Lighthouse: Optimize images don't support cross-domain images

[BenjaminWalsh]

Testing my live URL in Page speed insights gives me a list as long as my arm of images that can be optimized further...

https://developers.google.com/speed/pagespeed/insights/?url=http%3A%2F%2Fwww.partydelights.co.uk%2Fthemes%2Fteenage-mutant-ninja-turtles-party-supplies.aspx%3Fpmo%3D3

List

> Optimize the following images to reduce their size by 358.9KiB (27% reduction).
> Compressing http://images.partydelights.co.uk/…s/Turtle-Pinata-Kit-PINA062K_v2_ps14.jpg could save 51.1KiB (74% reduction).
> Compressing http://www.partydelights.co.uk/…tant-turtles/header-ninja-turtles_V2.jpg could save 22.3KiB (23% reduction).
> Compressing http://images.partydelights.co.uk/…s/ninja-turtles-bunting-TMNTBUNT_p60.jpg could save 20.9KiB (53% reduction).
> Compressing http://images.partydelights.co.uk/images/banners/PBANTMNTA/PBANTMNTA.jpg could save 14.2KiB (50% reduction).
> Compressing http://images.partydelights.co.uk/…z-Balloon-24-inch-Foil-FOIL2140_ps13.jpg could save 10KiB (28% reduction).
> Compressing http://images.partydelights.co.uk/…urtles-balloon-bouquet-FOILKIT1_ps15.jpg could save 9.8KiB (23% reduction).
> Compressing http://images.partydelights.co.uk/…blue-star-foil-balloon-FOILSTARB_th2.jpg could save 8.8KiB (70% reduction).
> Compressing http://images.partydelights.co.uk/…-Turtles-Scene-Setter-TMNT2SCEN_ps13.jpg could save 8.2KiB (23% reduction).
> Compressing http://images.partydelights.co.uk/…een-star-foil-balloon-FOILSTARKG_th2.jpg could save 7.3KiB (68% reduction).
> Compressing http://images.partydelights.co.uk/…-lilac-star-foil-balloon-FOIL336_th2.jpg could save 7.1KiB (67% reduction).
> Compressing http://images.partydelights.co.uk/…ble-Decorating-Kit-TMNT2TDEC_v2_ps13.jpg could save 7.1KiB (25% reduction).
> Compressing http://images.partydelights.co.uk/…-green-star-foil-balloon-FOIL328_th2.jpg could save 6.9KiB (66% reduction).
> Compressing http://images.partydelights.co.uk/…les/TMNT-Foil-Banner-4m-TMNTBANN_p60.jpg could save 6.8KiB (23% reduction).
> Compressing http://images.partydelights.co.uk/…ges/posters/TMNT-Poster-PSTR100_ps13.jpg could save 6.2KiB (22% reduction).
> Compressing http://images.partydelights.co.uk/…s/Ninja-Turtles-Banner-TMNT2LETT_p60.jpg could save 5.7KiB (25% reduction).
> Compressing http://images.partydelights.co.uk/…s-Hanging-Decorations-TMNT2HANG_ps13.jpg could save 5.6KiB (22% reduction).
> Compressing http://images.partydelights.co.uk/…les-Plastic-Tablecover-TMNT2TABL_p60.jpg could save 4.9KiB (26% reduction).
> Compressing http://images.partydelights.co.uk/…treamer-jumbo-500ft-v2-ROYB2STRE_p60.jpg could save 4.5KiB (23% reduction).
> Compressing http://images.partydelights.co.uk/…yal-blue-hanging-swirls-DECO443_ps13.jpg could save 4.5KiB (21% reduction).
> Compressing http://images.partydelights.co.uk/…upershape-Foil-Balloon-TMNTSUPE_ps13.jpg could save 4.4KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…inja-turtles-balloon-AIRW027_V2_ps15.jpg could save 4.4KiB (15% reduction).
> Compressing http://images.partydelights.co.uk/…a-Turtles-Party-Bag-Kit-TMNTBAGK_th2.jpg could save 4.3KiB (27% reduction).
> Compressing http://images.partydelights.co.uk/images/sweets/SWEE122/SWEE122_th2.jpg could save 4.1KiB (29% reduction).
> Compressing http://images.partydelights.co.uk/…ions/Kiwi-Tassel-Garland-DECO695_p60.jpg could save 3.9KiB (20% reduction).
> Compressing http://images.partydelights.co.uk/…Turtles-Crepe-Streamer-TMNT2STRE_p60.jpg could save 3.7KiB (25% reduction).
> Compressing http://images.partydelights.co.uk/…les-Stand-In-Photo-Prop-CUTO305_ps14.jpg could save 3.6KiB (17% reduction).
> Compressing http://images.partydelights.co.uk/…Ninja-Turtles-Confetti-TMNT2CONF_th2.jpg could save 3.6KiB (20% reduction).
