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保存动画Gif时iOS颜色不正确

animated-gif core-graphics uiimage swift ios

Skyler Lauren · 技术社区 · 8 年前

@1x 32 x 32

@10 x 320 x 320

@26 x 832 x 832

这是我用来创建gif的代码。。。

var kFrameCount = 0

for smdLayer in drawingToUse!.layers{
    if !smdLayer.hidden {
        kFrameCount += 1
    }
}

let loopingProperty = [String(kCGImagePropertyGIFLoopCount): 0]
let fileProperties: [String: AnyObject] = [String(kCGImagePropertyGIFDictionary): loopingProperty as AnyObject];

let frameProperty = [String(kCGImagePropertyGIFDelayTime):  Float(speedLabel.text!)!]
let frameProperties: [String: AnyObject] = [String(kCGImagePropertyGIFDictionary): frameProperty as AnyObject];

let documentsDirectoryPath = "file://\(NSTemporaryDirectory())"

if let documentsDirectoryURL = URL(string: documentsDirectoryPath){

    let fileURL = documentsDirectoryURL.appendingPathComponent("\(drawing.name)\(getScaleString()).gif")
    let destination = CGImageDestinationCreateWithURL(fileURL as CFURL, kUTTypeGIF, kFrameCount, nil)!

    CGImageDestinationSetProperties(destination, fileProperties as CFDictionary);

    for smdLayer in drawingToUse!.layers{

        if !smdLayer.hidden{

            let image = UIImage(smdLayer: smdLayer, alphaBlend: useAlphaLayers, backgroundColor: backgroundColorButton.backgroundColor!, scale: scale)
            CGImageDestinationAddImage(destination, image.cgImage!, frameProperties as CFDictionary)
        }
    }

    if (!CGImageDestinationFinalize(destination)) {
        print("failed to finalize image destination")
    }        
}

在我打电话之前,我已经输入了一个断点 CGImageDestinationAddImage(destination, image.cgImage!, frameProperties as CFDictionary) 图像非常精细,颜色正确。我希望有人知道我错过了什么。

这是一个示例项目。请注意,尽管预览中没有设置动画,但它正在保存动画gif,我在控制台中注销了图像的位置。

https://www.dropbox.com/s/pb52awaj8w3amyz/gifTest.zip?dl=0

2 回复 | 直到 8 年前

Sulthan 8 年前

let loopingProperty: [String: AnyObject] = [
    kCGImagePropertyGIFLoopCount as String: 0 as NSNumber,
    kCGImagePropertyGIFHasGlobalColorMap as String: false as NSNumber
]

注意,与PNG不同,GIF只能使用256色贴图,没有透明度。对于动画GIF,可以是全局或每帧颜色贴图。

不幸的是,核心图形不允许我们直接使用颜色映射,因此在GIF编码时会自动进行颜色转换。

似乎只需要关闭全局颜色贴图。还可以使用为每个帧显式设置颜色映射 kCGImagePropertyGIFImageColorMap

由于这似乎不可靠,让我们为每个帧创建自己的颜色图:

struct Color : Hashable {
    let red: UInt8
    let green: UInt8
    let blue: UInt8

    var hashValue: Int {
        return Int(red) + Int(green) + Int(blue)
    }

    public static func ==(lhs: Color, rhs: Color) -> Bool {
        return [lhs.red, lhs.green, lhs.blue] == [rhs.red, rhs.green, rhs.blue]
    }
}

struct ColorMap {
    var colors = Set<Color>()

    var exported: Data {
        let data = Array(colors)
            .map { [$0.red, $0.green, $0.blue] }
            .joined()

        return Data(bytes: Array(data))
    }
}

现在,让我们更新我们的方法:

func getScaledImages(_ scale: Int) -> [(CGImage, ColorMap)] {
    var sourceImages = [UIImage]()
    var result: [(CGImage, ColorMap)] = []

...

