Emphasis is the stressing of a particular area of focus rather than the presentation of a maze of details of equal importance. When a composition has no emphasis nothing stands out. However the effective use of emphasis calls attention to important areas of the painting. By placing emphasis on certain areas of the composition, an artist creates elements of interest which causes the eye to return to again and again.
One way of achieving emphasis is by creating center of interest, a.k.a. a focal point. A focal point is an area where the eye tends to center. It is the focus of the viewer's attention. A focal point is created by making one area of element of the painting dominant, or most important visually with all other areas contributing but subordinate. The focal point may be the largest, brightest, darkest, or most complex part of the whole, or it may get special attention because it stands out for some other reason. No more than one component should vie for primary attention. Where several components get equal billing, emphasis is canceled out.
The second way to create emphasis is by contrasting the primary element with its subordinates, or emphasis can be created by a sudden change in direction, size, shape, texture, color, tone or line.
No matter what element is chosen for emphasis it should never demand all the attention. Emphasis is necessary, but a good composition is one in which all the elements work together for a unifying effect
Examples of the effective use of Emphasis
In the painting on the left it is easy to see how the artist used light to emphasize the chef. He stands out as the main focal point of the entire the painting. On the painting on the right, the artist uses color to put emphasis on the cowboy riding the wild horse. The cowboy's shirt is the brightest color on the page so your eyes travel to that location.