如何调整 UIImage 的大小以减小上传图片的大小
How do I resize the UIImage to reduce upload image size
我一直在搜索 google，只遇到了减少 height/width 或一些如何通过 CoreImage 编辑 UIImage 外观的库。但是我还没有看到或找到一个库，post 解释了如何减小图像大小，所以当它上传时，它不是完整的图像大小。
到目前为止我有这个：
if image != nil {
//let data = NSData(data: UIImagePNGRepresentation(image))
let data = UIImagePNGRepresentation(image)
body.appendString("--\(boundary)\r\n")
body.appendString("Content-Disposition: form-data; name=\"image\"; filename=\"randomName\"\r\n")
body.appendString("Content-Type: image/png\r\n\r\n")
body.appendData(data)
body.appendString("\r\n")
}
它正在发送 12MB 的照片。我怎样才能将它减少到 1mb？谢谢！
如果您以 NSData 格式上传图片，请使用：
NSData *imageData = UIImageJPEGRepresentation(yourImage, floatValue);
yourImage 是你的 UIImage。
floatvalue是压缩值（0.0到1.0）
以上是将图片转JPEG.
PNG使用：UIImagePNGRepresentation
注意：以上代码在Objective-C中。请检查如何在 Swift.
中定义 NSData
这是我调整图片大小的方法。
-(UIImage *)resizeImage:(UIImage *)image
{
float actualHeight = image.size.height;
float actualWidth = image.size.width;
float maxHeight = 300.0;
float maxWidth = 400.0;
float imgRatio = actualWidth/actualHeight;
float maxRatio = maxWidth/maxHeight;
float compressionQuality = 0.5;//50 percent compression
if (actualHeight > maxHeight || actualWidth > maxWidth)
{
if(imgRatio < maxRatio)
{
//adjust width according to maxHeight
imgRatio = maxHeight / actualHeight;
actualWidth = imgRatio * actualWidth;
actualHeight = maxHeight;
}
else if(imgRatio > maxRatio)
{
//adjust height according to maxWidth
imgRatio = maxWidth / actualWidth;
actualHeight = imgRatio * actualHeight;
actualWidth = maxWidth;
}
else
{
actualHeight = maxHeight;
actualWidth = maxWidth;
}
}
CGRect rect = CGRectMake(0.0, 0.0, actualWidth, actualHeight);
UIGraphicsBeginImageContext(rect.size);
[image drawInRect:rect];
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
NSData *imageData = UIImageJPEGRepresentation(img, compressionQuality);
UIGraphicsEndImageContext();
return [UIImage imageWithData:imageData];
}
使用这个方法我的图像从 6.5 MB 减少到 104 KB。
Swift 4 码:
func resize(_ image: UIImage) -> UIImage {
var actualHeight = Float(image.size.height)
var actualWidth = Float(image.size.width)
let maxHeight: Float = 300.0
let maxWidth: Float = 400.0
var imgRatio: Float = actualWidth / actualHeight
let maxRatio: Float = maxWidth / maxHeight
let compressionQuality: Float = 0.5
//50 percent compression
if actualHeight > maxHeight || actualWidth > maxWidth {
if imgRatio < maxRatio {
//adjust width according to maxHeight
imgRatio = maxHeight / actualHeight
actualWidth = imgRatio * actualWidth
actualHeight = maxHeight
}
else if imgRatio > maxRatio {
//adjust height according to maxWidth
imgRatio = maxWidth / actualWidth
actualHeight = imgRatio * actualHeight
actualWidth = maxWidth
}
else {
actualHeight = maxHeight
actualWidth = maxWidth
}
}
let rect = CGRect(x: 0.0, y: 0.0, width: CGFloat(actualWidth), height: CGFloat(actualHeight))
UIGraphicsBeginImageContext(rect.size)
image.draw(in: rect)
let img = UIGraphicsGetImageFromCurrentImageContext()
let imageData = img?.jpegData(compressionQuality: CGFloat(compressionQuality))
UIGraphicsEndImageContext()
return UIImage(data: imageData!) ?? UIImage()
}
Xcode 9 • Swift 4 或更高版本
edit/update：对于iOS10+我们可以使用UIGraphicsImageRenderer。对于较旧的 Swift 语法检查编辑历史。
extension UIImage {
func resized(withPercentage percentage: CGFloat, isOpaque: Bool = true) -> UIImage? {
let canvas = CGSize(width: size.width * percentage, height: size.height * percentage)
let format = imageRendererFormat
format.opaque = isOpaque
return UIGraphicsImageRenderer(size: canvas, format: format).image {
_ in draw(in: CGRect(origin: .zero, size: canvas))
}
}
func resized(toWidth width: CGFloat, isOpaque: Bool = true) -> UIImage? {
let canvas = CGSize(width: width, height: CGFloat(ceil(width/size.width * size.height)))
let format = imageRendererFormat
format.opaque = isOpaque
return UIGraphicsImageRenderer(size: canvas, format: format).image {
_ in draw(in: CGRect(origin: .zero, size: canvas))
}
}
}
用法：
let image = UIImage(data: try! Data(contentsOf: URL(string:"http://i.stack.imgur.com/Xs4RX.jpg")!))!
