Tuesday, June 10, 2008

Depth and Edges

When one object sits in front of another in space, what happens at the location where the contours intersect each other? How can you create a sense of space between the object in front and the one behind?

Here’s a gray rectangle in front of a cross of white lines. All the edges are kept sharp. The result is that the rectangle appears to be sitting atop the lines, but it lies on the same two-dimensional plane.

If you soften all the edges of the white lines to an equal degree, the gray rectangle floats upward. This is how a camera would interpret a situation where two objects are on separate focal planes, assuming the camera was focused on the rectangle.

Instead, if you soften the edges of the rectangle and keep the white lines sharp, it looks like the camera has shifted its focus to the back plane. This creates a perceptual ambiguity. The gray rectangle still comes forward because it is superimposed, but the white lines also want to come forward because they’re in sharper focus.

Neither of these “photographic” interpretations is quite like the way we perceive things with our eyes. We don’t really see an entire area of a scene out of focus; we’re constantly adjusting our focus to create a sharp impression of the world.


Here is how I would suggest we might simulate our visual perception in paint. It’s similar to the photographic mode in #2, but this time the lines get progressively more out of focus as they pass behind the rectangle.

In addition, the vertical white line is softened to a greater degree than the horizontal line. The reason for this is the stereoscopic effect of our eyes. Since our eyes are set on a horizontal plane, vertical lines seen behind an object are doubled (and effectively blurred) more than the horizontal bars. You demonstrate this if you focus both of your eyes on your fingertip held in front of the mullions of a window.

In this detail from a Bouguereau, the contour of the farther leg of the angel figure is softened where it crosses the nearer leg.

In another of his paintings, the landscape lines are softened where they intersect the woman’s lower back.

And finally in this detail from a Waterhouse, the line of the green hill and the blue dress are softer where they cross behind the heads.

5 comments:

Darren said...
This comment has been removed by the author.
Erik Bongers said...

Again one of those tricks I had never heard of.

But if you ever sell those 4 abstract masterpieces, I'll take the 4th : it's the only one that's signed and thus much more valuable.

Dr. Hansford said...

absolutely mindblowing. as a film student, I've only used the photographic depth of field tricks in my drawings. (and even then, only rarely.)

I wonder if photographers have ever used similar manipulations in their work? or does it simply come across as "fake"?

yet another reason I wish I had spent more time drawing and painting.

Igor Busquets said...

Great post! thanks for sharing your know-how. The edges are import aspects of painting and drawing, i belive i understand it a little better because of your words!

Nana said...

That's very, very interesting! It might explain one of the reasons inking in comics is done the way it's done. In general, when you're rendering both the character and the background using inked contours, you will leave a small gap where the background lines intersect the character.
Compared to the colour examples you've shown here, it becomes very obvious that joining the lines in binary black and white will act to put the character and the background on the same plane.

I never thought about it in this way, it's a fascinating observation...
When viewing the real world, you can dynamically switch your focus to produce a sharp background plane or a sharp foreground plane. I guess that's why completely blurring the background or foreground, as the camera does, only gives a single-focus view.
In a static painting, you have to simulate that dynamic depth. Any one portion needs to be sharp when you focus your eyes on it, so you can't blur out large regions. However, by blurring background edges locally, you can achieve that sense of depth when the eye focuses on the foreground object.

Thank you very much, this has really made me think about the way we see things and the way we perceive depth.