I worked with the image in Photohop and determined the values. I blew up the image to be 24 x 48 and mapped out each value. Then I assigned colors to the values and traced them onto tracing paper.
I chose raw silk to stitch because it has a lot of body. I dyed it a deep blue/green because I wanted to have some of that color show through the stitching to influence the colors of thread I used. I knew this piece was going to be almost solid stitching, so planned to have a small border of the fabric showing when mounted to a stretched canvas.
I placed the tracing paper onto the silk and began stitching with the thread around each area to indicate the color to use to fill in that shape. Then I removed the tracing paper & filled in each area with thread.
Here's the finished stitching, which will be pillowcased and attached to a 1 1/2" deep stretched canvas with velcro.