let thumb1 = image.resized(withPercentage: 0.1)
let thumb2 = image.resized(toWidth: 72.0)
与 Leo Answer 相同，但对 SWIFT 2.0
进行了少量编辑
extension UIImage {
func resizeWithPercentage(percentage: CGFloat) -> UIImage? {
let imageView = UIImageView(frame: CGRect(origin: .zero, size: CGSize(width: size.width * percentage, height: size.height * percentage)))
imageView.contentMode = .ScaleAspectFit
imageView.image = self
UIGraphicsBeginImageContextWithOptions(imageView.bounds.size, false, scale)
guard let context = UIGraphicsGetCurrentContext() else { return nil }
imageView.layer.renderInContext(context)
guard let result = UIGraphicsGetImageFromCurrentImageContext() else { return nil }
UIGraphicsEndImageContext()
return result
}
func resizeWithWidth(width: CGFloat) -> UIImage? {
let imageView = UIImageView(frame: CGRect(origin: .zero, size: CGSize(width: width, height: CGFloat(ceil(width/size.width * size.height)))))
imageView.contentMode = .ScaleAspectFit
imageView.image = self
UIGraphicsBeginImageContextWithOptions(imageView.bounds.size, false, scale)
guard let context = UIGraphicsGetCurrentContext() else { return nil }
imageView.layer.renderInContext(context)
guard let result = UIGraphicsGetImageFromCurrentImageContext() else { return nil }
UIGraphicsEndImageContext()
return result
}
}
这是 user4261201 的回答，但在 swift 中，我目前正在使用：
func compressImage (_ image: UIImage) -> UIImage {
let actualHeight:CGFloat = image.size.height
let actualWidth:CGFloat = image.size.width
let imgRatio:CGFloat = actualWidth/actualHeight
let maxWidth:CGFloat = 1024.0
let resizedHeight:CGFloat = maxWidth/imgRatio
let compressionQuality:CGFloat = 0.5
let rect:CGRect = CGRect(x: 0, y: 0, width: maxWidth, height: resizedHeight)
UIGraphicsBeginImageContext(rect.size)
image.draw(in: rect)
let img: UIImage = UIGraphicsGetImageFromCurrentImageContext()!
let imageData:Data = UIImageJPEGRepresentation(img, compressionQuality)!
UIGraphicsEndImageContext()
return UIImage(data: imageData)!
}
以防有人正在寻找将调整大小图像小于1MB Swift 3和4.
只需复制并粘贴这个扩展名：
extension UIImage {
func resized(withPercentage percentage: CGFloat) -> UIImage? {
let canvasSize = CGSize(width: size.width * percentage, height: size.height * percentage)
UIGraphicsBeginImageContextWithOptions(canvasSize, false, scale)
defer { UIGraphicsEndImageContext() }
draw(in: CGRect(origin: .zero, size: canvasSize))
return UIGraphicsGetImageFromCurrentImageContext()
}
func resizedTo1MB() -> UIImage? {
guard let imageData = UIImagePNGRepresentation(self) else { return nil }
var resizingImage = self
var imageSizeKB = Double(imageData.count) / 1000.0 // ! Or devide for 1024 if you need KB but not kB
while imageSizeKB > 1000 { // ! Or use 1024 if you need KB but not kB
guard let resizedImage = resizingImage.resized(withPercentage: 0.9),
let imageData = UIImagePNGRepresentation(resizedImage)
else { return nil }
resizingImage = resizedImage
imageSizeKB = Double(imageData.count) / 1000.0 // ! Or devide for 1024 if you need KB but not kB
}
return resizingImage
}
}
和使用：
let resizedImage = originalImage.resizedTo1MB()
编辑：
请注意，它 阻塞 UI，所以如果您认为它适合您的情况，请转到 后台线程 。
使用 .resizeToMaximumBytes 调整 UIImage 的大小
这是我在 swift 3 中为调整 UIImage 的大小所做的。它将图像大小减小到小于 100kb。它按比例工作！
extension UIImage {
class func scaleImageWithDivisor(img: UIImage, divisor: CGFloat) -> UIImage {
let size = CGSize(width: img.size.width/divisor, height: img.size.height/divisor)
UIGraphicsBeginImageContext(size)
img.draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return scaledImage!
}
}
用法：
let scaledImage = UIImage.scaleImageWithDivisor(img: capturedImage!, divisor: 3)
根据Tung Fam的回答。调整到特定的文件大小。像 0.7 MB 你可以使用这个代码。
extension UIImage {
func resize(withPercentage percentage: CGFloat) -> UIImage? {
var newRect = CGRect(origin: .zero, size: CGSize(width: size.width*percentage, height: size.height*percentage))
UIGraphicsBeginImageContextWithOptions(newRect.size, true, 1)
self.draw(in: newRect)
defer {UIGraphicsEndImageContext()}
return UIGraphicsGetImageFromCurrentImageContext()
}
func resizeTo(MB: Double) -> UIImage? {
guard let fileSize = self.pngData()?.count else {return nil}
let fileSizeInMB = CGFloat(fileSize)/(1024.0*1024.0)//form bytes to MB
let percentage = 1/fileSizeInMB
return resize(withPercentage: percentage)
}
}
使用这个你可以控制你想要的尺寸：
func jpegImage(image: UIImage, maxSize: Int, minSize: Int, times: Int) -> Data? {
var maxQuality: CGFloat = 1.0
var minQuality: CGFloat = 0.0
var bestData: Data?
for _ in 1...times {
let thisQuality = (maxQuality + minQuality) / 2
guard let data = image.jpegData(compressionQuality: thisQuality) else { return nil }
let thisSize = data.count
if thisSize > maxSize {
maxQuality = thisQuality
} else {
minQuality = thisQuality
bestData = data
if thisSize > minSize {
return bestData
}
}
}
return bestData
}
方法调用示例：
jpegImage(image: image, maxSize: 500000, minSize: 400000, times: 10)
它将尝试获取最大和最小大小介于 maxSize 和 minSize 之间的文件，但只尝试 times 次。如果在这段时间内失败，它将 return nil。
我觉得最简单的方法是swift自己提供的将图片压缩成压缩数据下面是swift4.2
中的代码
let imageData = yourImageTobeCompressed.jpegData(compressionQuality: 0.5)
然后您可以发送此图像数据以上传到服务器。
Swift4.2
let imagedata = yourImage.jpegData(compressionQuality: 0.1)!
