5. What was the first step?

Photographers captured high-resolution images of the original at the Casa de Alfeñique Museum in Puebla, Mexico. 

To achieve maximum resolution, they divided the surface of the Lienzo into three rows and five columns. For each of the 15 sections, they created a 4 x 5 inch reprography plate (negative) and a scan. The quality is so high that individual threads of the cloth can be seen clearly.