Setting Colors in Font

Draw PDF 417 in Font Setting Colors

We re ready now to discuss the code for the Mandelbrot viewer application. For an appealing coloring, you need to produce some form of continuity in the color variation in the chosen range. You use an array of colors to store these values, but you need some procedure to fill this array so that colors change continuously. Colors in the Red Green Blue (RGB) space used in the graphics libraries are known to define a color space that is not perceived as continuous by human vision. A color space known to be more effective in this respect is the Hue Saturation Value (HSV), where a color is defined in terms of hue, color saturation, and the value of luminance (see Figure 11-8). This model was inspired by the method used by painters to create colors in oil painting.

Figure 11-8. The RGB (left) and HSV (right) color spaces and their geometric representation Figure 11-8 shows a typical geometric representation of the two color spaces. In the RGB color model the three axes represent the three base colors varying from black to the full color; in the HSV space, the angle is used to indicate the hue, the distance from the axis of the cone represents the saturation, and the value corresponds to the height of the point inside the cone. It s possible to define a conversion from RGB color space to HSV, and vice versa. Listing 11-5 shows the F# functions performing the conversions between the two models. These functions assume the three components R, G, and B are in the interval [0, 1] rather than integers between 0 and 255. Listing 11-5. Conversion from RGB to HSV, and Vice Versa let RGBtoHSV (r, g, b) = let (m:float) = min r (min g b) let (M:float) = max r (max g b) let delta = M - m let posh (h:float) = if h < 0.0 then h + 360.0 else h let deltaf (f:float) (s:float) = (f - s) / delta if M = 0.0 then (-1.0, 0.0, M) else let s = (M - m) / M if r = M then (posh(60.0 * (deltaf g b)), s, M) elif g = M then (posh(60.0 * (2.0 + (deltaf b r))), s, M) else (posh(60.0 * (4.0 + (deltaf r g))), s, M) let HSVtoRGB (h, s, v) = if s = 0.0 then (v, v, v) else let hs = h / 60.0 let i = floor (hs) let f = hs - i

let p let q let t match | 0 | 1 | 2 | 3 | 4 | _

= v * ( 1.0 - s ) = v * ( 1.0 - s * f ) = v * ( 1.0 - s * ( 1.0 - f )) int i with -> (v, t, p) -> (q, v, p) -> (p, v, t) -> (p, q, v) -> (t, p, v) -> (v, p, q)

To let users choose the coloring of the set, you create an array of 10 functions, given an integer between 0 and 250, for a corresponding color. The default color function is based on the HSV color model, and it simply uses the input parameter to set the hue of the color, leaving the saturation and luminance at the maximum values. The other functions use the RGB color space following directions in the color cube. You use the createPalette function to generate the color palette that will be used while drawing fractal points; the palette mutable variable holds this palette. Listing 11-6 shows the code dealing with colors. The pickColor function is responsible for mapping the iteration, it, at which the computation of the Mandelbrot set has terminated given the maximum number of iterations allowed, maxit. Listing 11-6. Color Palette Definition let makeColor (r, g, b) = Color.FromArgb(int32(r * 255.0), int32(g * 255.0), int32(b * 255.0)) let defaultColor i = makeColor(HSVtoRGB(360.0 * (float i / 250.0), 1.0, 1.0)) let coloring = [| defaultColor; (fun i -> Color.FromArgb(i, i, i)); (fun i -> Color.FromArgb(i, 0, 0)); (fun i -> Color.FromArgb(0, i, 0)); (fun i -> Color.FromArgb(0, 0, i)); (fun i -> Color.FromArgb(i, i, 0)); (fun i -> Color.FromArgb(i, 250 - i, 0)); (fun i -> Color.FromArgb(250 - i, i, i)); (fun i -> if i % 2 = 0 then Color.White else Color.Black); (fun i -> Color.FromArgb(250 - i, 250 - i, 250 - i)) |] let createPalette c = Array.init 253 (function | 250 -> Color.Black | 251 -> Color.White | 252 -> Color.LightGray | i -> c i)