Motion Blur

If we look at a brick wall, it's not moving and will look the same to us no matter how many frames per second we are looking at it. We can see all the details available to us because it's a stationary object and the various parts of the eye don't have to work too hard. Now then, same brick wall, but this time, were going to jump onto a bike and ride past it. The faster we go the less detail we can see, and the more blurred the wall looks. This is the Visual Cortex adding motion blur to perceived imagery so that rather than seeing everything in great detail, we are still able to perceive the effect of motion and direction as we ride by. The imagery is smoothly flowing from one point to the next and there are no jumps or flickering to be seen. If the eye wasn't to add this motion blur, we would get to see all of the details still but the illusion of moving imagery would be lost on us, with the brick wall sort of fading in and out to different points. It's pretty simple to test this.

Need a hand?

Take your hand and hold it in front of your face, palm towards you, and your fingers together. On the palm of your hand you can see all the lines and creases, the subtle differences in skin-tone; you may even be able to see a few veins at the joints of your fingers. Now move your hand slowly back and forth in front of you. You can still see the lines and creases, but the subtle shades in skin tone are less perceptible, and the veins have disappeared from perception completely. You can also still see the separations between fingers. Now move it back and forth fast. Gone are the lines and creases, the veins and the skin tones, replaced with a blurred image of your hands shape, filled with the overall colouring of your skin. You also see trails from your hand following it. Move your hand fast enough and you can perceive your hand going back and forth and merging with those trails. But it's moving smoothly, no stops and starts like a snapshot or one of those picture books you can flick through.

What's happening is that you simply don't have the room to process the information fast enough and to make sure the world we perceive around us is smooth and flowing, motion blur is added whilst details are dropped. Without the motion blur, the world around us would be a very different environment, with fast moving objects popping in and out of existence at high detail (damn lag &.), and making it very difficult for us to determine direction.

Let's go to the movies!

Ahh, the cinema, the big screen, the flicks (interesting slang word, the flicks &). Isn't it great? All that moving imagery goodness on a huge screen, your eye's naturally drawn to it since the rest of the theatre is pitch black. Ever thought about why it's so dark in there?

I've seen the light!

Movies run at 24 fps and they look perfectly smooth so surely 24 fps is enough for moving imagery to be perceived by the eye, right?

Ever had someone shine a bright light into your eyes? When they take the light away, you can still see an afterimage of that light for a bit. As the light surrounding you deepens the more the afterimage makes an impression on your retina. The same effect happens in the Cinema so that you perceive an afterimage of the previous frame, which to your mind is blended in with the next frame.

On the big screen, the image is projected in its entirety, one complete frame at a time, which in turn gives us an afterimage effect.

Films also have motion blur, so that much like the Visual Cortex, motion blur can help maintain the illusion of smooth moving imagery.

The faster the object, the more motion blur can be seen

Using a combination of the above, we are fooled into believing that the image we see is a smooth, flowing picture. But let's face it; we can't all sit in the dark at home to watch TV or play computer games.

M(otion)TV

Let's talk TV. PAL runs at about 25 frames per second, whereas NTSC runs at about 30 frames per second. Now regardless of which format we choose here, neither of these is actually at a high enough frame rate to give us the perception of smooth moving imagery. What's that you say? Your TV looks fine? Of course it does, because the moving imagery you are looking at is also displayed at a higher refresh rate. Unlike the big screen, TV's don't display one image after another, but draw the image line by line horizontally, which relates to 60 drawing's or refreshes every second. For NTSC, you have 30 fps but 60 refreshes of the screen per second. This amounts to each frame being drawn twice and therefore we have a higher frame rate.

Again, like the big screen, Motion Blur makes its presence known. Want to see this? Go get an action DVD, anything with fast moving objects. Now pause it whilst that object is moving. Looks blurred doesn't it, yet the DVD has frozen that point of the film on one singular frame.

Captains log ....

Using a succession of moving images, the two refreshes per frame fool us into believing there is two frames for every one frame. With the motion blur the eye believes we are watching a smoothly flowing picture.

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