How to set the opacity alpha of a UIImage

Question

I know you can do this with a UIImageView  but can it be done to a UIImage   I want to have the animation images array property of a UIImageView to be an array of the same image but with different opacities   Thoughts

User · Accepted Answer

I just needed to do this  but thought Steven s solution would be slow   This should hopefully use graphics HW   Create a category on UIImage   -  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

User · Answer

If you re experimenting with Metal rendering  amp  you re extracting the CGImage generated by imageByApplyingAlpha in the first reply  you may end up with a Metal rendering that s larger than you expect   While experimenting with Metal  you may want to change one line of code in imageByApplyingAlpha       UIGraphicsBeginImageContextWithOptions  self size  NO  1 0f       UIGraphicsBeginImageContextWithOptions  self size  NO  0 0f     If you re using a device with a scale factor of 3 0  like the iPhone 11 Pro Max  the 0 0 scale factor shown above will give you an CGImage that s three times larger than you re expecting   Changing the scale factor to 1 0 should avoid any scaling   Hopefully  this reply will save beginners a lot of aggravation

User · Answer

Set the opacity of its view it is showed in   UIImageView  imageView     UIImageView alloc  initWithImage  UIImage imageWithName   SomeName png     imageView alpha   0 5    Alpha runs from 0 0 to 1 0   Use this in an animation  You can change the alpha in an animation for an duration    UIView beginAnimations nil context NULL    UIView setAnimationDuration 1 0     Set alpha  UIView commitAnimations

User · Answer

there is much easier solution   -  UIImage   tranlucentWithAlpha  CGFloat alpha       UIGraphicsBeginImageContextWithOptions self size  NO  self scale        self drawAtPoint CGPointZero blendMode kCGBlendModeNormal alpha alpha       UIImage  image   UIGraphicsGetImageFromCurrentImageContext        UIGraphicsEndImageContext        return image

User · Answer

same result as others  different style   extension UIImage        func withAlpha   alpha  CGFloat  - gt  UIImage           return UIGraphicsImageRenderer size  size  image     in             draw at   zero  blendMode   normal  alpha  alpha

User · Answer

I realize this is quite late  but I needed something like this so I whipped up a quick and dirty method to do this       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 lt 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

User · Answer

Based on Alexey Ishkov s answer  but in Swift  I used an extension of the UIImage class   Swift 2   UIImage Extension   extension UIImage       func imageWithAlpha alpha  CGFloat  - gt  UIImage           UIGraphicsBeginImageContextWithOptions size  false  scale          drawAtPoint CGPointZero  blendMode   Normal  alpha  alpha          let newImage   UIGraphicsGetImageFromCurrentImageContext           UIGraphicsEndImageContext           return newImage           To use   let image   UIImage named   my image   let transparentImage   image imageWithAlpha 0 5    Swift 3 4 5   Note that this implementation returns an optional UIImage  This is because in Swift 3 UIGraphicsGetImageFromCurrentImageContext now returns an optional  This value could be nil if the context is nil or what not created with UIGraphicsBeginImageContext   UIImage Extension   extension UIImage       func image alpha  CGFloat  - gt  UIImage            UIGraphicsBeginImageContextWithOptions size  false  scale          draw at   zero  blendMode   normal  alpha  alpha          let newImage   UIGraphicsGetImageFromCurrentImageContext           UIGraphicsEndImageContext           return newImage           To use   let image   UIImage named   my image   let transparentImage   image  image alpha  0 5

User · Answer

Hey hey thanks from Xamarin user     Here it goes translated to 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                 Usage example   var MySupaImage   UIImage FromBundle  opaquestuff png   WithAlpha 0 15f

User · Answer

Swift 5  extension UIImage     func withAlphaComponent   alpha  CGFloat  - gt  UIImage        UIGraphicsBeginImageContextWithOptions size  false  scale      defer   UIGraphicsEndImageContext          draw at   zero  blendMode   normal  alpha  alpha      return UIGraphicsGetImageFromCurrentImageContext

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