ArtStation already does an excellent job of hosting images and retaining quality of images. However, there are some caveats and things that users have to understand, and some tricks to get the absolute best quality.
IMPORTANT: Export images - do not use Save As
It's important that you export images using the appropriate export features in your software package. For example in Photoshop, use the "File > Export > Export As" or the legacy "Save for Web" feature.
In your export settings, set your Color Space to "Convert to sRGB" and do NOT check the "Embed Color Profile" setting.
Do not use Photoshop's Save As feature
Photoshop's Save As feature will store all kinds of metadata and color profile information that can cause your image colors to go out of whack when displaying on the web.
Generally, web images should be sRGB and contain no metadata.
Artwork images are normalized
Generally, assets uploaded to artworks will be normalized using compression, conversion or resizing depending on what you upload. This is for many reasons: performance, adapting to the user's screen size, keeping CDN costs reasonable, etc.
Some users expect ArtStation to display full, uncompressed PNG files. The problem with this is that PNG files are massive compared to JPGs and forcing your end users to view full, uncompressed PNG's especially if you are uploading multiple, high-resolution images, is unreasonable.
There are some places on ArtStation where images are not compressed - notably on your ArtStation-powered website pages, we allow users to upload uncompressed images there.
How to get the best quality
ArtStation will convert images to JPG at 90% quality at 1920 width. However, if you have a 4K monitor, we will send the image in 4K if it is available.
To get the best quality where there's little to no perceptible loss of image quality, we recommend exporting your images as JPG, 100% quality, at 3840px width. At this resolution, generally what you upload is going to be what you get on the site if the viewing monitors accept it.
Where you'll run into quality loss
Generally, quality loss will happen during resizing and conversion from another format.
Resizing quality loss happens when an image is resized and the software (Photoshop, your Browser, ArtStation's image compressor) has to run anti-aliasing on it. This can blur out some very fine details due to anti-aliasing.
Things to note:
Make sure that what you export from Photoshop has the detail you want at the desired resolution. When exporting from Photoshop, you can set the resolution of the image - the problem is that when doing this, you might not realize that it actually is anti-aliasing your image during the resize and you'll lose detail already. The best way to avoid this is to resize the image FIRST, run any filters that you need to retain detail, then export it without resizing during export.
Browsers will resize the image and there may be some quality loss due to resizing. Keep in mind that ArtStation is a responsive website - that means that it will be used on many different screen sizes - from large 4k monitors all the way to tiny mobile screens. Web browsers will do their best to resize the image, but during the process, the anti-aliasing may blur out very fine details. This is unavoidable and is the nature of displaying images online.
There can be a quality loss from the conversion of PNG to JPG. For the vast majority of works uploaded, there's little to no quality loss that is perceptible to end users. However, certain kinds of works - e.g. vector graphics with very hard edges and opaque reds can have artefacting introduced from JPG compression. This is something that we are looking into, but at the moment we're just aware of the issue and still looking at options. It's not an ArtStation problem per se, it's the problem with JPG compression in general on certain types of graphics - and it doesn't affect the vast majority of works on ArtStation.
There are ways of retaining quality in those situations - such as introducing noise to your image, which gives the JPG more data to work with and will make artefacting much less noticeable.
Please keep in mind that images must be greater than 400px X 400px, less than 10,000px X 10,000px and less than 10MB, otherwise they won't upload.