> Compressing http://images.partydelights.co.uk/…azaroo-Orange-Face-Paint-FACE025_th2.jpg could save 3.2KiB (27% reduction).
> Compressing http://images.partydelights.co.uk/…bright-red-face-paint-face007_v3_th2.jpg could save 3KiB (25% reduction).
> Compressing http://images.partydelights.co.uk/images/balloons/TMNTMINI_th2.jpg could save 2.9KiB (30% reduction).
> Compressing http://images.partydelights.co.uk/…tles-Party-Invitations-TMNT2INVI_th2.jpg could save 2.9KiB (24% reduction).
> Compressing http://images.partydelights.co.uk/…l/three-tier-cake-stand-DOTSSTAN_th2.jpg could save 2.7KiB (27% reduction).
> Compressing http://images.partydelights.co.uk/…urtles-Party-Thank-You-TMNT2THAN_th2.jpg could save 2.7KiB (24% reduction).
> Compressing http://images.partydelights.co.uk/…les/Ninja-Turtles-Cups-TMNT2CUPS_th2.jpg could save 2.7KiB (26% reduction).
> Compressing http://images.partydelights.co.uk/…nja-Turtles-Party-Bags-TMNT2LOOT_th2.jpg could save 2.6KiB (24% reduction).
> Compressing http://images.partydelights.co.uk/…nja-Turtles-Party-Game-TMNT2GAME_th2.jpg could save 2.6KiB (24% reduction).
> Compressing http://images.partydelights.co.uk/…oons/ninja-turtle-balloon-BB137_ps13.jpg could save 2.6KiB (14% reduction).
> Compressing http://images.partydelights.co.uk/…Ninja-Turtles-Gift-Cup-TMNT2FCUP_th2.jpg could save 2.5KiB (25% reduction).
> Compressing http://images.partydelights.co.uk/…ja-Turtles-Plates-23cm-TMNT2PLAT_th2.jpg could save 2.4KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…-Turtles-Balloon-Weight-TMNTWEIG_th2.jpg could save 2.4KiB (22% reduction).
> Compressing http://images.partydelights.co.uk/…-Bright-Green-Face-Paint-FACE005_th2.jpg could save 2.4KiB (22% reduction).
> Compressing http://images.partydelights.co.uk/…a-Turtles-Paddle-Balls-TMNT2PADD_th2.jpg could save 2.4KiB (25% reduction).
> Compressing http://images.partydelights.co.uk/…ja-Turtles-Plates-17cm-TMNT2DESS_th2.jpg could save 2.3KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…/Ninja-Turtles-Napkins-TMNT2NAPK_th2.jpg could save 2.3KiB (20% reduction).
> Compressing http://images.partydelights.co.uk/…tles/TMNT-Foil-Balloon-TMNTFOIL2_th2.jpg could save 2.3KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…lue-royal-blue-and-red-TISS85_V2_th2.jpg could save 2.3KiB (22% reduction).
> Compressing http://images.partydelights.co.uk/…-Turtles-Favour-Bucket-TMNT2BUCK_th2.jpg could save 2.2KiB (24% reduction).
> Compressing http://images.partydelights.co.uk/…urtles-Beverage-Napkins-TMNT2BEV_th2.jpg could save 2.2KiB (23% reduction).
> Compressing http://images.partydelights.co.uk/…inatas/turtle-pinata-PINA062_v2_ps14.jpg could save 2.1KiB (18% reduction).
> Compressing http://images.partydelights.co.uk/…oo-Royal-Blue-Face-Paint-FACE032_th2.jpg could save 2.1KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…angelo-Cardboard-Cutout-CUTO302_ps14.jpg could save 2.1KiB (16% reduction).
> Compressing http://images.partydelights.co.uk/…TMNT-11-Latex-Balloons-TMNTBALL2_th2.jpg could save 2KiB (21% reduction).
> Compressing http://images.partydelights.co.uk/…onardo-Cardboard-Cutout-CUTO304_ps14.jpg could save 2KiB (15% reduction).
> Compressing http://images.partydelights.co.uk/…atello-Cardboard-Cutout-CUTO301_ps14.jpg could save 2KiB (15% reduction).
> Compressing http://images.partydelights.co.uk/…les/TMNT-Sticker-Strips-TMNTSTIC_th2.jpg could save 1.9KiB (18% reduction).
> Compressing http://images.partydelights.co.uk/…sonalised-confetti-CONPERSTRA_v2_co2.jpg could save 1.9KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…sonalised-confetti-CONPERSTRA_v2_co2.jpg could save 1.9KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…nja-Turtles-Card-Masks-TMNT2MASK_th2.jpg could save 1.8KiB (20% reduction).
> Compressing http://images.partydelights.co.uk/…ja-Turtles-Sweat-Bands-TMNT2SBAN_th2.jpg could save 1.8KiB (25% reduction).
