将 UIImage 转换为灰度以保持图像质量
Convert UIImage to grayscale keeping image quality
我有此扩展（在 obj-c 中找到，我将其转换为 Swift3）以获得相同的 UIImage 但灰度化：
public func getGrayScale() -> UIImage
{
let imgRect = CGRect(x: 0, y: 0, width: width, height: height)
let colorSpace = CGColorSpaceCreateDeviceGray()
let context = CGContext(data: nil, width: Int(width), height: Int(height), bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace, bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue).rawValue)
context?.draw(self.cgImage!, in: imgRect)
let imageRef = context!.makeImage()
let newImg = UIImage(cgImage: imageRef!)
return newImg
}
我可以看到灰色图像，但它的质量很差...我唯一能看到与质量相关的是上下文构造函数中的 bitsPerComponent: 8。但是看看 Apple 的文档，我得到的是：
显示iOS只支持8bpc...所以为什么我不能提高质量？
我会使用 CoreImage，它可能会保持质量。
func convertImageToBW(image:UIImage) -> UIImage {
let filter = CIFilter(name: "CIPhotoEffectMono")
// convert UIImage to CIImage and set as input
let ciInput = CIImage(image: image)
filter?.setValue(ciInput, forKey: "inputImage")
// get output CIImage, render as CGImage first to retain proper UIImage scale
let ciOutput = filter?.outputImage
let ciContext = CIContext()
let cgImage = ciContext.createCGImage(ciOutput!, from: (ciOutput?.extent)!)
return UIImage(cgImage: cgImage!)
}
根据您使用此代码的方式，出于性能原因，您可能希望在其外部创建 CIContext。
试试下面的代码：
注意： 代码已更新，错误已修复...
- 代码在 Swift 3.
中测试
originalImage 是您要转换的图像。
答案一：
var context = CIContext(options: nil)
更新： CIContext 是处理 rendering 的核心图像组件，核心图像的所有处理都在 CIContext.这有点类似于 Core Graphics 或 OpenGL context。有关更多信息，请参阅 Apple Doc.
func Noir() {
let currentFilter = CIFilter(name: "CIPhotoEffectNoir")
currentFilter!.setValue(CIImage(image: originalImage.image!), forKey: kCIInputImageKey)
let output = currentFilter!.outputImage
let cgimg = context.createCGImage(output!,from: output!.extent)
let processedImage = UIImage(cgImage: cgimg!)
originalImage.image = processedImage
}
您还需要考虑以下可以产生类似效果的过滤器
CIPhotoEffectMonoCIPhotoEffectTonal
答案 1 的输出：
答案 2 的输出：
改进的答案：
答案 2： 在应用 coreImage 过滤器之前自动调整输入图像
var context = CIContext(options: nil)
func Noir() {
//Auto Adjustment to Input Image
var inputImage = CIImage(image: originalImage.image!)
let options:[String : AnyObject] = [CIDetectorImageOrientation:1 as AnyObject]
let filters = inputImage!.autoAdjustmentFilters(options: options)
for filter: CIFilter in filters {
filter.setValue(inputImage, forKey: kCIInputImageKey)
inputImage = filter.outputImage
}
let cgImage = context.createCGImage(inputImage!, from: inputImage!.extent)
self.originalImage.image = UIImage(cgImage: cgImage!)
//Apply noir Filter
let currentFilter = CIFilter(name: "CIPhotoEffectTonal")
currentFilter!.setValue(CIImage(image: UIImage(cgImage: cgImage!)), forKey: kCIInputImageKey)
let output = currentFilter!.outputImage
let cgimg = context.createCGImage(output!, from: output!.extent)
let processedImage = UIImage(cgImage: cgimg!)
originalImage.image = processedImage
}
注意： 如果你想看到更好的 result.You 应该在 real device 而不是 simulator 上测试你的代码.. .
