Determine the position of the people in the drawing relative to the position of the lighting sources in the composition. Estimate the shade region of the cast shadows using the vanishing point of the shadows method for each different light source or determine these cast shadow regions from direct observation of the people used in the composition. Draw the outline of the cast shadow regions on the people and the objects in the composition.
Draw the regions for the cast shadows. These are shadows that are caused directly from another object that falls on a different object. Draw the cast shadow regions that fall on each person and on each object in the composition. Look around the regions of the nose to locate cast shadows on the people's faces. Examine the cast shadow regions for a definitive light-to-dark gradient. Determine the value of the darkest and lightest area of each cast shadow region and then calculate the light gradient rate with the equation: light gradient rate = (darkest value - lightest value)/pixels. Draw or mathematically generate the pixels in the cast shadow regions using the light gradient rate and the darkest and lightest values in the cast shadow region.
Draw the outline of the highlight, the general light, the reflected light and the form shadow (these are shadows on the sides of an object that are not caused by another object, but the object itself). Note that the reflected light regions are found in people's eyes and skin. The texture of the skin and angle of the light rays with the skin will determine how much light is reflected from the skin. Observe that highlights -- regions where the light source's light rays are highly focused -- are often found at the tip of nose and at the apex of other curved shapes on the people in the drawing. Determine the value of the darkest and lightest pixel of each light region and then determine the light gradient rate as calculated with the equation: light gradient rate = (darkest value - lightest value)/pixels. Draw or mathematically generate the pixels in each light region using the light gradient rate and the darkest and lightest values in each of the different light regions.
After you have shaded the people and objects in the composition, adjust the shading manually so it has the artistic effect and mood you want for each person in the composition. Adjust the lighting relative to each lighting region to maximize contrast between different regions. Use imaginary light sources so you can alter shading within different light regions to further accent specific elements, such as garments and jewelry, of the people in the composition.