UIImageJPEGRepresentation返回nil

Question

我使用CIFilters将图像转换为灰度并应用一些图像处理效果。在UIImageView中显示输出有效;图像显示并已按预期进行修改。

但是，每次调用UIImageJPEGRepresentation似乎都不会返回任何数据。它永远不会奏效。 使用原始彩色图像调用UIImageJPEGRepresentation工作正常。

这里发生了什么？为什么显示图像时jpeg转换失败？不抛出任何异常（设置异常断点，未命中）并且控制台中不显示任何消息。

let _cicontext = CIContext(options:nil)

// Set up grayscale and blur filters:
let grayIze = CIFilter(name: "CIColorControls")
let blur = CIFilter(name: "CIGaussianBlur")
grayIze.setValue(0, forKey:kCIInputSaturationKey)
grayIze.setValue(0.5, forKey: kCIInputBrightnessKey)
blur.setValue(4, forKey: kCIInputRadiusKey)

// Go!
let originalImage = CIImage(image: colorImageThatDefinitelyExists)
grayIze.setValue(originalImage, forKey: kCIInputImageKey)
blur.setValue(grayIze.outputImage, forKey: kCIInputImageKey)

let output = UIImage(CIImage: blur.outputImage)
let imageData: NSData? = UIImageJPEGRepresentation(output, 1.0) // Returns nil!?

修改：以下是基于Arbitur's answer的工作代码：

// Define an image context at the class level, which will only be initialized once:
static let imageContext = CIContext(options:nil)

// And here's the updated code in a function:
class func convertToGrayscale(image: UIImage)->UIImage?
{
    // Set up grayscale and blur filters:
    let filter1_grayIze = CIFilter(name: "CIColorControls")
    let filter2_blur = CIFilter(name: "CIGaussianBlur")
    filter1_grayIze.setValue(0, forKey:kCIInputSaturationKey)
    filter1_grayIze.setValue(0.5, forKey: kCIInputBrightnessKey)
    filter2_blur.setValue(4, forKey: kCIInputRadiusKey)

    // Go!
    let originalImage = CIImage(image: image)
    filter1_grayIze.setValue(originalImage, forKey: kCIInputImageKey)
    filter2_blur.setValue(filter1_grayIze.outputImage, forKey: kCIInputImageKey)
    let outputCIImage = filter2_blur.outputImage

    let temp:CGImageRef = imageContext.createCGImage(outputCIImage, fromRect: outputCIImage.extent())
    let ret = UIImage(CGImage: temp)
    return ret
}

// And finally, the function call:
    if let grayImage = ProfileImage.convertToGrayscale(colorImage)
    {
        let imageData: NSData? = UIImageJPEGRepresentation(grayImage, 1.0)
    }

Answer 1

UIImageJPEGRepresentation似乎使用了CGImage的{​​{1}}属性。问题是，当您使用UIImage初始化UIImage时，该属性为CIImage。

我的解决方案是在nil调用之前添加以下块：

（上次更新Swift 4）

UIImageJPEGRepresentation

Answer 2

我之前遇到过CIImage的问题并解决这个问题，我用CIImage做了一个CGImage，然后用CGImage做了一个UIImage。

Answer 3

丹尼尔的答案很有效。在他的答案之下转换为在Swift4中使用。

<强> Swift4

<?php
    $array = [
        [
            "poulecode" => 495271,
            "teamcode" => 277986,
            "teamnaam" => "JO19-1 (0225 Onder 19 competitie (najaar)) )"
        ], [
            "poulecode" => 500027,
            "teamcode" => 277986,
            "teamnaam" => "JO19-1 (B3200 Zwaluwen jeugdbeker Onder 19 poule) )"
        ], [
            "poulecode" => 524572,
            "teamcode" => 277986,
            "teamnaam" => "JO19-1 (0227 Onder 19 competitie (voorjaar)) )"
        ]
    ];

    $keyword = "voorjaar";

    // You can filter your array using array_filter function
    $result = array_filter( $array, function( $item ) use ( $keyword ) {
        return strpos( $item['teamnaam'], $keyword ) !== false;
    });

    // and then map result to your datastructure
    $result_ids = array_map( function($item){
        return $item['poulecode'];
    }, $result  );

    var_dump($result_ids);