Messages in this thread | | | Subject | Re: [PATCH] Apple USB Touchpad driver (new) | From | Peter Osterlund <> | Date | 10 Jul 2005 00:48:30 +0200 |
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Vojtech Pavlik <vojtech@suse.cz> writes:
> Btw, what I don't completely understand is why you need linear > regression, when you're not trying to detect motion or something like > that. Basic floating average, or even simpler filtering like the input > core uses for fuzz could work well enough I believe.
Indeed, this function doesn't make much sense:
+static inline int smooth_history(int x0, int x1, int x2, int x3) +{ + return x0 - ( x0 * 3 + x1 - x2 - x3 * 3 ) / 10; +}
In the X driver, a derivative estimate is computed from the last 4 absolute positions, and in that case the least squares estimate is given by the factors [.3 .1 -.1 -.3]. However, in this case you want to compute an absolute position estimate from the last 4 absolute positions, and in this case the least squares estimate is given by the factors [.25 .25 .25 .25], ie a floating average. If the function is changed to this:
+static inline int smooth_history(int x0, int x1, int x2, int x3) +{ + return (x0 + x1 + x2 + x3) / 4; +}
the standard deviation of the noise will be reduced by a factor of 2 compared to the unfiltered values. With the old smooth_history() function, the noise reduction will only be a factor of 1.29.
-- Peter Osterlund - petero2@telia.com http://web.telia.com/~u89404340 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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