Final answer:
Harold Rosenberg's statement about modern painting being an event rather than a picture pertains to the Abstract Expressionist movement, where the painting process formed the essence of the artwork. Action painting emphasized the physical act of creation, with artists like Jackson Pollock exemplifying this approach through their dynamic and expressive techniques.
Step-by-step explanation:
When Harold Rosenberg says that modern painting is "not a picture but an event," he is articulating a radical shift in the perception of painting that emerged with the Abstract Expressionist movement. According to Rosenberg's view, the act of painting itself, not the final artifact, is the true work of art.
The canvas becomes an arena for action, wherein the painter's gestures, the application of paint, and the overall process are what constitute the essence of the artwork—a dramatic event in itself. This notion was epitomized by the likes of Jackson Pollock, whose technique of dynamic gestural brushwork stood in contrast to the more static and calculated approaches of other art movements.
The Abstract Expressionist artists transformed large canvases into a field of action where traditional concepts like composition and figuration took a back seat to the importance of the moment-to-moment act of creation. The artists expressed their emotions through dramatic techniques such as dripping, pouring, and splattering paint, resulting in works that are experiences of their process rather than just depictions on a canvas. The focus on the physical act of painting brought with it, however, a new set of challenges and intense personal struggles for many artists within that sphere.