How do I prepare a fabric design for printing?

Meggiecat wrote the other day to ask the most obvious question about printing fabric on Spoonflower, which is "what do we need to do to prepare designs?"

I've delayed my response in the hope of being able to offer a bit more technical detail, but in the absence of a perfect response I'd like to go ahead and post a few suggestions. Please forgive me if I end up needing to revise any of this [likely].

File Resolution:
240 dpi is a minimum resolution for the design you wish to repeat in a pattern. If you want to be able to scale it up after you upload it, the image will need to be at least twice that. Updated info on preparing images is here.

Image Size:
You can take an image of any size (240 dpi or greater) and repeat it to create a pattern. Alternately, you could create the pattern repeat on your own computer and then upload a large file equal in size to the amount of fabric you wish to order. For example, the fabric we will be using is 44" wide (112 cm), so if you wanted to order a yard you could create an image that is 42" (the printable area) x 36" (or close to that). The file size limit is 25 MB, so if your design is large you will almost certainly have to use the JPG rather than the RIF format.

Fabric Size:
You can order a swatch (8"x8"), a fat quarter (18"x21") or any multiple of a linear yard (up to 3 yards).  We will always recommend that you order a swatch of your design before ordering a larger quantity. That will give you a chance to examine the colors firsthand to make sure they printed as intended.

Creating Repeats:
When you upload a design to your Spoonflower gallery, you will be able to create a pattern by tiling the image, using a half-step or half-brick repeat (which staggers the tiles), or by mirroring your image. In the case of tiling, in order for the pattern not to appear to be composed of a lot of individual rectangles, the design you upload will need to be composed so that the left side of the design 'joins' to the right side, and the top of the design 'joins' to the bottom. If you have a textile design program or Photoshop expertise, you can probably do this pretty easily. For the rest of us, however, we plan to post tutorials to help you through the process of creating patterns on your own.

File Types / Color Profile:
You will want to set up your files in LAB color profile or RGB profile with 8 Bits/Channel (rather than 16), and to save (and upload) them as .TIF, .JPG, or .PNG files with flattened layers. LAB is the ideal profile for printing. We cannot print from CMYK files. Do not compress the images.