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這篇文章給大家分享的是有關(guān)iOS如何實(shí)現(xiàn)圖片壓縮的內(nèi)容。小編覺得挺實(shí)用的,因此分享給大家做個(gè)參考,一起跟隨小編過來看看吧。
兩種壓縮圖片的方法:壓縮圖片質(zhì)量(Quality),壓縮圖片尺寸(Size)。
壓縮圖片質(zhì)量
NSData *data = UIImageJPEGRepresentation(image, compression); UIImage *resultImage = [UIImage imageWithData:data];
通過 UIImage 和 NSData 的相互轉(zhuǎn)化,減小 JPEG 圖片的質(zhì)量來壓縮圖片。UIImageJPEGRepresentation:: 第二個(gè)參數(shù) compression 取值 0.0~1.0,值越小表示圖片質(zhì)量越低,圖片文件自然越小。
壓縮圖片尺寸
UIGraphicsBeginImageContext(size); [image drawInRect:CGRectMake(0, 0, size.width, size.height)]; resultImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext();
給定所需的圖片尺寸 size,resultImage 即為原圖 image 繪制為 size 大小的圖片。
壓縮圖片使圖片文件小于指定大小
如果對(duì)圖片清晰度要求不高,要求圖片的上傳、下載速度快的話,上傳圖片前需要壓縮圖片。壓縮到什么程度要看具體情況,但一般會(huì)設(shè)定一個(gè)圖片文件最大值,例如 100 KB。可以用上訴兩種方法來壓縮圖片。假設(shè)圖片轉(zhuǎn)化來的 NSData 對(duì)象為 data,通過data.length即可得到圖片的字節(jié)大小。
壓縮圖片質(zhì)量
比較容易想到的方法是,通過循環(huán)來逐漸減小圖片質(zhì)量,直到圖片稍小于指定大小(maxLength)。
+ (UIImage *)compressImageQuality:(UIImage *)image toByte:(NSInteger)maxLength { CGFloat compression = 1; NSData *data = UIImageJPEGRepresentation(image, compression); while (data.length > maxLength && compression > 0) { compression -= 0.02; data = UIImageJPEGRepresentation(image, compression); // When compression less than a value, this code dose not work } UIImage *resultImage = [UIImage imageWithData:data]; return resultImage; }
這樣循環(huán)次數(shù)多,效率低,耗時(shí)長(zhǎng)。
可以通過二分法來優(yōu)化。
+ (UIImage *)compressImageQuality:(UIImage *)image toByte:(NSInteger)maxLength { CGFloat compression = 1; NSData *data = UIImageJPEGRepresentation(image, compression); if (data.length < maxLength) return image; CGFloat max = 1; CGFloat min = 0; for (int i = 0; i < 6; ++i) { compression = (max + min) / 2; data = UIImageJPEGRepresentation(image, compression); if (data.length < maxLength * 0.9) { min = compression; } else if (data.length > maxLength) { max = compression; } else { break; } } UIImage *resultImage = [UIImage imageWithData:data]; return resultImage; }
當(dāng)圖片大小小于 maxLength,大于 maxLength * 0.9 時(shí),不再繼續(xù)壓縮。最多壓縮 6 次,1/(2^6) = 0.015625 < 0.02,也能達(dá)到每次循環(huán) compression 減小 0.02 的效果。這樣的壓縮次數(shù)比循環(huán)減小 compression 少,耗時(shí)短。需要注意的是,當(dāng)圖片質(zhì)量低于一定程度時(shí),繼續(xù)壓縮沒有效果。也就是說,compression 繼續(xù)減小,data 也不再繼續(xù)減小。壓縮圖片質(zhì)量的優(yōu)點(diǎn)在于,盡可能保留圖片清晰度,圖片不會(huì)明顯模糊;缺點(diǎn)在于,不能保證圖片壓縮后小于指定大小。
壓縮圖片尺寸
與之前類似,比較容易想到的方法是,通過循環(huán)逐漸減小圖片尺寸,直到圖片稍小于指定大小(maxLength)。具體代碼省略。同樣的問題是循環(huán)次數(shù)多,效率低,耗時(shí)長(zhǎng)??梢杂枚址▉硖岣咝?,具體代碼省略。這里介紹另外一種方法,比二分法更好,壓縮次數(shù)少,而且可以使圖片壓縮后剛好小于指定大小(不只是 < maxLength, > maxLength * 0.9)。
