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Reducing image size with Downsampling [Using ImageIO]
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| func downsample(imageAt imageURL: URL, to pointSize: CGSize, scale: CGFloat = UIScreen.main.scale) -> UIImage? { | |
| // Create an CGImageSource that represent an image | |
| let imageSourceOptions = [kCGImageSourceShouldCache: false] as CFDictionary | |
| guard let imageSource = CGImageSourceCreateWithURL(imageURL as CFURL, imageSourceOptions) else { | |
| return nil | |
| } | |
| // Calculate the desired dimension | |
| let maxDimensionInPixels = max(pointSize.width, pointSize.height) * scale | |
| // Perform downsampling | |
| let downsampleOptions = [ | |
| kCGImageSourceCreateThumbnailFromImageAlways: true, | |
| kCGImageSourceShouldCacheImmediately: true, | |
| kCGImageSourceCreateThumbnailWithTransform: true, | |
| kCGImageSourceThumbnailMaxPixelSize: maxDimensionInPixels | |
| ] as CFDictionary | |
| guard let downsampledImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, downsampleOptions) else { | |
| return nil | |
| } | |
| // Return the downsampled image as UIImage | |
| return UIImage(cgImage: downsampledImage) | |
| } | |
| //DESCRIPTION: | |
| imageURL: The image URL. It can be a web URL or a local image path. | |
| pointSize: The desired size of the downsampled image. Usually, this will be the UIImageView's frame size. | |
| scale: The downsampling scale factor. Usually, this will be the scale factor associated with the screen (we usually refer to it as @2x or @3x). That's why you can see that its default value has been set to UIScreen.main.scale. | |
| //HOW TO USE: | |
| let filePath = Bundle.main.url(forResource: "image_name", withExtension: "jpg")! | |
| let downsampledImage = downsample(imageAt: filePath, to: yourImageView.bounds.size) | |
| yourImageView.image = downsampledImage |
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