A method for encoding information, comprising: specifying a digital value; and producing a symbol (28, 70, 80, 90, 100) that encodes the specified digital value in a set of color elements (72, 82, 92, 94, 102) having different, respective colors, to be identified in an image of the symbol as red, green, blue, cyan, magenta and yellow color elements, respectively; wherein the symbol is produced by applying cyan, magenta and yellow pigments to a substrate so as to produce the color elements, such that the color elements exhibit the following red, green, and blue intensity characteristics when measured in an sRGB color space: for the red color elements, the red intensity is greater than twice the blue and green intensities; for the green color elements, the green intensity is greater than twice the red and blue intensities; for the blue color elements, the blue intensity is greater than twice the red and green intensities; for the cyan color element, the blue and green intensities are both greater than twice the red intensity; for the magenta color element, the red and blue intensities are both greater than twice the green intensity; and for the yellow color element, the red and green intensities are both greater than twice the blue intensity; characterized in that the cyan, magenta and yellow pigments are chosen so as to maximize an optimization score S ≡ S reliability ∗ S Intensity, wherein S Intensity ≡ ∏ c L c 1 H c 0 + δ, wherein S reliability ≡ ∏ c 1 − H c 0 − L c 0 L c 1 − L c 0 − H c 1 − L c 1 H c 1 − H c 0, and wherein for each color c = red, green, blue, H 1 c and L 1 c are the highest and lowest observed values, respectively, of the color c among the color elements that are expected to contain the color c, while H 0 c and L 0 c are the highest and lowest observed values of the color c among the color elements that are expected not to contain the color c, and δ is a constant value. specifying a digital value; and producing a symbol (28, 70, 80, 90, 100) that encodes the specified digital value in a set of color elements (72, 82, 92, 94, 102) having different, respective colors, to be identified in an image of the symbol as red, green, blue, cyan, magenta and yellow color elements, respectively; wherein the symbol is produced by applying cyan, magenta and yellow pigments to a substrate so as to produce the color elements, such that the color elements exhibit the following red, green, and blue intensity characteristics when measured in an sRGB color space: for the red color elements, the red intensity is greater than twice the blue and green intensities; for the green color elements, the green intensity is greater than twice the red and blue intensities; for the blue color elements, the blue intensity is greater than twice the red and green intensities; for the cyan color element, the blue and green intensities are both greater than twice the red intensity; for the magenta color element, the red and blue intensities are both greater than twice the green intensity; and for the yellow color element, the red and green intensities are both greater than twice the blue intensity; characterized in that the cyan, magenta and yellow pigments are chosen so as to maximize an optimization score S ≡ S reliability ∗ S Intensity, wherein S Intensity ≡ ∏ c L c 1 H c 0 + δ, wherein S reliability ≡ ∏ c 1 − H c 0 − L c 0 L c 1 − L c 0 − H c 1 − L c 1 H c 1 − H c 0, and wherein for each color c = red, green, blue, H 1 c and L 1 c are the highest and lowest observed values, respectively, of the color c among the color elements that are expected to contain the color c, while H 0 c and L 0 c are the highest and lowest observed values of the color c among the color elements that are expected not to contain the color c, and δ is a constant value. for the red color elements, the red intensity is greater than twice the blue and green intensities; for the green color elements, the green intensity is greater than twice the red and blue intensities; for the blue color elements, the blue intensity is greater than twice the red and green intensities; for the cyan color element, the blue and green intensities are both greater than twice the red intensity; for the magenta color element, the red and blue intensities are both greater than twice the green intensity; and for the yellow color element, the red and green intensities are both greater than twice the blue intensity; characterized in that the cyan, magenta and yellow pigments are chosen so as to maximize an optimization score S ≡ S reliability ∗ S Intensity, wherein S Intensity ≡ ∏ c L c 1 H c 0 + δ, wherein S reliability ≡ ∏ c 1 − H c 0 − L c 0 L c 1 − L c 0 − H c 1 − L c 1 H c 1 − H c 0, and wherein for each color c = red, green, blue, H 1 c and L 1 c are the highest and lowest observed values, respectively, of the color c among the color elements that are expected to contain the color c, while H 0 c and L 0 c are the highest and lowest observed values of the color c among the color elements that are expected not to contain the color c, and δ is a constant value.