叠加混合模式公式？

Question

我有2种颜色:1种动态设置，另一种总是白色0.5 alpha。我想要计算得到的白色，就像它是绘制在动态颜色之上使用叠加混合模式。

我知道覆盖结合了、Multiply和屏幕混合模式。

多重混合模式的公式是：

Result Color = (Top Color) * (Bottom Color) /255

而屏幕混合模式是：

Result Color = 255 - [((255 - Top Color)*(255 - Bottom Color))/255]

如何计算叠加混合模式的结果颜色？

是否有一个UIColor扩展类可以不加限制地执行此操作？

Answer 1

公式分为两部分：

第一部分:如果下层值> 127.5，则执行以下操作-

值单位=(255-下层值)/127.5

最小值=下层值-(255-下层值)

叠加=(上层值*值单位)+最小值

第二部分:如果下层值< 127.5，则执行以下操作-

值Unit=Lower层值/127.5

叠加=上层值*值单位

从形式上可以看出，最终结果在很大程度上取决于上层值。如果上层值较高(较轻)，则最终结果可能更轻。

来自这里。

Answer 2

在威利的回答上，下面是移植到代码的公式：

CGFloat newComponents[4];
const CGFloat *topComponents = CGColorGetComponents([[UIColor colorWithRed:1 green:1 blue:1 alpha:1] CGColor]);
const CGFloat *components = CGColorGetComponents(self.color.CGColor);
const int n = CGColorGetNumberOfComponents(self.color.CGColor);

for(int i=0; i < n; i++) {

    if(components[i] > 0.5) {
        CGFloat value = (topComponents[i]-components[i])/0.5;
        CGFloat min = components[i]-(topComponents[i]-components[i]);
        newComponents[i] = topComponents[i]*value+min; 
    } else {
        CGFloat value = components[i]/0.5;
        newComponents[i] = topComponents[i]*value; 
    }
}

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
UIColor *resultColor = [UIColor colorWithCGColor:CGColorCreate(colorSpace, newComponents)];
CGColorSpaceRelease(colorSpace);

Answer 3

我不知道你的目标，可能是完全离题，但为什么不直接使用石英2D？

CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetBlendMode(ctx, kCGBlendModeOverlay);
... draw with overlay blending

CGBlendMode通过CGContextSetBlendMode覆盖，乘法，屏幕和更多.：

enum CGBlendMode {
    /* Available in Mac OS X 10.4 & later. */
    kCGBlendModeNormal,
    kCGBlendModeMultiply,
    kCGBlendModeScreen,
    kCGBlendModeOverlay,
    kCGBlendModeDarken,
    kCGBlendModeLighten,
    kCGBlendModeColorDodge,
    kCGBlendModeColorBurn,
    kCGBlendModeSoftLight,
    kCGBlendModeHardLight,
    kCGBlendModeDifference,
    kCGBlendModeExclusion,
    kCGBlendModeHue,
    kCGBlendModeSaturation,
    kCGBlendModeColor,
    kCGBlendModeLuminosity,

    /* Available in Mac OS X 10.5 & later. R, S, and D are, respectively,
       premultiplied result, source, and destination colors with alpha; Ra,
       Sa, and Da are the alpha components of these colors.

       The Porter-Duff "source over" mode is called `kCGBlendModeNormal':
         R = S + D*(1 - Sa)

       Note that the Porter-Duff "XOR" mode is only titularly related to the
       classical bitmap XOR operation (which is unsupported by
       CoreGraphics). */

    kCGBlendModeClear,          /* R = 0 */
    kCGBlendModeCopy,           /* R = S */
    kCGBlendModeSourceIn,       /* R = S*Da */
    kCGBlendModeSourceOut,      /* R = S*(1 - Da) */
    kCGBlendModeSourceAtop,     /* R = S*Da + D*(1 - Sa) */
    kCGBlendModeDestinationOver,    /* R = S*(1 - Da) + D */
    kCGBlendModeDestinationIn,      /* R = D*Sa */
    kCGBlendModeDestinationOut,     /* R = D*(1 - Sa) */
    kCGBlendModeDestinationAtop,    /* R = S*(1 - Da) + D*Sa */
    kCGBlendModeXOR,            /* R = S*(1 - Da) + D*(1 - Sa) */
    kCGBlendModePlusDarker,     /* R = MAX(0, (1 - D) + (1 - S)) */
    kCGBlendModePlusLighter     /* R = MIN(1, S + D) */
};
typedef enum CGBlendMode CGBlendMode; /* Available in Mac OS X 10.4 & later. */