images, which it depends on.
Is resize_mobile_images enabled by default?: No. resize_mobile_images is not in CoreFilters, the default RewriteLevel; it runs only when you enable it by name with EnableFilters.
How do I enable resize_mobile_images on Apache and nginx?: Add ModPagespeedEnableFilters resize_mobile_images on Apache or pagespeed EnableFilters resize_mobile_images; on nginx. On IIS, add pagespeed EnableFilters resize_mobile_images to pagespeed.config.

dedup_inlined_images — Deduplicate inlined images
inline_images — Inline images
inline_preview_images — Inline preview images
convert_gif_to_png — Convert GIF to PNG
convert_jpeg_to_avif — Convert JPEG to AVIF
convert_jpeg_to_progressive — Progressive JPEG
convert_jpeg_to_webp — Convert JPEG to WebP
convert_png_to_jpeg — Convert PNG to JPEG

This page is drawn from the resize_mobile_images entry on Image filters. Every filter in one table: PageSpeed filters.