UIImageJPEGRepresentation returns 无
UIImageJPEGRepresentation returns nil
我正在使用 CIFilters 将图像转换为灰度并应用一些图像处理效果。在 UIImageView 中显示输出是可行的;图像显示并按预期进行了修改。
但是,每次调用 UIImageJPEGRepresentation 似乎都return 没有数据。它永远行不通。
使用原始彩色图像调用 UIImageJPEGRepresentation 效果很好。
这是怎么回事?为什么在显示图像时 jpeg 转换可能会失败?没有抛出异常(设置异常断点,它没有命中)并且没有消息出现在控制台中。
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!?
编辑:这是工作代码,基于:
// 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)
}
我之前在使用 CIImage 时遇到过问题,为了解决这个问题,我用 CIImage 制作了一个 CGImage,然后用 CGImage 制作了一个 UIImage。
UIImageJPEGRepresentation
好像用了CGImage
属性的UIImage
。问题是,当你用 CIImage
初始化 UIImage
时,属性 是 nil
.
我的解决方案是在 UIImageJPEGRepresentation
调用之前添加以下块:
最后更新Swift5.1
if image.cgImage == nil {
guard
let ciImage = image.ciImage,
let cgImage = CIContext(options: nil).createCGImage(ciImage, from: ciImage.extent)
else {
return nil
}
image = UIImage(cgImage: cgImage)
}
丹尼尔的回答很有效。在他的答案下方转换为在 Swift4 中使用。
Swift4
if image?.cgImage == nil {
guard let ciImage = image?.ciImage, let cgImage = CIContext(options: nil).createCGImage(ciImage, from: ciImage.extent) else { return }
image = UIImage(cgImage: cgImage)
}
我正在使用 CIFilters 将图像转换为灰度并应用一些图像处理效果。在 UIImageView 中显示输出是可行的;图像显示并按预期进行了修改。
但是,每次调用 UIImageJPEGRepresentation 似乎都return 没有数据。它永远行不通。 使用原始彩色图像调用 UIImageJPEGRepresentation 效果很好。
这是怎么回事?为什么在显示图像时 jpeg 转换可能会失败?没有抛出异常(设置异常断点,它没有命中)并且没有消息出现在控制台中。
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!?
编辑:这是工作代码,基于
// 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)
}
我之前在使用 CIImage 时遇到过问题,为了解决这个问题,我用 CIImage 制作了一个 CGImage,然后用 CGImage 制作了一个 UIImage。
UIImageJPEGRepresentation
好像用了CGImage
属性的UIImage
。问题是,当你用 CIImage
初始化 UIImage
时,属性 是 nil
.
我的解决方案是在 UIImageJPEGRepresentation
调用之前添加以下块:
最后更新Swift5.1
if image.cgImage == nil {
guard
let ciImage = image.ciImage,
let cgImage = CIContext(options: nil).createCGImage(ciImage, from: ciImage.extent)
else {
return nil
}
image = UIImage(cgImage: cgImage)
}
丹尼尔的回答很有效。在他的答案下方转换为在 Swift4 中使用。
Swift4
if image?.cgImage == nil {
guard let ciImage = image?.ciImage, let cgImage = CIContext(options: nil).createCGImage(ciImage, from: ciImage.extent) else { return }
image = UIImage(cgImage: cgImage)
}