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 shadow to it, then return a whole new UIImage, shadow and all.

This is what I'm trying:

- (UIImage*)imageWithShadow {

    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef shadowContext = CGBitmapContextCreate(NULL, self.size.width, self.size.height + 1, CGImageGetBitsPerComponent(self.CGImage), 0, 
                                                 colourSpace, kCGImageAlphaPremultipliedLast);
    CGColorSpaceRelease(colourSpace);

    CGContextSetShadow(shadowContext, CGSizeMake(0, -1), 1);
    CGContextDrawImage(shadowContext, CGRectMake(0, 0, self.size.width, self.size.height), self.CGImage);

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

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

    return shadowedImage;
}

The result is that I get exactly the same image as before I put it through this method.

I am doing this the correct way, or is there something obvious I'm missing?

If the UIImage will be shown in a UIImageView, you can also just add a shadow effect to the view. See https://stackoverflow.com/questions/2044479/what-is-the-best-way-to-create-a-shadow-behind-a-uiimageview — zeroimpl, Sep 05 '19 at 04:58

score 17 · Accepted Answer · answered May 30 '10 at 16:23

There are several problems with your code:

The target image is too small. Be sure there enough place to draw the shadow.
Consider using CGContextSetShadowWithColor to define both the shadow and its color.
Don't forget that coordinate system is flipped, so the origin is bottom-left, not top-left.

By fixing these issues, the shadow should be drawn.

- (UIImage*)imageWithShadow {
    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef shadowContext = CGBitmapContextCreate(NULL, self.size.width + 10, self.size.height + 10, CGImageGetBitsPerComponent(self.CGImage), 0, 
                                             colourSpace, kCGImageAlphaPremultipliedLast);
    CGColorSpaceRelease(colourSpace);

    CGContextSetShadowWithColor(shadowContext, CGSizeMake(5, -5), 5, [UIColor blackColor].CGColor);
    CGContextDrawImage(shadowContext, CGRectMake(0, 10, self.size.width, self.size.height), self.CGImage);

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

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

    return shadowedImage;
}

Perfect! I was actually adding 1 to the height to draw the shadow, but the other stuff (setting the shadow, flipped coordinate system) was spot on. — Tom Irving, May 30 '10 at 16:45
Where would this code be implemented and how would you call it to add a shadow to an image? — Christian Schlensker, Dec 25 '10 at 05:38
The method assumes that the class can provide a CGImage and its dimensions. You can alter the method to take parameters (CGImage and CGSize) instead. — Laurent Etiemble, Dec 29 '10 at 14:55

score 12 · Answer 2 · edited Sep 23 '21 at 18:30

Swift 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)

Usage:

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

score 5 · Answer 3 · edited Sep 23 '21 at 18:30

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];

score 5 · Answer 4 · answered Aug 19 '20 at 19:50

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
    }
}

score 5 · Answer 5 · edited Sep 23 '21 at 18:31

I needed a method that would accept an UIImage as a parameter and return a slightly larger UIImage with shadows. The posts here have been very helpful to me so here's my method.

The returned image has a centered 5px shadow on each side.

+ (UIImage*)imageWithShadowForImage:(UIImage *)initialImage {

    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef shadowContext = CGBitmapContextCreate(NULL, initialImage.size.width + 10, initialImage.size.height + 10, CGImageGetBitsPerComponent(initialImage.CGImage), 0, colourSpace, kCGImageAlphaPremultipliedLast);
    CGColorSpaceRelease(colourSpace);
    
    CGContextSetShadowWithColor(shadowContext, CGSizeMake(0,0), 5, [UIColor blackColor].CGColor);
    CGContextDrawImage(shadowContext, CGRectMake(5, 5, initialImage.size.width, initialImage.size.height), initialImage.CGImage);
    
    CGImageRef shadowedCGImage = CGBitmapContextCreateImage(shadowContext);
    CGContextRelease(shadowContext);
    
    UIImage * shadowedImage = [UIImage imageWithCGImage:shadowedCGImage];
    CGImageRelease(shadowedCGImage);
    
    return shadowedImage;
}

score 4 · Answer 6 · answered Apr 15 '17 at 14:00

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
}

score 0 · Answer 7 · edited Nov 04 '15 at 06:19

0

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

self.shadowImage.CGImage

edited Nov 04 '15 at 06:19

itsji10dra

4,603
3
39
59

answered Feb 05 '13 at 07:11

Gautam Jain

2,913
30
25

score 0 · Answer 8 · answered Apr 04 '16 at 09:05

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
}

Create new UIImage by adding shadow to existing UIImage

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