Gulp photo compression?

Question

gulp.js

To optimize images, I use the gulp-imagemin plugin :

const options = [
    imagemin.mozjpeg({ progressive: true }),
    imagemin.optipng({ optimizationLevel: 3 }),
  ]

Judging by the description, compression will occur without loss of image quality. Is it so? I just tried to compress photos with a third-party service, and there, when compressed without quality loss, the results were worse.

Do my settings compress photos with loss of quality or not?) And do you know where you could compare 2 photos and understand whether it was compressed or not?)

Answer 1

There will always be loss of quality!
You can open 2 photos on 1 monitor and compare! Compressed will weigh less!

Answer 2

The quality loss depends on the level of compression. optimizationLevel: 3
Empirically, you can calculate the most optimal option, not noticeable to the eye.