Swift Image Crop Out Transparent Pixels (Swift 2.0)

UIImage+CropTransparent.swift

extension UIImage {

    func imageByCroppingTransparentPixels() -> UIImage {
        let rect = self.cropRectForImage()
        return cropImage(toRect: rect)
    }
    
    func cropRectForImage(image:UIImage) -> CGRect {
        let imageAsCGImage = image.CGImage
        let context:CGContextRef? = self.createARGBBitmapContext(imageAsCGImage!)
        if let context = context {
            let width = Int(CGImageGetWidth(imageAsCGImage))
            let height = Int(CGImageGetHeight(imageAsCGImage))
            let rect:CGRect = CGRect(x: 0.0, y: 0.0, width: CGFloat(width), height: CGFloat(height))
            CGContextDrawImage(context, rect, imageAsCGImage)
            
            var lowX:Int = width
            var lowY:Int = height
            var highX:Int = 0
            var highY:Int = 0
            let data:UnsafeMutablePointer<Void>? = CGBitmapContextGetData(context)
            if let data = data {
                let dataType:UnsafeMutablePointer<UInt8>? = UnsafeMutablePointer<UInt8>(data)
                if let dataType = dataType {
                    for y in 0..<height {
                        for x in 0..<width {
                            let pixelIndex:Int = (width * y + x) * 4 /* 4 for A, R, G, B */;
                            if (dataType[pixelIndex] != 0) { //Alpha value is not zero; pixel is not transparent.
                                if (x < lowX) { lowX = x };
                                if (x > highX) { highX = x };
                                if (y < lowY) { lowY = y};
                                if (y > highY) { highY = y};
                            }
                        }
                    }
                }
                free(data)
            } else {
                return CGRectZero
            }
            return CGRect(x: CGFloat(lowX), y: CGFloat(lowY), width: CGFloat(highX-lowX), height: CGFloat(highY-lowY))
            
        }
        return CGRectZero
    }
    
    func createARGBBitmapContext(inImage: CGImageRef) -> CGContext {
        var bitmapByteCount = 0
        var bitmapBytesPerRow = 0
        
        //Get image width, height
        let pixelsWide = CGImageGetWidth(inImage)
        let pixelsHigh = CGImageGetHeight(inImage)
        
        // Declare the number of bytes per row. Each pixel in the bitmap in this
        // example is represented by 4 bytes; 8 bits each of red, green, blue, and
        // alpha.
        bitmapBytesPerRow = Int(pixelsWide) * 4
        bitmapByteCount = bitmapBytesPerRow * Int(pixelsHigh)
        
        // Use the generic RGB color space.
        let colorSpace = CGColorSpaceCreateDeviceRGB()
        
        // Allocate memory for image data. This is the destination in memory
        // where any drawing to the bitmap context will be rendered.
        let bitmapData = malloc(bitmapByteCount)
        let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.PremultipliedFirst.rawValue)
        
        // Create the bitmap context. We want pre-multiplied ARGB, 8-bits
        // per component. Regardless of what the source image format is
        // (CMYK, Grayscale, and so on) it will be converted over to the format
        // specified here by CGBitmapContextCreate.
        let context = CGBitmapContextCreate(bitmapData, pixelsWide, pixelsHigh, 8, bitmapBytesPerRow, colorSpace, bitmapInfo.rawValue)
        
        return context!
    }
}

How could I modify this to crop white pixels? Thanks!

How could I modify this to crop white pixels? Thanks!

I guess, you can modify line 27 to get R, G, B.