Large Output Digital Graphics
Sign companies, blueprint shops and others offer large output digital graphics on a variety of materials ranging from paper, to fabric and vinyl. The inks for producing outdoor graphics come with warranties against fading for up to about five years. The fabricator will inform you as to the maximum width they can produce, and the output is usually sold by how long your finished piece will be. You can output anything you can create on your computer to fit the dimensions available and that will hold up when enlarged to the desired size. Check with the fabricator for all the file parameters and other information you will need. You will probably want to build or buy a frame on which to stretch the graphic output.
Home Printer Output of Large Graphics
Software programs such as Pro Poster allow you to expand an image to a large size by breaking it into pieces that you can print on your home printer and then paste together. For exterior use you will want to have a piece of exterior plywood to use as a base and a suitable adhesive for the paper. Be sure and coat with a waterproof coating when you are finished.
Using a Cartoon for a Painted Mural
If you plan to paint a mural, a good way to start is to create a "cartoon" or template of the image on paper. You can sketch an image by hand. Consider stylizing detailed photos or illustrations to reduce their detail with free programs at a website like Be Funky to make them easier to paint. You can then output the images on paper using one of the methods above.
Transfer the cartoon image to the surface to be painted by poking holes in the image outlines with a pounce wheel, ice pick, or similar tool; taping the paper to the surface; and then dabbing or spraying paint or rubbing charcoal through the holes to transfer the outline. Remove the paper and fill in the outline and mark for colors as needed.
Painting the Mural
Make sure you have a flat enough surface to paint or affix a stable material like exterior plywood if necessary. Prime the surface to be painted with a quality bonding primer or if your budget allows, use artist gesso. Transfer the cartoon image as described above. Use liquid acrylic artist colors to paint your image. If you are doing the mural as a group project it is a good idea to have one person coordinating the application of the different colors.
Protect the Mural
When you are finished painting the mural, protect it with a clear protective coat of acrylic polyurethane or varnish or a protective anti-graffiti finish such as AGS Anti-Graffiti Coat.