NSColor Methods That Use Color Spaces

Many color-creation factory methods of NSColor embed the name of the color space in the method name. You must specify the component values of the color after the keywords of the method. For example, colorWithDeviceCyan:magenta:yellow:black:alpha: creates the color using the color space designated by NSDeviceCMYKColorSpace. You would create a color in the calibrated HSB color space (which is designated by NSCalibratedRGBColorSpace in this case) using colorWithCalibratedHue:saturation:brightness:alpha:. Colors in named (catalog) and pattern color spaces also have their own factory creation methods: colorWithCatalogName:colorName: and colorWithPatternImage:

To create color objects in color spaces represented by NSColorSpace objects, use the colorWithColorSpace:components:count: method. As illustrated in Listing 1, you can obtain one of the predefined color-space objects by invoking the appropriate NSColorSpace class factory method (for example, genericCMYKColorSpace).

Listing 1  Creating a color from a predefined color-space object

float comps[] = {0.4, 0.2, 0.6, 0.0, 1.0};

NSColor *aColor = [NSColor colorWithColorSpace:[NSColorSpace genericCMYKColorSpace] components:comps count:5];

The main advantage of using the colorWithColorSpace:components:count: method to create colors is that you can use an object representing a custom color space (see Making Custom Color Spaces). You are not limited to the predefined color-space objects.

NSColorSpace objects have advantages over color-space names by virtue of being objects. For example, you can also query these objects about their properties, such as the number of components, the values of those component, and the localized name. You can also archive and unarchive color-space objects.

Some color-creation NSColor methods make no reference to a color space in their names. Some of these class factory methods create primary and secondary colors, such as blueColor and purpleColor; others, such as lightGrayColor, create grayscale colors. These NSColor factory methods assume a color space of calibrated RGB (NSCalibratedRGBColorSpace) or calibrated white (NSCalibratedWhiteColorSpace), as appropriate. In most cases the alpha component (opacity) is 1.0.

Other color-creation methods of NSColor create objects representing the standard colors of user-interface objects in macOS; examples of these methods include controlTextColor, gridColor, and windowFrameColor. You should not make any assumptions about the color space of these colors. Indeed, for any color object, it is a good practice not to assume its color space, but instead to convert it to the desired color space before using it. See Programming Guidelines for Color Spaces for more on this subject.

NSColor offers the colorUsingColorSpaceName: method for converting colors from once color space to another. This method takes a color-space name as an argument. Here’s an example of a use of this method, which converts the NSColor object created above from a CMYK to an RGB color space:

NSColor *bColor = [aColor colorUsingColorSpaceName:NSCalibratedRGBColorSpace];

The color object created by this method usually has component values that are different from the original object’s component values, but the colors look the same. Sometimes the color conversion is correct only for the current device; the method might even return nil if the requested conversion cannot be done.

Note that using the colorUsingColorSpace: method for converting a color between color spaces is acceptable, but that the resulting color is represented by a custom color space and will not respond to color space-specific methods. For example, the NSColor object created by the following method is in the RGB color space but represented by a custom color space (NSColorSpace), and thus raises an exception when you send it a redComponent message:

NSColor *cColor = [aColor colorUsingColorSpace:[NSColorSpace genericRGBColorSpace]];

To retrieve specific color attributes with colorUsingColorSpace:, use the getComponents: method as in the following example:

if(cColor){

    CGFloat components[4];

    [cColor getComponents:components];

}

Programming Guidelines for Color Spaces

Observe the following guidelines when dealing with NSColor objects and color spaces.

NSColor *aColor = [color colorUsingColorSpaceName:NSCalibratedRGBColorSpace];

if (aColor) {

    float rcomp = [aColor redComponent];

}