这是 objective c 中的一个类别。请注意，至关重要的是，此版本考虑了规模。
- (UIImage *)grayscaleImage{
return [self imageWithCIFilter:@"CIPhotoEffectMono"];
}
- (UIImage *)imageWithCIFilter:(NSString*)filterName{
CIImage *unfiltered = [CIImage imageWithCGImage:self.CGImage];
CIFilter *filter = [CIFilter filterWithName:filterName];
[filter setValue:unfiltered forKey:kCIInputImageKey];
CIImage *filtered = [filter outputImage];
CIContext *context = [CIContext contextWithOptions:nil];
CGImageRef cgimage = [context createCGImage:filtered fromRect:CGRectMake(0, 0, self.size.width*self.scale, self.size.height*self.scale)];
// Do not use initWithCIImage because that renders the filter each time the image is displayed. This causes slow scrolling in tableviews.
UIImage *image = [[UIImage alloc] initWithCGImage:cgimage scale:self.scale orientation:self.imageOrientation];
CGImageRelease(cgimage);
return image;
}
根据 Joe 的回答，我们很容易将 Original 转换为 B&W 。但是回到原始图像参考这些代码：
var context = CIContext(options: nil)
var startingImage : UIImage = UIImage()
func Noir() {
startingImage = imgView.image!
var inputImage = CIImage(image: imgView.image!)!
let options:[String : AnyObject] = [CIDetectorImageOrientation:1 as AnyObject]
let filters = inputImage.autoAdjustmentFilters(options: options)
for filter: CIFilter in filters {
filter.setValue(inputImage, forKey: kCIInputImageKey)
inputImage = filter.outputImage!
}
let cgImage = context.createCGImage(inputImage, from: inputImage.extent)
self.imgView.image = UIImage(cgImage: cgImage!)
//Filter Logic
let currentFilter = CIFilter(name: "CIPhotoEffectNoir")
currentFilter!.setValue(CIImage(image: UIImage(cgImage: cgImage!)), forKey: kCIInputImageKey)
let output = currentFilter!.outputImage
let cgimg = context.createCGImage(output!, from: output!.extent)
let processedImage = UIImage(cgImage: cgimg!)
imgView.image = processedImage
}
func Original(){
imgView.image = startingImage
}
Joe 的回答作为 Swift 4 的 UIImage 扩展，可以在不同的尺度下正常工作：
extension UIImage {
var noir: UIImage {
let context = CIContext(options: nil)
let currentFilter = CIFilter(name: "CIPhotoEffectNoir")!
currentFilter.setValue(CIImage(image: self), forKey: kCIInputImageKey)
let output = currentFilter.outputImage!
let cgImage = context.createCGImage(output, from: output.extent)!
let processedImage = UIImage(cgImage: cgImage, scale: scale, orientation: imageOrientation)
return processedImage
}
}
一个 Swift 4.0 扩展 returns 一个可选的 UIImage 以避免任何潜在的碰撞。
import UIKit
extension UIImage {
var noir: UIImage? {
let context = CIContext(options: nil)
guard let currentFilter = CIFilter(name: "CIPhotoEffectNoir") else { return nil }
currentFilter.setValue(CIImage(image: self), forKey: kCIInputImageKey)
if let output = currentFilter.outputImage,
let cgImage = context.createCGImage(output, from: output.extent) {
return UIImage(cgImage: cgImage, scale: scale, orientation: imageOrientation)
}
return nil
}
}
要使用这个：
let image = UIImage(...)
let noirImage = image.noir // noirImage is an optional UIImage (UIImage?)
以上所有解决方案都依赖于 CIImage，而 UIImage 通常将 CGImage 作为其基础图像，而不是 CIImage。所以这意味着你必须在开始时将底层图像转换为 CIImage，然后在最后将其转换回 CGImage（如果不这样做，则使用 [=14 构建 UIImage =] 会有效地为你做到这一点）。
虽然对于许多用例来说可能没问题，但 CGImage 和 CIImage 之间的转换不是免费的：它可能很慢，并且在转换时会产生很大的内存峰值。
所以我想提一个完全不同的解决方案，它不需要来回转换图像。它正在使用 Accelerate, and it's perfectly described by Apple here.