+ (UIImage *)compressImageSize:(UIImage *)image toByte:(NSUInteger)maxLength { UIImage *resultImage = image; NSData *data = UIImageJPEGRepresentation(resultImage, 1); NSUInteger lastDataLength = 0; while (data.length > maxLength && data.length != lastDataLength) { lastDataLength = data.length; CGFloat ratio = (CGFloat)maxLength / data.length; CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)), (NSUInteger)(resultImage.size.height * sqrtf(ratio))); // Use NSUInteger to prevent white blank UIGraphicsBeginImageContext(size); // Use image to draw (drawInRect:), image is larger but more compression time // Use result image to draw, image is smaller but less compression time [resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)]; resultImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); data = UIImageJPEGRepresentation(resultImage, 1); } return resultImage; }
[resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)];
是用新圖 resultImage 繪制,也可以用原圖 image 來繪制。用原圖繪制,壓縮后圖片更接近指定大小,但是壓縮次數(shù)較多,耗時(shí)較長(zhǎng)。一張大小為 6064 KB 的圖片,壓縮圖片尺寸,原圖繪制與新圖繪制結(jié)果如下
指定大小(KB) | 原圖繪制壓縮后大小(KB) | 原圖繪制壓縮次數(shù) | 新圖繪制壓縮后大小(KB) | 新圖繪制壓縮次數(shù) |
---|---|---|---|---|
500 | 498 | 6 | 498 | 3 |
300 | 299 | 4 | 296 | 3 |
100 | 99 | 5 | 98 | 3 |
50 | 49 | 6 | 48 | 3 |
兩種繪制方法壓縮后大小很接近,與指定大小也很接近,但原圖繪制壓縮次數(shù)可達(dá)到新圖繪制壓縮次數(shù)的兩倍。建議使用新圖繪制,減少壓縮次數(shù)。壓縮后圖片明顯比壓縮質(zhì)量模糊。
需要注意的是繪制尺寸的代碼
CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)), (NSUInteger)(resultImage.size.height * sqrtf(ratio)));,
每次繪制的尺寸 size,要把寬 width 和 高 height 轉(zhuǎn)換為整數(shù),防止繪制出的圖片有白邊。
壓縮圖片尺寸可以使圖片小于指定大小,但會(huì)使圖片明顯模糊(比壓縮圖片質(zhì)量模糊)。
兩種圖片壓縮方法結(jié)合
如果要保證圖片清晰度,建議選擇壓縮圖片質(zhì)量。如果要使圖片一定小于指定大小,壓縮圖片尺寸可以滿足。對(duì)于后一種需求,還可以先壓縮圖片質(zhì)量,如果已經(jīng)小于指定大小,就可得到清晰的圖片,否則再壓縮圖片尺寸。
+ (UIImage *)compressImage:(UIImage *)image toByte:(NSUInteger)maxLength { // Compress by quality CGFloat compression = 1; NSData *data = UIImageJPEGRepresentation(image, compression); if (data.length < maxLength) return image; CGFloat max = 1; CGFloat min = 0; for (int i = 0; i < 6; ++i) { compression = (max + min) / 2; data = UIImageJPEGRepresentation(image, compression); if (data.length < maxLength * 0.9) { min = compression; } else if (data.length > maxLength) { max = compression; } else { break; } } UIImage *resultImage = [UIImage imageWithData:data]; if (data.length < maxLength) return resultImage; // Compress by size NSUInteger lastDataLength = 0; while (data.length > maxLength && data.length != lastDataLength) { lastDataLength = data.length; CGFloat ratio = (CGFloat)maxLength / data.length; CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)), (NSUInteger)(resultImage.size.height * sqrtf(ratio))); // Use NSUInteger to prevent white blank UIGraphicsBeginImageContext(size); [resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)]; resultImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); data = UIImageJPEGRepresentation(resultImage, compression); } return resultImage; }
下面看下iOS圖片壓縮上傳的實(shí)現(xiàn)方法
需求
很多時(shí)候我們上傳圖片經(jīng)常遇到一些問題,要不就是圖片質(zhì)量變差,要不就是圖片太大等等問題。這里,我找到了一個(gè)算是目前比較符合需求的解決方案。在原有基礎(chǔ)上增加了動(dòng)態(tài)壓縮系數(shù),改寫成Swift版本。
實(shí)現(xiàn)思路
先調(diào)整分辨率,分辨率可以自己設(shè)定一個(gè)值,大于的就縮小到這分辨率,小余的就保持原本分辨率。然后再根據(jù)圖片最終大小來設(shè)置壓縮比,比如傳入maxSize = 30KB,最終計(jì)算大概這個(gè)大小的壓縮比。基本上最終出來的圖片數(shù)據(jù)根據(jù)當(dāng)前分辨率能保持差不多的大小同時(shí)不至于太模糊,跟微信,微博最終效果應(yīng)該是差不多的,代碼仍然有待優(yōu)化!
