Resize images (resize_images)

• resize_rendered_image_dimensions injects JavaScript that reports each image’s actual rendered dimensions on the client. On subsequent requests, mod_pagespeed resizes to the rendered size. Requires two page loads to take effect.

• 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.

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.