What causes image quality loss on Facebook?

Question

Facebook

Hello dear experts! I've been struggling with the image quality issue on Facebook for a long time now.
In particular, if there is a red color, it is pinched utterly. But after posting these images, it may look normal.
I am attaching examples of images with the same logo (the brand itself is smeared, but I hope it is clear what it is about), but the layouts themselves seem to be the same, the parameters are the same and are filled directly. What affects this "jack-like" color, and why is everything ok in one picture, but not in the second, although everything was saved and filled in the same way?
What could be the matter, where to dig?
Thank you very much in advance.

Answer 1

These are JPEG artifacts on the second picture. Why the difference in quality between the first and second, I don’t know, the first one seems to be even PNG, unlike the compressed second one.
Theoretically, if you have a logo in the form of a red rectangle, then you can try to reduce the artifacts at the edges of the logo.
Inside the jeepeg, the image is represented as one layer of Luma and two layers of Chroma-r and Chroma-b. Chroma is stored at half the width and height of the entire photo. That is, the chromaticity there is of very low quality.
Each layer is divided into blocks of 8x8 pixels (the actual size of such a block for color is 16x16 pixels).
Compression artifacts from any block do not affect its neighbors. Therefore, you can try to align the logo on a grid of 16 by 16 squares.
The red square is not aligned to the grid:
Aligned (the setting of the compression force of the jeep is the same):
For this to work, Facebook has not yet resized the uploaded images. And you need to bother with the grid. In general, I doubt that it helped =)

Answer 2

Previously, it helped to add noise : small, almost imperceptible to the eye - but it had a very good effect on compression algorithms.