Objective-C 相同：
接口：
@interface UIImage (Resize)
- (UIImage *)resizedWithPercentage:(CGFloat)percentage;
- (UIImage *)resizeTo:(CGFloat)weight isPng:(BOOL)isPng jpegCompressionQuality:(CGFloat)compressionQuality;
@end
实施：
#import "UIImage+Resize.h"
@implementation UIImage (Resize)
- (UIImage *)resizedWithPercentage:(CGFloat)percentage {
CGSize canvasSize = CGSizeMake(self.size.width * percentage, self.size.height * percentage);
UIGraphicsBeginImageContextWithOptions(canvasSize, false, self.scale);
[self drawInRect:CGRectMake(0, 0, canvasSize.width, canvasSize.height)];
UIImage *sizedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return sizedImage;
}
- (UIImage *)resizeTo:(CGFloat)weight isPng:(BOOL)isPng jpegCompressionQuality:(CGFloat)compressionQuality {
NSData *imageData = isPng ? UIImagePNGRepresentation(self) : UIImageJPEGRepresentation(self, compressionQuality);
if (imageData && [imageData length] > 0) {
UIImage *resizingImage = self;
double imageSizeKB = [imageData length] / weight;
while (imageSizeKB > weight) {
UIImage *resizedImage = [resizingImage resizedWithPercentage:0.9];
imageData = isPng ? UIImagePNGRepresentation(resizedImage) : UIImageJPEGRepresentation(resizedImage, compressionQuality);
resizingImage = resizedImage;
imageSizeKB = (double)(imageData.length / weight);
}
return resizingImage;
}
return nil;
}
用法：
#import "UIImage+Resize.h"
UIImage *resizedImage = [self.picture resizeTo:2048 isPng:NO jpegCompressionQuality:1.0];
当我尝试使用已接受的答案来调整图像的大小以便在我的项目中使用时，它会变得非常像素化和模糊。我最终得到了这段代码，可以在不添加像素化或模糊的情况下调整图像大小：
func scale(withPercentage percentage: CGFloat)-> UIImage? {
let cgSize = CGSize(width: size.width * percentage, height: size.height * percentage)
let hasAlpha = true
let scale: CGFloat = 0.0 // Use scale factor of main screen
UIGraphicsBeginImageContextWithOptions(cgSize, !hasAlpha, scale)
self.draw(in: CGRect(origin: CGPoint.zero, size: cgSize))
let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
return scaledImage
}
extension UIImage {
func resized(toValue value: CGFloat) -> UIImage {
if size.width > size.height {
return self.resize(toWidth: value)!
} else {
return self.resize(toHeight: value)!
}
}
我认为这里问题的核心是如何在上传到服务器之前可靠地将 UIImage 的数据缩小到一定大小，而不是仅仅缩小 UIImage 本身。
如果您不需要压缩到特定大小，使用 func jpegData(compressionQuality: CGFloat) -> Data? 效果很好。但是，对于某些情况，我发现能够压缩到特定指定文件大小以下很有用。在那种情况下，jpegData 是不可靠的，并且以这种方式迭代压缩图像会导致文件大小稳定（并且可能非常昂贵）。相反，我更喜欢像 那样减小 UIImage 本身的大小，然后转换为 jpegData 并反复检查减小的大小是否低于我选择的值（在我设置的边距内）。我根据当前文件大小与所需文件大小的比率调整压缩步长乘数，以加快最昂贵的第一次迭代（因为此时文件大小最大）。
Swift 5
extension UIImage {
func resized(withPercentage percentage: CGFloat, isOpaque: Bool = true) -> UIImage? {
let canvas = CGSize(width: size.width * percentage, height: size.height * percentage)
let format = imageRendererFormat
format.opaque = isOpaque
return UIGraphicsImageRenderer(size: canvas, format: format).image {
_ in draw(in: CGRect(origin: .zero, size: canvas))
}
}
func compress(to kb: Int, allowedMargin: CGFloat = 0.2) -> Data {
guard kb > 10 else { return Data() } // Prevents user from compressing below a limit (10kb in this case).
