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Appendix B: Signature Field Format
The SIGNATURE field is a string of characters. Each set of 4 characters represents a point on a 300 pixel wide x 100 pixel tall canvas.
Each set of 4 characters is comprised of 2 chars to represent the X value (pixel distance right from left side) and 2 chars to represent the Y value (pixel distance from down from top).
Each 2 char value is a base 28 encoded decimal number (similar to hex which is base 16). Possible values for each character are any numerical digit and the letters from “a” to “r” inclusive (“a” = 10, “b” = 11, etc. just like in hex, but up to “r” = 28). For example “3bac” can be calculated as: (3 x 281) + (11 x 280) = 84 + 11 = 95 from the left and (10 x 281) + (12 x 280) = 280 + 12 = 292 from the top, hence 3bac is a point at 95×292 pixels from the top left.
To include a space between 2 points (no line drawn on signature canvas) include a 0x0 point (encoded as “0000”) in the string.
Points outside the bounds of the 300×100 pixel canvas will not be rendered, and should not be included.
The SIGNATURE string can be a minimum length of 4 characters (1 point) and a maximum of 1600 characters (400 points).
The recording canvas should always have a 3:1 width to height ratio.
If the canvas that the signature is recorded on is of a larger size, the magnitude of the X and Y values should be scaled down proportionately to a 300×100 boundaries respectively.
Example SIGNATURE string: “4i1m621m00005a125a2e” will draw a 40×40 pixel “plus” symbol in the middle of the canvas.