Create new UIImage by adding shadow to existing UIImage

Question

I\'ve taken a look at this question: UIImage Shadow Trouble

But the accepted answer didn\'t work for me.

What I\'m trying to do is take a UIImage and add a s

Answer 1

I needed a bigger shadow for my UIImages. Here is my variant of the answer that allows for a customized shadow size with no offset.

    - (UIImage*)imageWithShadow:(UIImage*)originalImage BlurSize:(float)blurSize {

    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef shadowContext = CGBitmapContextCreate(NULL, originalImage.size.width + (blurSize*2), originalImage.size.height + (blurSize*2), CGImageGetBitsPerComponent(originalImage.CGImage), 0, colourSpace, kCGImageAlphaPremultipliedLast);
    CGColorSpaceRelease(colourSpace);

    CGContextSetShadowWithColor(shadowContext, CGSizeMake(0, 0), blurSize, [UIColor blackColor].CGColor);
    CGContextDrawImage(shadowContext, CGRectMake(blurSize, blurSize, originalImage.size.width, originalImage.size.height), originalImage.CGImage);

    CGImageRef shadowedCGImage = CGBitmapContextCreateImage(shadowContext);
    CGContextRelease(shadowContext);

    UIImage * shadowedImage = [UIImage imageWithCGImage:shadowedCGImage];
    CGImageRelease(shadowedCGImage);

    return shadowedImage;
}

Use it like:

UIImage *shadowedImage = [self imageWithShadow:myImage BlurSize:30.0f];

Answer 2

To make an image a CGImage as in this case , try

self.shadowImage.CGImage

Answer 3

GK100's answer in Swift 2 / iOS9

func addShadow(blurSize: CGFloat = 6.0) -> UIImage {

    let data : UnsafeMutablePointer<Void> = nil
    let colorSpace:CGColorSpace = CGColorSpaceCreateDeviceRGB()!
    let bitmapInfo : CGBitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.PremultipliedLast.rawValue)

    let myColorValues:[CGFloat] = [0.0, 0.0, 0.0, 0.8]
    let myColor = CGColorCreate(colorSpace, myColorValues)

    let shadowContext : CGContextRef = CGBitmapContextCreate(data, Int(self.size.width + blurSize), Int(self.size.height + blurSize), CGImageGetBitsPerComponent(self.CGImage), 0, colorSpace, bitmapInfo.rawValue)!

    CGContextSetShadowWithColor(shadowContext, CGSize(width: blurSize/2,height: -blurSize/2),  blurSize, myColor)
    CGContextDrawImage(shadowContext, CGRect(x: 0, y: blurSize, width: self.size.width, height: self.size.height), self.CGImage)

    let shadowedCGImage : CGImageRef = CGBitmapContextCreateImage(shadowContext)!
    let shadowedImage : UIImage = UIImage(CGImage: shadowedCGImage)

    return shadowedImage
}

Answer 4

Whilst trying to use some of the other examples here, I noticed that they seem to either hard-code the offset & blur, or do not correctly take them into account when sizing and positioning the output.

The following code solves these issues (it's based on the original work by Igor Kulagin):

extension UIImage {
    /// Returns a new image with the specified shadow properties.
    /// This will increase the size of the image to fit the shadow and the original image.
    func withShadow(blur: CGFloat = 6, offset: CGSize = .zero, color: UIColor = UIColor(white: 0, alpha: 0.8)) -> UIImage {

        let shadowRect = CGRect(
            x: offset.width - blur,
            y: offset.height - blur,
            width: size.width + blur * 2,
            height: size.height + blur * 2
        )
        
        UIGraphicsBeginImageContextWithOptions(
            CGSize(
                width: max(shadowRect.maxX, size.width) - min(shadowRect.minX, 0),
                height: max(shadowRect.maxY, size.height) - min(shadowRect.minY, 0)
            ),
            false, 0
        )
        
        let context = UIGraphicsGetCurrentContext()!

        context.setShadow(
            offset: offset,
            blur: blur,
            color: color.cgColor
        )
        
        draw(
            in: CGRect(
                x: max(0, -shadowRect.origin.x),
                y: max(0, -shadowRect.origin.y),
                width: size.width,
                height: size.height
            )
        )
        let image = UIGraphicsGetImageFromCurrentImageContext()!
        
        UIGraphicsEndImageContext()
        return image
    }
}

Answer 5

iOS8 / Swift version (made as an extension to UIImage):

extension UIImage {

    func addShadow(blurSize: CGFloat = 6.0) -> UIImage {

        let shadowColor = UIColor(white:0.0, alpha:0.8).cgColor

        let context = CGContext(data: nil,
                                width: Int(self.size.width + blurSize),
                                height: Int(self.size.height + blurSize),
                                bitsPerComponent: self.cgImage!.bitsPerComponent,
                                bytesPerRow: 0,
                                space: CGColorSpaceCreateDeviceRGB(),
                                bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)!

        context.setShadow(offset: CGSize(width: blurSize/2,height: -blurSize/2),
                          blur: blurSize,
                          color: shadowColor)
        context.draw(self.cgImage!,
                     in: CGRect(x: 0, y: blurSize, width: self.size.width, height: self.size.height),
                     byTiling:false)

        return UIImage(cgImage: context.makeImage()!)
    }
}

(converted from Laurent Etiemble's & capikaw answers)

EDIT 2016/10/31: converted to Swift 3, and removed all unnecessary stuff

Usage:

let sourceImage: UIImage(named: "some image")
let shadowImage = sourceImage.addShadow()

Answer 6

My method that draws a shadow on an image. It has custom shadow parameters and renders image in correct size and screen scale. Should be implemented in UIImage extension. (Swift 3).

func addingShadow(blur: CGFloat = 1, shadowColor: UIColor = UIColor(white: 0, alpha: 1), offset: CGSize = CGSize(width: 1, height: 1) ) -> UIImage {

    UIGraphicsBeginImageContextWithOptions(CGSize(width: size.width + 2 * blur, height: size.height + 2 * blur), false, 0)
    let context = UIGraphicsGetCurrentContext()!

    context.setShadow(offset: offset, blur: blur, color: shadowColor.cgColor)
    draw(in: CGRect(x: blur - offset.width / 2, y: blur - offset.height / 2, width: size.width, height: size.height))
    let image = UIGraphicsGetImageFromCurrentImageContext()!

    UIGraphicsEndImageContext()

    return image
}