let bytes = kb * 1024
var compression: CGFloat = 1.0
let step: CGFloat = 0.05
var holderImage = self
var complete = false
while(!complete) {
guard let data = holderImage.jpegData(compressionQuality: 1.0) else { break }
let ratio = data.count / bytes
if data.count < Int(CGFloat(bytes) * (1 + allowedMargin)) {
complete = true
return data
} else {
let multiplier:CGFloat = CGFloat((ratio / 5) + 1)
compression -= (step * multiplier)
}
guard let newImage = holderImage.resized(withPercentage: compression) else { break }
holderImage = newImage
}
return Data()
}
}
和用法：
let data = image.compress(to: 1000)
Swift 5.4 & Xcode 13
我对这里的解决方案不满意，它们根据给定的 KB 大小生成图像，因为它们中的大多数都使用 .jpegData(compressionQuality: x)。此方法不适用于大图像，因为即使将压缩质量设置为 0.0，大图像仍将保持较大，例如较新 iPhone 的纵向模式产生的 10 MB 压缩质量设置为 0.0 时仍会高于 1 MB。
因此我在这里使用了一些答案并重写了一个 Helper Struct，它在背景问题中转换图像：
import UIKit
struct ImageCompressor {
static func compress(image: UIImage, maxByte: Int,
completion: @escaping (UIImage?) -> ()) {
DispatchQueue.global(qos: .userInitiated).async {
guard let currentImageSize = image.jpegData(compressionQuality: 1.0)?.count else {
return completion(nil)
}
var iterationImage: UIImage? = image
var iterationImageSize = currentImageSize
var iterationCompression: CGFloat = 1.0
while iterationImageSize > maxByte && iterationCompression > 0.01 {
let percantageDecrease = getPercantageToDecreaseTo(forDataCount: iterationImageSize)
let canvasSize = CGSize(width: image.size.width * iterationCompression,
height: image.size.height * iterationCompression)
UIGraphicsBeginImageContextWithOptions(canvasSize, false, image.scale)
defer { UIGraphicsEndImageContext() }
image.draw(in: CGRect(origin: .zero, size: canvasSize))
iterationImage = UIGraphicsGetImageFromCurrentImageContext()
guard let newImageSize = iterationImage?.jpegData(compressionQuality: 1.0)?.count else {
return completion(nil)
}
iterationImageSize = newImageSize
iterationCompression -= percantageDecrease
}
completion(iterationImage)
}
}
private static func getPercantageToDecreaseTo(forDataCount dataCount: Int) -> CGFloat {
switch dataCount {
case 0..<3000000: return 0.05
case 3000000..<10000000: return 0.1
default: return 0.2
}
}
}
将图像压缩到最大 1 MB：
ImageCompressor.compress(image: image, maxByte: 1000000) { image in
guard let compressedImage = image else { return }
// Use compressedImage
}
}
我在研究 Swift 中的图像压缩和导出时遇到了这个问题，并以此为起点更好地理解问题并获得更好的技术。
UIGraphicsBeginImageContext()、UIGraphicsGetImageFromCurrentImageContext()、UIGraphicsEndImageContext() 过程是一种较旧的技术，已被 iron_john_bonney and leo-dabus 使用的 UIGraphicsImageRenderer 取代。他们的示例是作为 UIImage 的扩展编写的，而我选择编写一个独立的函数。可以通过比较（查看 UIGraphicsImageRenderer 调用和附近的调用）识别所需的方法差异，并且可以轻松地移植回 UIImage 扩展。
我认为这里使用的压缩算法有改进的潜力，所以我采取了一种方法，首先将图像调整为具有给定的总像素数，然后通过调整 jpeg 压缩来压缩它以实现指定的最终文件大小。指定像素总数的目的是避免陷入图像纵横比问题。虽然我没有做过详尽的调查，但我怀疑将图像缩放到指定的总像素数会使最终的 jpeg 图像文件大小处于一般范围内，然后可以使用 jpeg 压缩来确保文件大小限制以可接受的图像质量实现，前提是初始像素数不太高。
使用 UIGraphicsImageRenderer 时，CGRect 在 Apple 主机设备上以 逻辑 像素指定，这与输出 jpeg 中的实际像素不同。查看设备像素比率以了解这一点。为了获得设备像素比，我尝试从环境中提取它，但这些技术导致 playground 崩溃，所以我使用了一种效率较低的技术。
如果您将此代码粘贴到 Xcode playround 中并在 Resources 文件夹中放置一个适当的 .jpg 文件，则输出文件将放置在 Playground 输出文件夹中（使用实时视图中的快速查看找到这个位置）。
import UIKit
func compressUIImage(_ image: UIImage?, numPixels: Int, fileSizeLimitKB: Double, exportImage: Bool) -> Data {
var returnData: Data
if let origWidth = image?.size.width,
let origHeight = image?.size.height {
print("Original image size =", origWidth, "*", origHeight, "pixels")
let imgMult = min(sqrt(CGFloat(numPixels)/(origWidth * origHeight)), 1) // This multiplier scales the image to have the desired number of pixels
print("imageMultiplier =", imgMult)
let cgRect = CGRect(origin: .zero, size: CGSize(width: origWidth * imgMult, height: origHeight * imgMult)) // This is in *logical* pixels
let renderer = UIGraphicsImageRenderer(size: cgRect.size)
let img = renderer.image { ctx in
image?.draw(in: cgRect)
}
// Now get the device pixel ratio if needed...
var img_scale: CGFloat = 1
if exportImage {
img_scale = img.scale
}
print("Image scaling factor =", img_scale)
// ...and use to ensure *output* image has desired number of pixels
let cgRect_scaled = CGRect(origin: .zero, size: CGSize(width: origWidth * imgMult/img_scale, height: origHeight * imgMult/img_scale)) // This is in *logical* pixels
print("New image size (in logical pixels) =", cgRect_scaled.width, "*", cgRect_scaled.height, "pixels") // Due to device pixel ratios, can have fractional pixel dimensions
let renderer_scaled = UIGraphicsImageRenderer(size: cgRect_scaled.size)
let img_scaled = renderer_scaled.image { ctx in
image?.draw(in: cgRect_scaled)
}
var compQual = CGFloat(1.0)
returnData = img_scaled.jpegData(compressionQuality: 1.0)!
var imageSizeKB = Double(returnData.count) / 1000.0
print("compressionQuality =", compQual, "=> imageSizeKB =", imageSizeKB, "KB")
while imageSizeKB > fileSizeLimitKB {
compQual *= 0.9
returnData = img_scaled.jpegData(compressionQuality: compQual)!