这是一个演示这两种方法的 playground 示例。
import UIKit
import Accelerate
extension CIImage {
func toGrayscale() -> CIImage? {
guard let output = CIFilter(name: "CIPhotoEffectNoir", parameters: [kCIInputImageKey: self])?.outputImage else {
return nil
}
return output
}
}
extension CGImage {
func toGrayscale() -> CGImage {
guard let format = vImage_CGImageFormat(cgImage: self),
// The source image bufffer
var sourceBuffer = try? vImage_Buffer(
cgImage: self,
format: format
),
// The 1-channel, 8-bit vImage buffer used as the operation destination.
var destinationBuffer = try? vImage_Buffer(
width: Int(sourceBuffer.width),
height: Int(sourceBuffer.height),
bitsPerPixel: 8
) else {
return self
}
// Declare the three coefficients that model the eye's sensitivity
// to color.
let redCoefficient: Float = 0.2126
let greenCoefficient: Float = 0.7152
let blueCoefficient: Float = 0.0722
// Create a 1D matrix containing the three luma coefficients that
// specify the color-to-grayscale conversion.
let divisor: Int32 = 0x1000
let fDivisor = Float(divisor)
var coefficientsMatrix = [
Int16(redCoefficient * fDivisor),
Int16(greenCoefficient * fDivisor),
Int16(blueCoefficient * fDivisor)
]
// Use the matrix of coefficients to compute the scalar luminance by
// returning the dot product of each RGB pixel and the coefficients
// matrix.
let preBias: [Int16] = [0, 0, 0, 0]
let postBias: Int32 = 0
vImageMatrixMultiply_ARGB8888ToPlanar8(
&sourceBuffer,
&destinationBuffer,
&coefficientsMatrix,
divisor,
preBias,
postBias,
vImage_Flags(kvImageNoFlags)
)
// Create a 1-channel, 8-bit grayscale format that's used to
// generate a displayable image.
guard let monoFormat = vImage_CGImageFormat(
bitsPerComponent: 8,
bitsPerPixel: 8,
colorSpace: CGColorSpaceCreateDeviceGray(),
bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue),
renderingIntent: .defaultIntent
) else {
return self
}
// Create a Core Graphics image from the grayscale destination buffer.
guard let result = try? destinationBuffer.createCGImage(format: monoFormat) else {
return self
}
return result
}
}
为了测试，我使用了完整尺寸的 this 图片。
let start = Date()
var prev = start.timeIntervalSinceNow * -1
func info(_ id: String) {
print("\(id)\t: \(start.timeIntervalSinceNow * -1 - prev)")
prev = start.timeIntervalSinceNow * -1
}
info("started")
let original = UIImage(named: "Golden_Gate_Bridge_2021.jpg")!
info("loaded UIImage(named)")
let cgImage = original.cgImage!
info("original.cgImage")
let cgImageToGreyscale = cgImage.toGrayscale()
info("cgImage.toGrayscale()")
let uiImageFromCGImage = UIImage(cgImage: cgImageToGreyscale, scale: original.scale, orientation: original.imageOrientation)
info("UIImage(cgImage)")
let ciImage = CIImage(image: original)!
info("CIImage(image: original)!")
let ciImageToGreyscale = ciImage.toGrayscale()!
info("ciImage.toGrayscale()")
let uiImageFromCIImage = UIImage(ciImage: ciImageToGreyscale, scale: original.scale, orientation: original.imageOrientation)
info("UIImage(ciImage)")
结果（秒）
CGImage 方法大约需要 1 秒。总计：
original.cgImage : 0.5257829427719116
cgImage.toGrayscale() : 0.46222901344299316
UIImage(cgImage) : 0.1819549798965454
CIImage 方法大约需要 7 秒。总计：
CIImage(image: original)! : 0.6055610179901123
ciImage.toGrayscale() : 4.969912052154541
UIImage(ciImage) : 2.395193934440613
将图像以 JPEG 格式保存到磁盘时，使用 CGImage 创建的图像也比使用 CIImage 创建的图像小 3 倍（5 MB 对 17 MB）。两张图片的质量都很好。这是一个符合 SO 限制的小版本：
我有此扩展（在 obj-c 中找到，我将其转换为 Swift3）以获得相同的 UIImage 但灰度化：
public func getGrayScale() -> UIImage
{
let imgRect = CGRect(x: 0, y: 0, width: width, height: height)
let colorSpace = CGColorSpaceCreateDeviceGray()
let context = CGContext(data: nil, width: Int(width), height: Int(height), bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace, bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue).rawValue)
context?.draw(self.cgImage!, in: imgRect)
let imageRef = context!.makeImage()
let newImg = UIImage(cgImage: imageRef!)
