[maskros]

It's not just extra DNR applied, modern image and video compression formats almost make it a point to erase all detail and texture from images.

For example, compare the WebP and AVIF (VP8/AV1) compression artefacts with JPEG (and MPEG).

With WebP and AVIF all textures and low contrast details tend to be erased or smoothed out, preserving only high contrast parts of the image.

The JPEG image may have some visible ringing and block edge artefacts, but at least the textures and fine details are preserved!

[account42]

I've noticed that too with cwebp (and other libwebp-based tools) encoding for darker images. My guess was that they their difference function is using the wrong colorspace so it does not match the perceptive difference. My quick tests of cjxl fared much better so all hope is not lost.

But essentially, losless compression is all about throwing away impercetible details. Noise is an interesting case here because the presence and fequency of the noise (the texture) is significant to the viewer but having the noise match 1:1 is not. Which is why newer codecs remove the noise and then re-add generated noise during decoding.