Is jpeg_subsampling enabled by default?

Yes. jpeg_subsampling is in CoreFilters, the default RewriteLevel, so it runs unless you turn it off with DisableFilters. It is also part of the OptimizeForBandwidth level.

How do I turn off jpeg_subsampling?

Add ModPagespeedDisableFilters jpeg_subsampling on Apache or pagespeed DisableFilters jpeg_subsampling; on nginx. On IIS, add pagespeed DisableFilters jpeg_subsampling to pagespeed.config.

filter · Image filters

JPEG chroma subsampling (jpeg_subsampling)

Q: What does the jpeg_subsampling filter do?

jpeg_subsampling downsamples JPEG chroma channels (4:2:0 subsampling), reducing file size with minimal visual impact on photographic content.

Category:: Image
CoreFilters:: Yes
OptimizeForBandwidth:: Yes
Risk:: Generally safe

jpeg_subsampling downsamples JPEG chroma channels (4:2:0 subsampling), reducing file size with minimal visual impact on photographic content.

When to use it

In CoreFilters, the default RewriteLevel: it runs unless you disable it.
Part of OptimizeForBandwidth, the level that optimizes resources without changing their URLs.
Also switched on by recompress_images and rewrite_images.
Risk rating on these docs: Generally safe.

Risks

Stripping color profiles can cause subtle color shifts on wide-gamut displays or for images authored in non-sRGB color spaces. This affects a small fraction of web images.
Stripping metadata removes copyright and attribution information embedded in the file. The metadata is removed from the served variant only; original files on disk are not modified.

Configuration

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

Apache

ModPagespeedEnableFilters jpeg_subsampling

nginx

pagespeed EnableFilters jpeg_subsampling;

IIS (pagespeed.config)

pagespeed EnableFilters jpeg_subsampling

It is on by default under CoreFilters; to turn it off:

ModPagespeedDisableFilters jpeg_subsampling   # Apache
pagespeed DisableFilters jpeg_subsampling;   # nginx
pagespeed DisableFilters jpeg_subsampling   # IIS

On the worker

The worker runs its own pipeline, configured by flags. Its equivalent of this filter is the image pipeline transform. Always-on baseline under pagespeed on;; there is no per-transform off switch.

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

Frequently asked questions

What does the jpeg_subsampling filter do?: jpeg_subsampling downsamples JPEG chroma channels (4:2:0 subsampling), reducing file size with minimal visual impact on photographic content.
Is jpeg_subsampling enabled by default?: Yes. jpeg_subsampling is in CoreFilters, the default RewriteLevel, so it runs unless you turn it off with DisableFilters. It is also part of the OptimizeForBandwidth level.
How do I turn off jpeg_subsampling?: Add ModPagespeedDisableFilters jpeg_subsampling on Apache or pagespeed DisableFilters jpeg_subsampling; on nginx. On IIS, add pagespeed DisableFilters jpeg_subsampling to pagespeed.config.

strip_image_color_profile — Strip image color profiles
strip_image_meta_data — Strip image metadata
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
convert_to_avif_animated — Animated AVIF

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