When image optimization makes no difference in speed.

WordPress Mobile Speed


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Online speed tests like WebPagetest.org or Pingdom.com may recommend optimizing images.This can be a lot of work and often make little or no difference in the page speed. Why?

Images load in parallel in the browser. They all happen at once. With some exceptions for fat PNG images. So halving the image weight doesn’t half the load time. It may only make a small improvement like 5 percent – or none.

There are the original image size and the mathematically scaled image size. In theory, making the images the actual size would reduce page weight. But do the speed results improve much? Let’s find out:

Homepage header

255.9 k JPEG image format
2,560px × 786px
(scaled to 1,366px × 419px)

Blog post featured image

57.6 k JPEG image format
1,024px × 384px
(scaled to 710px × 266px)

Block Clones Ad for Pagepipe 5

Both pages load in about 400 milliseconds using a browser timer measurement.

In this example, 200k reduction reworking  image optimization makes no difference in speed.

Our recommendation: Ignore test recommendations. Usually. Keep the gain in perspective. Don’t waste your life chasing unrealistic goals

Optimizing or resizing these images more won’t make any difference in speed.

On some sites, it makes  a big difference. If the images loading in parallel take 4 seconds or more to load, you have an image optimization problem.

Here are suggestions to fix it:

REFERENCE: https://pagepipe.com/using-image-optimizer-web-utilities-for-improved-speed/

REFERENCE: https://pagepipe.com/the-fastest-alternatives-to-heavy-jpeg-images-for-page-speed/

REFERENCE: https://pagepipe-ebooks.com/crush-me-whats-wrong-with-wp-smush-image-optimization-plugin/

REFERENCE: https://speedhospital.org/wordpress-speed-tuning/


Steve Teare
performance engineer
April 2021


Other unconventional speed articles like this one:

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