> Compressing http://images.partydelights.co.uk/images/toys/TOYS035_th2.jpg could save 1.8KiB (25% reduction).
> Compressing http://images.partydelights.co.uk/…inja-Turtles-Party-Masks-MASK713_th2.jpg could save 1.8KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…nja-Turtles-Sunglasses-TMNT2GLAS_th2.jpg could save 1.7KiB (22% reduction).
> Compressing http://images.partydelights.co.uk/…rtles-Party-Bubbles-60ml-BUBB073_th2.jpg could save 1.7KiB (23% reduction).
> Compressing http://images.partydelights.co.uk/…aphael-Cardboard-Cutout-CUTO303_ps14.jpg could save 1.7KiB (13% reduction).
> Compressing http://images.partydelights.co.uk/…a-Turtles-Award-Ribbon-TMNT2AWAR_th2.jpg could save 1.7KiB (23% reduction).
> Compressing http://images.partydelights.co.uk/…-turtles/TMNT-Cone-Hats-TMNTHATS_th2.jpg could save 1.7KiB (25% reduction).
> Compressing http://images.partydelights.co.uk/…/ninja-turtles-tumbler-TMNTCUPS2_th2.jpg could save 1.6KiB (24% reduction).
> Compressing http://images.partydelights.co.uk/…azaroo-Purple-Face-Paint-FACE031_th2.jpg could save 1.6KiB (16% reduction).
> Compressing http://images.partydelights.co.uk/…es/ninja-turtles-badges-BADGE623_th2.jpg could save 1.6KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…-Balloon-30-inch-Foil-TMNTSUPE2_ps13.jpg could save 1.6KiB (14% reduction).
> Compressing http://images.partydelights.co.uk/…ibo-terrific-turtles-tub-SWEE297_th2.jpg could save 1.6KiB (18% reduction).
> Compressing http://images.partydelights.co.uk/…eady-to-roll-icing-green-SDEC209_th2.jpg could save 1.5KiB (22% reduction).
> Compressing http://images.partydelights.co.uk/…es-Balloon-12-inch-Foil-TMNTAIRF_th2.jpg could save 1.4KiB (24% reduction).
> Compressing http://images.partydelights.co.uk/…ions/green-hanging-fans-DECO439_ps13.jpg could save 1.4KiB (13% reduction).
> Compressing http://images.partydelights.co.uk/…urtles-plastic-cup-straw-CATE567_th2.jpg could save 1.3KiB (22% reduction).
> Compressing http://images.partydelights.co.uk/…/Ninja-Turtles-Pencils-TMNT2PENC_th2.jpg could save 1.3KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…il/purple-foil-weight-WEIG144_V2_th2.jpg could save 1.2KiB (14% reduction).
> Compressing http://images.partydelights.co.uk/…-turtles/TMNT-Straws-TMNTSTRA_v2_th2.jpg could save 1.1KiB (19% reduction).
> Compressing http://images.partydelights.co.uk/…s/TMNT-Rubber-Bracelets-TMNTBRAC_th2.jpg could save 1KiB (17% reduction).
> Compressing http://images.partydelights.co.uk/…x-balloon-11-inch-green-ball1147_th2.jpg could save 1KiB (20% reduction).
> Compressing http://images.partydelights.co.uk/…ime-Green-Plastic-Bucket-BOXF196_th2.jpg could save 1,015B (22% reduction).
> Compressing http://images.partydelights.co.uk/…s/sparkling-sugar-purple-SDEC179_th2.jpg could save 932B (14% reduction).
> Compressing http://images.partydelights.co.uk/…lloon-11-inch-royalblue-ball1145_th2.jpg could save 886B (16% reduction).
> Compressing http://images.partydelights.co.uk/…lloon-11-inch-limegreen-ball1137_th2.jpg could save 869B (22% reduction).
> Compressing http://images.partydelights.co.uk/images/balloons/CURL500EME_th2.jpg could save 866B (16% reduction).
> Compressing http://images.partydelights.co.uk/…t-turtles/TMNT-Blowouts-TMNTBLOW_th2.jpg could save 796B (16% reduction).
> Compressing http://images.partydelights.co.uk/…andy-buffet/Kiwi-Scoop-CBUFSCOO4_th2.jpg could save 767B (21% reduction).
> Compressing http://images.partydelights.co.uk/images/balloons/CURL500LAV_th2.jpg could save 745B (15% reduction).
> Compressing http://images.partydelights.co.uk/images/catering_rolls/CATE045_th2.jpg could save 634B (16% reduction).
> Compressing http://images.partydelights.co.uk/…-balloon-11-inch-purple-ball1139_th2.jpg could save 604B (14% reduction).
> Compressing http://images.partydelights.co.uk/…/plain/royal-blue-bowl-ROYB2BOWL_th2.jpg could save 563B (16% reduction).

