如何设置UIImage的不透明度/ alpha值？

Question

我知道你可以用UIImageView做到这一点，但它可以做到UIImage？我希望将UIImageView的动画图像数组属性设置为具有不同不透明度的相同图像的数组。思考？

Answer 1

我只是需要这样做，但认为史蒂文的解决方案会很慢。这应该有希望使用图形硬件。在UIImage的创建类别：

- (UIImage *)imageByApplyingAlpha:(CGFloat) alpha { 
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0f); 

    CGContextRef ctx = UIGraphicsGetCurrentContext(); 
    CGRect area = CGRectMake(0, 0, self.size.width, self.size.height); 

    CGContextScaleCTM(ctx, 1, -1); 
    CGContextTranslateCTM(ctx, 0, -area.size.height); 

    CGContextSetBlendMode(ctx, kCGBlendModeMultiply); 

    CGContextSetAlpha(ctx, alpha); 

    CGContextDrawImage(ctx, area, self.CGImage); 

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext(); 

    UIGraphicsEndImageContext(); 

    return newImage; 
} 

Answer 2

设置其视图的不透明度则表现出。

UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageWithName:@"SomeName.png"]]; 
imageView.alpha = 0.5; //Alpha runs from 0.0 to 1.0 

使用该动画中。您可以在一段时间内更改动画中的Alpha。

[UIView beginAnimations:nil context:NULL]; 
[UIView setAnimationDuration:1.0]; 
//Set alpha 
[UIView commitAnimations]; 

Answer 3

我意识到这是相当晚了，但我需要这样的东西，所以我掀起了一个快速和肮脏的方法来做到这一点。

+ (UIImage *) image:(UIImage *)image withAlpha:(CGFloat)alpha{ 

    // Create a pixel buffer in an easy to use format 
    CGImageRef imageRef = [image CGImage]; 
    NSUInteger width = CGImageGetWidth(imageRef); 
    NSUInteger height = CGImageGetHeight(imageRef); 
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 

    UInt8 * m_PixelBuf = malloc(sizeof(UInt8) * height * width * 4); 

    NSUInteger bytesPerPixel = 4; 
    NSUInteger bytesPerRow = bytesPerPixel * width; 
    NSUInteger bitsPerComponent = 8; 
    CGContextRef context = CGBitmapContextCreate(m_PixelBuf, width, height, 
               bitsPerComponent, bytesPerRow, colorSpace, 
               kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big); 

    CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef); 
    CGContextRelease(context); 

    //alter the alpha 
    int length = height * width * 4; 
    for (int i=0; i<length; i+=4) 
    { 
     m_PixelBuf[i+3] = 255*alpha; 
    } 


    //create a new image 
    CGContextRef ctx = CGBitmapContextCreate(m_PixelBuf, width, height, 
               bitsPerComponent, bytesPerRow, colorSpace, 
               kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big); 

    CGImageRef newImgRef = CGBitmapContextCreateImage(ctx); 
    CGColorSpaceRelease(colorSpace); 
    CGContextRelease(ctx); 
    free(m_PixelBuf); 

    UIImage *finalImage = [UIImage imageWithCGImage:newImgRef]; 
    CGImageRelease(newImgRef); 

    return finalImage; 
} 

Answer 4

有很多简单的解决方案：

- (UIImage *)tranlucentWithAlpha:(CGFloat)alpha 
{ 
    UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale); 
    [self drawAtPoint:CGPointZero blendMode:kCGBlendModeNormal alpha:alpha]; 
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext(); 
    UIGraphicsEndImageContext(); 
    return image; 
} 

Answer 5

基于阿列克谢Ishkov的回答，但是在斯威夫特

我用的UIImage类的扩展。

斯威夫特2：

的UIImage扩展：

extension UIImage { 
    func imageWithAlpha(alpha: CGFloat) -> UIImage { 
     UIGraphicsBeginImageContextWithOptions(size, false, scale) 
     drawAtPoint(CGPointZero, blendMode: .Normal, alpha: alpha) 
     let newImage = UIGraphicsGetImageFromCurrentImageContext() 
     UIGraphicsEndImageContext() 
     return newImage 
    } 
} 

要使用：

let image = UIImage(named: "my_image") 
let transparentImage = image.imageWithAlpha(0.5) 

斯威夫特3：

注意，此实现收益一个可选的UIImage。这是因为在Swift 3中UIGraphicsGetImageFromCurrentImageContext现在返回一个可选项。如果上下文为零，或者不使用UIGraphicsBeginImageContext创建，则此值可能为零。

的UIImage扩展：

extension UIImage { 
    func image(alpha: CGFloat) -> UIImage? { 
     UIGraphicsBeginImageContextWithOptions(size, false, scale) 
     draw(at: .zero, blendMode: .normal, alpha: alpha) 
     let newImage = UIGraphicsGetImageFromCurrentImageContext() 
     UIGraphicsEndImageContext() 
     return newImage 
    } 
} 

要使用：从Xamarin用户

let image = UIImage(named: "my_image") 
let transparentImage = image?.image(alpha: 0.5) 

Answer 6

嘿，嘿，谢谢！ :)这里有云转换为C＃

//*************************************************************************** 
public static class ImageExtensions 
//*************************************************************************** 
{ 
    //------------------------------------------------------------- 
    public static UIImage WithAlpha(this UIImage image, float alpha) 
    //------------------------------------------------------------- 
     { 
     UIGraphics.BeginImageContextWithOptions(image.Size,false,image.CurrentScale); 
     image.Draw(CGPoint.Empty, CGBlendMode.Normal, alpha); 
     var newImage = UIGraphics.GetImageFromCurrentImageContext(); 
     UIGraphics.EndImageContext(); 
     return newImage; 
     } 

} 

用例：

var MySupaImage = UIImage.FromBundle("opaquestuff.png").WithAlpha(0.15f);