Is insert_image_dimensions enabled by default?

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

How do I enable insert_image_dimensions on Apache and nginx?

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

filter · Image filters

Insert image dimensions (insert_image_dimensions)

Q: What does the insert_image_dimensions filter do?

insert_image_dimensions adds explicit width and height attributes to tags that lack them. This prevents layout shifts (CLS) but does not resize the image file itself. insert_img_dimensions is an accepted alternate spelling of the same filter.

Category:: Image
CoreFilters:: No
OptimizeForBandwidth:: No
Risk:: Generally safe

insert_image_dimensions adds explicit width and height attributes to <img> tags that lack them. This prevents layout shifts (CLS) but does not resize the image file itself. insert_img_dimensions is an accepted alternate spelling of the same filter.

How it works

insert_image_dimensions declares the intrinsic size of each image: it adds width and height attributes carrying the pixel dimensions of the image file itself, read from the copy the module decoded, to <img> and image <input> elements that declare no dimensions at all: no width attribute, no height attribute, and no dimension inside a style attribute. An element that already declares any of those is left alone. The browser uses the pair to reserve the image’s box before the file arrives, which is what removes the layout shift; the filter does not resize the image file and does not touch CSS sizing. It applies even to images the module decides not to optimize, as long as the file’s dimensions could be decoded. It does not apply when image URLs are preserved (ImagePreserveURLs, as under OptimizeForBandwidth). Images that inline_images turns into data: URIs get no dimensions from this filter; inline_images instead removes width and height attributes that match the image’s own size. Not a core filter; enable it by name.

When to use it

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

Risks

insert_image_dimensions can break responsive layouts that rely on the absence of explicit dimensions. Test with your CSS.

Configuration

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

Apache

ModPagespeedEnableFilters insert_image_dimensions

nginx

pagespeed EnableFilters insert_image_dimensions;

IIS (pagespeed.config)

pagespeed EnableFilters insert_image_dimensions

Parameter	Default	Description
`ImageLimitResizeAreaPercent`	100	Only resize if the result is this percentage of the original area or less

On the worker

The worker runs its own pipeline, configured by flags. Its equivalent of this filter is the image dimensions transform. Toggleable via --no-image-dimensions.

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

Frequently asked questions

What does the insert_image_dimensions filter do?: insert_image_dimensions adds explicit width and height attributes to <img> tags that lack them. This prevents layout shifts (CLS) but does not resize the image file itself. insert_img_dimensions is an accepted alternate spelling of the same filter.
Is insert_image_dimensions enabled by default?: No. insert_image_dimensions is not in CoreFilters, the default RewriteLevel; it runs only when you enable it by name with EnableFilters.
How do I enable insert_image_dimensions on Apache and nginx?: Add ModPagespeedEnableFilters insert_image_dimensions on Apache or pagespeed EnableFilters insert_image_dimensions; on nginx. On IIS, add pagespeed EnableFilters insert_image_dimensions to pagespeed.config.

resize_images — Resize images
resize_rendered_image_dimensions — Resize to rendered dimensions
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 insert_image_dimensions entry on Image filters. Every filter in one table: PageSpeed filters.