需求
很多時候我們上傳圖片經(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)上增加了動態(tài)壓縮系數(shù)，改寫成Swift版本，最底下貼出OC版本。
實現(xiàn)思路
先調(diào)整分辨率，分辨率可以自己設(shè)定一個值，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，最終計算大概這個大小的壓縮比。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！
實現(xiàn)代碼
Swift3.0之前舊版本壓縮模式（建議不用，性能太差）
// 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。
//思路：折半計算，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（推薦）
// MARK: - 降低質(zhì)量
func resetSizeOfImageData(sourceImage: 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(sourceImage,1.0)
let sizeOrigin = finallImageData?.count
let sizeOriginKB = sizeOrigin! / 1024
if sizeOriginKB <= maxSize {
return finallImageData! as NSData
}
//獲取原圖片寬高比
let sourceImageAspectRatio = sourceImage.size.width/sourceImage.size.height
//先調(diào)整分辨率
var defaultSize = CGSize(width: 1024, height: 1024/sourceImageAspectRatio)
let newImage = self.newSizeImage(size: defaultSize, sourceImage: sourceImage)
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。
*/
//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
let reduceWidth = 100.0
let reduceHeight = 100.0/sourceImageAspectRatio
if (defaultSize.width-CGFloat(reduceWidth)) <= 0 || (defaultSize.height-CGFloat(reduceHeight)) <= 0 {
break
}
defaultSize = CGSize(width: (defaultSize.width-CGFloat(reduceWidth)), height: (defaultSize.height-CGFloat(reduceHeight)))
let image = self.newSizeImage(size: defaultSize, sourceImage: 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, sourceImage: UIImage) -> UIImage {
var newSize = CGSize(width: sourceImage.size.width, height: sourceImage.size.height)
let tempHeight = newSize.height / size.height
let tempWidth = newSize.width / size.width
if tempWidth > 1.0 && tempWidth > tempHeight {
newSize = CGSize(width: sourceImage.size.width / tempWidth, height: sourceImage.size.height / tempWidth)
} else if tempHeight > 1.0 && tempWidth < tempHeight {
newSize = CGSize(width: sourceImage.size.width / tempHeight, height: sourceImage.size.height / tempHeight)
}
UIGraphicsBeginImageContext(newSize)
sourceImage.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
}
if index<=0 {
break
}
end = index - 1
} else {
break
}
}
return tempData
}
補充 OC 版本（推薦）
基于網(wǎng)友的要求，我把 OC 版本的代碼也貼出來。
- (NSData *)resetSizeOfImageData:(UIImage *)source_image maxSize:(NSInteger)maxSize {
//先判斷當(dāng)前質(zhì)量是否滿足要求，不滿足再進(jìn)行壓縮
__block NSData *finallImageData = UIImageJPEGRepresentation(sourceImage,1.0);
NSUInteger sizeOrigin = finallImageData.length;
NSUInteger sizeOriginKB = sizeOrigin / 1000;
if (sizeOriginKB <= maxSize) {
return finallImageData;
}
//獲取原圖片寬高比
CGFloat sourceImageAspectRatio = sourceImage.size.width/sourceImage.size.height;
//先調(diào)整分辨率
CGSize defaultSize = CGSizeMake(1024, 1024/sourceImageAspectRatio);
UIImage *newImage = [self newSizeImage:defaultSize image:sourceImage];
finallImageData = UIImageJPEGRepresentation(newImage,1.0);
//保存壓縮系數(shù)
NSMutableArray *compressionQualityArr = [NSMutableArray array];
CGFloat avg = 1.0/250;
CGFloat value = avg;
for (int i = 250; i >= 1; i--) {
value = 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。
*/
//思路：使用二分法搜索
finallImageData = [self halfFuntion:compressionQualityArr 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.length == 0) {
//每次降100分辨率
CGFloat reduceWidth = 100.0;
CGFloat reduceHeight = 100.0/sourceImageAspectRatio;
if (defaultSize.width-reduceWidth <= 0 || defaultSize.height-reduceHeight <= 0) {
break;
}
defaultSize = CGSizeMake(defaultSize.width-reduceWidth, defaultSize.height-reduceHeight);
UIImage *image = [self newSizeImage:defaultSize
image:[UIImage imageWithData:UIImageJPEGRepresentation(newImage,[[compressionQualityArr lastObject] floatValue])]];
finallImageData = [self halfFuntion:compressionQualityArr image:image sourceData:UIImageJPEGRepresentation(image,1.0) maxSize:maxSize];
}
return finallImageData;
}
#pragma mark 調(diào)整圖片分辨率/尺寸（等比例縮放）
- (UIImage *)newSizeImage:(CGSize)size image:(UIImage *)sourceImage {
CGSize newSize = CGSizeMake(sourceImage.size.width, sourceImage.size.height);
CGFloat tempHeight = newSize.height / size.height;
CGFloat tempWidth = newSize.width / size.width;
if (tempWidth > 1.0 && tempWidth > tempHeight) {
newSize = CGSizeMake(sourceImage.size.width / tempWidth, sourceImage.size.height / tempWidth);
} else if (tempHeight > 1.0 && tempWidth < tempHeight) {
newSize = CGSizeMake(sourceImage.size.width / tempHeight, sourceImage.size.height / tempHeight);
}
UIGraphicsBeginImageContext(newSize);
[sourceImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
#pragma mark 二分法
- (NSData *)halfFuntion:(NSArray *)arr image:(UIImage *)image sourceData:(NSData *)finallImageData maxSize:(NSInteger)maxSize {
NSData *tempData = [NSData data];
NSUInteger start = 0;
NSUInteger end = arr.count - 1;
NSUInteger index = 0;
NSUInteger difference = NSIntegerMax;
while(start <= end) {
index = start + (end - start)/2;
finallImageData = UIImageJPEGRepresentation(image,[arr[index] floatValue]);
NSUInteger sizeOrigin = finallImageData.length;
NSUInteger sizeOriginKB = sizeOrigin / 1024;
NSLog(@"當(dāng)前降到的質(zhì)量：%ld", (unsigned long)sizeOriginKB);
NSLog(@"\nstart：%zd\nend：%zd\nindex：%zd\n壓縮系數(shù)：%lf", start, end, (unsigned long)index, [arr[index] floatValue]);
if (sizeOriginKB > maxSize) {
start = index + 1;
} else if (sizeOriginKB < maxSize) {
if (maxSize-sizeOriginKB < difference) {
difference = maxSize-sizeOriginKB;
tempData = finallImageData;
}
if (index<=0) {
break;
}
end = index - 1;
} else {
break;
}
}
return tempData;
}
【更新日志】
2017年10月09日：修復(fù)了網(wǎng)友提出的二分法存在index為0時閃退問題。
2018年05月25日：將原本默認(rèn)設(shè)置圖片尺寸為1024*1024改成等比放大，同時降低分辨力也改成等比降低。
再一次感謝您花費時間閱讀這篇文章！
微博： @Danny_呂昌輝
博客： SuperDanny
