Convert raw image data to jpeg in swift

Question

I am trying to convert the raw image data to jpeg in swift. But unfortunately, the jpeg image created is skewed. Please find below the code used for the conversion.

let rawPtr = (rawImgData as NSData).bytes
let mutableRawPtr = UnsafeMutableRawPointer.init(mutating: rawPtr)
let context = CGContext.init(data: mutableRawPtr,
                             width: 750,
                             height: 1334,
                             bitsPerComponent: 32,
                             bytesPerRow: (8 * 750)/8,
                             space: CGColorSpaceCreateDeviceRGB(),
                             bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue())
let imageRef = CGContext.makeImage(context!)
let imageRep = NSBitmapImageRep(cgImage: imageRef()!)
let finalData = imageRep.representation(using: .jpeg,
                                        properties: [NSBitmapImageRep.PropertyKey.compressionFactor : 0.5])

Here's the converted jpeg image

Any help or pointers would be greatly appreciated. Thanks in advance!

you van just use like this `UIImage(data:imageData,scale:1.0) presuming the image's scale is 1` — Abdelahad Darwish, May 09 '18 at 16:11
@AbdelahadDarwish scaling is not the issue here. I am getting the desired scaling. The image is getting skewed. I wanted to know, whether this is because of the way I am trying to generate the jpeg image from the raw image data — Aravind G S, May 10 '18 at 04:55

score 1 · Accepted Answer · answered May 15 '19 at 10:11

Finally figured out the answer

var width:size_t?
var height:size_t?
let bitsPerComponent:size_t = 8
var bytesPerRow:size_t?
var bitmapInfo: UInt32
if #available(OSX 10.12, *) {
    bitmapInfo = UInt32(CGImageAlphaInfo.premultipliedFirst.rawValue) | UInt32(CGImageByteOrderInfo.order32Little.rawValue)
} else {
    bitmapInfo = UInt32(CGImageAlphaInfo.premultipliedFirst.rawValue)
}
let colorSpace = CGColorSpaceCreateDeviceRGB()

do {
    let streamAttributesFuture = self.bitmapStream?.streamAttributes()
    streamAttributesFuture?.onQueue(.main, notifyOfCompletion: { (streamAttributesFut) in

    })
    try streamAttributesFuture?.await()
    let dict = streamAttributesFuture?.result
    width = (dict?.attributes["width"] as! Int)
    height = (dict?.attributes["height"] as! Int)
    bytesPerRow = (dict?.attributes["row_size"] as! Int)

} catch let frameError{
    print("frame error = \(frameError)")
    return
}

let rawPtr = (data as NSData).bytes
let mutableRawPtr = UnsafeMutableRawPointer.init(mutating: rawPtr)
let context = CGContext.init(data: mutableRawPtr, width: width!, height: height!, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow!, space: colorSpace, bitmapInfo: bitmapInfo)
if context == nil {
    return
}

let imageRef = context?.makeImage()

let scaledWidth = Int(Double(width!) / 1.5)
let scaledHeight = Int(Double(height!) / 1.5)

let resizeCtx = CGContext.init(data: nil, width: scaledWidth, height: scaledHeight, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow!, space: colorSpace, bitmapInfo: bitmapInfo)
resizeCtx?.draw(imageRef!, in: CGRect(x: 0, y: 0, width: scaledWidth, height: scaledHeight))

resizeCtx?.interpolationQuality = .low

let resizedImgRef = resizeCtx?.makeImage()
let imageRep = NSBitmapImageRep(cgImage: resizedImgRef!)

let finalData = imageRep.representation(using: .jpeg, properties: [NSBitmapImageRep.PropertyKey.compressionFactor : compression])

score 0 · Answer 2 · answered May 10 '18 at 08:19

Try this, change imageName to what you want, and save it in any Directory

func convertToJPEG(image: UIImage) {
        if let jpegImage = UIImageJPEGRepresentation(image, 1.0){
            do {
                //Convert
                let tempDirectoryURL = URL(fileURLWithPath:  NSTemporaryDirectory(), isDirectory: true)
                let newFileName = "\(imageName.append(".JPG"))"
                let targetURL = tempDirectoryURL.appendingPathComponent(newFileName)
                try jpegImage.write(to: targetURL, options: [])
            }catch {
                print (error.localizedDescription)
                print("FAILED")
            }
        }else{
            print("FAILED")
        }
    }

I am running a CLI. Hence `UIImage` is not available. The raw data is converted to JPEG but the image is getting skewed.The above method just takes a `UIImage` and converts it into data and writes it to a file. I am actually looking for the reason why image is getting skewed — Aravind G S, May 10 '18 at 09:17

Convert raw image data to jpeg in swift

2 Answers2