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Spot product and brightness / Findmyicone

All,

I have a basic question that I am struggling with. When you look at the findmyicone sample code from WWDC 2010, you will see the following:

static const uint8_t orangeColor[] = {255, 127, 0};
uint8_t referenceColor[3];

// Remove luminance
static inline void normalize( const uint8_t colorIn[], uint8_t colorOut[] ) {

// Dot product
int sum = 0;
for (int i = 0; i < 3; i++)
sum += colorIn[i] / 3;

for (int j = 0; j < 3; j++)
colorOut[j] = (float) ((colorIn[j] / (float) sum) * 255);
}

And then it is called:

normalize(orangeColor, referenceColor);

Starting the debugger, it converts BGRA: (red 255, green 127, blue 0) to (red 0, green 255, blue 0). I looked on the Internet and so to find details about the brightness and the dot product, and there really is no information.

1- Can anyone direct me to what this function does?

2- Can you direct me to some useful topics / primer online?

Thanks again to KMB

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, , - , . - , GPU Gems Apple, ColorObjectTracking GPUImage framework:

vec3 normalizeColor(vec3 color)
{
    return color / max(dot(color, vec3(1.0/3.0)), 0.3);
}

vec4 maskPixel(vec3 pixelColor, vec3 maskColor)
{
    float  d;
    vec4   calculatedColor;

    // Compute distance between current pixel color and reference color
    d = distance(normalizeColor(pixelColor), normalizeColor(maskColor));

    // If color difference is larger than threshold, return black.
    calculatedColor =  (d > threshold)  ?  vec4(0.0)  :  vec4(1.0);

    //Multiply color by texture
    return calculatedColor;
}

, 1/3 (, ). , .

, , .

. - RGB Y, Cr Cb (Y, U V), (Cr Cb):

 vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
 vec4 textureColor2 = texture2D(inputImageTexture2, textureCoordinate2);

 float maskY = 0.2989 * colorToReplace.r + 0.5866 * colorToReplace.g + 0.1145 * colorToReplace.b;
 float maskCr = 0.7132 * (colorToReplace.r - maskY);
 float maskCb = 0.5647 * (colorToReplace.b - maskY);

 float Y = 0.2989 * textureColor.r + 0.5866 * textureColor.g + 0.1145 * textureColor.b;
 float Cr = 0.7132 * (textureColor.r - Y);
 float Cb = 0.5647 * (textureColor.b - Y);

 float blendValue = 1.0 - smoothstep(thresholdSensitivity, thresholdSensitivity + smoothing, distance(vec2(Cr, Cb), vec2(maskCr, maskCb)));

, , , Apple . , .

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