我怎样才能用渐变色调UIImage？

Question

我到处搜索，但没有找到解决方案。我有图像1.如何以渐变方式对它们进行编程以获得图像2和3？以下是这些图片：

我通过Photoshop应用于它们的色调是简单的双色线性渐变。

我的问题是：如何以编程方式实现此效果？

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解决方案：jrtc27给了我几乎成功的例子。我修复它（对于ARC）并使其可重用（使用UIImage的类别）。就这个：

- (UIImage *)tintedWithLinearGradientColors:(NSArray *)colorsArr {
    CGFloat scale = self.scale;
    UIGraphicsBeginImageContext(CGSizeMake(self.size.width * scale, self.size.height * scale));
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, 0, self.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    CGContextSetBlendMode(context, kCGBlendModeNormal);
    CGRect rect = CGRectMake(0, 0, self.size.width * scale, self.size.height * scale);
    CGContextDrawImage(context, rect, self.CGImage);

    // Create gradient

    UIColor *colorOne = [colorsArr objectAtIndex:1]; // top color
    UIColor *colorTwo = [colorsArr objectAtIndex:0]; // bottom color


    NSArray *colors = [NSArray arrayWithObjects:(id)colorOne.CGColor, (id)colorTwo.CGColor, nil];
    CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();
    CGGradientRef gradient = CGGradientCreateWithColors(space, (__bridge CFArrayRef)colors, NULL);

    // Apply gradient

    CGContextClipToMask(context, rect, self.CGImage);
    CGContextDrawLinearGradient(context, gradient, CGPointMake(0,0), CGPointMake(0,self.size.height * scale), 0);
    UIImage *gradientImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return gradientImage;
}

Answer 1

我相信以下内容应该有效 - 如果没有则做评论！

// Load image
UIImage *image = [UIImage imageNamed:@"MyCoolImage.png"];
CGFloat scale = image.scale;
UIGraphicsBeginImageContext(CGSizeMake(image.size.width * scale, image.size.height * scale));
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0, image.size.height);
CGContextScaleCTM(context, 1.0, -1.0);

CGContextSetBlendMode(context, kCGBlendModeMultiply);
CGRect rect = CGRectMake(0, 0, image.size.width * scale, image.size.height * scale);
CGContextDrawImage(context, rect, image.CGImage);

// Create gradient

UIColor *colorOne = ....;
UIColor *colorTwo = ....;

NSArray *colors = [NSArray arrayWithObjects:(id)colorOne.CGColor, (id)colorTwo.CGColor, nil];
CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();
CGGradientRef gradient = CGGradientCreateWithColors(space, (CFArrayRef)colors, NULL);

// Apply gradient

CGContextClipToMask(context, rect, image.CGImage);
CGContextDrawLinearGradient(context, gradient, CGPointMake(0,0), CGPointMake(0,image.size.height * scale), 0);
CGGradientRelease(gradient);
UIImage *gradientImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

感谢CoffeeShopped的基本想法。

Answer 2

编辑：这是一个支持非视网膜和视网膜显示的版本

该方法可以用作UIImage的类别

+ (UIImage *)imageWithGradient:(UIImage *)img startColor:(UIColor *)color1 endColor:(UIColor *)color2 {
    UIGraphicsBeginImageContextWithOptions(img.size, NO, img.scale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, 0, img.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    CGContextSetBlendMode(context, kCGBlendModeNormal);
    CGRect rect = CGRectMake(0, 0, img.size.width, img.size.height);
    //CGContextDrawImage(context, rect, img.CGImage);

    // Create gradient
    NSArray *colors = [NSArray arrayWithObjects:(id)color2.CGColor, (id)color1.CGColor, nil];
    CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();
    CGGradientRef gradient = CGGradientCreateWithColors(space, (__bridge CFArrayRef)colors, NULL);

    // Apply gradient
    CGContextClipToMask(context, rect, img.CGImage);
    CGContextDrawLinearGradient(context, gradient, CGPointMake(0,0), CGPointMake(0, img.size.height), 0);
    UIImage *gradientImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    CGGradientRelease(gradient);
    CGColorSpaceRelease(space);

    return gradientImage;
}

编辑：由sobri添加更改

Answer 3

Swift 4版。

import UIKit

extension UIImage {

func tintedWithLinearGradientColors(colorsArr: [CGColor]) -> UIImage {
    UIGraphicsBeginImageContextWithOptions(self.size, false, self.scale);
    guard let context = UIGraphicsGetCurrentContext() else {
        return UIImage()
    }
    context.translateBy(x: 0, y: self.size.height)
    context.scaleBy(x: 1, y: -1)

    context.setBlendMode(.normal)
    let rect = CGRect.init(x: 0, y: 0, width: size.width, height: size.height)

    // Create gradient
    let colors = colorsArr as CFArray
    let space = CGColorSpaceCreateDeviceRGB()
    let gradient = CGGradient(colorsSpace: space, colors: colors, locations: nil)

    // Apply gradient
    context.clip(to: rect, mask: self.cgImage!)
    context.drawLinearGradient(gradient!, start: CGPoint(x: 0, y: 0), end: CGPoint(x: 0, y: self.size.height), options: .drawsAfterEndLocation)
    let gradientImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return gradientImage!
}
}

Answer 4

Swift版本（作为UIImage扩展，使用remy的答案）：

extension UIImage {
    func tintedWithLinearGradientColors(colorsArr: [CGColor!]) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(self.size, false, self.scale);
        let context = UIGraphicsGetCurrentContext()
        CGContextTranslateCTM(context, 0, self.size.height)
        CGContextScaleCTM(context, 1.0, -1.0)

        CGContextSetBlendMode(context, kCGBlendModeNormal)
        let rect = CGRectMake(0, 0, self.size.width, self.size.height)

        // Create gradient

        let colors = colorsArr as CFArray
        let space = CGColorSpaceCreateDeviceRGB()
        let gradient = CGGradientCreateWithColors(space, colors, nil)

        // Apply gradient

        CGContextClipToMask(context, rect, self.CGImage)
        CGContextDrawLinearGradient(context, gradient, CGPointMake(0, 0), CGPointMake(0, self.size.height), 0)
        let gradientImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return gradientImage
    }
}