How to Compress Image Size

How to compress of reduce the size of an image before uploading to Parse as PFFile? (Swift)

Yes you can use UIImageJPEGRepresentation instead of UIImagePNGRepresentation to reduce your image file size. You can just create an extension UIImage as follow:

Xcode 8.2 • Swift 3.0.2

extension UIImage {
    enum JPEGQuality: CGFloat {
        case lowest  = 0
        case low     = 0.25
        case medium  = 0.5
        case high    = 0.75
        case highest = 1
    }

    /// Returns the data for the specified image in JPEG format.
    /// If the image object’s underlying image data has been purged, calling this function forces that data to be reloaded into memory.
    /// - returns: A data object containing the JPEG data, or nil if there was a problem generating the data. This function may return nil if the image has no data or if the underlying CGImageRef contains data in an unsupported bitmap format.
    func jpeg(_ quality: JPEGQuality) -> Data? {
        return UIImageJPEGRepresentation(self, quality.rawValue)
    }
}

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edit/update:

Xcode 10 Swift 4.2

extension UIImage {
    enum JPEGQuality: CGFloat {
        case lowest  = 0
        case low     = 0.25
        case medium  = 0.5
        case high    = 0.75
        case highest = 1
    }

    /// Returns the data for the specified image in JPEG format.
    /// If the image object’s underlying image data has been purged, calling this function forces that data to be reloaded into memory.
    /// - returns: A data object containing the JPEG data, or nil if there was a problem generating the data. This function may return nil if the image has no data or if the underlying CGImageRef contains data in an unsupported bitmap format.
    func jpeg(_ jpegQuality: JPEGQuality) -> Data? {
        return jpegData(compressionQuality: jpegQuality.rawValue)
    }
}

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Usage:

if let imageData = image.jpeg(.lowest) {
    print(imageData.count)
}

How to compress an image via Javascript in the browser?

In short:

• Read the files using the HTML5 FileReader API with .readAsArrayBuffer
• Create a Blob with the file data and get its url with window.URL.createObjectURL(blob)
• Create new Image element and set it's src to the file blob url
• Send the image to the canvas. The canvas size is set to desired output size
• Get the scaled-down data back from canvas via canvas.toDataURL("image/jpeg",0.7) (set your own output format and quality)
• Attach new hidden inputs to the original form and transfer the dataURI images basically as normal text
• On backend, read the dataURI, decode from Base64, and save it

Source: code.

Compress image size using Java

Unfortunately the lossy JPEG compression compresses far better than the lossless PNG compression. You could restrict width and height of the image and scale proportionally.

So I would switch to JPEG and restrict the size.

How to compress the image size using .NET Core?

I have used Magick.NET library which is available for both .NET and .NET Core to compress images. Refer to its documentation for more details.

In your case you either need to save the image temporarily somewhere and use the path (similar to my example), or convert it to an array of byte in memory and read that since it accept Byte[]

     using (MagickImage image = new MagickImage(@"YourImage.jpg"))
       {
           image.Format = image.Format; // Get or Set the format of the image.
           image.Resize(40, 40); // fit the image into the requested width and height. 
           image.Quality = 10; // This is the Compression level.
           image.Write("YourFinalImage.jpg");                 
        }

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