4 Replies
      Latest reply on Jan 4, 2020 5:20 AM by adib
      adib Level 1 Level 1 (0 points)

        I've ran into a problem when reading a high-efficiency image file and converting it into 24-bit (packed without alpha channel) vImage for further processing. The resulting image has vertical black bands in some parts and other vertical bands in which some channels are missing (i.e has a magenta or green tone to it). The problem appears ony when the source image is 3000x2000 pixels or greater.

         

        Here is a Playground code to reproduce the issue – unfortunately I can't find a way to attach files here.

         

        import Cocoa
        import Accelerate
        
        // width: 2000 pixels results in no banding
        // but width 3000 pixels results in banded image
        let imageFileURL = Bundle.main.url(forResource: "sample_3000", withExtension: "heic")!
        let imageSource  = CGImageSourceCreateWithURL(imageFileURL as CFURL, nil)!
        let originalImage = CGImageSourceCreateImageAtIndex(imageSource, 0, nil)!
        
        let colorSpace = CGColorSpace(name: CGColorSpace.sRGB)!
        
        var expectedImageFormat = vImage_CGImageFormat(
            bitsPerComponent: UInt32(8),
            bitsPerPixel: UInt32(8 * 3),
            colorSpace: Unmanaged.passUnretained(colorSpace),
            bitmapInfo: CGBitmapInfo(rawValue: CGBitmapInfo.byteOrder32Big.rawValue | CGImageAlphaInfo.none.rawValue),
            version: 0,
            decode: nil,
            renderingIntent: originalImage.renderingIntent
        )
        
        
        var buff = vImage_Buffer()
        buff.height = vImagePixelCount(originalImage.height)
        buff.width = vImagePixelCount(originalImage.width)
        buff.rowBytes = Int(buff.width) * (Int(expectedImageFormat.bitsPerPixel) + 7) / Int(expectedImageFormat.bitsPerComponent)
        
        let bufferData = NSMutableData(length: Int(buff.height) * buff.rowBytes)!
        buff.data = bufferData.mutableBytes
        
        let initErr = vImageBuffer_InitWithCGImage(&buff, &expectedImageFormat, nil, originalImage, numericCast(kvImagePrintDiagnosticsToConsole | kvImageNoAllocate))
        guard initErr == kvImageNoError else {
            print("error creating image: \(initErr)")
            abort()
        }
        
        var convertError = kvImageNoError
        let convertedImageUnmanaged = vImageCreateCGImageFromBuffer(
            &buff,
            &expectedImageFormat,
            nil, // callback
            nil, // user data
            numericCast(kvImagePrintDiagnosticsToConsole | kvImageNoAllocate),
            &convertError
        )
        
        guard convertError == kvImageNoError else {
            print("error converting image: \(convertError)")
            abort()
        }
        
        let convertedImage = convertedImageUnmanaged!.takeRetainedValue()
        // show the image – has vertical banding
        
        // write it to a temp file
        let tempBase = URL(fileURLWithPath:NSTemporaryDirectory())
        let tempDir = tempBase.appendingPathComponent(UUID().uuidString, isDirectory: true)
        try FileManager.default.createDirectory(at: tempDir, withIntermediateDirectories: true, attributes: nil)
        
        let targetURL = tempDir.appendingPathComponent("result.tiff")
        try NSImage(cgImage: convertedImage, size: .zero).tiffRepresentation?.write(to: targetURL)
        print("Result image written to directory \(tempDir)")
        
        

        Environment:

         

        • Xcode 11.3 (11C29)
        • macOS 10.15.2 (19C57)

         

        In case anybody from Apple is watching, this is filed as FB7497362 and also contains the Playground bundle along with sample input and output images.