Create new UIImage by adding shadow to existing UIImage
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];
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()
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;
}
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;
}