but Lighthouse is only reporting one of these images as needing attention...

…mutant-turtles/header-ninja-turtles_V2.jpg
100 KB
14 KB (14%)

Should the results be the same as in page speed insights?
I was hoping to use Lighthouse for this test before my images get published.

[ebidel]

I suspect some of the difference comes from what images Lighthouse is considering vs. all images on the page (what Page Speed looks at).

In LH 2.0, we're ignoring cross-origin images because processing them through canvas was very slow. We also updated the jpeg quality threshold to 0.92 (from of 0.8) which would change things a bit. PSI uses q=0.8, for example.

In your PSI list, it looks like most images are x-origin, so Lighthouse is ignoring them from the start. Yea, checked...mutant-turtles/header-ninja-turtles_V2.jpg is the only one from www.partdelights.co.uk :)

Something else worth noting: PSI uses imagemagick to suggestion optimizations. I ran some of your images through ImageOptim that PSI says would have 60-70% savings. ImageOptim showed 0% savings for those images :(

cc @patrickhulce we should probably bring back x-domain images. Images are such a large part of the web and close parity with PSI is important.

[patrickhulce]

@BenjaminWalsh there are a few differences at the moment between PSI and Lighthouse that makes the LH check less strict.

1. Lighthouse only checks images on your domain due to CORS tainting. We previously had a workaround but it was relatively inaccurate and slowed runtimes considerably. We'll eventually bring this back, but some work needs to be done before we can.
2. The check that Lighthouse does for quality savings is less aggressive than PSI (does not lower the JPEG quality as much and mostly looks for excessive metadata and reasonable quality).
3. Lighthouse does not flag negligible savings less than 4kb (which comprises most of your list)

[BenjaminWalsh]

Thanks guys, that explains perfectly why I'm seeing these differences in reports. Is this going to be added to the roadmap for lighthouse?

[patrickhulce]

Bringing back savings for x-origin images is definitely on our roadmap, but it will take some time. Even once a fix is implemented in Chrome we'll need to wait ~6-12 weeks for the support to make its way to Chrome stable.

There are currently no immediate plans to make the check more aggressive, but we're always striving to align performance recommendations and periodically re-evaluate our thresholds.

[paulirish]

Fixed by #3087