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Method for efficient 4-point software for touch screen calibration

IP.com Disclosure Number: IPCOM000012192D
Publication Date: 2003-Apr-16
Document File: 4 page(s) / 108K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for efficient 4-point software for touch screen calibration. Benefits include improved usability.

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Method for efficient 4-point software for touch screen calibration

Disclosed is a method for efficient 4-point software for touch screen calibration. Benefits include improved usability.

Background

      Handheld devices with touch screen capability contain a digitizer that reads the raw X and Y coordinates of the point where a stylus has touched the screen panel. A touch screen driver converts the raw X and Y point into X and Y pixels, called GuiX and GuiY, which are used by the kernel and the GUI (see Figure 1). The problem with the reporting of the raw points by the digitizer is that the screen on some hardware appears to be skewed. The fact that some screens appear more skewed than others can be directly attributed to the variability in manufacturing.

For example, raw P1(x) should be the same as raw P2(x), theoretically. However, in reality raw P2(x) could be less or more than raw P1(x) (see Figure 2).

      Conventional solutions use a 3-point solution at three corners to translate the raw points into GUI points. While this solution can be accurate in three corners of the screen, the fourth corner is most likely miscalibrated, yielding bad translation.

Description

      The disclosed method is an efficient 4-point software for touch screen calibration. The method translates raw points to GUI points accurately and efficiently. A series of equations describe the translation of the points:

First, start with the equations needed to calculate GuiX.

Define Left as the line that describes the leftmost vertical skew of the screen as reported by the digitizer. See Figure 2. Eq(1) shows how to find that line equation.

Left =                                                                            eq(1)                   

      Values P1(x), P1(y), P2(x), P2(y) are all constants determined by tapping on the lower left corner and upper left corner, respectively. RawY is a variable obtained from the digitizer.

              Define Right as the line that describes the rightmost vertical skew of the screen as reported by the digitizer. See Figure 2. Eq(2) shows how to find that line equation.

Right =                                                                         eq(2)

              Where P3(x), P3(y), P4(x), P4(y) are all constants determined by tapping on the lower right corner and upper right corner, respectively. RawY is a variable obtained from the digitizer.

Now that the leftmost and rightmost vertical lines have been modeled, interpolation then can be used to figure out GuiX given RawX. Eq(3) shows the interpolation equation.

              GuiX =                                                                                 eq(3)

Similar analysis can be used to figure out GuiY.

              Define Lower as the line that describes the lowest horizontal skew of t...