Sharing some wisdom from the Sign-Up.to Client Success team…
When a campaign is saved, we automatically re-sample images – this involves making the image file size smaller so that when a subscriber receives your campaign it doesn’t take ages to download any included images. All being well this process of re-sampling doesn’t have any impact on the quality of the rendered image in the received campaign. However there’s a couple of things you can do to help optimise the performance of images in your campaigns.
Firstly, before including any images try re-sizing them to the dimensions of the component where they’ll be placed. Approximately and larger is OK as the re-sampling will take care of the details, although smaller may result in poor image quality. What is the right size? Here is a handy guide to the pixel dimensions of each of the most commonly used components.
Secondly, use the image format which best suits the image type.
There are some practical limitations to re-sampling images which require the use of the correct image type (JPEG vs PNG/GIF) for the image that you’re uploading. PNG/GIF images should be used for things like logos, where there’s a lot of blank space, copy, defined lines and similar graphical elements. JPEG images should be used for things like photos and real world scenes.
So if you’re experiencing issues with pixellation or poor quality images try the above. That should do the trick.