return newImg
}
我可以看到灰色图像，但它的质量很差...我唯一能看到与质量相关的是上下文构造函数中的 bitsPerComponent: 8。但是看看 Apple 的文档，我得到的是：
显示iOS只支持8bpc...所以为什么我不能提高质量？
我会使用 CoreImage，它可能会保持质量。
func convertImageToBW(image:UIImage) -> UIImage {
let filter = CIFilter(name: "CIPhotoEffectMono")
// convert UIImage to CIImage and set as input
let ciInput = CIImage(image: image)
filter?.setValue(ciInput, forKey: "inputImage")
// get output CIImage, render as CGImage first to retain proper UIImage scale
let ciOutput = filter?.outputImage
let ciContext = CIContext()
let cgImage = ciContext.createCGImage(ciOutput!, from: (ciOutput?.extent)!)
return UIImage(cgImage: cgImage!)
}
根据您使用此代码的方式，出于性能原因，您可能希望在其外部创建 CIContext。
试试下面的代码：
注意： 代码已更新，错误已修复...
- 代码在 Swift 3. 中测试
originalImage是您要转换的图像。
答案一：
var context = CIContext(options: nil)
更新： CIContext 是处理 rendering 的核心图像组件，核心图像的所有处理都在 CIContext.这有点类似于 Core Graphics 或 OpenGL context。有关更多信息，请参阅 Apple Doc.
func Noir() {
let currentFilter = CIFilter(name: "CIPhotoEffectNoir")
currentFilter!.setValue(CIImage(image: originalImage.image!), forKey: kCIInputImageKey)
let output = currentFilter!.outputImage
let cgimg = context.createCGImage(output!,from: output!.extent)
let processedImage = UIImage(cgImage: cgimg!)
originalImage.image = processedImage
}
您还需要考虑以下可以产生类似效果的过滤器
CIPhotoEffectMonoCIPhotoEffectTonal
答案 1 的输出：
答案 2 的输出：
改进的答案：
答案 2： 在应用 coreImage 过滤器之前自动调整输入图像
var context = CIContext(options: nil)
func Noir() {
//Auto Adjustment to Input Image
var inputImage = CIImage(image: originalImage.image!)
let options:[String : AnyObject] = [CIDetectorImageOrientation:1 as AnyObject]
let filters = inputImage!.autoAdjustmentFilters(options: options)
for filter: CIFilter in filters {
filter.setValue(inputImage, forKey: kCIInputImageKey)
inputImage = filter.outputImage
}
let cgImage = context.createCGImage(inputImage!, from: inputImage!.extent)
self.originalImage.image = UIImage(cgImage: cgImage!)
//Apply noir Filter
let currentFilter = CIFilter(name: "CIPhotoEffectTonal")
currentFilter!.setValue(CIImage(image: UIImage(cgImage: cgImage!)), forKey: kCIInputImageKey)
let output = currentFilter!.outputImage
let cgimg = context.createCGImage(output!, from: output!.extent)
let processedImage = UIImage(cgImage: cgimg!)
originalImage.image = processedImage
}
注意： 如果你想看到更好的 result.You 应该在 real device 而不是 simulator 上测试你的代码.. .
