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Function Reference

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The tint transformation function for such a color space must be able to compute one color from

arbitrary combinations of these three colors. So, we need essentially a blend function expressed in

PostScript syntax.

The definition of a blend function is not difficult but long because the entire code is stack based.

However, let us first keep in mind what we need to do. We have already three values on the stack

when the function is executed. These are the tint values which were passed to the DeviceN color

space. We need to multiply the tint values with the four components of the alternate color

representations of all three channels and finally we need to combine these three colors so that we get

the resulting output color. This sounds difficult, because a lot of multiplications and additions are

required to produce the wished result, but you'll see it's easier as it looks like.

The used colors in the DeviceN color space are defined as follows:

Colorant name

CMYK representation

PANTONE 345 CVC (coated)

{0.38, 0.00, 0.34, 0.0} or { 97,

0,

87, 0}

PANTONE 293 CVC (coated)

{1.00, 0.56, 0.00, 0.0} or {255, 143,

0, 0}

Yellow

{0.00, 0.00, 1.00, 0.0} or {

0,

0, 255, 0}

The CMYK color values of the spot colors are taken from the color picker of Adobe's Photoshop.

Now, we have all information we need to create the PostScript calculator function.

The multiplication of the color channels with the tint values must be done for all three colors

included in the color space. Because these are repeating operations we can easily develop a function

that creates the necessary code for us:

// The following function creates the PostScript code to multiply the tint

// values with the components of the CMYK color representation. 0 and 1

// color values are optimized to more efficient code.

UI32 AddOperator(char* Dest, float Value, UI32 Index)

{

if (Value == 0.0f)

// Zero is always zero

return sprintf(Dest, "0 ");

else if (Value == 1.0f) // 1.0 represents the tint value

return sprintf(Dest, "%d index ", Index);

else // Other color values must be multiplied with the tint value

return sprintf(Dest, "%d index %.2f mul ", Index, Value);

}

// Note that this function does not allocate memory. The string must be long enough to hold the

// resulting PostScript code. The function can be used to create the blend function for DeviceN color

// spaces with up to 32 color channels. The alternate color space must be DeviceCMYK or an ICCBased

// color space whose base color space is in turn DeviceCMYK. Since the alternate color space must be

// DeviceCMYK, NumColorants is always a multiple of 4!

void CreateBlendFunction(

char* Dest,

// Destination string buffer

float* Colorants,

// Array of color values

UI32 NumColorants) // Must be a multiple of 4!

{

UI32 i, j, len = 1;

UI32 numColors = NumColorants / 4;

UI32

index = numColors - 1;

Dest[0] = '{'; // The PostScript code must be enclosed in braces

for (i = 0; i < 4; i++, index++)

{

for (j = 0; j < NumColorants; j += 4)

{

// Create code to multiply the tint values with the color values

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