GIF错误地导出最后一行像素

Question

我正在CGImageDestinationAddImage一个快速的项目中使用从照片创建动画GIF文件.这一切都很好,除了最终GIF中的底行像素总是相同的(这些是我添加的第一张照片中的像素).照片大小相同(600x600像素).

我注意到这发生在运行iOS 9.3.5的iPad 2上,但它在运行iOS 10.2的iPad Pro 12.9上工作正常.所以这可能与32位与64位或iOS版本有关.

有谁知道这是一个已知问题,还是我做错了什么？我在下面粘贴了我的代码.

// Load photos
var photos = [Data]()

for index in 1...5 {
    if let imageDataURL = Bundle.main.url(forResource: "photo_\(index)", withExtension: "jpg"),
        let data = try? Data(contentsOf: imageDataURL, options: []) {

        photos.append(data)
    }
}

// Create the GIF

let temporaryDirectory = NSTemporaryDirectory()
let url = URL(fileURLWithPath: temporaryDirectory).appendingPathComponent("slideshow.gif")

guard let destination = CGImageDestinationCreateWithURL(url as CFURL, kUTTypeGIF, photos.count, nil) else {
    return
}

// Repeat forever by setting the loop count to 0
let gifFileProperties = [kCGImagePropertyGIFLoopCount as String: 0]
let fileProperties = [kCGImagePropertyGIFDictionary as String: gifFileProperties]

CGImageDestinationSetProperties(destination, fileProperties as CFDictionary)

// Set the frame delay to 2 seconds
let gifFrameProperties = [kCGImagePropertyGIFDelayTime as String: 2.0]
let frameProperties = [kCGImagePropertyGIFDictionary as String: gifFrameProperties]

for photo in photos {

    if let imageProvider = CGDataProvider(data: photo as CFData),
        let cgimage = CGImage(jpegDataProviderSource: imageProvider, decode: nil, shouldInterpolate: true, intent: .defaultIntent) {
        CGImageDestinationAddImage(destination, cgimage, frameProperties as CFDictionary)
    }
}

guard CGImageDestinationFinalize(destination) else {
    return
}

// Get the gif data.
let gifData = try? Data(contentsOf: url)