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I think video is a series of picture frames. Consider a black & white scenario (no RGB). A picture frame is a 2D array of pixel. Each pixel has a single color. A pixel can't be half black or half white. It will be filled completely with one shade of color.

Consider 2 consecutive frames of video - let's say frame 1 and frame 2 .
Suppose frame 1 has a square-shaped object with coordinates $(x_1,y_1)$, $(x_2,y_2)$, $(x_3,y_3)$ and $(x_4,y_4)$ (top-left, top-right, bottom-right and bottom-left, respectively).

Now, if the object moves to the right then in frame 2 its coordinates can be $(x_1+1,y_1)$, $(x_2+1,y_2)$, $(x_3+1,y_3)$ and $(x_4+1,y_4)$ (top-left, top-right, bottom-right and bottom-left, respectively).

How is less than that possible?

Royi
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user1371666
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    Can you clarify what your question is? – MBaz Mar 22 '17 at 16:00
  • I am more inclined to vote for the question to remain open at this point, provided that it is rephrased to more accurately reflect its subject. In the meantime, please see [this link](https://en.wikipedia.org/wiki/Sub-pixel_resolution). Can you please provide a practical example of what the ideal output of determining sub pixel movement be in your application? – A_A Mar 22 '17 at 16:14
  • I am not able to comprehend that an object can move by less than a pixel in consecutive frames. – user1371666 Mar 23 '17 at 14:58
  • Also read the wiki link - it says anti aliasing is done so that we don't get jagged edges . Seems they fill corner pixel by lighter black so that sharp stair case isn't apparent. – user1371666 Mar 23 '17 at 15:02

1 Answers1

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The frame is 2D Grid which samples the continuous world in Discrete way.

Leave alone video for a second.
Let's talk about taking a photo of a white paper laid on a black surface.
The photo is taken from above and let's assume there is no lens issues.
Do you expect the end of the paper to end at edge of a pixel of the camera perfectly?

It won't.
The end of the paper will fall in the middle of a pixel.
Let's say that now this pixel (I leave out the blurring due to limited Frequency Sampling) has 70% White and 30% Black.
Now the camera moves the smallest movement and now the pixel is 30% White and 70% Black.

This is a less than 1 pixel movement.

Royi
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