In order to obtain a pencil sketch (that is, a black-and-white drawing) of the camera frame, we will make use of two image-blending techniques, known as dodging and burning. These terms refer to techniques employed during the printing process in traditional photography; here, photographers would manipulate the exposure time of a certain area of a darkroom print in order to lighten or darken it. Dodging lightens an image, whereas burning darkens it. Areas that were not supposed to undergo changes were protected with a mask.
Today, modern image editing programs, such as Photoshop and Gimp, offer ways to mimic these effects in digital images. For example, masks are still used to mimic the effect of changing the exposure time of an image, wherein areas of a mask with relatively intense values will expose the image more, thus lightening the...