    var colorMap = ColorMap()
    let pixelData = imageRef.dataProvider!.data
    let rawData: UnsafePointer<UInt8> = CFDataGetBytePtr(pixelData)

    for y in 0 ..< imageRef.height{
        for _ in 0 ..< scale {
            for x in 0 ..< imageRef.width{
                 let offset = y * imageRef.width * 4 + x * 4

                 let color = Color(red: rawData[offset], green: rawData[offset + 1], blue: rawData[offset + 2])
                 colorMap.colors.insert(color)

                 for _ in 0 ..< scale {
                     pixelPointer[byteIndex] = rawData[offset]
                     pixelPointer[byteIndex+1] = rawData[offset+1]
                     pixelPointer[byteIndex+2] = rawData[offset+2]
                     pixelPointer[byteIndex+3] = rawData[offset+3]

                     byteIndex += 4
                }
            }
        }
    }

    let cgImage = context.makeImage()!
    result.append((cgImage, colorMap))

和

func createAnimatedGifFromImages(_ images: [(CGImage, ColorMap)]) -> URL {

...

    for (image, colorMap) in images {
        let frameProperties: [String: AnyObject] = [
            String(kCGImagePropertyGIFDelayTime): 0.2 as NSNumber,
            String(kCGImagePropertyGIFImageColorMap): colorMap.exported as NSData
        ]

        let properties: [String: AnyObject] = [
            String(kCGImagePropertyGIFDictionary): frameProperties as AnyObject
        ];

        CGImageDestinationAddImage(destination, image, properties as CFDictionary);
    }

Marc Palmer 8 年前

接下来,这里有一些关于正在发生的量化失败的更多背景。如果通过运行GIF输出 imagemagick 要为具有全局颜色图和每帧颜色图的版本提取调色板,需要深入了解问题的根源:

$ convert test.gif -format %c -depth 8 histogram:info:- 28392: ( 0, 0, 0,255) #000000FF black 240656: ( 71,162, 58,255) #47A23AFF srgba(71,162,58,1) 422500: (147,221,253,255) #93DDFDFF srgba(147,221,253,1) 676: (255,255,255,255) #FFFFFFFF white 2704: ( 71,162, 58,255) #47A23AFF srgba(71,162,58,1) 676: (147,221,253,255) #93DDFDFF srgba(147,221,253,1) 2704: ( 71,162, 58,255) #47A23AFF srgba(71,162,58,1) 676: (147,221,253,255) #93DDFDFF srgba(147,221,253,1) 2704: ( 71,162, 58,255) #47A23AFF srgba(71,162,58,1) 676: (147,221,253,255) #93DDFDFF srgba(147,221,253,1)

具有每帧彩色地图的版本: $ convert test.gif -format %c -depth 8 histogram:info:- 28392: ( 0, 0, 0,255) #000000FF black 237952: ( 71,163, 59,255) #47A33BFF srgba(71,163,59,1) 2704: (113, 78, 0,255) #714E00FF srgba(113,78,0,1) 421824: (147,221,253,255) #93DDFDFF srgba(147,221,253,1) 676: (246, 81,249,255) #F651F9FF srgba(246,81,249,1) 676: (255,255,255,255) #FFFFFFFF white 28392: ( 0, 0, 0,255) #000000FF black 237952: ( 71,163, 59,255) #47A33BFF srgba(71,163,59,1) 2704: (113, 78, 0,255) #714E00FF srgba(113,78,0,1) 421824: (147,221,253,255) #93DDFDFF srgba(147,221,253,1) 676: (246, 81,249,255) #F651F9FF srgba(246,81,249,1) 676: (255,255,255,255) #FFFFFFFF white 28392: ( 0, 0, 0,255) #000000FF black 237952: ( 71,163, 59,255) #47A33BFF srgba(71,163,59,1) 2704: (113, 78, 0,255) #714E00FF srgba(113,78,0,1) 421824: (147,221,253,255) #93DDFDFF srgba(147,221,253,1) 676: (246, 81,249,255) #F651F9FF srgba(246,81,249,1) 676: (255,255,255,255) #FFFFFFFF white 28392: ( 0, 0, 0,255) #000000FF black 237952: ( 71,163, 59,255) #47A33BFF srgba(71,163,59,1) 2704: (113, 78, 0,255) #714E00FF srgba(113,78,0,1) 421824: (147,221,253,255) #93DDFDFF srgba(147,221,253,1) 676: (246, 81,249,255) #F651F9FF srgba(246,81,249,1) 676: (255,255,255,255) #FFFFFFFF white

246 和 113

多种颜色。这就指出了ImageIO中调色板量化的一个非常明显的错误。在有限的调色板中不应有重复条目。