Thanks for writing in. And thank you to everyone else who has shared similar feedback.
So, tl;dr—this is actually a blog theme issue. Your theme is not showing images in posts created by the new editor as you expect.
GIFs uploaded via the legacy editor or the new editor are actually processed the same way. There is no difference in bit depth or in resolution. You can see this by looking at your posts inside the Tumblr dashboard instead (e.g. instead of yourblog.tumblr.com/post/id, go to tumblr.com/yourblog/id).
The reason why you see a quality difference is because posts created by the new editor are treated as text posts by older blog themes. Themes often add padding around all the content of a text post—including any images that appear in it. If your theme presents posts as 540px wide, then in a text post, with that additional padding, the available space for your images is actually less than 540px. As a result, the browser will scale your images down to fit, and when this happens, image quality takes a hit.
The solution—update to a more modern, up-to-date theme, like Vision or Stereo. Theme developer @eggdesign also built a theme template that works with new posts, that you can build on top of! These modern themes apply padding only to text blocks rather than the whole post, so image blocks receive no padding and are served at their full 540px width, just like the Dashboard. From what we’ve seen, this fixes all of the issues about perceived GIF quality on blogs.
We know. Changing your theme is a lot of work. In the near future, we’re looking into ways to make this transition easier—for example, helping you identify themes that work well with new posts in the Theme Garden. But working with new posts is the way forward—the new posts use a format that opens up a lot of opportunities in the future.
Why can’t you add post types to posts from the new editor? Why not serve new posts as photo posts instead of text posts?
The new editor uses a new post format, called Neue Post Format (NPF). NPF has given us a huge boost in flexibility when it comes to what content can be in posts—remember the time when you couldn’t even upload images to reblogs? Or how old chat and quote posts magically change authors? NPF helped us fix both of these things. It removed constraints—including post types, which limit each post to one specific type of content.
But existing blog themes still need to be able to display these posts. Because NPF posts can include media anywhere (while most of the old post types have a rigid structure for media), it was safest for us to categorize NPF posts as the least constrained post type—text posts. It’s the best we can do to make these posts backward-compatible with existing blog themes.
In lieu of post types, we’ve added an {NPF} theme variable per post that custom themes can leverage. Theme developers must update their themes to take advantage of this new data to retain full control of the HTML output of posts.
You can read more about these decisions, and the Neue Post Format specification, here and here.
Thanks for your feedback, and keep it coming!