實(shí)現(xiàn)代碼
Swift3.0之前舊版本壓縮模式
// MARK: - 降低質(zhì)量 func resetSizeOfImageData(source_image: UIImage, maxSize: Int) -> NSData { //先調(diào)整分辨率 var newSize = CGSize(width: source_image.size.width, height: source_image.size.height) let tempHeight = newSize.height / 1024 let tempWidth = newSize.width / 1024 if tempWidth > 1.0 && tempWidth > tempHeight { newSize = CGSize(width: source_image.size.width / tempWidth, height: source_image.size.height / tempWidth) } else if tempHeight > 1.0 && tempWidth < tempHeight { newSize = CGSize(width: source_image.size.width / tempHeight, height: source_image.size.height / tempHeight) } UIGraphicsBeginImageContext(newSize) source_image.drawAsPatternInRect(CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)) let newImage = UIGraphicsGetImageFromCurrentImageContext() UIGraphicsEndImageContext() //先判斷當(dāng)前質(zhì)量是否滿足要求,不滿足再進(jìn)行壓縮 var finallImageData = UIImageJPEGRepresentation(newImage,1.0) let sizeOrigin = Int64((finallImageData?.length)!) let sizeOriginKB = Int(sizeOrigin / 1024) if sizeOriginKB <= maxSize { return finallImageData! } //保存壓縮系數(shù) let compressionQualityArr = NSMutableArray() let avg = CGFloat(1.0/250) var value = avg for var i = 250; i>=1; i-- { value = CGFloat(i)*avg compressionQualityArr.addObject(value) } //調(diào)整大小 //說明:壓縮系數(shù)數(shù)組compressionQualityArr是從大到小存儲(chǔ)。 //思路:折半計(jì)算,如果中間壓縮系數(shù)仍然降不到目標(biāo)值maxSize,則從后半部分開始尋找壓縮系數(shù);反之從前半部分尋找壓縮系數(shù) finallImageData = UIImageJPEGRepresentation(newImage, CGFloat(compressionQualityArr[125] as! NSNumber)) if Int(Int64((UIImageJPEGRepresentation(newImage, CGFloat(compressionQualityArr[125] as! NSNumber))?.length)!)/1024) > maxSize { //拿到最初的大小 finallImageData = UIImageJPEGRepresentation(newImage, 1.0) //從后半部分開始 for idx in 126..<250 { let value = compressionQualityArr[idx] let sizeOrigin = Int64((finallImageData?.length)!) let sizeOriginKB = Int(sizeOrigin / 1024) print("當(dāng)前降到的質(zhì)量:\(sizeOriginKB)") if sizeOriginKB > maxSize { print("\(idx)----\(value)") finallImageData = UIImageJPEGRepresentation(newImage, CGFloat(value as! NSNumber)) } else { break } } } else { //拿到最初的大小 finallImageData = UIImageJPEGRepresentation(newImage, 1.0) //從前半部分開始 for idx in 0..<125 { let value = compressionQualityArr[idx] let sizeOrigin = Int64((finallImageData?.length)!) let sizeOriginKB = Int(sizeOrigin / 1024) print("當(dāng)前降到的質(zhì)量:\(sizeOriginKB)") if sizeOriginKB > maxSize { print("\(idx)----\(value)") finallImageData = UIImageJPEGRepresentation(newImage, CGFloat(value as! NSNumber)) } else { break } } } return finallImageData! }
Swift3.0版本二分法壓縮模式