imageSizeKB = Double(returnData.count) / 1000.0
print("compressionQuality =", compQual, "=> imageSizeKB =", imageSizeKB, "KB")
}
} else {
returnData = Data()
}
return returnData
}
let image_orig = UIImage(named: "input.jpg")
let image_comp_data = compressUIImage(image_orig, numPixels: Int(4e6), fileSizeLimitKB: 1300, exportImage: true)
func getDocumentsDirectory() -> URL {
let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
return paths[0]
}
let filename = getDocumentsDirectory().appendingPathComponent("output.jpg")
try? image_comp_data.write(to: filename)
来源包括 Jordan Morgan, and Hacking with Swift。
我一直在搜索 google，只遇到了减少 height/width 或一些如何通过 CoreImage 编辑 UIImage 外观的库。但是我还没有看到或找到一个库，post 解释了如何减小图像大小，所以当它上传时，它不是完整的图像大小。
到目前为止我有这个：
if image != nil {
//let data = NSData(data: UIImagePNGRepresentation(image))
let data = UIImagePNGRepresentation(image)
body.appendString("--\(boundary)\r\n")
body.appendString("Content-Disposition: form-data; name=\"image\"; filename=\"randomName\"\r\n")
body.appendString("Content-Type: image/png\r\n\r\n")
body.appendData(data)
body.appendString("\r\n")
}
它正在发送 12MB 的照片。我怎样才能将它减少到 1mb？谢谢！
如果您以 NSData 格式上传图片，请使用：
NSData *imageData = UIImageJPEGRepresentation(yourImage, floatValue);
yourImage 是你的 UIImage。
floatvalue是压缩值（0.0到1.0）
以上是将图片转JPEG.
PNG使用：UIImagePNGRepresentation
注意：以上代码在Objective-C中。请检查如何在 Swift.
中定义 NSData这是我调整图片大小的方法。
-(UIImage *)resizeImage:(UIImage *)image
{
float actualHeight = image.size.height;
float actualWidth = image.size.width;
float maxHeight = 300.0;
float maxWidth = 400.0;
float imgRatio = actualWidth/actualHeight;
float maxRatio = maxWidth/maxHeight;
float compressionQuality = 0.5;//50 percent compression
if (actualHeight > maxHeight || actualWidth > maxWidth)
{
if(imgRatio < maxRatio)
{
//adjust width according to maxHeight
imgRatio = maxHeight / actualHeight;
actualWidth = imgRatio * actualWidth;
actualHeight = maxHeight;
}
else if(imgRatio > maxRatio)
{
//adjust height according to maxWidth
imgRatio = maxWidth / actualWidth;
actualHeight = imgRatio * actualHeight;
actualWidth = maxWidth;
}
else
{
actualHeight = maxHeight;
actualWidth = maxWidth;
}
}
CGRect rect = CGRectMake(0.0, 0.0, actualWidth, actualHeight);
UIGraphicsBeginImageContext(rect.size);
[image drawInRect:rect];
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
NSData *imageData = UIImageJPEGRepresentation(img, compressionQuality);
UIGraphicsEndImageContext();
return [UIImage imageWithData:imageData];
}
使用这个方法我的图像从 6.5 MB 减少到 104 KB。
Swift 4 码:
func resize(_ image: UIImage) -> UIImage {
var actualHeight = Float(image.size.height)
var actualWidth = Float(image.size.width)
let maxHeight: Float = 300.0
let maxWidth: Float = 400.0
var imgRatio: Float = actualWidth / actualHeight
let maxRatio: Float = maxWidth / maxHeight
let compressionQuality: Float = 0.5
//50 percent compression
if actualHeight > maxHeight || actualWidth > maxWidth {
if imgRatio < maxRatio {
//adjust width according to maxHeight
imgRatio = maxHeight / actualHeight
actualWidth = imgRatio * actualWidth
actualHeight = maxHeight
}
else if imgRatio > maxRatio {
//adjust height according to maxWidth
imgRatio = maxWidth / actualWidth
actualHeight = imgRatio * actualHeight
actualWidth = maxWidth
}
else {
actualHeight = maxHeight
actualWidth = maxWidth
}
}
let rect = CGRect(x: 0.0, y: 0.0, width: CGFloat(actualWidth), height: CGFloat(actualHeight))
UIGraphicsBeginImageContext(rect.size)
image.draw(in: rect)
let img = UIGraphicsGetImageFromCurrentImageContext()
let imageData = img?.jpegData(compressionQuality: CGFloat(compressionQuality))
UIGraphicsEndImageContext()
return UIImage(data: imageData!) ?? UIImage()
}
Xcode 9 • Swift 4 或更高版本
edit/update：对于iOS10+我们可以使用UIGraphicsImageRenderer。对于较旧的 Swift 语法检查编辑历史。
extension UIImage {
func resized(withPercentage percentage: CGFloat, isOpaque: Bool = true) -> UIImage? {
let canvas = CGSize(width: size.width * percentage, height: size.height * percentage)
let format = imageRendererFormat
format.opaque = isOpaque
return UIGraphicsImageRenderer(size: canvas, format: format).image {
_ in draw(in: CGRect(origin: .zero, size: canvas))
}
}
func resized(toWidth width: CGFloat, isOpaque: Bool = true) -> UIImage? {
let canvas = CGSize(width: width, height: CGFloat(ceil(width/size.width * size.height)))
let format = imageRendererFormat
format.opaque = isOpaque
return UIGraphicsImageRenderer(size: canvas, format: format).image {
_ in draw(in: CGRect(origin: .zero, size: canvas))
}
}
}
用法：
let image = UIImage(data: try! Data(contentsOf: URL(string:"http://i.stack.imgur.com/Xs4RX.jpg")!))!
