I found this article that really makes me frown.
https://support.pixlr.com/hc/en-us/articles/209350208-A-quick-primer-on-image-resolution-DPI-and-professional-printers-
You need to create something to a very detailed specification (sized to spec)
If you've spoken to a printer about making a t-shirt and they want you to deliver a 300dpi file in an uncompressed format, you might be able to use our tools to do it. It depends on the quality of the file you begin with. (Ultimately, it's really all about the pixels, not about the DPI. Check out this article, The Myth of DPI, if you want to delve into the subject a bit more.) If you're starting with a very large image, you can edit it in Pixlr Desktop or Pixlr Editor for the web and save it out as an uncompressed TIFF. Be aware, though, that our apps aren't really designed for professional graphic designers who might need very fine-grained tools to meet very detailed specifications. For example, our apps aren't designed for CMYK output. That said, Pixlr Editor contains many graphic design tools that will work just fine for you, and Pixlr for Mac and PC can handle large, high resolution files.
The bottom line:
- As with most things in life, the quality of output depends on the quality of input. Start with the highest resolution or largest images you can to get the best results.
- Pixlr apps aren't designed to be an all-in-one solution for graphic designers, but if you have some knowledge about image editing, you will find that they will work for many projects and will help you avoid paying for an expensive professional solution.
- If you've never created anything to give to a professional printer and are overwhelmed by the specifications they require, it's probably best to give them the highest quality image you can and ask them very nicely to help with the layout of the image for printing.