Juan, thanks for posting.

Inserting the images directly in the post, directly renders the image via an image tag which has much higher quality rendering than within a cloud notebook. This, unfortunately, is something that is not great. I have some workarounds proposed below but those still involve non-trivial effort.

Problem: Poor raster quality when rendering Images (GraphicsBox[RasterBox[...]] under the hood) in cloud notebooks.

Explanation: When rendering images and raster formats in a cloud notebook, the Wolfram Cloud generates and displays a separate image based on the underlying GraphicsBox expression. That image is created with $ImageResolution = 72 which is the reason for the low-quality. That choice of ImageResolution is a combination of various legacy constraints and very real performance considerations.

Key Things:

1. We are actively working on a more general solution to improve image quality generally, and expect to release that in a Wolfram Cloud version prior to the end of the year. As, in I am literally reviewing a pull request specifically about this as I write this up.
2. This only affects cloud notebook rendering of such images in the Environment (/env), Deployed (/obj), and /statichtml views.
3. The underlying quality of the image as saved in the notebook is NOT affected
4. You can still generate an image of higher quality and save it as a file or CloudObject

I gave this same explanation and a few possible workarounds using some internal methods for directly rendering images, here: https://www.wolframcloud.com/obj/7201d94d-3157-44d6-8827-1fdf64f87c38, which I "added" a copy of to this post. Those workarounds use internal methods that essentially bypass the WL kernel to display the image data as is.