let thumb1 = image.resized(withPercentage: 0.1)
let thumb2 = image.resized(toWidth: 72.0)
与 Leo Answer 相同，但对 SWIFT 2.0
进行了少量编辑 extension UIImage {
func resizeWithPercentage(percentage: CGFloat) -> UIImage? {
let imageView = UIImageView(frame: CGRect(origin: .zero, size: CGSize(width: size.width * percentage, height: size.height * percentage)))
imageView.contentMode = .ScaleAspectFit
imageView.image = self
UIGraphicsBeginImageContextWithOptions(imageView.bounds.size, false, scale)
guard let context = UIGraphicsGetCurrentContext() else { return nil }
imageView.layer.renderInContext(context)
guard let result = UIGraphicsGetImageFromCurrentImageContext() else { return nil }
UIGraphicsEndImageContext()
return result
}
func resizeWithWidth(width: CGFloat) -> UIImage? {
let imageView = UIImageView(frame: CGRect(origin: .zero, size: CGSize(width: width, height: CGFloat(ceil(width/size.width * size.height)))))
imageView.contentMode = .ScaleAspectFit
imageView.image = self
UIGraphicsBeginImageContextWithOptions(imageView.bounds.size, false, scale)
guard let context = UIGraphicsGetCurrentContext() else { return nil }
imageView.layer.renderInContext(context)
guard let result = UIGraphicsGetImageFromCurrentImageContext() else { return nil }
UIGraphicsEndImageContext()
return result
}
}
这是 user4261201 的回答，但在 swift 中，我目前正在使用：
func compressImage (_ image: UIImage) -> UIImage {
let actualHeight:CGFloat = image.size.height
let actualWidth:CGFloat = image.size.width
let imgRatio:CGFloat = actualWidth/actualHeight
let maxWidth:CGFloat = 1024.0
let resizedHeight:CGFloat = maxWidth/imgRatio
let compressionQuality:CGFloat = 0.5
let rect:CGRect = CGRect(x: 0, y: 0, width: maxWidth, height: resizedHeight)
UIGraphicsBeginImageContext(rect.size)
image.draw(in: rect)
let img: UIImage = UIGraphicsGetImageFromCurrentImageContext()!
let imageData:Data = UIImageJPEGRepresentation(img, compressionQuality)!
UIGraphicsEndImageContext()
return UIImage(data: imageData)!
}
以防有人正在寻找将调整大小图像小于1MB Swift 3和4.
只需复制并粘贴这个扩展名：
extension UIImage {
func resized(withPercentage percentage: CGFloat) -> UIImage? {
let canvasSize = CGSize(width: size.width * percentage, height: size.height * percentage)
UIGraphicsBeginImageContextWithOptions(canvasSize, false, scale)
defer { UIGraphicsEndImageContext() }
draw(in: CGRect(origin: .zero, size: canvasSize))
return UIGraphicsGetImageFromCurrentImageContext()
}
func resizedTo1MB() -> UIImage? {
guard let imageData = UIImagePNGRepresentation(self) else { return nil }
var resizingImage = self
var imageSizeKB = Double(imageData.count) / 1000.0 // ! Or devide for 1024 if you need KB but not kB
while imageSizeKB > 1000 { // ! Or use 1024 if you need KB but not kB
guard let resizedImage = resizingImage.resized(withPercentage: 0.9),
let imageData = UIImagePNGRepresentation(resizedImage)
else { return nil }
resizingImage = resizedImage
imageSizeKB = Double(imageData.count) / 1000.0 // ! Or devide for 1024 if you need KB but not kB
}
return resizingImage
}
}
和使用：
let resizedImage = originalImage.resizedTo1MB()
编辑： 请注意，它 阻塞 UI，所以如果您认为它适合您的情况，请转到 后台线程 。
使用 .resizeToMaximumBytes 调整 UIImage 的大小
这是我在 swift 3 中为调整 UIImage 的大小所做的。它将图像大小减小到小于 100kb。它按比例工作！
extension UIImage {
class func scaleImageWithDivisor(img: UIImage, divisor: CGFloat) -> UIImage {
let size = CGSize(width: img.size.width/divisor, height: img.size.height/divisor)
UIGraphicsBeginImageContext(size)
img.draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return scaledImage!
}
}
用法：
let scaledImage = UIImage.scaleImageWithDivisor(img: capturedImage!, divisor: 3)
根据Tung Fam的回答。调整到特定的文件大小。像 0.7 MB 你可以使用这个代码。
extension UIImage {
func resize(withPercentage percentage: CGFloat) -> UIImage? {
var newRect = CGRect(origin: .zero, size: CGSize(width: size.width*percentage, height: size.height*percentage))
UIGraphicsBeginImageContextWithOptions(newRect.size, true, 1)
self.draw(in: newRect)
defer {UIGraphicsEndImageContext()}
return UIGraphicsGetImageFromCurrentImageContext()
}
func resizeTo(MB: Double) -> UIImage? {
guard let fileSize = self.pngData()?.count else {return nil}
let fileSizeInMB = CGFloat(fileSize)/(1024.0*1024.0)//form bytes to MB
let percentage = 1/fileSizeInMB
return resize(withPercentage: percentage)
}
}
使用这个你可以控制你想要的尺寸：
func jpegImage(image: UIImage, maxSize: Int, minSize: Int, times: Int) -> Data? {
var maxQuality: CGFloat = 1.0
var minQuality: CGFloat = 0.0
var bestData: Data?
for _ in 1...times {
let thisQuality = (maxQuality + minQuality) / 2
guard let data = image.jpegData(compressionQuality: thisQuality) else { return nil }
let thisSize = data.count
if thisSize > maxSize {
maxQuality = thisQuality
} else {
minQuality = thisQuality
bestData = data
if thisSize > minSize {
return bestData
}
}
}
return bestData
}
方法调用示例：
jpegImage(image: image, maxSize: 500000, minSize: 400000, times: 10)
它将尝试获取最大和最小大小介于 maxSize 和 minSize 之间的文件，但只尝试 times 次。如果在这段时间内失败，它将 return nil。
我觉得最简单的方法是swift自己提供的将图片压缩成压缩数据下面是swift4.2
中的代码let imageData = yourImageTobeCompressed.jpegData(compressionQuality: 0.5)
然后您可以发送此图像数据以上传到服务器。
Swift4.2
let imagedata = yourImage.jpegData(compressionQuality: 0.1)!
