Here is a t-shirt I designed for my friend Andrew of Bertha's Mussels in Fells Point. He wanted a t-shirt that connected his legendary bumper sticker with the memory of his dad's sweet VW bus from the 70s. I found a photo of a bus online and opened it in Adobe Photoshop. I made all the design and color edits in Photoshop and exported 3 spot channels in DCS2 format. The color plates were placed and positives were printed from Adobe Illustrator. 
The DCS (Digital Color Separation) format is a version of the standard EPS format that lets you save spot color channels in Photoshop. Spot channels are not the same as the CMYK (Cyan, Magenta, Yellow and Black) channels. Spot channels allow the designer to use the Pantone color space which is referred to as PMS colors. Basically, to understand the difference between CMYK and spot colors think of the color green. To create green in the CMYK color format you print the cyan and yellow equally thus blending together to make green. Spot colors rely on the purity of the chosen green represented in the swatch book and there is no need for blended channels (channels = color plates/separations)
The black channel from the original bus photo was converted to a spot channel. The same black channel was used to create a mid-tone color. Using "Levels" I isolated the mid-tone and converted it to a spot channel and set it to Pantone 130. To achieve the white high-light I used the original black channel, inverted and pushed the histogram in the levels palette to isolate the brightest part of the photo. This selection was converted to a spot channel and set to white.
What is really cool about exporting spot channels from photoshop is that the .eps file when placed into Illustrator or In Design bring the spot channels into the layout program. Once the spot channels are in the swatch palette you can then use those swatches in the layout to color vector art and be output on the same color separation.Understanding Color Separations
Spot Channel Tutorial
