How we change what others think, feel, believe and do
Eye Seeks Line
When we look at a scene, the first thing our eyes do is to seek contrast, typically through differences in light and dark. When we have found this, we check to seek if this contrast area extends, such that there is a line for our eye to follow.
In other words, lines are hugely important in helping us to make sense our what we see.
In the examples below, the top row has high contrast black-and-white, while the second row has lower-contrast gray-and-gray. On the left example, there is a sharp contrast where a line can clearly be seen up the middle. This becomes progressively harder to distinguish as we move to the left. This makes more work for the eye and may lead to ignoring or not even noticing a low contrast transition.
Notice also how the eye finds the outer black line around the top examples and quickly follows this to see that it is an enclosing line.
What we call a line is usually two contrasts over three zones, being one side of the line, in the line and then the other side of the line. In other words, there is a contrast between one side of the line and the line, then between the line and the other side of the line. A pure mathematical line is one dimensional. Visually, it may be seen simply as a line with dark on one side and light on the other. We see this at the edge of objects, for example in looking at a dark bird against a light sky. In fact such a separating line is easier to see than a line drawn with a pen as the contrasting areas either side of the line stretch for a longer space (a fine line can be difficult to distinguish).
The real benefit of a line that we seek is that it helps us divide our visual world up into objects. Lines mark the edges between things. On one side is this and on the other side is that. When we have a separated object, we can then identify it and know what to do about it. We can also understand it in relation to other objects and the containing context and background.
Good lines have sudden transitions in contrast, rather than fading from dark to light over a notable distance. When we have hazy lines we can only distinguish hazy shapes which leave us with uncertainty and cause more cognitive effort in working out what is in front of us. We generally pay more attention to sharper, more distinct lines. Beyond ease, another reason for this is that indistinct lines are more likely to be seen in the distance. Sharper, more contrastive lines are often closer and hence may need to be addressed sooner.
When you are presenting graphic objects or photographs, pay attention to lines and where they go. We are attracted to lines, making them a means of gaining and holding attention.