Objective-C 相同：
接口：
@interface UIImage (Resize)
- (UIImage *)resizedWithPercentage:(CGFloat)percentage;
- (UIImage *)resizeTo:(CGFloat)weight isPng:(BOOL)isPng jpegCompressionQuality:(CGFloat)compressionQuality;
@end
实施：
#import "UIImage+Resize.h"
@implementation UIImage (Resize)
- (UIImage *)resizedWithPercentage:(CGFloat)percentage {
CGSize canvasSize = CGSizeMake(self.size.width * percentage, self.size.height * percentage);
UIGraphicsBeginImageContextWithOptions(canvasSize, false, self.scale);
[self drawInRect:CGRectMake(0, 0, canvasSize.width, canvasSize.height)];
UIImage *sizedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return sizedImage;
}
- (UIImage *)resizeTo:(CGFloat)weight isPng:(BOOL)isPng jpegCompressionQuality:(CGFloat)compressionQuality {
NSData *imageData = isPng ? UIImagePNGRepresentation(self) : UIImageJPEGRepresentation(self, compressionQuality);
if (imageData && [imageData length] > 0) {
UIImage *resizingImage = self;
double imageSizeKB = [imageData length] / weight;
while (imageSizeKB > weight) {
UIImage *resizedImage = [resizingImage resizedWithPercentage:0.9];
imageData = isPng ? UIImagePNGRepresentation(resizedImage) : UIImageJPEGRepresentation(resizedImage, compressionQuality);
resizingImage = resizedImage;
imageSizeKB = (double)(imageData.length / weight);
}
return resizingImage;
}
return nil;
}
用法：
#import "UIImage+Resize.h"
UIImage *resizedImage = [self.picture resizeTo:2048 isPng:NO jpegCompressionQuality:1.0];
当我尝试使用已接受的答案来调整图像的大小以便在我的项目中使用时，它会变得非常像素化和模糊。我最终得到了这段代码，可以在不添加像素化或模糊的情况下调整图像大小：
func scale(withPercentage percentage: CGFloat)-> UIImage? {
let cgSize = CGSize(width: size.width * percentage, height: size.height * percentage)
let hasAlpha = true
let scale: CGFloat = 0.0 // Use scale factor of main screen
UIGraphicsBeginImageContextWithOptions(cgSize, !hasAlpha, scale)
self.draw(in: CGRect(origin: CGPoint.zero, size: cgSize))
let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
return scaledImage
}
extension UIImage {
func resized(toValue value: CGFloat) -> UIImage {
if size.width > size.height {
return self.resize(toWidth: value)!
} else {
return self.resize(toHeight: value)!
}
}
我认为这里问题的核心是如何在上传到服务器之前可靠地将 UIImage 的数据缩小到一定大小，而不是仅仅缩小 UIImage 本身。
如果您不需要压缩到特定大小，使用 func jpegData(compressionQuality: CGFloat) -> Data? 效果很好。但是，对于某些情况，我发现能够压缩到特定指定文件大小以下很有用。在那种情况下，jpegData 是不可靠的，并且以这种方式迭代压缩图像会导致文件大小稳定（并且可能非常昂贵）。相反，我更喜欢像
Swift 5
extension UIImage {
func resized(withPercentage percentage: CGFloat, isOpaque: Bool = true) -> UIImage? {
let canvas = CGSize(width: size.width * percentage, height: size.height * percentage)
let format = imageRendererFormat
format.opaque = isOpaque
return UIGraphicsImageRenderer(size: canvas, format: format).image {
_ in draw(in: CGRect(origin: .zero, size: canvas))
}
}
func compress(to kb: Int, allowedMargin: CGFloat = 0.2) -> Data {
guard kb > 10 else { return Data() } // Prevents user from compressing below a limit (10kb in this case).
