UIColor CMYK和Lab值

Question

简单的问题，更像是复杂的答案：

如何从UIColor对象(如果有帮助，我知道其RGB值)中获取CMYK值和Lab值？

我发现这是关于获取CMYK值的，但我无法从中获得任何精确值，尽管它无处不在，但我听说它不是一个很好的代码片段。

CGFloat rgbComponents[4];
    [color getRed:&rgbComponents[0] green:&rgbComponents[1] blue:&rgbComponents[2] alpha:&rgbComponents[3]];

    CGFloat k = MIN(1-rgbComponents[0], MIN(1-rgbComponents[1], 1-rgbComponents[2]));
    CGFloat c = (1-rgbComponents[0]-k)/(1-k);
    CGFloat m = (1-rgbComponents[1]-k)/(1-k);
    CGFloat y = (1-rgbComponents[2]-k)/(1-k);

Answer 1

对于基于国际商会的颜色转换，可以使用Little Color Management System。(我刚刚将下载存档中的所有.c和.h文件添加到一个iOS Xcode项目中。它编译并运行了以下代码，没有出现任何问题。)

备注: RGB和CMYK是设备相关的颜色空间，Lab是设备无关的颜色空间。因此，要从RGB转换为Lab，您必须选择独立于设备(或“校准”)的RGB颜色空间进行转换，例如sRGB。

Little CMS带有sRGB和Lab色彩空间的内置配置文件。从sRGB到Lab的转换如下所示：

创建颜色变换：

cmsHPROFILE rgbProfile = cmsCreate_sRGBProfile();
cmsHPROFILE labProfile = cmsCreateLab4Profile(NULL);
cmsHTRANSFORM xform = cmsCreateTransform(rgbProfile, TYPE_RGB_FLT, labProfile,
                                         TYPE_Lab_FLT,
                                         INTENT_PERCEPTUAL, 0);
cmsCloseProfile(labProfile);
cmsCloseProfile(rgbProfile);

转换颜色：

float rgbValues[3];
// fill rgbValues array with input values ...
float labValues[3];
cmsDoTransform(xform, rgbValues, labValues, 1);
// labValues array contains output values.

处理颜色变换：

cmsDeleteTransform(xform);

当然，转换将只创建一次，并用于所有颜色转换。

对于RGB到CMYK的转换，你也可以使用Little CMS，但你必须提供一个ICC-Profile，例如从免费的Adobe下载页面ICC profile downloads for Mac OS。

RGB到CMYK转换的代码示例：

float rgb[3]; // fill with input values (range 0.0 .. 1.0)
float cmyk[4]; // output values (range 0.0 .. 100.0)

cmsHPROFILE rgbProfile = cmsCreate_sRGBProfile();

// The CMYK profile is a resource in the application bundle:
NSString *cmykProfilePath = [[NSBundle mainBundle] pathForResource:@"YourCMYKProfile.icc" ofType:nil];
cmsHPROFILE cmykProfile = cmsOpenProfileFromFile([cmykProfilePath fileSystemRepresentation], "r");

cmsHTRANSFORM xform = cmsCreateTransform(rgbProfile, TYPE_RGB_FLT, cmykProfile,
                                         TYPE_CMYK_FLT,
                                         INTENT_PERCEPTUAL, 0);

cmsCloseProfile(cmykProfile);
cmsCloseProfile(rgbProfile);

cmsDoTransform(xform, rgb, cmyk, 1);

cmsDeleteTransform(xform);

Answer 2

要获得LAB值，需要将RGB值转换为XYZ值，然后再将XYZ值转换为RGB值。

- (NSMutableArray *) convertRGBtoLABwithColor: (UIColor *)color



////make variables to get rgb values
CGFloat red3;
CGFloat green3;
CGFloat blue3;
//get rgb of color
[color getRed:&red3 green:&green3 blue:&blue3 alpha:nil];

float red2 = (float)red3*255;
float blue2 = (float)blue3*255;
float green2 = (float)green3*255;

//first convert RGB to XYZ

// same values, from 0 to 1
red2 = red2/255;
green2 = green2/255;
blue2 = blue2/255;

// adjusting values
if(red2 > 0.04045)
{
    red2 = (red2 + 0.055)/1.055;
    red2 = pow(red2,2.4);
} else {
    red2 = red2/12.92;
}

if(green2 > 0.04045)
{
    green2 = (green2 + 0.055)/1.055;
    green2 = pow(green2,2.4);
} else {
    green2 = green2/12.92;
}

if(blue2 > 0.04045)
{
    blue2 = (blue2 + 0.055)/1.055;
    blue2 = pow(blue2,2.4);
} else {
    blue2 = blue2/12.92;
}

red2 *= 100;
green2 *= 100;
blue2 *= 100;

//make x, y and z variables
float x;
float y;
float z;

// applying the matrix to finally have XYZ
x = (red2 * 0.4124) + (green2 * 0.3576) + (blue2 * 0.1805);
y = (red2 * 0.2126) + (green2 * 0.7152) + (blue2 * 0.0722);
z = (red2 * 0.0193) + (green2 * 0.1192) + (blue2 * 0.9505);

//then convert XYZ to LAB

x = x/95.047;
y = y/100;
z = z/108.883;

// adjusting the values
if(x > 0.008856)
{
    x = powf(x,(1.0/3.0));
} else {
    x = ((7.787 * x) + (16/116));
}

if(y > 0.008856)
{
    y = pow(y,(1.0/3.0));
} else {
    y = ((7.787 * y) + (16/116));
}

if(z > 0.008856)
{
    z = pow(z,(1.0/3.0));
} else {
    z = ((7.787 * z) + (16/116));
}

//make L, A and B variables
float l;
float a;
float b;

//finally have your l, a, b variables!!!!
l = ((116 * y) - 16);
a = 500 * (x - y);
b = 200 * (y - z);

NSNumber *lNumber = [NSNumber numberWithFloat:l];
NSNumber *aNumber = [NSNumber numberWithFloat:a];
NSNumber *bNumber = [NSNumber numberWithFloat:b];

//add them to an array to return.
NSMutableArray *labArray = [[NSMutableArray alloc] init];
[labArray addObject:lNumber];
[labArray addObject:aNumber];
[labArray addObject:bNumber];

return labArray;
}