Advanced Video Editing


Contrast & Affinity
and
The Illusion of Depth

You want to make your story visually interesting, but you’re wrestling with the problem of making better pictures. Otherwise, without interesting pictures, you’ll quickly lose your audience. So to keep your audience watching requires an understanding of visual structure within the screen space. To start, it’s important to know the Principle of Contrast and Affinity as described by Bruce Block in his book, The Visual Story:

Contrast = differences = more visual intensity

Affinity = sameness = less visual intensity

The audience gets bored if they perceive that objects within the shot all look the same. Once you add contrast, suddenly the audience views it with interest. Visual intensity depends on the audience’s emotional reaction to the imagery. Consider an image with few visual components and one with a great deal many, such as contrasting lines. Which one is more visually intense? If the visual components within a shot look much the same, then the affinity is said to lack intensity.  


The image below shows an example of Affinity. There are fewer contrasting lines that divide up the image and, therefore, the image lacks intensity.  

The image below shows an example of contrast, where there are many contrasting lines. The image is said to have more intensity. 


In every shot there are visual components that lead to some sort of reaction from the audience. According to Block, these cues consist of space, lines, shapes, tones and movement. Understanding these visual components will help you value the importance of picture composition.

The physical nature of the picture screen is strictly two-dimensional – it has width and height, but not depth. As photographers, the challenge is to create the illusion of depth within a two-dimensional screen space. Viewers then accept the two-dimensional picture as a realistic representation of the three-dimensional world. The audience can only experience this if you can convey depth cues. 


Depth Cues

Depth cues create the illusion of three-dimensions in two-dimensional screen space. To achieve depth you need to reveal perspective. Standing directly in front of a subject, like the bulletin board in the illustration below, lacks perspective. That’s because all the lines (drawn from the top and bottom and the sides of the bulletin board) run parallel to each other. The lines remain parallel no matter how far we might extend them beyond the frame. When we look at an object squarely from the front, we refer to this view as the Frontal Plane. Because there isn't any real sense of depth, the image appears flat. If you want to get away from an image that looks flat, then a simple change of perspective is all it takes. 


Types of Perspectives

According to Block in his book, The Visual Story, there are three basic types of perspective: one-point, two-point and three-point.

One-Point Perspective is the simplest. By positioning yourself closer to one side of the object you can start to reveal depth. The visual cue for depth is seen where the top and bottom of the plane appear to converge at a single point. We call this point the Vanishing Point (VP), which is classically depicted as a set of railroad tracks that appear to converge in the distance. Of course, the rails always remain parallel, but they only appear to converge in the distance. The rails create a longitudinal plane that extends toward the vanishing point, and this is why we equate the convergence of the tracks with distance. The VP is an important depth cue that makes the two-dimensional screen picture seem to have a depth of its own. 

In the image below, the lines from the top and bottom of the bulletin board converge towards the right. If we extend them well beyond the picture frame the lines will will appear to meet at the vanishing point. 



Two-point perspective occurs when the longitudinal plane can be given a second vanishing point. In the example with the bulletin board, the top and bottom lines converge to a vanishing point on one side of the frame. But simply raising or lowering the perspective can make lines from the side of the bulletin board appear to converge above or below the frame. 



You can also create two vanishing points from two separate longitudinal surfaces, such as the corner of a building or even the corner wall of a room. 

Three-point perspective is generated when you create three vanishing points. You can see this in a view of the object shot from below and from the corner. The lines from the side of the object appear to converge above the frame, and the lines from the top and bottom appear to converge to the left and right.  


Try to find ways to achieve perspective in your images, where the lines appear to converge from a certain object in the shot. At the point where they converge you could even place a person of interest, such as a reporter doing a stand-up or an interview subject. Our eyes tend to be drawn towards the vanishing point. Find ways to exploit lines in your background that can be used to direct the eyes to the subject of interest. 



In the image above, the lines in the corridor appear to converge towards the subject. 

Size Difference

You can also achieve perspective from the size difference of objects in the shot. When you have objects of known size in the frame, such as a row of computers, the one in the background appears smaller, which is a visual cue that conveys distance. Therefore, the shot has depth when you position an object in the foreground plane and one in the background.




The size change is a visual cue that creates the illusion of depth. Forced perspective is an enhancement of this principle that can make objects seem larger or smaller than they really are just by changing their distance to the camera. Director Peter Jackson used this technique in the Lord of the Rings and The Hobbit trilogies by displacing objects several feet in depth from the camera to make Hobbits appear much smaller in relation to others. 




Textural Detail
You also achieve the illusion of depth when the image conveys an object’s textural detail. Every object has some form of textural detail, which you can only really see when it’s close. You see less detail the farther away the object. The visual cue is much like size and change of perspective.

 

Tonal Separation
We see another depth cue in the brightness of objects. We may be accustomed to seeing lighter objects appear closer to the camera and darker objects farther away. Colour separation is also a depth cue that conveys perspective along changes between warm colours and cool ones. We often describe warm colours as more vibrant, such as red, orange and yellow. Cool colours, like blue and green, appear more subdued. According to researchers, warm colours seem closer to the camera than cool ones due to a human psychological response to different wavelengths of light.


Overlap
When objects appear to overlap, the one behind appears farther away, which suggests depth. Move the camera around until you can produce overlap between objects in the shot. For example, getting a shot of two cyclists where one appears to overlap the other, or students in a classroom.

 

Focus
Finally, objects that are blurred appear to be farther away, whilst those sharply focussed appear closer. In terms of depth of field, the shallow depth of field creates the illusion of depth. Our eyes are always drawn to objects that are in focus. That’s why our attention is more fully drawn to the person in an interview shot with a shallow depth of field. If the person is interviewed directly in front of a wall, they appear to become part of the background and our eyes will begin wander. Our eyes are always drawn to objects that are in focus.