let bytes = kb * 1024
var compression: CGFloat = 1.0
let step: CGFloat = 0.05
var holderImage = self
var complete = false
while(!complete) {
guard let data = holderImage.jpegData(compressionQuality: 1.0) else { break }
let ratio = data.count / bytes
if data.count < Int(CGFloat(bytes) * (1 + allowedMargin)) {
complete = true
return data
} else {
let multiplier:CGFloat = CGFloat((ratio / 5) + 1)
compression -= (step * multiplier)
}
guard let newImage = holderImage.resized(withPercentage: compression) else { break }
holderImage = newImage
}
return Data()
}
}
和用法：
let data = image.compress(to: 1000)
Swift 5.4 & Xcode 13
我对这里的解决方案不满意，它们根据给定的 KB 大小生成图像，因为它们中的大多数都使用 .jpegData(compressionQuality: x)。此方法不适用于大图像，因为即使将压缩质量设置为 0.0，大图像仍将保持较大，例如较新 iPhone 的纵向模式产生的 10 MB 压缩质量设置为 0.0 时仍会高于 1 MB。
因此我在这里使用了一些答案并重写了一个 Helper Struct，它在背景问题中转换图像：
import UIKit
struct ImageCompressor {
static func compress(image: UIImage, maxByte: Int,
completion: @escaping (UIImage?) -> ()) {
DispatchQueue.global(qos: .userInitiated).async {
guard let currentImageSize = image.jpegData(compressionQuality: 1.0)?.count else {
return completion(nil)
}
var iterationImage: UIImage? = image
var iterationImageSize = currentImageSize
var iterationCompression: CGFloat = 1.0
while iterationImageSize > maxByte && iterationCompression > 0.01 {
let percantageDecrease = getPercantageToDecreaseTo(forDataCount: iterationImageSize)
let canvasSize = CGSize(width: image.size.width * iterationCompression,
height: image.size.height * iterationCompression)
UIGraphicsBeginImageContextWithOptions(canvasSize, false, image.scale)
defer { UIGraphicsEndImageContext() }
image.draw(in: CGRect(origin: .zero, size: canvasSize))
iterationImage = UIGraphicsGetImageFromCurrentImageContext()
guard let newImageSize = iterationImage?.jpegData(compressionQuality: 1.0)?.count else {
return completion(nil)
}
iterationImageSize = newImageSize
iterationCompression -= percantageDecrease
}
completion(iterationImage)
}
}
private static func getPercantageToDecreaseTo(forDataCount dataCount: Int) -> CGFloat {
switch dataCount {
case 0..<3000000: return 0.05
case 3000000..<10000000: return 0.1
default: return 0.2
}
}
}
将图像压缩到最大 1 MB：
ImageCompressor.compress(image: image, maxByte: 1000000) { image in
guard let compressedImage = image else { return }
// Use compressedImage
}
}
我在研究 Swift 中的图像压缩和导出时遇到了这个问题，并以此为起点更好地理解问题并获得更好的技术。
UIGraphicsBeginImageContext()、UIGraphicsGetImageFromCurrentImageContext()、UIGraphicsEndImageContext() 过程是一种较旧的技术，已被 iron_john_bonney and leo-dabus 使用的 UIGraphicsImageRenderer 取代。他们的示例是作为 UIImage 的扩展编写的，而我选择编写一个独立的函数。可以通过比较（查看 UIGraphicsImageRenderer 调用和附近的调用）识别所需的方法差异，并且可以轻松地移植回 UIImage 扩展。
我认为这里使用的压缩算法有改进的潜力，所以我采取了一种方法，首先将图像调整为具有给定的总像素数，然后通过调整 jpeg 压缩来压缩它以实现指定的最终文件大小。指定像素总数的目的是避免陷入图像纵横比问题。虽然我没有做过详尽的调查，但我怀疑将图像缩放到指定的总像素数会使最终的 jpeg 图像文件大小处于一般范围内，然后可以使用 jpeg 压缩来确保文件大小限制以可接受的图像质量实现，前提是初始像素数不太高。
使用 UIGraphicsImageRenderer 时，CGRect 在 Apple 主机设备上以 逻辑 像素指定，这与输出 jpeg 中的实际像素不同。查看设备像素比率以了解这一点。为了获得设备像素比，我尝试从环境中提取它，但这些技术导致 playground 崩溃，所以我使用了一种效率较低的技术。
如果您将此代码粘贴到 Xcode playround 中并在 Resources 文件夹中放置一个适当的 .jpg 文件，则输出文件将放置在 Playground 输出文件夹中（使用实时视图中的快速查看找到这个位置）。
import UIKit
func compressUIImage(_ image: UIImage?, numPixels: Int, fileSizeLimitKB: Double, exportImage: Bool) -> Data {
var returnData: Data
if let origWidth = image?.size.width,
let origHeight = image?.size.height {
print("Original image size =", origWidth, "*", origHeight, "pixels")
let imgMult = min(sqrt(CGFloat(numPixels)/(origWidth * origHeight)), 1) // This multiplier scales the image to have the desired number of pixels
print("imageMultiplier =", imgMult)
let cgRect = CGRect(origin: .zero, size: CGSize(width: origWidth * imgMult, height: origHeight * imgMult)) // This is in *logical* pixels
let renderer = UIGraphicsImageRenderer(size: cgRect.size)
let img = renderer.image { ctx in
image?.draw(in: cgRect)
}
// Now get the device pixel ratio if needed...
var img_scale: CGFloat = 1
if exportImage {
img_scale = img.scale
}
print("Image scaling factor =", img_scale)
// ...and use to ensure *output* image has desired number of pixels
let cgRect_scaled = CGRect(origin: .zero, size: CGSize(width: origWidth * imgMult/img_scale, height: origHeight * imgMult/img_scale)) // This is in *logical* pixels
print("New image size (in logical pixels) =", cgRect_scaled.width, "*", cgRect_scaled.height, "pixels") // Due to device pixel ratios, can have fractional pixel dimensions
let renderer_scaled = UIGraphicsImageRenderer(size: cgRect_scaled.size)
let img_scaled = renderer_scaled.image { ctx in
image?.draw(in: cgRect_scaled)
}
var compQual = CGFloat(1.0)
returnData = img_scaled.jpegData(compressionQuality: 1.0)!
var imageSizeKB = Double(returnData.count) / 1000.0
print("compressionQuality =", compQual, "=> imageSizeKB =", imageSizeKB, "KB")
while imageSizeKB > fileSizeLimitKB {
compQual *= 0.9
returnData = img_scaled.jpegData(compressionQuality: compQual)!
imageSizeKB = Double(returnData.count) / 1000.0
print("compressionQuality =", compQual, "=> imageSizeKB =", imageSizeKB, "KB")
}
} else {
returnData = Data()
}
return returnData
}
let image_orig = UIImage(named: "input.jpg")
let image_comp_data = compressUIImage(image_orig, numPixels: Int(4e6), fileSizeLimitKB: 1300, exportImage: true)
func getDocumentsDirectory() -> URL {
let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
return paths[0]
}
let filename = getDocumentsDirectory().appendingPathComponent("output.jpg")
try? image_comp_data.write(to: filename)
来源包括 Jordan Morgan, and Hacking with Swift。