How to apply LUT (from .png) to an image? (Swift + Xcode) - swift

Question

I am trying to apply a LUT to an image by pressing a button.
Because, I am new to programming I mostly copied code and tried to modify it for my own project. I get no error messages, but when I try to press the button there is no effect on the image.
When I change the filter-name to sth. different than: "CIColorCube", the app even crashes with the error message: "Unexpectedly found nil while unwrapping an Optional value"
My LUT Image that I am using. (size: 512x512)
func colorCubeFilterFromLUT(imageName : String) -> CIFilter? {
let size = 512
let lutImage = UIImage(named: "LUT.png")!.cgImage
let lutWidth = lutImage!.width
let lutHeight = lutImage!.height
let rowCount = lutHeight / size
let columnCount = lutWidth / size
if ((lutWidth % size != 0) || (lutHeight % size != 0) || (rowCount * columnCount != size)) {
NSLog("Invalid colorLUT %#", "LUT.png");
return nil
}
let bitmap = getBytesFromImage(image: UIImage(named: "LUT.png"))!
let floatSize = MemoryLayout<Float>.size
let cubeData = UnsafeMutablePointer<Float>.allocate(capacity: size * size * size * 4 * floatSize)
var z = 0
var bitmapOffset = 0
for _ in 0 ..< rowCount {
for y in 0 ..< size {
let tmp = z
for _ in 0 ..< columnCount {
for x in 0 ..< size {
let alpha = Float(bitmap[bitmapOffset]) / 255.0
let red = Float(bitmap[bitmapOffset+1]) / 255.0
let green = Float(bitmap[bitmapOffset+2]) / 255.0
let blue = Float(bitmap[bitmapOffset+3]) / 255.0
let dataOffset = (z * size * size + y * size + x) * 4
cubeData[dataOffset + 3] = alpha
cubeData[dataOffset + 2] = red
cubeData[dataOffset + 1] = green
cubeData[dataOffset + 0] = blue
bitmapOffset += 4
}
z += 1
}
z = tmp
}
z += columnCount
}
let colorCubeData = NSData(bytesNoCopy: cubeData, length: size * size * size * 4 * floatSize, freeWhenDone: true)
// create CIColorCube Filter
let filter = CIFilter(name: "CIColorCube")
filter?.setValue(colorCubeData, forKey: "inputCubeData")
filter?.setValue(size, forKey: "inputCubeDimension")
return filter
}
func getBytesFromImage(image:UIImage?) -> [UInt8]?
{
var pixelValues: [UInt8]?
if let imageRef = image?.cgImage {
let width = Int(imageRef.width)
let height = Int(imageRef.height)
let bitsPerComponent = 8
let bytesPerRow = width * 4
let totalBytes = height * bytesPerRow
let bitmapInfo = CGImageAlphaInfo.premultipliedLast.rawValue | CGBitmapInfo.byteOrder32Little.rawValue
let colorSpace = CGColorSpaceCreateDeviceRGB()
var intensities = [UInt8](repeating: 0, count: totalBytes)
let contextRef = CGContext(data: &intensities, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo)
contextRef?.draw(imageRef, in: CGRect(x: 0.0, y: 0.0, width: CGFloat(width), height: CGFloat(height)))
pixelValues = intensities
}
return pixelValues!
}
#IBAction func filterRetro(_ sender: Any) {
let inputImage = CIImage(image: photo.image!)
let filteredImage = inputImage?.applyingFilter("CIColorCube")
let renderedImage = context.createCGImage(filteredImage!, from: (filteredImage?.extent)!)
photo.image = UIImage(cgImage: renderedImage!)
}

Answer 1

Please add this code in your IBAction func filterRetro
if let photoImage = photo.image {
let inputImage = CIImage(image: photoImage)
let filteredImage = inputImage.applyingFilter("CIColorCube")
let filteredExtent = filteredImage.extent
/* hoping this will return a CGImage */
let renderedImage = context.createCGImage(filteredImage, from: filteredExtent)
photo.image = UIImage(cgImage: renderedImage)
}
The issue with optional wrapping inside the button press action is solved. But not with whole code. Let me know whether this works or not.
[edit]
inputImage.applyingFilter("name") method is calling the CIFilter.init(name). For which doc says,
The name of the filter. You must make sure the name is spelled
correctly, otherwise your app will run but not produce any output
images. For that reason, you should check for the existence of the
filter after calling this method.
I would suggest using a separate variable to create the filter and if the filter exists then only apply to the image.
let filter = CIFilter("CIColorCube")
if filter {
let filteredImage = inputImage.applyingFilter("CIColorCube")
}
try this.
thanks,
J