平滑地应用渐变到UIImage

我正在尝试使用CoreGraphic将渐变应用于UIImage; 但是，我得到的结果并不是很好。 我想在图像的底部创建一个黑色到透明的渐变，为我创建一个对比，让我放置一些文本。 然而，我能够的渐变与图像不能很好地融合; 你可以清楚地看到中心的分离 。 我正在寻找的结果就像这个应用程序： http ： //capptivate.co/2014/02/17/yummly-3/我应该如何应用渐变来实现这一目标？ （我必须将它应用于大量图像）。

我的结果：

这是我的代码：

func imageWithGradient(img:UIImage!) -> UIImage{ UIGraphicsBeginImageContext(img.size) var context = UIGraphicsGetCurrentContext() img.drawAtPoint(CGPointMake(0, 0)) let colorSpace = CGColorSpaceCreateDeviceRGB() let locations:[CGFloat] = [0.50, 1.0] //1 = opaque //0 = transparent let bottom = UIColor(red: 0, green: 0, blue: 0, alpha: 0.5).CGColor let top = UIColor(red: 0, green: 0, blue: 0, alpha: 0).CGColor let gradient = CGGradientCreateWithColors(colorSpace, [top, bottom], locations) let startPoint = CGPointMake(img.size.width/2, 0) let endPoint = CGPointMake(img.size.width/2, img.size.height) CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0) let image = UIGraphicsGetImageFromCurrentImageContext() UIGraphicsEndImageContext() return image } 

Answer 1

SWIFT 3

 func imageWithGradient(img:UIImage!) -> UIImage { UIGraphicsBeginImageContext(img.size) let context = UIGraphicsGetCurrentContext() img.draw(at: CGPoint(x: 0, y: 0)) let colorSpace = CGColorSpaceCreateDeviceRGB() let locations:[CGFloat] = [0.0, 1.0] let bottom = UIColor(red: 0, green: 0, blue: 0, alpha: 0.5).cgColor let top = UIColor(red: 0, green: 0, blue: 0, alpha: 0).cgColor let colors = [top, bottom] as CFArray let gradient = CGGradient(colorsSpace: colorSpace, colors: colors, locations: locations) let startPoint = CGPoint(x: img.size.width/2, y: 0) let endPoint = CGPoint(x: img.size.width/2, y: img.size.height) context!.drawLinearGradient(gradient!, start: startPoint, end: endPoint, options: CGGradientDrawingOptions(rawValue: UInt32(0))) let image = UIGraphicsGetImageFromCurrentImageContext() UIGraphicsEndImageContext() return image! } 

Answer 2

我在Swift游乐场尝试了这个，我无法复制你所描述的确切问题，但是这里有一些你可以尝试的建议。

你可以改变你在渐变中设置光圈的方式，我认为使用光圈而不是移动渐变更有意义，移动起点，即不是从顶边开始，而是从垂直中心开始，像这样的东西

 UIGraphicsBeginImageContext(image.size) var context = UIGraphicsGetCurrentContext() image.drawAtPoint(CGPointMake(0, 0)) let colorSpace = CGColorSpaceCreateDeviceRGB() let locations:[CGFloat] = [0.0, 1.0] let bottom = UIColor(red: 0, green: 0, blue: 0, alpha: 0.5).CGColor let top = UIColor(red: 0, green: 0, blue: 0, alpha: 0).CGColor let gradient = CGGradientCreateWithColors(colorSpace, [top, bottom], locations) let startPoint = CGPointMake(image.size.width / 2, image.size.height / 2) let endPoint = CGPointMake(image.size.width / 2, image.size.height) CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0) let finalImage = UIGraphicsGetImageFromCurrentImageContext() UIGraphicsEndImageContext() 

通知位置现在为0和1，而startPoint y坐标向下移动。

或者，看看将kCGGradientDrawsBeforeStartLocation作为CGContextDrawLinearGradient的选项传递，因为这也可能有所不同。