这是 objective c 中的一个类别。请注意，至关重要的是，此版本考虑了规模。
- (UIImage *)grayscaleImage{
return [self imageWithCIFilter:@"CIPhotoEffectMono"];
}
- (UIImage *)imageWithCIFilter:(NSString*)filterName{
CIImage *unfiltered = [CIImage imageWithCGImage:self.CGImage];
CIFilter *filter = [CIFilter filterWithName:filterName];
[filter setValue:unfiltered forKey:kCIInputImageKey];
CIImage *filtered = [filter outputImage];
CIContext *context = [CIContext contextWithOptions:nil];
CGImageRef cgimage = [context createCGImage:filtered fromRect:CGRectMake(0, 0, self.size.width*self.scale, self.size.height*self.scale)];
// Do not use initWithCIImage because that renders the filter each time the image is displayed. This causes slow scrolling in tableviews.
UIImage *image = [[UIImage alloc] initWithCGImage:cgimage scale:self.scale orientation:self.imageOrientation];
CGImageRelease(cgimage);
return image;
}
根据 Joe 的回答，我们很容易将 Original 转换为 B&W 。但是回到原始图像参考这些代码：
var context = CIContext(options: nil)
var startingImage : UIImage = UIImage()
func Noir() {
startingImage = imgView.image!
var inputImage = CIImage(image: imgView.image!)!
let options:[String : AnyObject] = [CIDetectorImageOrientation:1 as AnyObject]
let filters = inputImage.autoAdjustmentFilters(options: options)
for filter: CIFilter in filters {
filter.setValue(inputImage, forKey: kCIInputImageKey)
inputImage = filter.outputImage!
}
let cgImage = context.createCGImage(inputImage, from: inputImage.extent)
self.imgView.image = UIImage(cgImage: cgImage!)
//Filter Logic
let currentFilter = CIFilter(name: "CIPhotoEffectNoir")
currentFilter!.setValue(CIImage(image: UIImage(cgImage: cgImage!)), forKey: kCIInputImageKey)
let output = currentFilter!.outputImage
let cgimg = context.createCGImage(output!, from: output!.extent)
let processedImage = UIImage(cgImage: cgimg!)
imgView.image = processedImage
}
func Original(){
imgView.image = startingImage
}
Joe 的回答作为 Swift 4 的 UIImage 扩展，可以在不同的尺度下正常工作：
extension UIImage {
var noir: UIImage {
let context = CIContext(options: nil)
let currentFilter = CIFilter(name: "CIPhotoEffectNoir")!
currentFilter.setValue(CIImage(image: self), forKey: kCIInputImageKey)
let output = currentFilter.outputImage!
let cgImage = context.createCGImage(output, from: output.extent)!
let processedImage = UIImage(cgImage: cgImage, scale: scale, orientation: imageOrientation)
return processedImage
}
}
一个 Swift 4.0 扩展 returns 一个可选的 UIImage 以避免任何潜在的碰撞。
import UIKit
extension UIImage {
var noir: UIImage? {
let context = CIContext(options: nil)
guard let currentFilter = CIFilter(name: "CIPhotoEffectNoir") else { return nil }
currentFilter.setValue(CIImage(image: self), forKey: kCIInputImageKey)
if let output = currentFilter.outputImage,
let cgImage = context.createCGImage(output, from: output.extent) {
return UIImage(cgImage: cgImage, scale: scale, orientation: imageOrientation)
}
return nil
}
}
要使用这个：
let image = UIImage(...)
let noirImage = image.noir // noirImage is an optional UIImage (UIImage?)
以上所有解决方案都依赖于 CIImage，而 UIImage 通常将 CGImage 作为其基础图像，而不是 CIImage。所以这意味着你必须在开始时将底层图像转换为 CIImage，然后在最后将其转换回 CGImage（如果不这样做，则使用 [=14 构建 UIImage =] 会有效地为你做到这一点）。
虽然对于许多用例来说可能没问题，但 CGImage 和 CIImage 之间的转换不是免费的：它可能很慢，并且在转换时会产生很大的内存峰值。
所以我想提一个完全不同的解决方案，它不需要来回转换图像。它正在使用 Accelerate, and it's perfectly described by Apple here.
