如何設置UIImage的不透明度/ alpha值？

Question

我知道你可以用UIImageView做到這一點，但它可以做到UIImage？我希望將UIImageView的動畫圖像數組屬性設置爲具有不同不透明度的相同圖像的數組。思考？

Answer 1

我只是需要這樣做，但認爲史蒂文的解決方案會很慢。這應該有希望使用圖形硬件。在UIImage的創建類別：

- (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

設置其視圖的不透明度則表現出。

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

使用該動畫中。您可以在一段時間內更改動畫中的Alpha。

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

Answer 3

我意識到這是相當晚了，但我需要這樣的東西，所以我掀起了一個快速和骯髒的方法來做到這一點。

+ (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

有很多簡單的解決方案：

- (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

基於阿列克謝Ishkov的回答，但是在斯威夫特

我用的UIImage類的擴展。

斯威夫特2：

的UIImage擴展：

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，此實現收益一個可選的UIImage。這是因爲在Swift 3中UIGraphicsGetImageFromCurrentImageContext現在返回一個可選項。如果上下文爲零，或者不使用UIGraphicsBeginImageContext創建，則此值可能爲零。

的UIImage擴展：

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：從Xamarin用戶

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

Answer 6

嘿，嘿，謝謝！ :)這裏有雲轉換爲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);