// MARK: - 降低質(zhì)量 func resetSizeOfImageData(source_image: UIImage!, maxSize: Int) -> NSData { //先判斷當(dāng)前質(zhì)量是否滿足要求,不滿足再進(jìn)行壓縮 var finallImageData = UIImageJPEGRepresentation(source_image,1.0) let sizeOrigin = finallImageData?.count let sizeOriginKB = sizeOrigin! / 1024 if sizeOriginKB <= maxSize { return finallImageData! as NSData } //先調(diào)整分辨率 var defaultSize = CGSize(width: 1024, height: 1024) let newImage = self.newSizeImage(size: defaultSize, source_image: source_image) finallImageData = UIImageJPEGRepresentation(newImage,1.0); //保存壓縮系數(shù) let compressionQualityArr = NSMutableArray() let avg = CGFloat(1.0/250) var value = avg var i = 250 repeat { i -= 1 value = CGFloat(i)*avg compressionQualityArr.add(value) } while i >= 1 /* 調(diào)整大小 說明:壓縮系數(shù)數(shù)組compressionQualityArr是從大到小存儲(chǔ)。 */ //思路:使用二分法搜索 finallImageData = self.halfFuntion(arr: compressionQualityArr.copy() as! [CGFloat], image: newImage, sourceData: finallImageData!, maxSize: maxSize) //如果還是未能壓縮到指定大小,則進(jìn)行降分辨率 while finallImageData?.count == 0 { //每次降100分辨率 if defaultSize.width-100 <= 0 || defaultSize.height-100 <= 0 { break } defaultSize = CGSize(width: defaultSize.width-100, height: defaultSize.height-100) let image = self.newSizeImage(size: defaultSize, source_image: UIImage.init(data: UIImageJPEGRepresentation(newImage, compressionQualityArr.lastObject as! CGFloat)!)!) finallImageData = self.halfFuntion(arr: compressionQualityArr.copy() as! [CGFloat], image: image, sourceData: UIImageJPEGRepresentation(image,1.0)!, maxSize: maxSize) } return finallImageData! as NSData } // MARK: - 調(diào)整圖片分辨率/尺寸(等比例縮放) func newSizeImage(size: CGSize, source_image: UIImage) -> UIImage { var newSize = CGSize(width: source_image.size.width, height: source_image.size.height) let tempHeight = newSize.height / size.height let tempWidth = newSize.width / size.width if tempWidth > 1.0 && tempWidth > tempHeight { newSize = CGSize(width: source_image.size.width / tempWidth, height: source_image.size.height / tempWidth) } else if tempHeight > 1.0 && tempWidth < tempHeight { newSize = CGSize(width: source_image.size.width / tempHeight, height: source_image.size.height / tempHeight) } UIGraphicsBeginImageContext(newSize) source_image.draw(in: CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)) let newImage = UIGraphicsGetImageFromCurrentImageContext() UIGraphicsEndImageContext() return newImage! } // MARK: - 二分法 func halfFuntion(arr: [CGFloat], image: UIImage, sourceData finallImageData: Data, maxSize: Int) -> Data? { var tempFinallImageData = finallImageData var tempData = Data.init() var start = 0 var end = arr.count - 1 var index = 0 var difference = Int.max while start <= end { index = start + (end - start)/2 tempFinallImageData = UIImageJPEGRepresentation(image, arr[index])! let sizeOrigin = tempFinallImageData.count let sizeOriginKB = sizeOrigin / 1024 print("當(dāng)前降到的質(zhì)量:\(sizeOriginKB)\n\(index)----\(arr[index])") if sizeOriginKB > maxSize { start = index + 1 } else if sizeOriginKB < maxSize { if maxSize-sizeOriginKB < difference { difference = maxSize-sizeOriginKB tempData = tempFinallImageData } end = index - 1 } else { break } } return tempData }
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