这是一个演示这两种方法的 playground 示例。
import UIKit
import Accelerate
extension CIImage {
func toGrayscale() -> CIImage? {
guard let output = CIFilter(name: "CIPhotoEffectNoir", parameters: [kCIInputImageKey: self])?.outputImage else {
return nil
}
return output
}
}
extension CGImage {
func toGrayscale() -> CGImage {
guard let format = vImage_CGImageFormat(cgImage: self),
// The source image bufffer
var sourceBuffer = try? vImage_Buffer(
cgImage: self,
format: format
),
// The 1-channel, 8-bit vImage buffer used as the operation destination.
var destinationBuffer = try? vImage_Buffer(
width: Int(sourceBuffer.width),
height: Int(sourceBuffer.height),
bitsPerPixel: 8
) else {
return self
}
// Declare the three coefficients that model the eye's sensitivity
// to color.
let redCoefficient: Float = 0.2126
let greenCoefficient: Float = 0.7152
let blueCoefficient: Float = 0.0722
// Create a 1D matrix containing the three luma coefficients that
// specify the color-to-grayscale conversion.
let divisor: Int32 = 0x1000
let fDivisor = Float(divisor)
var coefficientsMatrix = [
Int16(redCoefficient * fDivisor),
Int16(greenCoefficient * fDivisor),
Int16(blueCoefficient * fDivisor)
]
// Use the matrix of coefficients to compute the scalar luminance by
// returning the dot product of each RGB pixel and the coefficients
// matrix.
let preBias: [Int16] = [0, 0, 0, 0]
let postBias: Int32 = 0
vImageMatrixMultiply_ARGB8888ToPlanar8(
&sourceBuffer,
&destinationBuffer,
&coefficientsMatrix,
divisor,
preBias,
postBias,
vImage_Flags(kvImageNoFlags)
)
// Create a 1-channel, 8-bit grayscale format that's used to
// generate a displayable image.
guard let monoFormat = vImage_CGImageFormat(
bitsPerComponent: 8,
bitsPerPixel: 8,
colorSpace: CGColorSpaceCreateDeviceGray(),
bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue),
renderingIntent: .defaultIntent
) else {
return self
}
// Create a Core Graphics image from the grayscale destination buffer.
guard let result = try? destinationBuffer.createCGImage(format: monoFormat) else {
return self
}
return result
}
}
为了测试，我使用了完整尺寸的 this 图片。
let start = Date()
var prev = start.timeIntervalSinceNow * -1
func info(_ id: String) {
print("\(id)\t: \(start.timeIntervalSinceNow * -1 - prev)")
prev = start.timeIntervalSinceNow * -1
}
info("started")
let original = UIImage(named: "Golden_Gate_Bridge_2021.jpg")!
info("loaded UIImage(named)")
let cgImage = original.cgImage!
info("original.cgImage")
let cgImageToGreyscale = cgImage.toGrayscale()
info("cgImage.toGrayscale()")
let uiImageFromCGImage = UIImage(cgImage: cgImageToGreyscale, scale: original.scale, orientation: original.imageOrientation)
info("UIImage(cgImage)")
let ciImage = CIImage(image: original)!
info("CIImage(image: original)!")
let ciImageToGreyscale = ciImage.toGrayscale()!
info("ciImage.toGrayscale()")
let uiImageFromCIImage = UIImage(ciImage: ciImageToGreyscale, scale: original.scale, orientation: original.imageOrientation)
info("UIImage(ciImage)")
结果（秒）
CGImage 方法大约需要 1 秒。总计：
original.cgImage : 0.5257829427719116
cgImage.toGrayscale() : 0.46222901344299316
UIImage(cgImage) : 0.1819549798965454
CIImage 方法大约需要 7 秒。总计：
CIImage(image: original)! : 0.6055610179901123
ciImage.toGrayscale() : 4.969912052154541
UIImage(ciImage) : 2.395193934440613
将图像以 JPEG 格式保存到磁盘时，使用 CGImage 创建的图像也比使用 CIImage 创建的图像小 3 倍（5 MB 对 17 MB）。两张图片的质量都很好。这是一个符合 SO 限制的小版本：