Is convert_png_to_jpeg enabled by default?

Yes. convert_png_to_jpeg 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 convert_png_to_jpeg?

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

filter · Image filters

Convert PNG to JPEG (convert_png_to_jpeg)

Q: What does the convert_png_to_jpeg filter do?

convert_png_to_jpeg converts PNG images with no alpha channel (fully opaque) to JPEG, which is typically much smaller for photographic content.

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

convert_png_to_jpeg converts PNG images with no alpha channel (fully opaque) to JPEG, which is typically much smaller for photographic content.

How it works

convert_png_to_jpeg turns a PNG into a JPEG only when the module’s image analysis says the file is photographic, meaning not sensitive to compression noise, and it has no transparent pixels. The analysis is what protects flat graphics: a logo or a diagram analyzes as non-photographic and keeps its PNG. On a photographic PNG without transparency the filter authorizes lossy encoding, and the format that ships depends on the browser: when the request prefers WebP and convert_jpeg_to_webp is on, the file becomes WebP rather than JPEG; otherwise it is re-encoded as JPEG at the JPEG quality setting. A PNG with transparency is never made a JPEG. The converted file is kept only when it is smaller (ImageLimitOptimizedPercent), and a PNG carrying a C2PA content-credentials manifest is left untouched so its provenance chain survives. The filter runs in CoreFilters through rewrite_images.

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

convert_png_to_jpeg drops the alpha channel on opaque PNGs. mod_pagespeed checks for alpha before converting, but semi-transparent pixels at the boundary may cause subtle edge artifacts.

Configuration

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

Apache

ModPagespeedEnableFilters convert_png_to_jpeg

nginx

pagespeed EnableFilters convert_png_to_jpeg;

IIS (pagespeed.config)

pagespeed EnableFilters convert_png_to_jpeg

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

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

Parameter	Default	Description
`ProgressiveJpegMinBytes`	10240	Minimum JPEG size before converting to progressive
`WebpRecompressionQuality`	80	Quality for lossy WebP conversion
`WebpAnimatedRecompressionQuality`	70	Quality for animated WebP conversion

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

Frequently asked questions

What does the convert_png_to_jpeg filter do?: convert_png_to_jpeg converts PNG images with no alpha channel (fully opaque) to JPEG, which is typically much smaller for photographic content.
Is convert_png_to_jpeg enabled by default?: Yes. convert_png_to_jpeg 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 convert_png_to_jpeg?: Add ModPagespeedDisableFilters convert_png_to_jpeg on Apache or pagespeed DisableFilters convert_png_to_jpeg; on nginx. On IIS, add pagespeed DisableFilters convert_png_to_jpeg to pagespeed.config.

convert_gif_to_png — Convert GIF to PNG
convert_jpeg_to_progressive — Progressive JPEG
convert_jpeg_to_webp — Convert JPEG to WebP
convert_to_webp_animated — Animated WebP
convert_to_webp_lossless — Lossless WebP
convert_jpeg_to_avif — Convert JPEG to AVIF
convert_to_avif_animated — Animated AVIF
convert_to_avif_lossless — Lossless AVIF

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